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Background:Oncoplastic partial mastectomy (OPM) is a technique utilized to improve aesthetic and survivorship outcomesin patients with localized breast cancer. This technique leads to breast tissue rearrangement, which can have an impact on target definition for boost radiotherapy (BRT). The aim of this study was to determine if the choice of surgical technique independently affected the decision to deliver a radiation boost.Materials and Methods: This was a retrospective study of patients treated between January 2017 and December 2018. We selected consecutive patients based on surgical procedure; 50 undergoing standard breast conserving surgery and 50 having had an OPM. The primary outcome was average treatment effect (ATE) of surgery type on reception of BRT, accounting for patient age, tumor grade, lymphovascular space invasion, margin status and ER status as potential confounding variables. Secondary outcomes included ATE of surgery type on the time to reception of radiotherapy and incidence of ipsilateral breast tumor recurrence (IBTR). The ratio of boost seroma volume to pathologic tumor size was also compared between the two groups. Treatment effects regression adjustment and inverse-probability weighted analysis was used to estimate ATEs for both primary and secondary outcomes.Results: Median age was 64 years (range 37 – 88). The median tumor size was 1.5 cm (range 0.1 – 6.5). The majority of patients were ≤ stage IIA (78%), invasive ductal subtype (80%), LVSI negative (78%), margin negative (90%) and ER/PR +ve (69%). Overall, surgical technique was not associated with differences in the proportion of patients receiving BRT (ATE 6.0% (95% CI -4.5, 16.0)). There were no differences in delays to radiation treatment between the two groups (ATE 32.8 days (95% CI -22.1, 87.7)). With a median follow-up time of 419 days (range 30 – 793), there were only 5 recurrences, with 1 case of IBTR in each group. There was no difference in the ratio of seroma volume to tumor size between the two groups (p=0.38).Conclusions: OPM did not affect the decision to offer localized BRT following standard whole breast radiotherapy, or significantly affect treatment times or radiation volumes. The decision to offer OPM should include a multi-disciplinary approach.