ESTRO 2025 - Abstract Book

S4349

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

an additional boost of 10 Gy to the tumor bed. Both treatment plans aimed to achieve adequate target volume coverage and meet OAR doses constraints. Dose volume histograms for the ipsilateral lung, heart, left ventricle (LV) and left anterior descending artery (LAD) were statistically compared, using the t student test. The EQD of DEGRO [1] dose constraints for the LAD and LV were calculated and used for dosimetric comparison. Results: All plans achieved acceptable target coverage (V95%≥95%). Compared to CPAP-3DCRT, CPAP-VMAT plans showed significantly increased MHD and V4.4Gy for the heart and LV (Table 1). The mean V5Gy lung was 64.8% versus 39.2% (p=0.00), respectively in CPAP-VMAT versus CPAP-3DCRT. Nonetheless, comparative DVHs for high doses favoured CPAP-VMAT plans for all OAR. Doses to the LAD were significantly lower in CPAP-VMAT plans with a reduction of 33% and 50% for Dmean LAD and Dmax LAD (mean absolute reduction of 15 Gy, p=0.00), respectively. No significant difference was found for Dmean Lung between the two plans. Both plans met dose constraints for the ipsilateral lung, but V17Gy and V28.5Gy were significantly lower in CPAP-VMAT plans compared to CPAP-3DCRT.

Conclusion: Combining VMAT to CPAP in left-sided breast cancer RT provided better heart, cardiac subvolumes and lung sparing against high doses. However, the large low-dose-bath (≤ 5 Gy) is still a concern. Further studies are needed to evaluate the clinical outcomes and long-term risks of low-dose exposure. The choice of treatment technique should take into account all associated risk factors and should ideally be personalized for each patient.

Keywords: Breast radiotherapy; VMAT; CPAP

References: 1. Piroth MD, Baumann R, Budach W, Dunst J, Feyer P, Fietkau R, Haase W, Harms W, Hehr T, Krug D, Röser A, Sedlmayer F, Souchon R, Wenz F, Sauer R. Heart toxicity from breast cancer radiotherapy : Current findings, assessment, and prevention. Strahlenther Onkol. 2019 Jan;195(1):1-12. doi: 10.1007/s00066-018-1378-z. Epub 2018 Oct 11. PMID: 30310926; PMCID: PMC6329735.