ESTRO 2020 Abstract book

S559 ESTRO 2020

ipsilateral breast tumor recurrence (IBTR) after APBI compared to whole breast irradiation (WBI). To help address these uncertainties, we characterized the clinical outcomes of APBI in women under 50 treated at our institution. Material and Methods All women under 50 years of age treated with APBI from 2003–2018 at a single institution were identified. Those with at least one year of follow-up were analyzed for IBTR, progression-free survival (PFS), toxicity and cosmesis. Multivariable logistic regression (MVA) was performed to identify which variables were independently associated with IBTR. Results We identified 147 patients under 50 who received APBI for either invasive breast cancer (86 patients, 59%) or DCIS (61 patients, 41%) who had at least 1 year of follow-up after completion of APBI. Median age at APBI was 46 years (range, 27– 49). Of these, 123 (84%) were GEC-ESTRO “intermediate-risk” due to age <50 alone, and the remaining 24 (16%) were “high-risk” due to <50 with additional adverse factors (12 patients) or being ≤40 (12 patients). Modalities were HDR brachytherapy using either multicatheter interstitial implant (ISI) (n=35) or single- entry strut-adjusted volume implant (SAVI) (n=21), both to 34 Gy in 10 BID fractions, or external beam radiotherapy (EBRT) with either 3D-conformal (3DCRT) (n=43) or MR- guided RT (MRgRT) (n=48), both to 38.5 Gy in 10 BID fractions in most. Adjuvant chemotherapy was used in 24 patients (16%). Median follow-up was 6.0 years (range, 1.0 – 16.6). There were 8 patients (7 in “cautionary”, 1 in “unsuitable”) who developed IBTR (cumulative rate, 5.4%), a median 3.0 years after APBI. Kaplan-Meier estimates of 5-year IBTR, freedom from distant metastases, and PFS were 93.8%, 98.1%, and 92.7% respectively. No variables were independently associated with IBTR on MVA. Cosmesis was good-to-excellent in 89.7% after APBI. Conclusion For women under 50 years of age, APBI results in excellent long-term disease control. Cosmetic outcomes are good- to-excellent in most patients. Our results suggest that APBI is a reasonable alternative to WBI in select women under 50, and further efforts to enroll this poorly represented group on prospective trials should be prioritized. PO-0963 Impact of regional nodal Irradiation on lung dose in hypofractionated radiation of breast cancer M. Bohli 1 , Z. Fessi 1 , A. Hamdoun 1 , J. Yahyaoui 1 , R. Moujahed 1 , L. Kochbati 1 1 Abderrahman Mami Hospital, radiation oncology, Ariana, Tunisia Purpose or Objective Ipsilateral lung is one of the main organ at risk in breast radiation. The proximity of sub-volumes (level 3 and Level 4 regional lymph nodes) to the lung is an important determinant of radiation pneumonitis risk. Experimental models showed that the lung apex was more radioresistant than the base due to non-uniform distribution of alveoli throughout the lung. Our purpose was to study the contribution of supra and sub clavicular (periclavicular) field on the lung irradiation and to analyze factors that influence the mean dose (D_mean) to the lung. Material and Methods During the year 2018, 78 patients were treated with adjuvant loco-regional hypofractionnated radiation for breast cancer. Conservative surgery or modified radical mastectomy were included. A dose regimen of 40 Gy/15 fractions is used with a tumor bed boost of 13.35Gy/5 fractions after conservative surgery. All treatment plans were mono-isocentric. Dosimetric data for ipsilateral lung, with and without periclavicular field were recorded (D_mean, volume receiving 4Gy (V4Gy), V8Gy, V10Gy,

To evaluate the tolerability, patient-reported quality of life (QOL) and cosmetic outcomes of a novel external beam APBI regimen, delivered in a single fraction postoperatively. Material and Methods We enrolled 50 patients with low-risk, hormone-sensitive stage 0 or I breast cancer from 2015-2018 on a prospective phase I/II trial to receive single-fraction high-gradient partial breast irradiation (SFHGPBI) after lumpectomy for node-negative invasive or in-situ breast cancer. The surgical bed was prescribed 15-22 Gy and the breast tissue within 1 cm of the surgical bed was simultaneously prescribed 5-7 Gy in one fraction, using MR-guided RT in all but 2 patients. CTCAEv4.0 toxicity, patient-reported QOL, qualitative and quantitative cosmesis, and pain were prospectively assessed pre-RT, post-RT at 2 weeks, 8 weeks, 6 months, every 6 months for 2 years, then annually for a total of 5 years. Score differences along time points were assessed using a mixed repeated measures model with a heterogeneous autoregressive covariance structure. The least square mean and accompanied standard error were estimated for each time point from the mixed model for repeated measures. Results The median age was 65 (range, 52–84). Ten patients (20%) had small volume DCIS while the remainder had stage I disease. At a median follow-up of 25 months, we evaluated toxicity, patient and physician-reported cosmesis, and patient-reported QOL. There was no CTCAEv4.0 grade 3+ toxicity. Only 34% of patients experienced grade 1 erythema. Good-to-excellent pretreatment cosmesis, per the dichotomized 4-point Aaronson-modified Harris scale, was present in 100% and 98% per physicians and patients, respectively, and did not change post-SFHGPBI. Quantitative cosmesis by percentage of breast retraction assessment (pBRA) was 8.4% pre-RT (95% CI 7.1–9.7), and significantly improved post RT at 6.4% (95% CI 5.1-7.6) and 6.8.% (5.0–8.6) at 24- and 36-months’ post treatment respectively (p=0.0026). Patient-reported QOL per EORTC QLQ-C30 and BR-23 did not decline other than temporarily in the systemic therapy effects and hair loss domains, both of which returned to pretreatment values. Breast symptoms significantly improved after treatment. Per the 10-cm visual analog pain scale, no (0 cm), mild (>0 to <4), and moderate (>4 to <7) pain was reported by 26, 23, and 1 patient pre-RT, respectively, with the proportion of patients experiencing no pain steadily improving after treatment. No patient reported severe pain requiring narcotics. There was one noninvasive in-breast recurrence in a separate untreated quadrant 18 months post-SFHGPBI and one isolated axillary recurrence 30 months post-SFHGPBI, both salvaged successfully. There were no distant recurrences or cancer- related deaths observed. Conclusion APBI delivered in a single fraction postoperatively using external beam techniques is a novel, feasible, well- tolerated regimen. SFHGPBI does not adversely affect cosmesis or QOL as reported by both physicians and patients. PO-0962 APBI in Women Under 50: Long-Term Outcomes in a Poorly Represented Cohort W. Kennedy 1 , J. Stanley 1 , R. Brenneman 1 , S. Duriseti 1 , P. Gabani 1 , M. Gang 1 , L. Ochoa 1 , M. Altman 1 , J.E. Zoberi 1 , M. Thomas 1 , I. Zoberi 1 1 Washington University School of Medicine, Radiation Oncology, St. Louis, USA Purpose or Objective Current GEC-ESTRO guidelines recommend that delivering APBI in women under 50 is either ‘cautionary’ or ‘unsuitable’, primarily because this cohort is poorly represented on clinical trials supporting APBI. Conflicting evidence exists whether younger women have increased