D. N. Sharma1,2, S. K. Saini2, A. Pashupathy Iyer3, M. Jha3, and Y. I. K N3; 1National Cancer Institute, All India Institute of Medical Sciences, New Delhi, India, 2All India Institute of Medical Sciences, New Delhi, India, 3All India Institute of Medical Sciences, New Delhi, India, New Delhi, India
Purpose/Objective(s): Accelerated partial breast irradiation (APBI) following breast conservation surgery (BCS) is considered a standard adjuvant treatment in select group of breast cancer patients. The rate of local recurrence in most studies that compared whole breast irradiation (WBI) and APBI was around 3 to 4%, The criteria for selection of patients for APBI generally include patients of age greater than 50 years, tumor size less than 3 cm, node negative disease, absence of LVSI or extensive ductal carcinoma in situ and negative surgical margins. A group of patients who may be too advanced to fall into the stringent criteria for APBI, yet do not have a high risk of local recurrence. Such patients could merit a smaller volume of irradiation viz. involved quadrant irradiation (IQI) rather than WBI. IQI will potentially reduce dose to organs at risk without compromising local control. Materials/
Methods: Following are the inclusion criteria:1) Histologically proven IDC, 2) partial response/ complete response to neo-adjuvant chemotherapy eligible for BCS3) tumor size between 3-5 cm with any nodal status undergoing BCS4) negative margins. Patients are excluded if they have 1) age >75 years and < 35years 2) past history of breast cancer RT. Sample size was calculated using Cox 1-sided non-inferiority design. The power of trial was placed at 80% with a p value fixed at 0.05. The baseline rate of primary end point (IBTR) was considered as 6%. Setting a non-inferiority margin of 5 %, with a power of 80%, and expecting a dropout rate of 5%, a total of 588 (294 in each arm) subjects are to be recruited at 1:1 randomization. A dose of 38.5Gy in 10 fractions over 10 days is prescribed to the involved quadrant (along with regional nodal if indicated). For WBI, the prescription dose is 50 Gy in 25 fractions over 5 weeks. Patients are followed up at 3 monthly intervals for the first 2 years followed by 6 monthly for next 3 years for clinical examination. IBTR is be defined as date of diagnosis of recurrence (clinical examination or biopsy or imaging) from date of BCS. Cosmesis is assessed at baseline 2 weeks after BCS followed by at 3, 6, 12 and 24 months after surgery. For statistical analysis, Kaplan Meier method and log rank test are used. Results: Here we present the results of first 15 patients recruited in the IQI arm since June 2023.Median age of the patients was 53 years. T size ranged from 2.6 cm to 5.5 cm (median 3.8 cm). Axilla was pathologically negative in 10 patients. All 15 patients have completed the prescribed IQI treatment. Mean dose received by the 20% ipsilateral lung (V20) was 2.3 Gy. Preliminary early clinical results (6 months) revealed no IBTR in any of the patients. No skin changes greater than Grade 1 erythema were noticed during or at the end of treatment. Cosmesis was good or excellent in all cases. Conclusion: The initial results of our ongoing phase III trial suggests that post BCS, IQI is feasible (as an alternate to WBI) in patients not eligible for APBI. Completion of our trial will determine the role of IQI in such patients.
