Publications

@article{decunha_new_2018,

title = {A new delivery system to resolve dosimetric issues in intravascular brachytherapy},

author = {Joseph M. DeCunha and Shirin A. Enger},

doi = {10.1016/j.brachy.2018.01.012},

issn = {1873-1449},

year  = {2018},

date = {2018-06-01},

journal = {Brachytherapy},

volume = {17},

number = {3},

pages = {634--643},

abstract = {PURPOSE: Renewed interest is being expressed in intravascular brachytherapy (IVBT). A number of unresolved issues exist in the discipline. Providing a homogeneous and adequate dose to the target remains difficult in IVBT. The guidewire that delivers the device to the target, arterial plaques, and stent struts are all known to reduce the dose delivered to target. The viability and efficacy of a proposed IVBT delivery system designed to resolve the issue of guidewire attenuation is evaluated and compared to that of a popular and commercially available IVBT device. 

METHODS AND MATERIALS: Monte Carlo simulations are conducted to determine distributions of absorbed dose around an existing and proposed IVBT delivery system. 

RESULTS: For the Novoste Beta-Cath 3.5F (TeamBest®), dose in water varies by 10% as a function of angle in the plane perpendicular to the delivery catheter due to off-centering of seeds in the catheter. Dose is reduced by 52% behind a stainless steel guidewire and 64% behind a guidewire, arterial plaque, and stent strut for the Novoste Beta-Cath 3.5F. Dose is not perturbed by the presence of a guidewire for the proposed device and is reduced by 46% by an arterial plaque and stent strut. 

CONCLUSIONS: Dose attenuation by guidewire is likely the single greatest source of dose attenuation in IVBT in terms of absolute dose reduction and is greater than previously reported for the Novoste Beta-Cath 3.5F. The Novoste Beta-Cath 3.5F delivers an inhomogeneous dose to target. A delivery system is proposed, which resolves the issue of guidewire attenuation in IVBT and should reduce treatment times.},

keywords = {Brachytherapy, Catheterization, Catheters, Computer Simulation, Coronary Vessels, Humans, Intravascular, Monte Carlo Method, Physics, Radiation Dosage, Radiometry, Restenosis, Stents, Strontium Radioisotopes},

pubstate = {published},

tppubtype = {article}

}

@article{mann-krzisnik_influence_2018,

title = {The influence of tissue composition uncertainty on dose distributions in brachytherapy},

author = {Dylan Mann-Krzisnik and Frank Verhaegen and Shirin A. Enger},

doi = {10.1016/j.radonc.2018.01.007},

issn = {1879-0887},

year  = {2018},

date = {2018-03-01},

journal = {Radiotherapy and Oncology: Journal of the European Society for Therapeutic Radiology and Oncology},

volume = {126},

number = {3},

pages = {394--410},

abstract = {BACKGROUND AND PURPOSE: Model-based dose calculation algorithms (MBDCAs) have evolved from serving as a research tool into clinical practice in brachytherapy. This study investigates primary sources of tissue elemental compositions used as input to MBDCAs and the impact of their variability on MBDCA-based dosimetry. 

MATERIALS AND METHODS: Relevant studies were retrieved through PubMed. Minimum dose delivered to 90% of the target (D90), minimum dose delivered to the hottest specified volume for organs at risk (OAR) and mass energy-absorption coefficients (μen/ρ) generated by using EGSnrc "g" user-code were compared to assess the impact of compositional variability. 

RESULTS: Elemental composition for hydrogen, carbon, oxygen and nitrogen are derived from the gross contents of fats, proteins and carbohydrates for any given tissue, the compositions of which are taken from literature dating back to 1940-1950. Heavier elements are derived from studies performed in the 1950-1960. Variability in elemental composition impacts greatly D90 for target tissues and doses to OAR for brachytherapy with low energy sources and less for 192Ir-based brachytherapy. Discrepancies in μen/ρ are also indicative of dose differences. 

CONCLUSIONS: Updated elemental compositions are needed to optimize MBDCA-based dosimetry. Until then, tissue compositions based on gross simplifications in early studies will dominate the uncertainties in tissue heterogeneity.},

keywords = {Algorithms, Body Composition, Brachytherapy, Elemental composition, Humans, Mass energy-absorption coefficient, MBDCA, Organs at Risk, Radiotherapy Dosage, Review, Tissue heterogeneity, Uncertainty},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_microdosimetric_2018,

title = {Microdosimetric Evaluation of Current and Alternative Brachytherapy Sources-A Geant4-DNA Simulation Study},

author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},

doi = {10.1016/j.ijrobp.2017.09.040},

issn = {1879-355X},

year  = {2018},

date = {2018-01-01},

journal = {International Journal of Radiation Oncology, Biology, Physics},

volume = {100},

number = {1},

pages = {270--277},

abstract = {PURPOSE: Radioisotopes such as 75Se, 169Yb, and 153Gd have photon energy spectra and half-lives that make them excellent candidates as alternatives to 192Ir for high-dose-rate brachytherapy. The aim of the present study was to evaluate the relative biological effectiveness (RBE) of current (192Ir, 125I, 103Pd) and alternative (75Se, 169Yb, 153Gd) brachytherapy radionuclides using Monte Carlo simulations of lineal energy distributions. 

METHODS AND MATERIALS: Brachytherapy sources (microSelectron v2 [192Ir, 75Se, 169Yb, 153Gd], SelectSeed [125I], and TheraSeed [103Pd]) were placed in the center of a spherical water phantom with a radius of 40 cm using the Geant4 Monte Carlo simulation toolkit. The kinetic energy of all primary, scattered, and fluorescence photons interacting in a scoring volume were tallied at various depths from the source. Electron tracks were generated by sampling the photon interaction spectrum and tracking all the interactions down to 10 eV using the event-by-event capabilities of the Geant4-DNA models. The dose mean lineal energy (y¯D) values were obtained through random sampling of transfer points and overlaying spherical scoring volumes within the associated volume of the tracks. The scoring volume diameter was determined by fitting the y¯D ratio for 125I to its observed RBE. 

RESULTS: y¯D increased with the increasing distance from the source for 192Ir, 75Se, and 169Yb, remained constant for 153Gd and 125I, and decreased for 103Pd. The diameter at which the y¯D ratio coincided with the RBE of 1.15 to 1.20 for 125I was ∼25 to 40 nm. The RBE (reference 1 MeV photons) at high doses and dose rates for 192Ir, 75Se, 169Yb, 153Gd, 125I, and 103Pd was 1.028 to 1.034, 1.05 to 1.07, 1.12 to 1.15, 1.16 to 1.21, 1.15 to 1.20, and 1.17 to 1.22, respectively. 

CONCLUSIONS: The radiation quality of the radionuclides under investigation was greater than that of high-energy photons. The present study has provided a set of values to modify the prescription doses for brachytherapy to account for the variation in radiation quality among radionuclides.},

keywords = {Brachytherapy, Gadolinium, Imaging, Iodine Radioisotopes, Iridium Radioisotopes, Linear Energy Transfer, Monte Carlo Method, Phantoms, Radioisotopes, Radiometry, Radiotherapy Dosage, Relative Biological Effectiveness, Selenium Radioisotopes, Ytterbium},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_practical_2017,

title = {Practical aspects of 153Gd as a radioactive source for use in brachytherapy},

author = {Gabriel Famulari and Tomas Urlich and Andrea Armstrong and Shirin A. Enger},

doi = {10.1016/j.apradiso.2017.09.028},

issn = {1872-9800},

year  = {2017},

date = {2017-12-01},

journal = {Applied Radiation and Isotopes: Including Data, Instrumentation and Methods for Use in Agriculture, Industry and Medicine},

volume = {130},

pages = {131--139},

abstract = {The goal of this study was to investigate the production, purification and immobilization techniques for a 153Gd brachytherapy source. We have investigated the maximum attainable specific activity of 153Gd through the irradiation of Gd2O3 enriched to 30.6% 152Gd at McMaster Nuclear Reactor. The advantage of producing 153Gd through this production pathway is the possibility to irradiate pre-sealed pellets of 152Gd enriched Gd2O3, thereby removing the need to perform chemical separation with large quantities of radio-impurities. However, small amounts of long-lived impurities are produced from the irradiation of enriched 152Gd targets due to traces of Eu in the sample. If the amount of impurities produced is deemed unacceptable, 153Gd can be isolated as an aqueous solution, chemically separated from impurities and loaded onto a sorbent with a high affinity for Gd before encapsulation.},

keywords = {(153)Gd, Brachytherapy, Gadolinium, Humans, Neutron Capture Therapy, Nuclear Reactors, Radiochemical separation, Radioisotopes, Radionuclide production, Radiotherapy Dosage, Specific activity, Thermal neutron capture cross section},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_microdosimetry_2017,

title = {Microdosimetry calculations for monoenergetic electrons using Geant4-DNA combined with a weighted track sampling algorithm},

author = {Gabriel Famulari and Piotr Pater and Shirin A. Enger},

doi = {10.1088/1361-6560/aa71f6},

issn = {1361-6560},

year  = {2017},

date = {2017-07-01},

journal = {Physics in Medicine and Biology},

volume = {62},

number = {13},

pages = {5495--5508},

abstract = {The aim of this study was to calculate microdosimetric distributions for low energy electrons simulated using the Monte Carlo track structure code Geant4-DNA. Tracks for monoenergetic electrons with kinetic energies ranging from 100 eV to 1 MeV were simulated in an infinite spherical water phantom using the Geant4-DNA extension included in Geant4 toolkit version 10.2 (patch 02). The microdosimetric distributions were obtained through random sampling of transfer points and overlaying scoring volumes within the associated volume of the tracks. Relative frequency distributions of energy deposition f(textgreaterE)/f(textgreater0) and dose mean lineal energy ([Formula: see text]) values were calculated in nanometer-sized spherical and cylindrical targets. The effects of scoring volume and scoring techniques were examined. The results were compared with published data generated using MOCA8B and KURBUC. Geant4-DNA produces a lower frequency of higher energy deposits than MOCA8B. The [Formula: see text] values calculated with Geant4-DNA are smaller than those calculated using MOCA8B and KURBUC. The differences are mainly due to the lower ionization and excitation cross sections of Geant4-DNA for low energy electrons. To a lesser extent, discrepancies can also be attributed to the implementation in this study of a new and fast scoring technique that differs from that used in previous studies. For the same mean chord length ([Formula: see text]), the [Formula: see text] calculated in cylindrical volumes are larger than those calculated in spherical volumes. The discrepancies due to cross sections and scoring geometries increase with decreasing scoring site dimensions. A new set of [Formula: see text] values has been presented for monoenergetic electrons using a fast track sampling algorithm and the most recent physics models implemented in Geant4-DNA. This dataset can be combined with primary electron spectra to predict the radiation quality of photon and electron beams.},

keywords = {Algorithms, DNA, DNA Damage, Electrons, Imaging, Monte Carlo Method, Phantoms, Photons, Radiometry},

pubstate = {published},

tppubtype = {article}

}

@article{decunha_investigation_2017,

title = {Investigation of a New Device to Improve Dosimetric Outcomes in Intravascular Brachytherapy},

author = {Joseph M. DeCunha and Shirin A. Enger},

url = {https://www.brachyjournal.com/article/S1538-4721(17)30207-6/abstract},

doi = {10.1016/j.brachy.2017.04.146},

issn = {1538-4721, 1873-1449},

year  = {2017},

date = {2017-05-01},

urldate = {2017-05-01},

journal = {Brachytherapy},

volume = {16},

number = {3},

pages = {S80},

abstract = {Coronary artery disease is amongst the main causes of death in developed countries. 

Percutaneous Transluminal Coronary Angioplasty (PTCA or angioplasty) is a procedure 

used to open stenoted (narrowed) arteries. Restenosis (renarrowing) of the treated 

vessel is a major complication of PTCA. A metal mesh tube (stent) is expanded inside 

the vessel to prevent restenosis. Tissue stress incurred during angioplasty and stenting 

can provoke rapid proliferation of neointimal cells leading to in stent restenosis 

(ISR).},

note = {Publisher: Elsevier},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{decunha_retrospective_2017,

title = {A retrospective analysis of catheter-based sources in intravascular brachytherapy},

author = {Joseph M. DeCunha and Christian Janicki and Shirin A. Enger},

url = {https://www.sciencedirect.com/science/article/pii/S1538472117300077},

doi = {10.1016/j.brachy.2017.01.004},

issn = {1538-4721},

year  = {2017},

date = {2017-05-01},

urldate = {2017-05-01},

journal = {Brachytherapy},

volume = {16},

number = {3},

pages = {586--596},

abstract = {Purpose 

Coronary artery disease involves the deposition of plaque along the walls of a coronary artery leading to narrowed or blocked vessels (stenosis) and is one of the main causes of death in developed countries. Percutaneous transluminal coronary angioplasty (PTCA) is used to reverse stenosis. Restenosis (renarrowing) of the treated vessel is a major complication of PTCA. A metal mesh tube (stent) can be placed inside the vessel to prevent restenosis. Tissue stress incurred during PTCA and stenting can provoke neointimal cell proliferation leading to in-stent restenosis (ISR). Intravascular brachytherapy (IVBT), a form of internal radiotherapy, is used to treat ISR. Renewed interest in IVBT is being expressed as a treatment for patients with ISR in drug-eluting stents. Current treatment planning (TP) of IVBT is extremely limited and assumes human tissue can be approximated by water. The interactions of arterial plaque, guidewires, and the stent have been shown to attenuate radiation significantly but are ignored in TP. Other models have determined the degree of attenuation by each factor in isolation. For the first time, we create a model with several inhomogenities present to determine whether attenuation by multiple inhomogenities combines linearly or if a larger dose reduction than anticipated is realized. We are also able to evaluate a spatial distribution of dose around the source and in arterial walls. 

Methods and Materials 

A dosimetric analysis of two commercially available IVBT systems was performed in a Monte Carlo–based particle simulation (Geant4). Absorbed dose was calculated using a model of a human coronary artery with a calcified plaque and stent. Dose delivered in water was also calculated to evaluate the accuracy of a water approximation. 

Results 

Dose as a function of θ shows significant variation around IVBT sources. For the Guidant Galileo, dose is reduced by 20% behind stent struts and as much as 66% in a region occluded by the guidewire, plaque, and stent. For the Novoste Beta Cath device, delivered dose is reduced by 19% and 58%, respectively, in the same regions. 

Conclusions 

Our findings show that the water approximation used in clinical practice to calculate dose is inaccurate when inhomogeneities are present. Methods proposed for calculating dose perturbations in IVBT may underestimate the magnitude of dose reduction. Increasing source dwell time seems unlikely to resolve dosimetric issues in IVBT. The effectiveness of currently existing β-emitting devices may be reduced in patients with complex lesions at the treatment site. Investigation of new radioisotopes and off-centering devices should be considered to improve dose outcomes.},

keywords = {Attenuation, Brachytherapy, Dose, Dosimetry, Intracoronary, Intravascular, Physics, Planning, Restenosis, Treatment},

pubstate = {published},

tppubtype = {article}

}

@article{quast_brachytherapy_2016,

title = {A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry},

author = {Ulrich Quast and Theodor W. Kaulich and José T. Álvarez-Romero and Sa Carlsson Tedgren and Shirin A. Enger and David C. Medich and Firas Mourtada and Jose Perez-Calatayud and Mark J. Rivard and G. Abu Zakaria},

doi = {10.1016/j.ejmp.2016.03.008},

issn = {1724-191X},

year  = {2016},

date = {2016-06-01},

journal = {Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB)},

volume = {32},

number = {6},

pages = {741--748},

abstract = {INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector's response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient μ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector's response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources. 

CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon's penetration probability and scattering potential.},

keywords = {Absorbed dose to water, Brachytherapy, Detector response, Effective energy, Photon brachytherapy radiation quality index, Photons, Radiation, Radiometry, Scattering, Uncertainty},

pubstate = {published},

tppubtype = {article}

}

@article{tran_geant4_2016,

title = {Geant4 Monte Carlo simulation of absorbed dose and radiolysis yields enhancement from a gold nanoparticle under MeV proton irradiation},

author = {H. N. Tran and M. Karamitros and V. N. Ivanchenko and S. Guatelli and S. McKinnon and K. Murakami and T. Sasaki and S. Okada and M. C. Bordage and Z. Francis and Z. El Bitar and M. A. Bernal and J. I. Shin and S. B. Lee and Ph. Barberet and T. T. Tran and J. M. C. Brown and T. V. Nhan Hao and S. Incerti},

url = {https://www.sciencedirect.com/science/article/pii/S0168583X16000653},

doi = {10.1016/j.nimb.2016.01.017},

issn = {0168-583X},

year  = {2016},

date = {2016-04-01},

urldate = {2021-09-07},

journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},

volume = {373},

pages = {126--139},

abstract = {Gold nanoparticles have been reported as a possible radio-sensitizer agent in radiation therapy due to their ability to increase energy deposition and subsequent direct damage to cells and DNA within their local vicinity. Moreover, this increase in energy deposition also results in an increase of the radiochemical yields. In this work we present, for the first time, an in silico investigation, based on the general purpose Monte Carlo simulation toolkit Geant4, into energy deposition and radical species production around a spherical gold nanoparticle 50nm in diameter via proton irradiation. Simulations were preformed for incident proton energies ranging from 2 to 170MeV, which are of interest for clinical proton therapy.},

keywords = {Geant4-DNA, Nanoparticle, Proton beam, Radiation therapy, Radiolysis},

pubstate = {published},

tppubtype = {article}

}

@article{pater_proton_2016b,

title = {Proton and light ion RBE for the induction of direct DNA double strand breaks},

author = {Piotr Pater and Gloria Bäckstöm and Fernanda Villegas and Anders Ahnesjö and Shirin A. Enger and Jan Seuntjens and Issam El Naqa},

url = {https://aapm.onlinelibrary.wiley.com/doi/abs/10.1118/1.4944870},

doi = {10.1118/1.4944870},

issn = {2473-4209},

year  = {2016},

date = {2016-01-01},

urldate = {2021-09-07},

journal = {Medical Physics},

volume = {43},

number = {5},

pages = {2131--2140},

abstract = {Purpose: To present and characterize a Monte Carlo (MC) tool for the simulation of the relative biological effectiveness for the induction of direct DNA double strand breaks () for protons and light ions. Methods: The MC tool uses a pregenerated event-by-event tracks library of protons and light ions that are overlaid on a cell nucleus model. The cell nucleus model is a cylindrical arrangement of nucleosome structures consisting of 198 DNA base pairs. An algorithm relying on k-dimensional trees and cylindrical symmetries is used to search coincidences of energy deposition sites with volumes corresponding to the sugar–phosphate backbone of the DNA molecule. Strand breaks (SBs) are scored when energy higher than a threshold is reached in these volumes. Based on the number of affected strands, they are categorized into either single strand break (SSB) or double strand break (DSB) lesions. The number of SBs composing each lesion (i.e., its size) is also recorded. is obtained by taking the ratio of DSB yields of a given radiation field to a 60Co field. The MC tool was used to obtain SSB yields, DSB yields, and as a function of linear energy transfer (LET) for protons (1H+), 4He2+, 7Li3+, and 12C6+ ions. Results: For protons, the SSB yields decreased and the DSB yields increased with LET. At ≈24.5 keV μm−1, protons generated 15% more DSBs than 12C6+ ions. The varied between 1.24 and 1.77 for proton fields between 8.5 and 30.2 keV μm−1, and it was higher for iso-LET ions with lowest atomic number. The SSB and DSB lesion sizes showed significant differences for all radiation fields. Generally, the yields of SSB lesions of sizes ≥2 and the yields of DSB lesions of sizes ≥3 increased with LET and increased for iso-LET ions of lower atomic number. On the other hand, the ratios of SSB to DSB lesions of sizes 2–4 did not show variability with LET nor projectile atomic number, suggesting that these metrics are independent of the radiation quality. Finally, a variance of up to 8% in the DSB yields was observed as a function of the particle incidence angle on the cell nucleus. This simulation effect is due to the preferential alignment of ion tracks with the DNA nucleosomes at specific angles. Conclusions: The MC tool can predict SSB and DSB yields for light ions of various LET and estimate . In addition, it can calculate the frequencies of different DNA lesion sizes, which is of interest in the context of biologically relevant absolute dosimetry of particle beams.},

note = {_eprint: https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1118/1.4944870},

keywords = {biological effects of ionising particles, biomolecular effects of radiation, Cell Nucleus, cell nucleus model, cellular effects of radiation, DNA, DNA double-strand breaks, Dosimetry, Dosimetry/exposure assessment, Energy transfer, Genomics, Ion beams, Ion radiation effects, Monte Carlo calculations, Monte Carlo methods, Monte Carlo simulations, Monte Carlo track structure, Protons, RBE, Schottky barriers, Scintigraphy},

pubstate = {published},

tppubtype = {article}

}

@article{poole_determination_2015,

title = {Determination of subcellular compartment sizes for estimating dose variations in radiotherapy},

author = {Christopher M. Poole and Anders Ahnesjö and Shirin A. Enger},

doi = {10.1093/rpd/ncv305},

issn = {1742-3406},

year  = {2015},

date = {2015-09-01},

journal = {Radiation Protection Dosimetry},

volume = {166},

number = {1-4},

pages = {361--364},

abstract = {The variation in specific energy absorbed to different cell compartments caused by variations in size and chemical composition is poorly investigated in radiotherapy. The aim of this study was to develop an algorithm to derive cell and cell nuclei size distributions from 2D histology samples, and build 3D cellular geometries to provide Monte Carlo (MC)-based dose calculation engines with a morphologically relevant input geometry. Stained and unstained regions of the histology samples are segmented using a Gaussian mixture model, and individual cell nuclei are identified via thresholding. Delaunay triangulation is applied to determine the distribution of distances between the centroids of nearest neighbour cells. A pouring simulation is used to build a 3D virtual tissue sample, with cell radii randomised according to the cell size distribution determined from the histology samples. A slice with the same thickness as the histology sample is cut through the 3D data and characterised in the same way as the measured histology. The comparison between this virtual slice and the measured histology is used to adjust the initial cell size distribution into the pouring simulation. This iterative approach of a pouring simulation with adjustments guided by comparison is continued until an input cell size distribution is found that yields a distribution in the sliced geometry that agrees with the measured histology samples. The thus obtained morphologically realistic 3D cellular geometry can be used as input to MC-based dose calculation programs for studies of dose response due to variations in morphology and size of tumour/healthy tissue cells/nuclei, and extracellular material.},

keywords = {Algorithms, Breast Neoplasms, Cell Nucleus, Computer Simulation, Computer-Assisted, ErbB-2, Female, Humans, Image Processing, Imaging, Immunoenzyme Techniques, Male, Monte Carlo Method, Prostatic Neoplasms, Radiotherapy Dosage, Radiotherapy Planning, Receptor, Signal Processing, Subcellular Fractions, Three-Dimensional},

pubstate = {published},

tppubtype = {article}

}

@article{adams_interstitial_2014,

title = {Interstitial rotating shield brachytherapy for prostate cancer},

author = {Quentin E. Adams and Jinghzu Xu and Elizabeth K. Breitbach and Xing Li and Shirin A. Enger and William R. Rockey and Yusung Kim and Xiaodong Wu and Ryan T. Flynn},

doi = {10.1118/1.4870441},

issn = {2473-4209},

year  = {2014},

date = {2014-05-01},

journal = {Medical Physics},

volume = {41},

number = {5},

pages = {051703},

abstract = {PURPOSE: To present a novel needle, catheter, and radiation source system for interstitial rotating shield brachytherapy (I-RSBT) of the prostate. I-RSBT is a promising technique for reducing urethra, rectum, and bladder dose relative to conventional interstitial high-dose-rate brachytherapy (HDR-BT). 

METHODS: A wire-mounted 62 GBq(153)Gd source is proposed with an encapsulated diameter of 0.59 mm, active diameter of 0.44 mm, and active length of 10 mm. A concept model I-RSBT needle/catheter pair was constructed using concentric 50 and 75 μm thick nickel-titanium alloy (nitinol) tubes. The needle is 16-gauge (1.651 mm) in outer diameter and the catheter contains a 535 μm thick platinum shield. I-RSBT and conventional HDR-BT treatment plans for a prostate cancer patient were generated based on Monte Carlo dose calculations. In order to minimize urethral dose, urethral dose gradient volumes within 0-5 mm of the urethra surface were allowed to receive doses less than the prescribed dose of 100%. 

RESULTS: The platinum shield reduced the dose rate on the shielded side of the source at 1 cm off-axis to 6.4% of the dose rate on the unshielded side. For the case considered, for the same minimum dose to the hottest 98% of the clinical target volume (D(98%)), I-RSBT reduced urethral D(0.1cc) below that of conventional HDR-BT by 29%, 33%, 38%, and 44% for urethral dose gradient volumes within 0, 1, 3, and 5 mm of the urethra surface, respectively. Percentages are expressed relative to the prescription dose of 100%. For the case considered, for the same urethral dose gradient volumes, rectum D(1cc) was reduced by 7%, 6%, 6%, and 6%, respectively, and bladder D(1cc) was reduced by 4%, 5%, 5%, and 6%, respectively. Treatment time to deliver 20 Gy with I-RSBT was 154 min with ten 62 GBq (153)Gd sources. 

CONCLUSIONS: For the case considered, the proposed(153)Gd-based I-RSBT system has the potential to lower the urethral dose relative to HDR-BT by 29%-44% if the clinician allows a urethral dose gradient volume of 0-5 mm around the urethra to receive a dose below the prescription. A multisource approach is necessary in order to deliver the proposed (153)Gd-based I-RSBT technique in reasonable treatment times.},

keywords = {Brachytherapy, Catheters, Computer-Assisted, Equipment Design, Gadolinium, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Needles, Nickel, Platinum Compounds, Prostatic Neoplasms, Radiation Protection, Radioisotopes, Radiotherapy Dosage, Radiotherapy Planning, Rectum, Time Factors, Titanium, Urethra, Urinary Bladder},

pubstate = {published},

tppubtype = {article}

}

@article{enger_gadolinium-153_2013,

title = {Gadolinium-153 as a brachytherapy isotope},

author = {Shirin A. Enger and Darrell R. Fisher and Ryan T. Flynn},

doi = {10.1088/0031-9155/58/4/957},

issn = {1361-6560},

year  = {2013},

date = {2013-02-01},

journal = {Physics in Medicine and Biology},

volume = {58},

number = {4},

pages = {957--964},

abstract = {The purpose of this work was to present the fundamental dosimetric characteristics of a hypothetical (153)Gd brachytherapy source using the AAPM TG-43U1 dose-calculation formalism. Gadolinium-153 is an intermediate-energy isotope that emits 40-100 keV photons with a half-life of 242 days. The rationale for considering (153)Gd as a brachytherapy source is for its potential of patient specific shielding and to enable reduced personnel shielding requirements relative to (192)Ir, and as an isotope for interstitial rotating shield brachytherapy (I-RSBT). A hypothetical (153)Gd brachytherapy source with an active core of 0.84 mm diameter, 10 mm length and specific activity of 5.55 TBq of (153)Gd per gram of Gd was simulated with Geant4. The encapsulation material was stainless steel with a thickness of 0.08 mm. The radial dose function, anisotropy function and photon spectrum in water were calculated for the (153)Gd source. The simulated (153)Gd source had an activity of 242 GBq and a dose rate in water 1 cm off axis of 13.12 Gy h(-1), indicating that it would be suitable as a low-dose-rate or pulsed-dose-rate brachytherapy source. The beta particles emitted have low enough energies to be absorbed in the source encapsulation. Gadolinium-153 has an increasing radial dose function due to multiple scatter of low-energy photons. Scattered photon dose takes over with distance from the source and contributes to the majority of the absorbed dose. The anisotropy function of the (153)Gd source decreases at low polar angles, as a result of the long active core. The source is less anisotropic at polar angles away from the longitudinal axes. The anisotropy function increases with increasing distance. The (153)Gd source considered would be suitable as an intermediate-energy low-dose-rate or pulsed-dose-rate brachytherapy source. The source could provide a means for I-RSBT delivery and enable brachytherapy treatments with patient specific shielding and reduced personnel shielding requirements relative to (192)Ir.},

keywords = {Anisotropy, Brachytherapy, Equipment Design, Gadolinium, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Photons, Prostatic Neoplasms, Radiation, Radiation Protection, Radioisotopes, Radiotherapy Dosage, Scattering},

pubstate = {published},

tppubtype = {article}

}

@article{enger_layered_2012,

title = {Layered mass geometry: a novel technique to overlay seeds and applicators onto patient geometry in Geant4 brachytherapy simulations},

author = {Shirin A. Enger and Guillaume Landry and Michel D'Amours and Frank Verhaegen and Luc Beaulieu and Makoto Asai and Joseph Perl},

doi = {10.1088/0031-9155/57/19/6269},

issn = {1361-6560},

year  = {2012},

date = {2012-10-01},

journal = {Physics in Medicine and Biology},

volume = {57},

number = {19},

pages = {6269--6277},

abstract = {A problem faced by all Monte Carlo (MC) particle transport codes is how to handle overlapping geometries. The Geant4 MC toolkit allows the user to create parallel geometries within a single application. In Geant4 the standard mass-containing geometry is defined in a simulation volume called the World Volume. Separate parallel geometries can be defined in parallel worlds, that is, alternate three dimensional simulation volumes that share the same coordinate system with the World Volume for geometrical event biasing, scoring of radiation interactions, and/or the creation of hits in detailed readout structures. Until recently, only one of those worlds could contain mass so these parallel worlds provided no solution to simplify a complex geometric overlay issue in brachytherapy, namely the overlap of radiation sources and applicators with a CT based patient geometry. The standard method to handle seed and applicator overlay in MC requires removing CT voxels whose boundaries would intersect sources, placing the sources into the resulting void and then backfilling the remaining space of the void with a relevant material. The backfilling process may degrade the accuracy of patient representation, and the geometrical complexity of the technique precludes using fast and memory-efficient coding techniques that have been developed for regular voxel geometries. The patient must be represented by the less memory and CPU-efficient Geant4 voxel placement technique, G4PVPlacement, rather than the more efficient G4NestedParameterization (G4NestedParam). We introduce for the first time a Geant4 feature developed to solve this issue: Layered Mass Geometry (LMG) whereby both the standard (CT based patient geometry) and the parallel world (seeds and applicators) may now have mass. For any area where mass is present in the parallel world, the parallel mass is used. Elsewhere, the mass of the standard world is used. With LMG the user no longer needs to remove patient CT voxels that would include for example seeds. The patient representation can be a regular voxel grid, conducive to G4NestedParam, and the patient CT derived materials remain exact, avoiding the inaccuracy of the backfilling technique. Post-implant dosimetry for one patient with (125)I permanent seed implant was performed using Geant4 version 9.5.p01 using three different geometrical techniques. The first technique was the standard described above (G4PVPlacement). The second technique placed patient voxels as before, but placed seeds with LMG (G4PVPlacement+LMG). The third technique placed patient voxels through G4NestedParam and seeds through LMG (G4NestedParam+LMG). All the scenarios were calculated with 3 different image compression factors to manipulate the number of voxels. Additionally, the dosimetric impact of the backfilling technique was investigated for the case of calcifications in close proximity of sources. LMG eliminated the need for backfilling and simplified geometry description. Of the two LMG techniques, G4PVPlacement+LMG had no benefit to calculation time or memory use, actually increasing calculation time, but G4NestedParam+LMG reduced both calculation time and memory. The benefits of G4NestedParam+LMG over standard G4PVPlacement increased with increasing voxel numbers. For the case of calcifications in close proximity to sources, LMG not only increased efficiency but also yielded more accurate dose calculation than G4PVPlacement. G4NestedParam in combination with LMG present a new, efficient approach to simulate radiation sources that overlap patient geometry. Cases with brachytherapy applicators would constitute a direct extension of the method.},

keywords = {Brachytherapy, Computer-Assisted, Humans, Monte Carlo Method, Radiotherapy Dosage, Radiotherapy Planning},

pubstate = {published},

tppubtype = {article}

}

@article{enger_dose_2012,

title = {Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies},

author = {Shirin A. Enger and Anders Ahnesjö and Frank Verhaegen and Luc Beaulieu},

doi = {10.1088/0031-9155/57/14/4489},

issn = {1361-6560},

year  = {2012},

date = {2012-07-01},

journal = {Physics in Medicine and Biology},

volume = {57},

number = {14},

pages = {4489--4500},

abstract = {It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for ¹⁰³Pd or ¹²⁵I) to 300 keV (close to the mean energy of (¹⁹²Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm³). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.},

keywords = {Brachytherapy, Cell Line, Cell Nucleus, Humans, Monte Carlo Method, Photons, Radiation Dosage, Radiotherapy Dosage, Water},

pubstate = {published},

tppubtype = {article}

}

@article{enger_exploring_2012,

title = {Exploring (57)Co as a new isotope for brachytherapy applications},

author = {Shirin A. Enger and Hans Lundqvist and Michel D'Amours and Luc Beaulieu},

doi = {10.1118/1.3700171},

issn = {0094-2405},

year  = {2012},

date = {2012-05-01},

journal = {Medical Physics},

volume = {39},

number = {5},

pages = {2342--2345},

abstract = {PURPOSE: The characteristics of the radionuclide (57)Co make it interesting for use as a brachytherapy source. (57)Co combines a possible high specific activity with the emission of relatively low-energy photons and a half-life (272 days) suitable for regular source exchanges in an afterloader. (57)Co decays by electron capture to the stable (57)Fe with emission of 136 and 122 keV photons. 

METHODS: A hypothetical (57)Co source based on the Flexisource brachytherapy encapsulation with the active core set as a pure cobalt cylinder (length 3.5 mm and diameter 0.6 mm) covered with a cylindrical stainless-steel capsule (length 5 mm and thickness 0.125 mm) was simulated using Geant4 Monte Carlo (MC) code version 9.4. The radial dose function, g(r), and anisotropy function F(r,θ), for the line source approximation were calculated following the TG-43U1 formalism. The results were compared to well-known (192)Ir and (125)I radionuclides, representing the higher and the lower energy end of brachytherapy, respectively. 

RESULTS: The mean energy of photons in water, after passing through the core and the encapsulation material was 123 keV. This hypothetical (57)Co source has an increasing g(r) due to multiple scatter of low-energy photons, which results in a more uniform dose distribution than (192)Ir. 

CONCLUSIONS: (57)Co has many advantages compared to (192)Ir due to its low-energy gamma emissions without any electron contamination. (57)Co has an increasing g(r) that results in a more uniform dose distribution than (192)Ir due to its multiple scattered photons. The anisotropy of the (57)Co source is comparable to that of (192)Ir. Furthermore, (57)Co has lower shielding requirements than (192)Ir.},

keywords = {Anisotropy, Brachytherapy, Cobalt Radioisotopes, Monte Carlo Method, Radiation, Radiometry, Scattering},

pubstate = {published},

tppubtype = {article}

}

@article{enger_modeling_2011,

title = {Modeling a hypothetical 170Tm source for brachytherapy applications},

author = {Shirin A. Enger and Michel D'Amours and Luc Beaulieu},

doi = {10.1118/1.3626482},

issn = {0094-2405},

year  = {2011},

date = {2011-10-01},

journal = {Medical Physics},

volume = {38},

number = {10},

pages = {5307--5310},

abstract = {PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons. 

METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation. 

RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively. 

CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.},

keywords = {Algorithms, Brachytherapy, Computer Simulation, Computer-Assisted, Electrons, Equipment Design, Gold, Humans, Models, Monte Carlo Method, Photons, Platinum, Radioisotopes, Radiotherapy Planning, Stainless Steel, Theoretical, Thulium, Titanium},

pubstate = {published},

tppubtype = {article}

}

@article{xu_algorithm_2011,

title = {An algorithm for efficient metal artifact reductions in permanent seed},

author = {Chen Xu and Frank Verhaegen and Denis Laurendeau and Shirin A. Enger and Luc Beaulieu},

doi = {10.1118/1.3519988},

issn = {0094-2405},

year  = {2011},

date = {2011-01-01},

journal = {Medical Physics},

volume = {38},

number = {1},

pages = {47--56},

abstract = {PURPOSE: In permanent seed implants, 60 to more than 100 small metal capsules are inserted in the prostate, creating artifacts in x-ray computed tomography (CT) imaging. The goal of this work is to develop an automatic method for metal artifact reduction (MAR) from small objects such as brachytherapy seeds for clinical applications. 

METHODS: The approach for MAR is based on the interpolation of missing projections by directly using raw helical CT data (sinogram). First, an initial image is reconstructed from the raw CT data. Then, the metal objects segmented from the reconstructed image are reprojected back into the sinogram space to produce a metal-only sinogram. The Steger method is used to determine precisely the position and edges of the seed traces in the raw CT data. By combining the use of Steger detection and reprojections, the missing projections are detected and replaced by interpolation of non-missing neighboring projections. 

RESULTS: In both phantom experiments and patient studies, the missing projections have been detected successfully and the artifacts caused by metallic objects have been substantially reduced. The performance of the algorithm has been quantified by comparing the uniformity between the uncorrected and the corrected phantom images. The results of the artifact reduction algorithm are indistinguishable from the true background value. 

CONCLUSIONS: An efficient algorithm for MAR in seed brachytherapy was developed. The test results obtained using raw helical CT data for both phantom and clinical cases have demonstrated that the proposed MAR method is capable of accurately detecting and correcting artifacts caused by a large number of very small metal objects (seeds) in sinogram space. This should enable a more accurate use of advanced brachytherapy dose calculations, such as Monte Carlo simulations.},

keywords = {Algorithms, Artifacts, Brachytherapy, Humans, Imaging, Metals, Monte Carlo Method, Phantoms, Tomography, X-Ray Computed},

pubstate = {published},

tppubtype = {article}

}

@article{enger_monte_2006,

title = {Monte Carlo calculations of thermal neutron capture in gadolinium: a comparison of GEANT4 and MCNP with measurements},

author = {Shirin A. Enger and Per Munck af Rosenschöld and Arash Rezaei and Hans Lundqvist},

doi = {10.1118/1.2150787},

issn = {0094-2405},

year  = {2006},

date = {2006-02-01},

journal = {Medical Physics},

volume = {33},

number = {2},

pages = {337--341},

abstract = {GEANT4 is a Monte Carlo code originally implemented for high-energy physics applications and is well known for particle transport at high energies. The capacity of GEANT4 to simulate neutron transport in the thermal energy region is not equally well known. The aim of this article is to compare MCNP, a code commonly used in low energy neutron transport calculations and GEANT4 with experimental results and select the suitable code for gadolinium neutron capture applications. To account for the thermal neutron scattering from chemically bound atoms [S(alpha,beta)] in biological materials a comparison of thermal neutron fluence in tissue-like poly(methylmethacrylate) phantom is made with MCNP4B, GEANT4 6.0 patch1, and measurements from the neutron capture therapy (NCT) facility at the Studsvik, Sweden. The fluence measurements agreed with MCNP calculated results considering S(alpha,beta). The location of the thermal neutron peak calculated with MCNP without S(alpha,beta) and GEANT4 is shifted by about 0.5 cm towards a shallower depth and is 25%-30% lower in amplitude. Dose distribution from the gadolinium neutron capture reaction is then simulated by MCNP and compared with measured data. The simulations made by MCNP agree well with experimental results. As long as thermal neutron scattering from chemically bound atoms are not included in GEANT4 it is not suitable for NCT applications.},

keywords = {Computer-Assisted, Fast Neutrons, Gadolinium, Humans, Imaging, Monte Carlo Method, Neutron Capture Therapy, Phantoms, Radiologic, Radiometry, Radiotherapy Planning, Reproducibility of Results, Technology},

pubstate = {published},

tppubtype = {article}

}

@article{enger_gadolinium_2006,

title = {Gadolinium neutron capture brachytherapy (GdNCB), a new treatment method for intravascular brachytherapy},

author = {Shirin A. Enger and Arash Rezaei and Per Munck af Rosenschöld and Hans Lundqvist},

doi = {10.1118/1.2146050},

issn = {0094-2405},

year  = {2006},

date = {2006-01-01},

journal = {Medical Physics},

volume = {33},

number = {1},

pages = {46--51},

abstract = {Restenosis is a major problem after balloon angioplasty and stent implantation. The aim of this study is to introduce gadolinium neutron capture brachytherapy (GdNCB) as a suitable modality for treatment of stenosis. The utility of GdNCB in intravascular brachytherapy (IVBT) of stent stenosis is investigated by using the GEANT4 and MCNP4B Monte Carlo radiation transport codes. To study capture rate, Kerma, absorbed dose and absorbed dose rate around a Gd-containing stent activated with neutrons, a 30 mm long, 5 mm diameter gadolinium foil is chosen. The input data is a neutron spectrum used for clinical neutron capture therapy in Studsvik, Sweden. Thermal neutron capture in gadolinium yields a spectrum of high-energy gamma photons, which due to the build-up effect gives an almost flat dose delivery pattern to the first 4 mm around the stent. The absorbed dose rate is 1.33 Gy/min, 0.25 mm from the stent surface while the dose to normal tissue is in order of 0.22 Gy/min, i.e., a factor of 6 lower. To spare normal tissue further fractionation of the dose is also possible. The capture rate is relatively high at both ends of the foil. The dose distribution from gamma and charge particle radiation at the edges and inside the stent contributes to a nonuniform dose distribution. This will lead to higher doses to the surrounding tissue and may prevent stent edge and in-stent restenosis. The position of the stent can be verified and corrected by the treatment plan prior to activation. Activation of the stent by an external neutron field can be performed days after catherization when the target cells start to proliferate and can be expected to be more radiation sensitive. Another advantage of the nonradioactive gadolinium stent is the possibility to avoid radiation hazard to personnel.},

keywords = {Biological, Blood Vessel Prosthesis, Brachytherapy, Computer Simulation, Computer-Assisted, Gadolinium, Graft Occlusion, Humans, Models, Monte Carlo Method, Neutron Capture Therapy, Radiometry, Radiotherapy Dosage, Radiotherapy Planning, Relative Biological Effectiveness, Statistical, Stents, Vascular},

pubstate = {published},

tppubtype = {article}

}

@article{noauthor_novel_nodate,

title = {A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.14459},

doi = {10.1002/mp.14459},

urldate = {2021-09-08},

keywords = {},

pubstate = {published},

tppubtype = {article}

}