ESTRO 38 Abstract book

S311 ESTRO 38

To determine if treating large breasted women with adjuvant breast radiotherapy (RT) in the prone position reduces acute skin toxicity when compared to the supine position. Material and Methods From 2013 to 2018 a total of 357 large breasted women (bra size 40in and/or D cup or greater) from 5 centres in Canada receiving adjuvant RT to the breast alone were randomized to the supine or prone position. Patients were initially treated to 50Gy/25 fractions (conventional fractionation), though the protocol was amended at 3 years to allow 42.5Gy/16 fractions (hypofractionation) which was almost exclusively used from that time onwards. Randomization was blocked on postoperative RT boost. Acute toxicity including moist desquamation (MD), erythema, and pain as per CTCAE 4.03, was assessed by an observer blinded to treatment position at baseline, weekly during RT and up to 6 wks post treatment. Comparison of the frequency of grade 2-3 MD between treatment arms was performed using a two sample two-sided test of proportions providing an OR and its associated 95% CI. Multivariable logistic regression analysis evaluated the relative risk of acute skin toxicity as the dependent variable. The various independent variables tested included the treatment position, boost delivery, fractionation, breast size, and chemotherapy. Results A total of 357 patients were accrued, 182 treated supine and 175 prone. 180 received conventional fractionation (92 supine, 88 prone) and 177 treated with hypofractionation (90 supine, 87 prone). On bivariate analysis there was significantly more acute MD in patients treated supine compared to prone (39.6% vs 26.9%; OR 1.8, CI 1.1-2.8, P=0.01). This association was confirmed on multivariate analysis with increased MD in the supine position (OR 1.9, CI 1.2-3.1, P<0.01). Additional factors independently associated with MD included use of RT boost (OR 2.8, CI 1.6-4.7, P<0.01), conventional fractionation (OR 3.0, CI 1.8-4.9, P<0.01) and larger bra size (OR 2.4, CI 1.4-3.9, P<0.01). There was no association between MD and chemotherapy. Similar analyses showed only boost and conventional fractionation were associated with erythema and pain. In an unplanned subset analysis, there was significantly more acute MD in patients treated with conventional fractionation compared to those treated with hypofractionation (OR 2.5, CI 1.6 – 4.0, P < 0.0001 ) and this was true for both the supine (OR 2.7, CI 1.5-5.0, P<0.0001) and prone (OR 2.4, CI 1.2-4.8, P<0.0001) positions. Conclusion This multicentre single blinded RCT confirms that treatment in the prone position leads to significantly less acute MD compared to the supine position in large breasted women receiving adjuvant radiotherapy. It also shows increased toxicity using an RT boost and conventional fractionation. OC-0594 Acute toxicity results after breast-conserving therapy in “boost vs no boost (BONBIS)” DCIS trial C. Bourgier 1 , D. Cowen 2 , C. Lemanski 1 , F. Castan 3 , S. Rivera 4 , B. De La Lande 5 , K. Peignaux 6 , M. Le Blanc- Onfroy 7 , A. Benyoucef 8 , A. Mege 9 , Z. Douadi-Gaci 10 , S. Racadot 11 , I. Latorzeff 12 , U. Schick 13 , S. Jacquot 14 , C. Massabeau 15 , P. Guilbert 16 , J. Geffrelot 17 , S. Ellis 18 , I. Lecouillard 19 , C. Breton-Callu 20 , A. Richard-Tallet 21 , P. Bontemps 22 , P. Fenoglietto 1 , D. Azria 1 1 ICM-Val d'Aurelle, Radiation Oncology, Montpellier, France; 2 CHU La Timone, Radiation Oncology, Marseille, France; 3 ICM-Val d'Aurelle, Biostatistic Department, Montpellier, France; 4 Gustave Roussy, Radiation Oncology, Villejuif, France ; 5 Curie Saint Cloud, Radiation Oncology, Saint Cloud, France ; 6 Centre Georges François Leclerc, Radiation Oncology, Dijon, France ; 7 Centre René Gauducheau, Radiation Oncology, Saint Herbain, France ; 8 Centre Henri Becquerel,

37% and 65% of patients had no fibrosis and 50% and 29% mild fibrosis at the tumor area . The global cosmetic outcome was good-excellent in 70% after 6 months, 88% after 2 years and 93% after 5 years (figure 1). Patients were very satisfied/satisfied with the cosmetic outcome in 78% after 6 months, 84% after 2 years and 93% after 5 years . An LR was detected in 4 patients: 3 were located along the biopsy trajectory. Subsequently, we adjusted the protocol by surgical removal of the biopsy route.

Characteristics Median age (yrs) 68 (60-87) Tumour size (mm) 12 (5-27) Grade

1 2 3

35 89

(27%) (68%)

7 (5%)

Subtype ER+/PR+/HER2- ER+/PR-/HER2- ER-/PR-/HER2- HER2+ Systemic therapy Hormonal Chemotherapy

86 36

(65%)

(27%) 8 (6%) 2 (2%)

89/129 (64%) 5/129 (4%)

Conclusion PAPBI is a feasible and promising treatment for low-risk breast cancer patients resulting in excellent cosmetic outcome and limited fibrosis, presumably due to removal of the high dose area. Postoperative complications are comparable to surgical complications before PBI. Cosmetic outcome improved over time. A few recurrences in the biopsy tract occurred before adjustment of the protocol. OC-0593 Prone breast radiotherapy reduces acute skin toxicity – results from a multicentre single blind RCT D. Vesprini 1 , M. Davidson 2 , S. Bosnic 3 , L. Fenkell 4 , D. Comsa 4 , P. Truong 5 , E. Wai 5 , M. El-Mallah 6 , L. Garcia 6 , C. Stevens 7 , M. Follwell 7 , H. Gotthardt 3 , S. Zhu 3 , A. Kiss 8 , E. Rakovitch 1 , J. Pignol 9 1 Sunnybrook Odette Cancer Centre- University of Toronto, Radiation Oncology, Toronto, Canada ; 2 Sunnybrook Odette Cancer Centre- University of Toronto, Medical Physics, Toronto, Canada ; 3 Sunnybrook Odette Cancer Centre, Radiation Oncology, Toronto, Canada ; 4 Southlake Regional Health Centre- University of Toronto, Radiation Medicine Program, Newmarket, Canada ; 5 Victoria and University of British Columbia, Radiation Oncology, Victoria, Canada ; 6 Durham Regional Cancer Centre, Radiation Oncology, Oshawa, Canada ; 7 Simcoe Muskoka Regional Cancer Centre- University of Toronto, Radiation Oncology, Barrie, Canada; 8 University of Toronto, Institute of Health Policy- Management and Evaluation, Toronto, Canada; 9 Dalhousie University, Radiation Oncology, Halifax, Canada

Purpose or Objective