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Comparison of Two RapidArc Delivery Strategies in Stereotactic Body Radiotherapy of Stage I and II Peripheral Lung Tumors with Unflattened Beams

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B Huang

B Huang*1, J Lu1 , P Lin2 , J Chen1 , Y Kuang3 , C Chen1, (1) Cancer Hospital of Shantou University Medical College, Shantou, Guangdong Province, China, (2) The Second Affiliated Hospital of Shantou University Medical College, Shantou, Guangdong Province, China,(3) University of Nevada, Las Vegas, Las Vegas, NV


TH-C-12A-2 Thursday 10:15AM - 12:15PM Room: 12A

Purpose:The full arcs strategy used in SBRT with RapidArc and unflattened (FFF) beams in large and heterogeneous peripheral non-small-cell lung cancer (NSCLC) appears to be suboptimal as it increases the disadvantageous dose to the contralateral lung, which potentially increases the toxicity to surrounding tissues. In this study, we investigated, for the first time, the dose delivery strategies using partial arcs (PA) and the fully rotational arcs with avoidance sectors (FAAS) for SBRT with FFF beams in peripheral NSCLC patients.

Methods:Eighteen patients with NSCLC (stage I and II) were selected for this study. Nine patients with a GTV <= 10cc were designated as the small tumor group. The remaining nine patients with a GTV between 10 cc and 44 cc were assigned to the large tumor group. The treatment plans were generated in eighteen patients using PA and FAAS, respectively, and delivered with a Varian TrueBeam Linac. Dosimetry of the target and organs at risk (OAR), total MU, out-of-field dose, and delivery time were analyzed. Delta4 and Portal dosimetry were employed to evaluate the delivery accuracy.

Results:For the small tumor group, the FAAS plans significantly achieved a better conformity index, the lower total MU and out-of-field dose, a shorter treatment time, and the reduced doses to cord, heart, and lung (p < 0.05). But the target doses were slightly higher than that delivered by PA plans. For the large tumor group, the PA plans significantly attained a better conformity index and a shorter treatment time (p < 0.05). Furthermore, all plans achieved a high pass rate, with all the gamma indices greater than 97% at the Γ3mm, 3% threshold.

Conclusion:This study suggests that FAAS strategy is more beneficial for small tumor patients undergoing lung SBRT with FFF beams. However, for large tumor patients, PA strategy is recommended.

Funding Support, Disclosures, and Conflict of Interest: NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship

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