Room: Exhibit Hall | Forum 1
Purpose: To evaluate the dosimetric difference, multi-criteria optimization (MCO) planning efficiency and radiobiological benefits for 10-MV vs. 6-MV VMAT.
Methods: 16 patients with deep-seated tumors (five GYN with nodes, five pancreatic, three prostate without nodes and three with nodes), originally treated by 6-MV MCO-VMAT, were re-planned for 10-MV MCO-VMAT. 13 patients had one course and the three prostate+nodes patients had two, resulting in 19 MCO-VMAT plans plus three composite plans. The 6- and 10-MV plans were blind-reviewed by three radiation oncologists. Organ dose, integral dose and total MU were compared with a paired t-test. Navigation efficiency was quantified by the difference before and after navigation. All 6- and 10-MV plans were QA-ed using ArcCheck on the same linac and same day. The excess relative risk (ERR) for secondary malignancies was assessed using data from BEIR VII report. Total neutron dose from 10-MV was <1 cGy for all patients and thus ignored.
Results: Physicians preferred 10-MV for 14 individual plans plus all three composite plans, 6-MV for two plans, and had no preference on three. On average, the 10-MV plans provided mean dose reduction >1 Gy for bone marrow, kidneys, femurs, small bowel, rectum and bladder in GYN patients, for liver, small and large bowels in pancreatic patients, for femurs in all prostate patients, and for small bowel, rectum and bladder in prostate+nodes patients. The 10-MV plans resulted in 6.8% reduction on integral dose (p<0.0001), but a 5.7% increase in total MU (p=0.012). Navigation was more efficient for 10-MV in 74% of the 263 targets and organs. All 10-MV plans passed clinical QA. Substantial ERR reduction over 1 was found for kidneys, bladder and rectum for 10-MV.
Conclusion: 10-MV VMAT can decrease organ and integral dose, improve planning efficiency and may reduce the risk of secondary malignancies compared to 6-MV VMAT.