ESTRO 38 Abstract book

S727 ESTRO 38

and high conformity across multiple institutions and clinicians, which demonstrate a substantial improvement over major APBI trial dosimetry constraints . EP-1327 Impact of neoadjuvant radiotherapy in locally advanced breast carcinoma C. Sousa 1 , L. Pinto 2 , M. Cruz 1 , A. Neto 1 , J. Bastos 3 , C. Miranda 1 , G. Melo 1 , L. Khouri 1 , P. Figueiredo 4 , P. Alves 5 1 Instituto Português de Oncologia de Coimbra, Radiotherapy, Coimbra, Portugal ; 2 Instituto Português de Oncologia de Coimbra, Medical Oncology, Coimbra, Portugal ; 3 Instituto Português de Oncologia de Coimbra, Regional Oncology Registry of the Centre, Coimbra, Portugal ; 4 Instituto Português de Oncologia de Coimbra, Anatomical Pathology, Coimbra, Portugal ; 5 Instituto Português de Oncologia de Coimbra- Faculty of Medicine - University of Coimbra, Radiotherapy, Coimbra, Portugal Purpose or Objective The therapeutic approach in locally advanced breast carcinoma remains a clinical challenge. Standard treatment involves systemic therapy with chemotherapy (NACT) and / or hormone therapy (NAHT), surgery and radiation therapy when indicated. More than a third of patients are refractory to systemic cancer treatment, with maintenance of inoperability criteria. There are few data in the literature about alternative treatment when systemic therapy fails. With this study, we intend to evaluate the impact of neoadjuvant radiotherapy (NART) in the treatment of the locally advanced carcinoma. Material and Methods We conducted a retrospective study including female patients, diagnosed with locally advanced invasive breast carcinoma, stages IIB to IIIC, submitted to NART between January 2014 and December 2015 at our institution. The radiotherapy regimens varied between 26Gy / 4Fr / 2,5weeks ± 30Gy / 10Fr / 2weeks, 50Gy / 25Fr / 5weeks and 60 Gy / 30Fr / 6weeks on the breast volume, supraclavicular and axillary lymph node region. The evaluation of pathological response (pR) was made based on Pinder criteria, divided into three groups: 1 - complete response, 2 - partial response > 90% and 3 - partial response ≤ 90%; Primary endpoint: pathological response (pR); Secondary endpoints: overall survival (OS), progression-free survival (PFS). Performed descriptive analysis and survival analysis with Kaplan-Meier method. Results From a total of 51 patients submitted to NART, 42 were included, with a median age of 59 (32-86) years. The most frequent clinical stages were IIIA and IIIB, corresponding to 40.5% and 38.1%, respectively; 35 (83.3%) had lymph node involvement. 22 (52.4%) were basal like (n = 11) and luminal like (n = 11). 26 (61.9%) underwent NACT with anthracyclines and taxanes, 13 (30.9%) NAHT, 5 (11.9%) NART in monotherapy. All included patients underwent mastectomized. Our results: 6 (14.3%) had complete response, 2 of which had only NART. 87% of patients with pR > 90% were under 69 years old. 36 months OS was 64% and PFS was 60%. Subgroup analysis showed 36 months OS of 87% in group 2 versus 48% in group 3, 91% luminal A versus 27% basal like (p <0.05). After surgery, 19 (45.2%) progressed, of which 17 had distant metastasis, correlated with a worse prognosis (p <0.05). Conclusion This retrospective study confirms that NART is an effective downsizing treatment in locally advanced breast carcinoma, allowing surgical resection regardless of systemic treatment performed. The pR > 90% is correlated with a better OS. These findings corroborate the literature, with the basal like intrinsic subtype and distant metastasis correlated with worse prognosis.

clinical trial investigating a new external beam APBI regimen, delivering 27 Gy in five consecutive daily fractions with dosimetry constraints consistent with major APBI trials such as ACCEL and NSABP B-39/RTOG- 0413 (https://clinicaltrials.gov/NCT00103181). For the ACCEL trial, more rigorous dosimetry guidelines were established to ensure consistent and highly conformal dose distributions to address the hypothesis that poor dose conformity is important in causing cosmetic deterioration. These dosimetry guidelines were based on a retrospective planning study that required substantial APBI planning expertise to implement. In the current work, the clinical implementation of these dosimetry guidelines (recommendations and allowed variations) across multiple institutions is evaluated in the context of major APBI trial dosimetry constraints (Table 1). For 215 patients accrued to the ACCEL trial, dose-volume parameters were evaluated to determine the achievability of rigorous dosimetry guidelines in a heterogeneous clinical setting.

Results 215 patients planned by 12 dosimetrists and reviewed by 10 physicians and 10 physicists across three institutions were included. All APBI plans met NSABP B-39/RTOG-0413 and ACCEL trial dosimetry constraints . Normal tissue dosimetry guidelines for ipsilateral breast, lung, contralateral breast, heart, as well as high dose conformity, were satisfied by 95% of patients within the recommended or allowed variations. The mean (± standard deviation) of the ipsilateral breast V 50% was 30.8 (±7.8) % which is a significant improvement on the V 50% less than 50% dose constraint of the NSABP B-39/RTOG-0413 and ACCEL trials (Figure 1). Similarly, the mean (± standard deviation) of the high dose (volume of 95% prescription dose) ipsilateral breast constraint was 10.5 (±3.6) % as compared to the NSABP B-39/RTOG-0413 and ACCEL trial constraint of less than 25%.

Conclusion The dosimetry guidelines are stringent compared to major APBI trial constraints but this work demonstrated they are clinically achievable. These dosimetry guidelines provide a tangible means of ensuring consistency in plan quality