Evaluation of Electron Contamination in Cancer Treatment with Megavoltage Photon Beams: Monte Carlo Study
Background: Megavoltage beams used in radiotherapy are contaminated with secondary electrons. Different parts of linac head and air above patient act as a source of this contamination. This contamination can increase damage to skin and subcutaneous tissue during radiotherapy. Monte Carlo simulat...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Shiraz University of Medical Sciences
2015-03-01
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| Series: | Journal of Biomedical Physics and Engineering |
| Subjects: | |
| Online Access: | http://www.jbpe.org/Journal_OJS/JBPE/index.php/jbpe/article/view/328 |
| Summary: | Background: Megavoltage beams used in radiotherapy are contaminated with secondary
electrons. Different parts of linac head and air above patient act as a source of
this contamination. This contamination can increase damage to skin and subcutaneous
tissue during radiotherapy.
Monte Carlo simulation is an accurate method for dose calculation in medical dosimetry
and has an important role in optimization of linac head materials. The aim of this
study was to calculate electron contamination of Varian linac.
Materials and Method: The 6MV photon beam of Varian (2100 C/D) linac
was simulated by Monte Carlo code, MCNPX, based on its company’s instructions.
The validation was done by comparing the calculated depth dose and profiles of simulation
with dosimetry measurements in a water phantom (error less than 2%). The
Percentage Depth Dose (PDDs), profiles and contamination electron energy spectrum
were calculated for different therapeutic field sizes (5×5 to 40×40 cm2
) for both linacs.
Results: The dose of electron contamination was observed to rise with increase in
field size. The contribution of the secondary contamination electrons on the surface
dose was 6% for 5×5 cm2
to 27% for 40×40 cm2
, respectively.
Conclusion: Based on the results, the effect of electron contamination on patient
surface dose cannot be ignored, so the knowledge of the electron contamination is
important in clinical dosimetry. It must be calculated for each machine and considered
in Treatment Planning Systems. |
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| ISSN: | 2251-7200 2251-7200 |