Speaker
Description
Evaluation of secondary cancer risk after radiotherapy in high- and intermediate-risk
prostate cancer patients
Background and Purpose:
External beam radiotherapy is the primary approach for cancer treatment. This method can result in radiation-induced second cancers that mainly affect healthy tissues and organs at risk due to out-of-field doses. This study aimed to evaluate the risk of secondary cancer using the excess absolute risk (EAR) assessment method for OARs which includes thirty prostate cancer patients with high and intermediate risks who received either 6 MV three-dimensional conformal radiotherapy (3D CRT) or modulated volumetric arc therapy (VMAT).
Materials and Methods:
Two types of planning target volumes including PTV1 and PTV2 were defined for each modality. VMAT plans were generated for prostate cancer with simultaneous integrated boost, in which PTV1 received 76 Gy, and 56 Gy for PTV2. The PTV2 in this case was the sum of the pelvic lymph nodes and seminal vesicles. In the case of 3D CRT, PTV1 received 46 Gy including the prostate, seminal vesicles, and pelvic lymph nodes and PTV2 received 28 Gy only for prostate cancer, The EAR was evaluated using the Schneider concept based on the organ equivalent dose (OED). Thus, the EAR of the rectum, bladder, pelvic bone, and healthy pelvic tissues were calculated and compared using three models such as the Mechanistic model, the Exponential Linear model, and specific mechanistic models of sarcoma.
Results:
The analysis results based on mean EAR values for the rectum, bladder, pelvic bones, and healthy pelvic tissues using three different dose-response models were presented in Table 1. Statistically significant differences in the mean EAR values were observed between the 3D CRT and VMAT for the rectum and bladder respectively. Furthermore, the mean EAR values in the rectum for the 3D CRT were higher than those evaluated using VMAT. In the case of the bladder, a similar trend was observed only in one case (3.76±0.62 >3.74±0.62). No statistically significant differences in the mean EAR values were observed between the 3D CRT and VMAT for pelvic bone and healthy pelvic tissue.
Conclusion:
The overall EARs analysis for both radiation modalities indicated that 3DCRT's risk of inducing carcinoma in the rectum was higher than that of VMAT. However, prospective clinical trials with a larger patient cohort would be necessary to validate predicted models.
| Abstract Category | Medical Physics |
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