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Monte Carlo modeling of electron beams from a NEPTUN 10PC medical linear accelerator

Jabbari N., Hashemi-Malayeri B.

Nukleonika

2009

Vol. 54, No. 4

233-238

The Monte Carlo (MC) simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation. With the rapid development of computer technology, MC-based treatment planning for radiation therapy is becoming practical. A basic requirement for MC treatment planning is a detailed knowledge of radiation beams of medical linear accelerators (linacs). A practical approach to acquire this knowledge is to perform MC simulation of radiation transport for linacs. The aims of this study were: modeling of the electron beams from the NEPTUN 10PC linear accelerator (linac) with the MC method, obtaining of the energy spectra of electron beams, and providing the phase-space files for the electron beams of this linac at different field sizes. Electron beams produced by the linac were modeled using the BEAMnrc MC system. Central axis depth-dose curves and dose profiles of the electron beams were measured experimentally and also calculated with the MC system for different field sizes and energies. In order to benchmark the simulated models, the percent depth dose (PDD) and dose-profile curves calculated with the MC system were compared with those measured experimentally with diode detectors in an RFA 300 water phantom. The results of this study showed that the PDD and dose-profile curves calculated by the MC system using the phase-space data files matched well with the measured values. This study demonstrates that the MC phase-space data files can be used to generate accurate MC dose distributions for electron beams from NEPTUN 10PC medical linac.

Monte Carlo calculation of scattered radiation from applicators in low energy clinical electron beams

Jabbari N., Hashemi-Malayeri B., Farajollahi A. R., Kazemnejad A.

Nukleonika

2007

Vol. 52, nr 3

97-103

. In radiotherapy with electron beams, scattered radiation from an electron applicator influences the dose distribution in the patient. The contribution of this radiation to the patient dose is significant, even in modern accelerators. In most of radiotherapy treatment planning systems, this component is not explicitly included. In addition, the scattered radiation produced by applicators varies based on the applicator design as well as the field size and distance from the applicators. The aim of this study was to calculate the amount of scattered dose contribution from applicators. We also tried to provide an extensive set of calculated data that could be used as input or benchmark data for advanced treatment planning systems that use Monte Carlo algorithms for dose distribution calculations. Electron beams produced by a NEPTUN 10PC medical linac were modeled using the BEAMnrc system. Central axis depth dose curves of the electron beams were measured and calculated, with and without the applicators in place, for different field sizes and energies. The scattered radiation from the applicators was determined by subtracting the central axis depth dose curves obtained without the applicators from that with the applicator. The results of this study indicated that the scattered radiation from the electron applicators of the NEPTUN 10PC is significant and cannot be neglected in advanced treatment planning systems. Furthermore, our results showed that the scattered radiation depends on the field size and decreases almost linearly with depth.