Room: Exhibit Hall
Purpose: To compare treatment plan quality and feasibility of VMAT for left breast/chest-wall radiotherapy including internal mammary (IM), supraclavicular (S/C) and axillary (AX) nodes using continuous positive airway pressure (CPAP) and free breathing (FB) for patients who were unable to reproduce deep inspiration breath hold (DIBH).
Methods: Two patients were selected for this preliminary study. All PTVs (left breast/chest-wall, IM, S/C, and AX) were contoured according to RTOG 1304. Single isocenter VMAT (RapidArc) plans were generated with CPAP and FB CT images using four 180Â° partial arcs with 2 cm overlapping jaws (two clockwise and two counterclockwise; gantry angle 310Â°-130Â°) to encompass PTVs with involved supraclavicular and IMN with 30Â° or 330Â° collimator angles, using Eclipse TPS. Prescribed dose to PTV was 50 Gy in 25 fractions without boost dose. Treatment plans were evaluated by a single radiation oncologist.
Results: Both CPAP and FB VMAT plans showed comparable PTV coverages and judged clinically acceptable per RTOG 1304. CPAP plans decreased heart dose compared to FB plans. The mean heart dose was 4.65Â±0.25 Gy for CPAP and 6.39Â±051 Gy for FB plans. CPAP inflated thorax and displaced left-side diaphragm â‰¥2.5 cm inferiorly compared to FB which increased the left lung volume 30% or more. CPAP plans lowered radiation dose to lung compared to FB plans. The mean ipsilateral lung dose was 14.83Â±0.58 Gy vs. 18.07Â±0.98 Gy and V20Gy was 26.50Â±3.09% vs. 28.4Â±15.56% for CPAP and FB plans, respectively. The mean total lung dose was 8.69Â±0.49 Gy vs. 9.62Â±0.94 Gy, and mean contralateral lung dose 2.87Â±0.23 Gy and 3.30Â±0.45 Gy for CPAP and FB plans, respectively.
Conclusion: Based on our study, single isocenter CPAP VMAT plan can lower radiation dose to the heart and lung over FB VMAT plan in treating the left breast/chest-wall radiotherapy including IM, S/C, and AX.