Purpose: To evaluate the potential advantages of jaw tracking for intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in spine radiosurgery. Methods: VMAT and IMRT plans were retrospectively generated for ten patients. Six plans for each patient were created in the Eclipse treatment planning system for a Varian Truebeam equipped with a Millennium 120 MLC. Plans were created to study IMRT and VMAT plans with and without jaw tracking, as well as IMRT plans of different flattening filter free (FFF) energies. Plans were prescribed to the 90% isodose line to 16 or 18 Gy in one fraction to cover 95% of the target. Planning target volume (PTV) coverage, conformity index (CI), dose to spinal cord, distance to fall off from the 90% to 50% isodose line (DTF), as well as delivery time were evaluated. Ion chamber and film measurements were performed to verify calculated and measured dose distributions. Results: Jaw tracking decreased the spinal cord dose for both IMRT and VMAT plans, but a larger decrease was seen with the IMRT plans (p=0.004 vs p=0.04). The average D10% for the spinal cord was least for the 6MV FFF IMRT plan with jaw tracking and was greatest for the 10MV FFF plan without jaw tracking. Treatment times between IMRT and VMAT plans with or without jaw tracking were not significantly different. Measured plans showed greater than 98.5% agreement for planar dose gamma analysis (3%/2 mm) and less than 2.5% for point dose analysis compared to calculated plans. Conclusion: Jaw tracking can be used to help decrease spinal cord dose without any change in treatment delivery or calculation accuracy. Lower dose to the spinal cord was achieved using 6 MV beams compared to 10 MV beams, though 10 MV may be justified in some cases to decrease skin dose.
Purpose: The effect of beam energy IMRT plans for prostate cancer was studied for competing IMRT plans optimized for delivery with either 6 or 15 MV beams. Methods: This retrospective planning study included 10 patients treated for localized prostate cancer. A dose of 66 Gy was prescribed in 33 daily fractions of 2 Gy. For inverse IMRT treatment planning, we used a 7‐coplanar non‐opposed beam arrangement at 0, 50, 100, 150, 210, 260 and 310 degree angles. To ensure that differences among plans are due only to energy selection, the beam arrangement, number of beam, and dose constraints were kept constant for all plans. The DVHs for the 6 and 15 MV plans were compared for PTV and for OARs such as the rectum, bladder and both femoral heads. Doses received by the 95% and 5% volume of PTV were less than or equal to 1% for 6 MV compared to 15 MV plan for 10 patients.Results: Percentage of doses received by the 10, 30 and 50% volume of bladder were less than or equal to 1%. Percentage of doses received by the 10, 30, and 50% volume of rectum were 1∼2% higher for 6 MV photons. Also, percentage of dosed received by the 10% and 50% volume of femur head were 4∼5% higher for 6 MV Conclusions: There is no greater advantage from 15 MV as compared with 6 MV in 95% volume of PTV coverage. Also, percentage dose received by 5% volume of PTV was no remarkable difference in 6 and 15 MV plan. However, percentage doses received by OARs volume were higher 6 MV. Therefore, we recommend the use of 15 MV for IMRT of prostate cancer to achieve better in target coverage and integral dose which can be reduce by using IMRT of 15 MV.
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