ESTRO 2021 Abstract Book

S938

ESTRO 2021

APBI guidelines.

PO-1130 Radiation Induced Skin Toxicity after HypoFractionated Radiotherapy: A prospective analysis M. Sharma 1 , K.S. Chufal 1 , A.K. Pahuja 1 , I. Ahmad 1 , R.L. Chowdhary 1 , M. Gairola 1 1 Rajiv Gandhi Cancer Institute & Research Centre, Radiation Oncology, New Delhi, India Purpose or Objective To study the evolution of radiation-induced skin toxicity (RIST) in a prospective cohort of Indian women treated with hypofractionated radiotherapy (HFRT) after breast conservation surgery (BCS). Materials and Methods After IRB approval, 52 women with pathologically proven, early-stage invasive breast cancer after undergoing BCS, with an indication for adjuvant HFRT were prospectively enrolled in this single-arm, observational study. The treating radiation oncologist decided treatment volumes, and all patients received whole breast irradiation (WBI) with regional nodal irradiation, to a dose of 42.5 Gy in 16 Fx over 3.2 weeks, followed by a lumpectomy cavity boost (10 Gy in 4 Fx). WBI was delivered using Forward IMRT (along with DIBH for left-sided breast cancer patients) and a lumpectomy boost utilised electron beam (energy selected based on the maximum depth of cavity from the surface; determined by surgical clips seen on simulation CT & pre- operative imaging). The primary endpoint of this study was to analyse RIST in Indian women undergoing HFRT. All patients were evaluated weekly during RT. Subsequently, they were evaluated at one week, two weeks and three months after completion of RT. Grades of RIST were recorded as per CTCAE (v5). Results The mean age was 44.7 yrs (range 21-80) with 75% of the women younger than 50. The most common site of RIST was upper outer quadrant (46%) followed by upper inner quadrant (17%) and lower outer quadrant (15%). Overall, 17 of 52 (34%) patients developed grade 3 or higher RIST, whereas the rest developed Grade 2 or less. In the supra-clavicular region, most patients developed Grade 2 RIST in week 4 (23%) and week 5 (23%). In the axillary region, Grade 3 RIST developed in 9.6% of patients in week 4, which increased to 19.2% by week 5. Majority of the patients developed Grade 2 RIST in week 4 (48%), week 5 (55.7%) and week 6 (50%). In the infra-mammary fold, Grade 3 RIST was seen in 9.6% of patients in week 4, which progressed to 17.3% in week 5. Grade 2 RIST developed in 65.8% of patients in week 4 and 67.3% by week 5.

In upper outer quadrant, 5.7% of patients developed grade 3 RIST in week 5 and 7.6 % by week 6. Grade 2 RIST was seen in 36.5% in week 4 and 55.7 % by week 5. Only one patient developed grade 3 RIST in week !ve in the upper inner quadrant, which persisted till week 6, while a majority of the patients developed grade 2 RIST by week 4 (26.9%), which increased to 50% by week 5. Similarly, only one patient developed grade 3 RIST in LOQ and LIQ by week 5. Grade 2 RIST was seen in 36.5% of patients in LOQ and 28.8% of patients in LIQ by week 4, which increased to 48% and 50 % by week 5, respectively. By the end of 3 months, grade 1 RIST persisted in 7.6% of patients in LOQ and 9.6% in LIQ.