ESTRO 2025 - Abstract Book

S2860

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

3186

Digital Poster Advancing Lung Cancer Radiotherapy Using VMAT with Dynamic Collimator Rotation and Modulated Ports for Improved Dosimetric Endpoints and Efficiency Yin Gao 1 , Michael Salerno 1 , Melissa Vila 1 , Taoran Li 1,2 , Lei Dong 1 , Kevin Teo 1 1 Radiation Oncology, University of Pennsylvania, Philadelphia, USA. 2 Medical Affairs, Varian Medical Systems, Palo Alto, USA Purpose/Objective: Lung cancer treatment planning is challenging due to the need to limit the dose to the lungs and heart, reducing risks of complications like radiation pneumonitis and cardiac injury. A novel solution, RapidArc Dynamic-RAD (Varian Medical Systems, Palo Alto, USA), leverages the conformality of VMAT with IMRT-like modulation ports, including using a dynamic collimator. This study, for the first time, evaluates RAD in lung cancer radiotherapy by comparing plan quality and planning efficiency with conventional VMAT. Material/Methods: We selected 11 lung cancer patients (9 with T3 tumors and mediastinal node involvement, and 2 with T1 tumors), target segmentations were verified by a radiation oncologist, with an average target volume of 560±195cc. Four treatment plans were created for each patient by a dosimetrist following institutional guidelines: (1) conventional VMAT with 1-2 arcs, half or full based on target size/location; (2) RAD balancing modulated ports and arcs (RAD-Arc); (3) RAD emphasizing modulated ports (RAD-Static); and (4) RAD prioritizing arcs (RAD-Balanced). All RAD plans used one arc (half or full) with 2–3 modulated ports. The modulated ports were empirically placed medially to minimize lung dose (see Fig. 1). Dynamic collimator rotation was optimized in all RAD plans. All plans used 6MV photon, with a prescription of 66Gy in 33 fractions, and normalization set to PTV D95%=95%. Dose metrics and planning times were compared between VMAT and RAD plans using a two-tailed paired t-test (p≤0.05). Results: RAD, regardless of emphasis on arcs or modulated ports, showed superior OAR sparing, particularly lungs, heart, left anterior descending artery (LAD), and cord, compared to VMAT. The RAD-Arc plan reduced LAD V15Gy by 1.03±1.97Gy, heart V5Gy by 5.15±4.59%, and spinal cord max dose by 1.82±3.97Gy. The RAD-Static plan decreased lung V5Gy, V20Gy, V25Gy, and mean dose by 6.33±2.97%, 2.43±2.43%, 1.64±1.47%, and 0.92±0.58Gy, respectively, with statistical significance. Lung V50Gy slightly increased (~0.3%) due to normalization based on target coverage, which is considered clinically acceptable. Statistical comparisons are summarized in Figure 2. Overall, RAD achieved clear reductions in dose to all OARs. Additionally, RAD improved planning efficiency, reducing average planning time to ~12 minutes, significantly faster than VMAT, which required ~45 minutes.