ESTRO 2021 Abstract Book

S943

ESTRO 2021

FromMarch-2020 to January-2021, 138 patients with a median age of 58.5years (range 31-87) were treated according to our institution ultra-hypofractionated radiotherapy schedule after breast conserving surgery (BCS).Clinical staging (AJCC): Tis 29p (21%) , T1a 10p (7.5%), T1b% 36p (26%), T1c 54p (39%), T2 9p (6.5%). All patients were pN0 Radiotherapy comprises whole breast receiving 26Gy@5.2Gy/day with a simultaneous integrated boost (SIB) to all patients up to a total dose of 29Gy@5.8Gy/day in 111p (80%) and 30Gy@6Gy/day in 27p (20%) with close/focally affected margins. WBI+SIB was delivered by conformal 3-D technique in 130p (94%), VMAT in 6p (4%) and 3-D with deep inspiration breath hold (DIBH) in 2p (1.5%).Treatment beam arrangement for SIB comprised of coplanar 2 beams in 1p (1%), 3 beams in 43p (31%), 4 beams in 77p (56%), 5 beams in 11p (8%) and 2 arcs in 6p (4%). Dose constraints are detailed in table 1 Systemic therapy: 136p (98.5%) received hormone therapy and 12p (9%) systemic or targeted chemotherapy.

OAR

Ipsilateral lung

V12<20%

Contralateral lung

Dmean<5.6 Gy

V3.6 <10%

Heart

V12 <5%

V7<5%

V1.5 < 30%

Contralateral Breast

V3.6 < 30 %

Spinal Canal Dmax< 27 Gy D0.01 cc< 22.5 Gy OAR: organs at risk;, Dmean: mean dose; Dmax: maximal dose

Results With a median follow-up of 3.5months (range1-11), acute tolerance was acceptable with null o mild toxicity: 69p (50%) developed skin toxicity grade 1 and 3p (2%) grade 2. No other acute toxicities were observed A comparative analysis was performed with the Chi-Square test. We found a weak but significant relation between age (< 56 years-old) and dermitis G1-2 (p = 0,048), however w3e could not demonstrate any relation with use of chemotherapy (p = 0.33), homonotherapy (p = 0.06), breast PTV ( p = 0.12), boost PTV (p = 0.47) or ratio boost PTV/breast PTV (p = 0.27) and tolerance. Conclusion Ultra-hypofractionated WBI with SIB in 5 fractions along one-week is feasible and well tolerated although longer follow-up is necessary to confirm these results. PO-1136 Radiotherapy for breast cancer in women with autoimmune rheumatologic diseases. L. Gasparini 1 , L. Gasparini 2 , L.A. Ursini 1 , M. Nuzzo 3 , M. Di Tommaso 3 , F.C. Di Guglielmo 1 , M. Borgia 1 , D. Genovesi 1,2 , L. Caravatta 1 1 SS. Annunziata Hospital, Department of Radiation Oncology, Chieti, Italy; 2 G. D'Annunzio University, Department of Neuroscience, Imaging and Clinical Sciences, Chieti, Italy; 3 SS. Annunziata Hospital, Department of Radiation Oncology, Chieti, Italy Purpose or Objective Autoimmune rheumatologic diseases (ARDs) are chronic and heterogeneous disorders, described to be an absolute or relative contraindication for radiotherapy (RT) due to increased RT-related acute and late toxicity. This study retrospectively describes toxicity rates in patients with ARDs treated with curative-intent RT for breast cancer in our Center. Materials and Methods We retrospectively included patients affected by breast cancer and ARDs who had access to our Center between January 2014 and January 2021, and reviewed for treatment attendance and RT-related toxicity, according to Common Terminology Criteria for Adverse Events scoring scale. Results Thirty-nine women with ARDs were considered (mean age 60y) (table 1). Despite indication of curative RT for breast cancer, 9 patients (23%) did not start treatment for severe active-phase disease and specialist contraindication. Thirty patients underwent RT; 20 (66.7%) were in treatment with immune-system suppressant agents. Except for steroids, these agents were interrupted during RT in all cases. Twenty-seven patients received whole breast RT, 2 patients whole breast and supraclavicular, 1 patient underwent chest wall + supraclavicular (svc) irradiation. For 90% of the patients a conventional fractionation was chosen. Hypofractionation (2,66-2,67Gy/die) was administered in 3 cases (10%), while 1 patient (3.3%) received 44,20Gy (1,70Gy/die) according to rheumatologist opinion. A tumor bed boost of 10Gy, 2Gy/die, was prescribed in 24 (80%) cases (table 2). Acute skin toxicity was recorded in 17 patients (56.7%) as grade 1, in 8 patients (26.7%) as grade 2. The patients completed RT without breaks except for 1 with Behcet Syndrome who, following specialist suggestion, temporally suspended RT because of systemic exacerbation, until resolution. Late toxicity was reported in 29 patients (96.7%) (median follow-up 29 months): grade 1 skin toxicity was recorded in 3 cases (10%), grade 2 skin toxicity in 1 case (3.3%). No other acute or late toxicities were reported. After RT all the patients repeated rheumatologic evaluation, and still now none of them presented disease exacerbation or needed further therapy for their autoimmune condition.