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Abstract P3-12-17: Can radiation dosimetric parameters explain severe skin reaction during adjuvant whole breast irradiation applying field-in-field technique?

Aim: Although modern radiotherapy such as field-in-field technique decreased the radiation toxicity, skin reaction is still frequent and main problem during adjuvant whole breast irradiation. Our study investigated various radiation dosimetric and clinical parameters as the risk factors of severe skin reaction. Methods: From January 2012 to December 2014, total 219 patients with breast conserving surgery and adjuvant whole breast irradiation were retrospectively reviewed. All patients took both whole breast irradiation (50 Gy/25 fractions) and boost to the tumor bed (10 - 15 Gy). Skin reaction was measured by comparing the photography of radiation field between the first day of whole breast irradiation and boost therapy. For each axilla and inferior fold, the intensity (score 1 to 5) and extent (score 0 to 1) of erythema were recorded and summed. The severe skin reaction was defined as score 5 or 6. The relations of various radiation dosimetric parameters for radiotherapy planning, personal breast characteristics and clinical factors to severe skin reaction were evaluated using the Logistic regression tests. Results: Total 75 (34%) and 57 (26%) patients showed the severe skin reaction to axilla and inferior fold, respectively. The variables of P l 0.2 in univariate analyses including age, the body mass index, the breast height, the V 100 , the calculated point dose in radiation planning system, the breast separation, the field size, and the gradient of inferior fold entered the multivariate analyses. Age (P=0.013 (OR = 0.950, 95% CI 0.913 - 0.989)), the body mass index (P = 0.015 (OR = 1.123, 95% CI 1.023 - 1.233)), the calculated axilla point dose (P = 0.091 (OR = 1.064, 95% CI 0.990 - 1.142)), and the gradient of inferior fold (P = 0.073 (OR = 1.029, 95% CI 0.997 - 1.063)) were risk factors for severe axilla skin reaction, whereas age (P = 0.018 (OR = 0.948, 95% CI 0.907 - 0.991)) and the V 100 (P l 0.001 (OR = 1.005, 95% CI 1.003 - 1.007)) were for severe inferior fold skin reaction. Conclusion: In addition to clinical factor and personal breast characteristics, the radiation dosimetric parameters such as calculated point dose and V 100 could be another predictive factors of severe skin reaction. Citation Format: Yoon WS, Lee NK, Lee JA, Yang DS, Kim CY, Son GS, Chang YW. Can radiation dosimetric parameters explain severe skin reaction during adjuvant whole breast irradiation applying field-in-field technique?. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-12-17.