Purpose: Very high energy electrons (VHEEs) present promising clinical advantages over conventional beams. They are able to target deep-seated tumors due to their increased range and improved ...penumbra compared to low energy electrons. VHEEs are also relatively insensitive to tissue heterogeneities, and are able to be electromagnetically scanned. These advantages facilitate their use in conjunction with spatial fractionation techniques or FLASH irradiations. However, the lack of radiobiological data concerning their biological efficacy is a limiting factor. This study aims to characterize different VHEE beams against clinically available beams by making use of Monte Carlo (MC) based numerical simulations to compare their macroand microdosimetric properties.Methods: All simulations were performed on GATE version 8.2. A solid water phantom was irradiated by the following beams: 5, 20, 100, and 300 MeV electrons, a 60Co source (1.25 MeV photons), 105 MeV protons, 194.2 MeV/nucleon 12C ions, and 262 MeV/nucleon 20Ne ions. The dose-averaged linear energy transfer (¯(L_d )) was evaluated as the macrodosimetric quantity of interest. On a microscopic scale, the lineal energy y was used in order to account for the stochasticity of irradiations. The dose-mean lineal energy ¯(y_d ) and the lineal energy distribution described as a function of its dose density, d(y), were calculated. A tissue equivalent proportional counter (TEPC) was implemented in GATE to record the lineal energy spectra. Finally, the modified microdosimetric kinetic model (MKM) was used to calculate the respective cell survival curves using biological parameters of HSG cell line and the lineal energy spectra as inputs.Results: From the macrodosimetric point of view, VHEEs present a potential improved biological efficacy over clinical photon/electron beams due to their increased ¯(L_d ). At a depth of 4 cm in water, the ratio of 300 MeV ¯(L_d ) values to other particles is 0.2, 1.9, 3.2, and 2.4 for protons, 100 MeV electrons, 20 MeV electrons, and photons respectively. The microdosimetric data, however, suggests no increased biological effectiveness of VHEEs over clinical electron beams, as seen in Figure 1 and Table 1. No significant differences were found between their lineal energy spectra nor their ¯(y_d ) depth profiles. Correspondingly, application of the MKM yielded similar cell survival curves, resulting in relative biological effectiveness (RBE10) values for VHEEs of approximately 1. Furthermore, RBE values of 1.2, 2.9 and 3.3 were obtained for proton, carbon-ion and neon-ion beams respectively, while ¯(L_d ) values above 200 keV/µm and lineal energies as high as 2000 keV/µm were obtained in the Bragg peak region for neon-ions.Conclusion: This study represents a first step towards a full evaluation of the biological efficacy of VHEE beams. The biologically relevant information obtained from these theoretical MC simulations could be used to complement further experiments which explore the radiobiological response to VHEE treatment.
Purpose:
To investigate behaviors that may be in conflict with ethical standards of the Medical Physics Residency (MedPhys) Match process and with best practices for adhering to non-discrimination ...regulations of the Equal Employment Opportunity Commission (EEOC).
Methods:
A confidential survey was sent to registered applicants and program directors for the 2014/2015 MedPhys Match. Survey questions included demographics, application, interview and post-interview experiences, match results, and overall satisfaction with the process.
Results:
Of the 402 candidates emailed, 109 completed the survey. 48% of the respondents did match with a residency position in 2015. Of the 77 program directors emailed, 42 completed the survey. Selected results of the surveys are included. 69% of candidate respondents indicated that they were asked during interviews where else they were interviewing; 31.7% of those respondents indicated that they were uncomfortable or very uncomfortable answering. 40% of candidate respondents (39% of males, 41% of females) indicated that they were asked about their marital or relationship status. 23% of the respondents (19% of males, 33% of females) indicated that they were asked about children or plans to have children. 57% who were asked this question (27% of males, 89% of females) indicated that they were uncomfortable/very uncomfortable answering. 29% were told by a program that they were “ranked to match” or told their rank prior to the match deadline. Only 13% indicated that they were asked by a program how highly they were going to rank that program or asked which program they would rank number one. Among that 13%, 64% indicated that they were uncomfortable/very uncomfortable answering.
Conclusion:
In the inaugural year of the MedPhys Match, there were instances of ethical violations and discriminatory interviewing. Training on the Match rules and EEOC guidelines can decrease these instances and thereby increase the fairness of the residency selection process.
TU‐F‐19A‐01: New Member Symposium Sherouse, G; Miller, R
Medical physics (Lancaster),
June 2014, 2014-06-00, Letnik:
41, Številka:
6Part27
Journal Article
Recenzirano
As a new member of the AAPM, it’s easy to feel overwhelmed by the size and complexity of the association and to be unaware of the benefits and opportunities available to members. At this year’s AAPM ...annual meeting in Austin, we will host a New Member Symposium where you can learn more about the organization, member resources, and opportunities to get involved.
Learning Objectives:
1.Welcome, introduction to, and overview of AAPM organization
2.Introduction to medical physics profession
Registered attendees will receive a raffle ticket for a drawing at the symposium to win a complimentary registration for the 2015 Annual Meeting in Anaheim!
In addition, all new members who register for the Symposium will receive a drink ticket, good for one complimentary soda or beer served during the social following.
Brachytherapy is a well-established therapeutic technique for treating tumours involving the placement of radioactive encapsulated sources close to or in direct contact with a tumour. Considering ...this type of treatments, the purpose of this work is to incorporate Monte Carlo (MC) simulation into brachytherapy treatment planning. This approach allows for precise estimation of dose distribution in target organs as well as in Organs At Risk (OAR), due to the accuracy of the MC methods in describing dose deposition.
To carry out this work, the medical image visualization and dose analysis tools provided by the open-source planner PlanUNC (PLUNC) were utilized. Additionally, a set of programs was developed which automatize the main steps of a treatment planning segmentation, from DICOM images, exporting geometries determining materials and seeds positions, creating an input file for the simulation code (MCNP6.2) and, finally, reading and visualization of the simulation results in the format of the used planning software. With this methodology, results of 3D dose distribution, isodoses curves, Dose-Volume Histograms (DVH), and absorbed dose in OAR were obtained. Thus, the integration of the MC simulation into PLUNC for brachytherapy treatments, has demonstrate its utility for this purpose, showing adaptability to different anatomical geometries and extensibility to various types of treatments.
•More accuracy in patient dose estimation when using Monte Carlo simulation.•Methodology has been designed to incorporate Monte Carlo into brachytherapy planning.•Realistic simulations with patient CT images allows calculating dose distribution.•Adequate accuracies and computing times compared to real planning treatment.•In-depth analysis of medically valid outcome data for brachytherapy treatments.
PurposeTargeted alpha therapy (TAT) takes advantage of the short‐range and high linear‐energy‐transfer of α‐particles and is increasingly used, especially for the treatment of metastatic lesions. ...Nevertheless, dosimetry of α‐emitters is challenging for the very same reasons, even for in vitro experiments. Assumptions, such as the uniformity of the distribution of radionuclides in the culture medium, are commonly made, which could have a profound impact on dose calculations. In this study we measured the spatial distribution of α‐emitting 212Pb coupled to an anti‐VCAM‐1 antibody (212Pb‐αVCAM‐1) and its evolution over time in the context of in vitro irradiations.MethodsTwo experimental setups were implemented without cells to measure α‐particle count rates and energy spectra in culture medium containing 15 kBq of 212Pb‐α‐VCAM‐1. Silicon detectors were placed above and below cell culture dishes for 20 hours. One of the dishes had a 2.5‐µm‐thick mylar‐base allowing easy detection of the α‐particles. Monte Carlo simulations were performed to analyze experimental spectra. Experimental setups were modelled and α‐energy spectra were simulated in the silicon detectors for different decay positions in the culture medium. Simulated spectra were then used to deconvolute experimental spectra to determine the spatial distribution of 212Pb‐αVCAM‐1 in the medium. This distribution was finally used to calculate the dose deposition in cell culture experiments.ResultsExperimental count rates and energy spectra showed differences in measurements taken at the top and the bottom of dishes and temporal variations that did not follow 212Pb decay. The radionuclide spatial distribution was shown to be composed of a uniform distribution and concentration gradients at the top and the bottom, which were subjected to temporal variations that may be explained by gravity and electrostatic attraction. The absorbed dose in cells calculated from this distribution was compared with the dose expected for a uniform and static distribution and found to be 1.75 times higher, which is highly significant to interpret biological observations.ConclusionThis study demonstrated that accurate dosimetry of α‐emitters requires the experimental determination of radionuclide spatial and temporal distribution and highlighted that in vitro assessment of dose for TAT cannot only rely on a uniform distribution of activity in the culture medium. The reliability and reproducibility of future experiments should benefit from specifically developed dosimetry tools and methods.
PDF
