Biomedical subjects

Brian Wang

Publications and source records attributed to Brian Wang.

5 recordsLinked to original sources

PubMed2005

Simulation of organ-specific patient effective dose due to secondary neutrons in proton radiation treatment.

Cancer patients undergoing radiation treatment are exposed to high doses to the target (tumour), intermediate doses to adjacent tissues and low doses from scattered radiation to all parts of the body. In the case of proton therapy, secondary neutrons generated in the accelerator head and inside the patient reach many areas in the patient body. Due to the improved efficacy of management of cancer patients, the number of long term survivors post-radiation treatment is increasing substantially. This results in concern about the risk of radiation-induced cancer appearing at late post-treatment times. This paper presents a case study to determine the effective dose from secondary neutrons in patients undergoing proton treatment. A whole-body patient model, VIP-Man, was employed as the patient model. The geometry dataset generated from studies made on VIP-Man was implemented into the GEANT4 Monte Carlo code. Two proton treatment plans for tumours in the lung and paranasal sinus were simulated. The organ doses and ICRP-60 radiation and tissue weighting factors were used to calculate the effective dose. Results show whole body effective doses for the two proton plans of 0.162 Sv and 0.0266 Sv, respectively, to which the major contributor is due to neutrons from the proton treatment nozzle. There is a substantial difference among organs depending on the treatment site.

Computer Simulation↗

PubMed2005

Monte Carlo study of MOSFET dosemeter characteristics: dose dependence on photon energy, direction and dosemeter composition.

MOSFET dosemeters are emerging as a versatile tool in various medical physics and health physics dose measurements. It is an important but difficult task to understand their energy and directional dependences because of their unique features. This paper presents a study to characterise a MOSFET dosemeter using Monte Carlo simulation method. Monoenergetic photon beams ranging from 15 to 6 MeV were simulated to study the energy and angular dependences. The results were compared with published experimental data. The Monte Carlo model also provided insightful information on optimising the dosemeter design by examining how various regions of the dosemeter contributed to the dose. Detailed energy deposition processes were further analysed by tracking individual particles inside the dosemeter.

Electrons↗

PubMed2005

Adjoint Monte Carlo method for prostate external photon beam treatment planning: an application to 3D patient anatomy.

Recently, the theoretical framework of the adjoint Monte Carlo (AMC) method has been developed using a simplified patient geometry. In this study, we extended our previous work by applying the AMC framework to a 3D anatomical model called VIP-Man constructed from the Visible Human images. First, the adjoint fluxes for the prostate (PTV) and rectum and bladder (organs at risk (OARs)) were calculated on a spherical surface of 1 m radius, centred at the centre of gravity of PTV. An importance ratio, defined as the PTV dose divided by the weighted OAR doses, was calculated for each of the available beamlets to select the beam angles. Finally, the detailed doses in PTV and OAR were calculated using a forward Monte Carlo simulation to include the electron transport. The dose information was then used to generate dose volume histograms (DVHs). The Pinnacle treatment planning system was also used to generate DVHs for the 3D plans with beam angles obtained from the AMC (3D-AMC) and a standard six-field conformal radiation therapy plan (3D-CRT). Results show that the DVHs for prostate from 3D-AMC and the standard 3D-CRT are very similar, showing that both methods can deliver prescribed dose to the PTV. A substantial improvement in the DVHs for bladder and rectum was found for the 3D-AMC method in comparison to those obtained from 3D-CRT. However, the 3D-AMC plan is less conformal than the 3D-CRT plan because only bladder, rectum and PTV are considered for calculating the importance ratios. Nevertheless, this study clearly demonstrated the feasibility of the AMC in selecting the beam directions as a part of a treatment planning based on the anatomical information in a 3D and realistic patient anatomy.

Dose-Response Relationship, Radiation↗

PubMed2005

Dose mapping using MCNP5 mesh tallies.

Rensselaer Polytechnic Institute has a 69.6 GBq (1.88 Ci) (137)Cs source that is used for research, calibration of various instruments, and teaching. Recently it was calibrated using ion chambers. The source and room were also modeled in Monte Carlo N-Particle transport code (MCNP5) to determine if the use of a new feature called mesh tallies produces a dose map in the entire room that agrees with the measured results. The dose rate in the hallway, while the source is exposed, was also calculated. It was found that the dose rates calculated from the MCNP5 are in reasonable agreement with the measured results and theoretical predictions. It was also confirmed that the dose rates where the user often stays during the measurement are well below the annual limits. This project shows that the MCNP5 mesh tallies are useful tool for dose mapping in many operational radiation protection situations.

Cesium Radioisotopes↗

PubMed2004

Monte Carlo modeling of a high-sensitivity MOSFET dosimeter for low- and medium-energy photon sources.

Metal-oxide-semiconductor field effect transistor (MOSFET) dosimeters are increasingly utilized in radiation therapy and diagnostic radiology. While it is difficult to characterize the dosimeter responses for monoenergetic sources by experiments, this paper reports a detailed Monte Carlo simulation model of the High-Sensitivity MOSFET dosimeter using Monte Carlo N-Particle (MCNP) 4C. A dose estimator method was used to calculate the dose in the extremely thin sensitive volume. Efforts were made to validate the MCNP model using three experiments: (1) comparison of the simulated dose with the measurement of a Cs-137 source, (2) comparison of the simulated dose with analytical values, and (3) comparison of the simulated energy dependence with theoretical values. Our simulation results show that the MOSFET dosimeter has a maximum response at about 40 keV of photon energy. The energy dependence curve is also found to agree with the predicted value from theory within statistical uncertainties. The angular dependence study shows that the MOSFET dosimeter has a higher response (about 8%) when photons come from the epoxy side, compared with the kapton side for the Cs-137 source.

Computer Simulation↗