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PURPOSE/OBJECTIVE: The Danish Breast Cancer Group (DBCG) IMN2 study investigated the gain from internal mammary node irradiation (IMNI) in node-positive breast cancer patients. IMNI was indicated in right-sided patients, but not in left-sided. Target volume delineations were based on bony landmarks in contrast to the contemporary vessel-based ESTRO consensus guideline. Our objective was to compare IMNI doses in right-sided versus left-sided patients. MATERIAL/METHODS: Treatment plans and delineated structures including CTVnIMN (IMNₒld) from 2008 to 2014 were collected from the DBCG RT Nation study. During the study period, IMNₒld was only delineated in right-sided patients. Right and left-sided CTVnIMN structures were auto-segmented following the ESTRO guidelines (IMNESTRO). Due to cranial discordance between IMNₒld and IMNESTRO, the IMNESTRO models were separated into IMNESTROcranial and IMNESTROᵢntercostal space (IC) 1-3, IC1-4, and IC4ₒnly. RESULTS: Treatment plans for 2837 patients were available (62. 5 % of patients in the IMN2 study). In right-sided patients, the median IMNₒld dose coverage (92. 4 %) was higher than IMNESTRO (71. 7 %), p < 0. 001. Dose coverage in IMNESTROIC1-3 was comparable to IMNₒld. Comparing IMNESTROIC1-3 in all patients by laterality, the median CTVnV90% was 94. 6 % (IQR 64. 8-100. 0) in right-sided patients and 20. 4 % (IQR 0. 9-55. 8) in left-sided patients, p < 0. 001. For right-sided patients, median CTVV90% was 82. 3 % in IMNESTROIC4ₒnly. Median mean heart doses were lower in right-sided patients (1. 2 Gy) than in left-sided (2. 3 Gy), p < 0. 001. Median mean lung doses were higher in right-sided patients (16. 0 Gy) than in left-sided (12. 7 Gy), p < 0. 001. CONCLUSION: For IMNESTROIC1-3, we found a significantly higher IMN dose coverage in right-sided than in left-sided patients supporting treatment according to study guidelines in the DBCG IMN2 study.
Refsgaard et al. (Fri,) studied this question.