Purpose: This study was aimed to study the effects oflow‐ and high‐energy intensity‐modulated (IMRT)photon beams on the planning of target volume and thecritical organs in cases of prostate cancer. Methods: Thirty plans were generated using either 6 MV or 15 MValone, and both 6 and 15 MV beams. For each plangenerated using suitable planning objectives and doseconstraints, which was set to be identical except thebeam energy. The plans were analyzed in terms of targetcoverage, conformity, and homogeneity regardless ofbeam energy. Results: Mean percentage of V 70Gy ofrectal wall in 6 MV, 15 MV and mixed‐energy plans was16.9%, 17.8%, and 16.4%, respectively, while the meanpercentage of V 40Gy was 53.6%, 52.3%, and 50.4%.The mean dose to femoral heads in 6 MV, 15 MV, andmixed‐energy plans were 30.1 Gy, 25.5 Gy, and 25.4 Gy,respectively. The integral dose of 6 MV plans was 10%(on average) larger than those of 15 MV or mixed‐energyplans. Conclusion: The preliminary results suggested thatmixed‐energy IMRT plans may take an advantage of thedosimetric characteristics of low‐ and high‐energybeams. Although the reduction of dose to the organs atrisk may not be clinically relevant, in this study, mixingenergy in an IMRT plans showed better OAR sparingand for deep‐seated tumors, the overall plan quality wasimproved.
Influence of distinct radiotherapy techniques to induce second cancer risks in left breast cancer. Material and methods: Ten female patients with intact left breast cancer. Two treatment plans for each patient: 1) two tangential beams 3D-Conformal radiotherapy, 2) intensity-modulated radiotherapy (IMRT) plan. Estimation of second cancer risk from Organ equivalent dose models (OEDs) in three dose-response model for organs at risk in left breast cases. Results: The P-value for OED models in 3D-IMRT for left lung, both lung, heart, right lung, right breast, thyroid, liver and spinal cord in linear dose model was 0.016, 0.005, 0.019, 3.95E−06, 5.79E−07, 0.003, 1.78E−10 and 0.000206475 respectively, for linear exponential dose model 0.0577, 0.024, 0.031, 3.40E−06, 3.28E−07, 0.003, 2.01E−10 and 0.000120072 respectively and in plateau dose model 0.088, 0.042, 0.039, 3.18E−06, 2.53E−07, 0.003, 2.27E−10 and 9.00535E−05 respectively. Conclusion: organ equivalent dose models for organs at risk increasing in IMRT than tangential beams.
Influence of dosimetric considerations in evaluating second cancer risks in prostate cancer. Material and methods: Fifteen patients in this study suffering from early stage of prostate cancer, each patient underwent three plans: 1) Three-dimensional conformal radiation therapy (3DCRT), 2) Rotation therapy (Arc therapy), and 3) intensity-modulated radiation therapy (IMRT) plan. Estimate secondary metastasis risk models: Excess Relative Risk (ERR) and Excess absolute risk (EAR) based on age of exposure by taking dosimetry data from Dose Volume Histograms (DVHs) to calculate risk models. Result: The second cancer risk models (ERR and EAR) for organs at risk OARs decrease with increasing age of exposure for 3D-CRT, ARC and IMRT and there is no significant difference for ERR and EAR model for developing second cancer risk in 3D-CRT, ARC and IMRT.
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