Victor Daniel Diaz Martinez

Ph.D. Student
Department of Physics
Detector Development

Bio

Víctor Díaz began his academic career as part of the first graduating class of the Biomedical Physics program in Mexico, becoming one of the program’s first eight graduates in 2018. He subsequently worked as an adjunct professor in the same program, teaching radiation physics and radiological protection, and as an instructor at the Mexican Society of Radiology and Imaging (SMRI). He later completed his M.Sc. in Medical Physics at McGill University, where he is currently a Ph.D. candidate in Dr. Shirin Enger’s research group. His doctoral research focuses on the development and characterization of radiation detection systems for medical physics applications.

Current Projects

Quality Assurance detector for Alpha-DaRT

Diffusing alpha-emitter radiotherapy (Alpha-DaRT) is an interstitial technique developed by Alpha-Tau, Israel that uses 224Ra-loaded sources. These sources are loaded in different-sized applicators however, an uncertainty related to these sources is the activity per seed, and activity per applicator. The labeling of these applicators/seeds needs to be verified before insertion to avoid error when executing the treatment plan. Detectors currently used to perform QA protocols on these applicators, such as well-type ionization chambers and Geiger Counters, are not adaptable to the different sizes of the applicators and cannot provide information on the total activity per applicator or activity per seed.
Victor has been actively working with Dr. Enger and Dr. Lior in the design, simulation, and development of a QA detection system for Alpha-DaRT.
This interdisciplinary project has given Victor the opportunity to combine his knowledge acquired during his undergraduate and graduate studies regarding radiation detectors, radiation physics, and radiation safety.

2025

Dumančić, Mirta; Kalinowski, Jonathan; Diaz-Martinez, Victor D; Li, Joanna; Behmand, Behnaz; DeCunha, Joseph M; Enger, Shirin A

Microdosimetry calculations in situ for clinically relevant photon sources and their correlation with the early DNA damage response Journal Article

In: Medical Physics, vol. 52, iss. 7, no. e17979, 2025, ISSN: 2473-4209.

Abstract | Links | BibTeX

@article{nokey,

title = {Microdosimetry calculations in situ for clinically relevant photon sources and their correlation with the early DNA damage response},

author = {Mirta Dumančić and Jonathan Kalinowski and Victor D Diaz-Martinez and Joanna Li and Behnaz Behmand and Joseph M DeCunha and Shirin A Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.17979},

doi = {10.1002/mp.17979},

issn = {2473-4209},

year  = {2025},

date = {2025-07-15},

urldate = {2025-07-15},

journal = {Medical Physics},

volume = {52},

number = {e17979},

issue = {7},

abstract = {Background:

Radiobiological data suggests variations in relative biological effectiveness (RBE) between clinically used photon-based sources. A microdosimetric formalism using Monte Carlo (MC) methods can mechanistically describe the photon RBE. Experimentally derived RBE based on DNA double-strand breaks (RBEDSB) has been shown to scale with the microdosimetry quantity dose-mean lineal energy (yD).



Purpose:

To calculate microdosimetric spectra for clinically relevant photon sources, spanning from soft x-rays produced by a 50 kVp x-ray source through various brachytherapy sources up to a 6 MV medical linac. Furthermore, we investigated the correlation between RBEDSB and yD of different photon sources.



Methods:

Photon sources simulated include low-energy x-rays (50 kVp), orthovoltage x-rays (225 kVp), high-dose-rate brachytherapy sources (75Se, 192Ir and 60Co), and a 6 MV medical linac. Secondary electron spectra at the cellular level were calculated for in vitro cell irradiation setups using Geant4 MC-based packages, RapidBrachyMCTPS and RapidExternalBeam. The obtained spectra were used in MicroDose, a microdosimetry simulation software, to obtain microdosimetric quantities, including single-event lineal energy (y) and specific energy (z) spectra, and dose-mean and frequency-mean quantities (yF, yD, zsF, zsD). Uniform spherical targets (1–14 μm radius) and realistic HeLa and PC3 cell nucleus models were simulated using cell size data obtained from literature and nuclei size data from confocal microscopy imaging. Radiobiological experiments using γH2AX foci quantified DNA double-strand breaks for HeLa and PC3 cells after irradiations with 50 and 225 kVp, 192Ir, and 6 MV linac, and RBEDSB was determined using 225 kVp as the reference.



Results:

The calculated yD (yF) is within the 3.5–1.2 keV/μm range (1.8–0.2 keV/μm) for 1 μm simulated target size between the lowest energy 50 kVp x-ray source and the highest energy 6 MV linac source, respectively. For the HeLa and PC3 cell nuclei models based on microscopy data, yD (yF) spans from 1.6 to 0.6 keV/μm (0.7 to 0.2 keV/μm). When compared between different target sizes, yD (yF) ranges from 3.5 to 1.0 (1.8–0.4) keV/μm between 1 and 10 μm radius targets for the 50 kVp x-ray source. A smaller change is observed for 6 MV linac, ranging from 1.2 to 0.5 keV/μm and 0.23 to 0.22 keV/μm for yD and yF, respectively. For the simulated 75Se source currently under investigation, the calculated yD values are 11%–24% higher relative to those of 192Ir in the range of target sizes between 1 and 14 μm in radius. RBEDSB for HeLa cells was 1.4 ± 0.7 for 50 kVp x-rays, 0.5 ± 0.2 for 192Ir, and 0.7 ± 0.4 for 6 MV linac irradiations. For PC3 cells, RBEDSB was 1.3 ± 0.6, 0.8 ± 0.4 and 0.5 ± 0.3 for 50 kVp, 192Ir and 6 MV linac, respectively. Measured RBEDSB values are consistent with yD ratios of the corresponding photon sources for HeLa and PC3 nucleus models.



Conclusions:

Microdosimetric spectra strongly depend on the simulated energy of photon sources and target size, with yD and zsD decreasing by a factor of ≈2–3 between diagnostic 50 kVp and 6 MV therapeutic x-rays for target sizes from 1–14 μm in radius. The early damage RBEDSB indicates this stochastic change in energy density between various photon sources as the yields of γH2AX foci per nucleus scale with yD of the source.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

Background:
Radiobiological data suggests variations in relative biological effectiveness (RBE) between clinically used photon-based sources. A microdosimetric formalism using Monte Carlo (MC) methods can mechanistically describe the photon RBE. Experimentally derived RBE based on DNA double-strand breaks (RBEDSB) has been shown to scale with the microdosimetry quantity dose-mean lineal energy (yD).

Purpose:
To calculate microdosimetric spectra for clinically relevant photon sources, spanning from soft x-rays produced by a 50 kVp x-ray source through various brachytherapy sources up to a 6 MV medical linac. Furthermore, we investigated the correlation between RBEDSB and yD of different photon sources.

Methods:
Photon sources simulated include low-energy x-rays (50 kVp), orthovoltage x-rays (225 kVp), high-dose-rate brachytherapy sources (75Se, 192Ir and 60Co), and a 6 MV medical linac. Secondary electron spectra at the cellular level were calculated for in vitro cell irradiation setups using Geant4 MC-based packages, RapidBrachyMCTPS and RapidExternalBeam. The obtained spectra were used in MicroDose, a microdosimetry simulation software, to obtain microdosimetric quantities, including single-event lineal energy (y) and specific energy (z) spectra, and dose-mean and frequency-mean quantities (yF, yD, zsF, zsD). Uniform spherical targets (1–14 μm radius) and realistic HeLa and PC3 cell nucleus models were simulated using cell size data obtained from literature and nuclei size data from confocal microscopy imaging. Radiobiological experiments using γH2AX foci quantified DNA double-strand breaks for HeLa and PC3 cells after irradiations with 50 and 225 kVp, 192Ir, and 6 MV linac, and RBEDSB was determined using 225 kVp as the reference.

Results:
The calculated yD (yF) is within the 3.5–1.2 keV/μm range (1.8–0.2 keV/μm) for 1 μm simulated target size between the lowest energy 50 kVp x-ray source and the highest energy 6 MV linac source, respectively. For the HeLa and PC3 cell nuclei models based on microscopy data, yD (yF) spans from 1.6 to 0.6 keV/μm (0.7 to 0.2 keV/μm). When compared between different target sizes, yD (yF) ranges from 3.5 to 1.0 (1.8–0.4) keV/μm between 1 and 10 μm radius targets for the 50 kVp x-ray source. A smaller change is observed for 6 MV linac, ranging from 1.2 to 0.5 keV/μm and 0.23 to 0.22 keV/μm for yD and yF, respectively. For the simulated 75Se source currently under investigation, the calculated yD values are 11%–24% higher relative to those of 192Ir in the range of target sizes between 1 and 14 μm in radius. RBEDSB for HeLa cells was 1.4 ± 0.7 for 50 kVp x-rays, 0.5 ± 0.2 for 192Ir, and 0.7 ± 0.4 for 6 MV linac irradiations. For PC3 cells, RBEDSB was 1.3 ± 0.6, 0.8 ± 0.4 and 0.5 ± 0.3 for 50 kVp, 192Ir and 6 MV linac, respectively. Measured RBEDSB values are consistent with yD ratios of the corresponding photon sources for HeLa and PC3 nucleus models.

Conclusions:
Microdosimetric spectra strongly depend on the simulated energy of photon sources and target size, with yD and zsD decreasing by a factor of ≈2–3 between diagnostic 50 kVp and 6 MV therapeutic x-rays for target sizes from 1–14 μm in radius. The early damage RBEDSB indicates this stochastic change in energy density between various photon sources as the yields of γH2AX foci per nucleus scale with yD of the source.

2024

Diaz-Martinez, Victor D; Cyr, Mélodie; Devic, Slobodan; Tomic, Nada; Lewis, David F; Enger, Shirin A

Investigation of dosimetric characteristics of radiochromic film in response to alpha particles emitted from Americium-241 Journal Article

In: 2024.

Links | BibTeX

2022

Martinez, Victor Daniel Diaz; Carroll, Liam; Enger, Shirin A.

Monte Carlo Simulation of the 224Ra Decay Chain and the Diffusion of 220Rn for Diffusing Alpha-Emitters Radiotherapy Proceedings Article

In: MEDICAL PHYSICS, pp. E828–E828, WILEY 111 RIVER ST, HOBOKEN 07030-5774, NJ USA 2022.

BibTeX

Martinez, Victor Daniel Diaz; Cyr, Melodie; Slobodan, Devic; Tomic, Nada; Lewis, David F; Enger, Shirin A.

Use of the Monte Carlo Method to Relate GAFCHROMIC (R) EBT3 Film Response to Absorbed Dose for Alpha Particle Dosimetry Proceedings Article

In: MEDICAL PHYSICS, pp. 5653–5653, WILEY 111 RIVER ST, HOBOKEN 07030-5774, NJ USA 2022.

BibTeX