Abstract
The application of intensity‐modulated radiation therapy (IMRT) has enabled the delivery of high doses to the target volume while sparing the surrounding normal tissues. The drawbacks of intensity modulation, as implemented using a computer‐controlled multileaf collimator (MLC), are the larger number of monitor units (MUs) and longer beam‐on time as compared with conventional radiotherapy. Additionally, IMRT uses more beam directions—typically 5 – 9 for prostate treatment—to achieve highly conformal dose and normal‐tissue sparing. In the present work, we study radiation‐induced cancer risks attributable to IMRT delivery using MLC for prostate patients.Whole‐body computed tomography scans were used in our study to calculate (according to report no. 116 from the National Council on Radiation Protection and Measurements) the effective dose equivalent received by individual organs. We used EGS4 and MCSIM to compute the dose for IMRT and three‐dimensional conformal radiotherapy. The effects of collimator rotation, distance from the treatment field, and scatter and leakage contribution to the whole‐body dose were investigated. We calculated the whole‐body dose equivalent to estimate the increase in the risk of secondary malignancies.Our results showed an overall doubling in the risk of secondary malignancies from the application of IMRT as compared with conventional radiotherapy. This increase in the risk of secondary malignancies is not necessarily related to a relative increase in MUs. The whole‐body dose equivalent was also affected by collimator rotation, field size, and the energy of the photon beam. Smaller field sizes of low‐energy photon beams (that is, 6 MV) with the MLC axis along the lateral axis of the patient resulted in the lowest whole‐body dose. Our results can be used to evaluate the risk of secondary malignancies for prostate IMRT patients.PACS: 87.53.wz, 87.53.‐j
Highlights
15 Stathakis et al.: Monte Carlo determination of radiation-induced...(3D-CRT) and, more recently, intensity-modulated radiotherapy (IMRT)
Advanced radiotherapy treatments with IMRT can deliver dose distributions that are more conformal to the tumor targets and that simultaneously minimize radiation damage to the surrounding normal tissues.[1,2,3,4,5,6,7]
linear accelerator (LINAC) verification and head leakage Monte Carlo simulations of the Siemens Primus 6-MV, 10-MV, and 18-MV beams were verified by comparing the MCSIM dose calculations with measurements for various fields
Summary
15 Stathakis et al.: Monte Carlo determination of radiation-induced...(3D-CRT) and, more recently, intensity-modulated radiotherapy (IMRT). Advanced radiotherapy treatments with IMRT can deliver dose distributions that are more conformal to the tumor targets and that simultaneously minimize radiation damage to the surrounding normal tissues.[1,2,3,4,5,6,7]. Depending on the design of the accelerator’s multileaf collimator (MLC) and the treatment optimization system used, a usual prostate IMRT treatment may consist of 50 – 100 MLC field segments that may take 3 – 10 times the MUs of a comparable 3D-CRT or conventional prostate treatment.[8,9] Compared with conventional treatments, IMRT uses more beam directions (typically 5 – 9) to achieve optimal dose conformity to the target volume while reducing the dose to the surrounding critical structures. IMRT treatment may substantially increase the normal-tissue volume receiving low-dose radiation over the dose seen in conventional and 3D-CRT treatment
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