S2363
Physics - Quality assurance and auditing
ESTRO 2026
while the site-specific planning target volume (PTV) was covered by 95–105% of the prescribed dose, allowing hotspots of 105–110% in <2 cm ³ . For the whole breast, V40Gy was aimed to be ≤ 50%. Organs of interest included the heart, with V17Gy ≤ 5% and V35Gy ≤ 1%, and the ipsilateral lung, with mean dose (Dmean) ≤ 16Gy and V17Gy ≤ 25%. Dose metrics were extracted from planned 3D distributions of individual treatment plans collected in DcmCollab, and patient and treatment characteristics were obtained from the trial database3. Differences between groups were assessed using the Wilcoxon rank-sum test (p < 0.05). Results: All 238 patients in the PBI arm were analysed (Table 1). Target coverage across all volumes met the protocol- defined planning objectives. The median mean dose (Dmean) for CTVp_PBI, PTVp_PBI and tumour bed was 40Gy. Median V95% was 100% for both CTVp_PBI and the tumour bed, and 97.8% for PTVp_PBI. Dose homogeneity was consistent with protocol criteria, with a median V105% of 0.0% for CTVp_PBI. Hotspot volumes ≥ 2 cm ³ occurred in 18 patients (8%), and the median whole breast V40Gy was 21.2% (IQR, 14.6– 29.0).For ipsilateral lung, median Dmean was 1.52Gy, and V17Gy was 1.50%; no significant differences were observed by laterality or gating status (Table 1, Figure 1). For heart, median Dmean was higher for left- versus right-sided tumours (0.25Gy vs. 0.12Gy); respiratory gating tended to reduce Dmean for left- sided tumours (0.23 vs. 0.29 Gy); not significant. Median V17Gy was 0% across all subgroups. Conclusion: PBI in the DBCG RT Natural Trial achieved high target coverage with minimal hotspots; heart and ipsilateral lung doses were consistently low, in accordance with the protocol-defined planning strategy.
References: 1
Offersen BV, Alsner J, Nielsen HM et al. Partial Breast Irradiation Versus Whole Breast Irradiation for Early Breast Cancer Patients in a Randomized Phase III Trial: The Danish Breast Cancer Group Partial Breast Irradiation Trial. J Clin Oncol 2022; 40 (36): 4189-
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