S1994
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Purpose/Objective: With the ongoing improvement in breast cancer (BC) management and patient survival, long-term radiation induced toxicities, particularly cardiac and pulmonary, have become a major concern.Therefore, optimizing radiotherapy techniques to balance target coverage and organ at risk (OAR) sparing, has become essential.This study aimed to perform a dosimetric comparison of 3D conformal radiotherapy (3D-CRT), VMAT, and hybrid VMAT (H-VMAT) techniques for left- sided locoregional BC radiotherapy. Material/Methods: Twenty-five patients previously treated with 3D-CRT for left-sided breast cancer were selected. All patients received locoregional radiotherapy including the internal mammary chain (IMC). The prescribed dose was 40.05 Gy in 15 fractions. DICOM data from the original plans were used to generate virtual VMAT and H-VMAT plans for each patient. The H-VMAT plans included two tangential static fields that delivered 53% of the prescribed dose and the dynamic partial arcs providing the final 47% of the prescribed dose to CTV.Cumulative dose-volume histograms were used to compare dose distributions within the CTV and OARs (heart, left lung, right lung, right breast) Results: All plans achieved adequate CTV coverage. Compared with 3D-CRT, both VMAT and H-VMAT provided significantly better target coverage (CTV : V95 > 98%, p = 0.006). Both techniques also resulted in significantly improved heart sparing, with lower V17 Gy and V35 Gy values compared with 3D-CRT. Compared with H- VMAT, VMAT achieved the greatest reduction in heart doses (V17 Gy: p = 0.0001; V35 Gy: p = 0.0001). Similar results were observed for the left lung, with significantly lower mean dose (Dmean), V17 Gy, and V28.5 Gy in VMAT and H-VMAT plans compared to 3D- CRT.However, compared to H-VMAT, VMAT was associated with increased doses to contralateral organs, including the right lung (Dmean: p = 0.0001; V10 Gy: p = 0.006; V5 Gy: p = 0.003) and the right breast (V5 Gy: p = 0.0001). Conclusion: VMAT and H-VMAT both provided superior target coverage compared with 3D-CRT. VMAT achieved the greatest reduction in heart and left lung doses, providing the most effective organ sparing, but increased exposure to contralateral organs. The H- VMAT technique appears to provide a balanced compromise between dosimetric quality and organ sparing, representing a practical alternative when advanced heart-sparing techniques are unavailable. Keywords: breast cancer, radiotherapy, hybrid VMAT,
(D0.1cc: p = 0.130, V10: p = 0.144). D0.1cc decreased by a maximum of 5.41 Gy in PVs and 5.47 Gy in LPV, whereas RPV showed a smaller reduction of 2.57 Gy. For PV V10Gy, the maximum reduction in category 2 reached 11.1% for PVs and 18.5% for LPV, while in category 3, the reductions were 22.8% and 37.3%, respectively. The reduction for RPV was minimal (<3%). PTV coverage and other OAR metrics were not significantly different between standard plans and PV- sparing plans (Figure 1).
Conclusion: Including PVs in optimization can reduce PV doses without compromising target coverage or other OAIs, evidencing the feasibility of PV-optimised VMAT plans. Incorporating PVs during optimization achieved meaningful dose reductions in category 2 particularly where PV and LPV doses often decreased below proposed tolerance thresholds, without compromising PTV coverage or other OAIs. References: 1. Walls GM et al. Pulmonary vein dose and risk of atrial fibrillation in patients with non-small cell lung cancer following definitive radiotherapy: An NI-HEART analysis. Radiother Oncol 2024;192:110085. 2. Butler S et al. Predictors of atrial fibrillation after lung cancer radiotherapy. JACC Adv 2024;6(6).10.1016/j.jaccao.2024.08.007.3. Zei PC et al. Zei PC et al. Cardiac substructure radiation dose and associations with tachyarrhythmia and bradyarrhythmia after lung cancer radiotherapy. JACC Adv 2024;6(4).10.1016/j.jaccao.2024.07.0054. Feng AH et al. A planning strategy may reduce the risk of heart diseases and radiation pneumonia: Avoiding the specific heart substructures. J Appl Clin Med Phys 2023;24(12).10.1002/acm2.14119 Keywords: Pulmonary Vein, lung cancer, Radiotherapy Digital Poster 4343 Optimizing sparing in left-sided locoregional breast radiotherapy: VMAT vs Hybrid VMAT vs 3D-CRT Mouna Ben Rejeb, Siwar Abdessaied, Roua Toumi, Raja Oueslati, Ghada Abdessatar, Aouatef Hamdoun, Rihab Hddad, Lotfi Kochbati Radiation Oncology, Abderrahman Mami Hospital, Ariana, Tunisia
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