ESTRO 38 Abstract book

S729 ESTRO 38

From November 2012 to July 2018, 103 IOERT procedures were carried out on 102 patients (one patient had a bilateral synchronous cancer and received the boost bilaterally): in 53 of them (51.46%) IOERT boost was followed by conventional WBRT group 1) and in 50 of them (48.54%) by hypofractionated WBRT (group 2). Median age was 67 years (range: 43-85 years); median follow-up was 40 months (range 6-73 months). Acute toxicity after IORT boost was present in 19 women (G1 in 14; G2 in 5 cases). Acute toxicity at the end of WBRT was evaluated in 97 patients (two patients refused WBRT; one patients underwent mastectomy and two were lost to follow-up): 74 of them (76.29%) experienced G1 and 7 of them (7.22%) G2 skin toxicity. No differences were observed between the two groups. Late toxicity was evaluable in 89/97 patients (91.75%) with a minimal follow-up of 6 months (47 in group 1 and 42 in group 2): 19 of them (21.35%) reported G1 and 6 of them (6.74%) G2 toxicity. A statistically significant difference in late toxicity was observed in the two groups in favour of the group treated with hypofractionated WBRT (p=0.004) (Fig. 1). No local recurrences were observed in the 97 women who concluded the whole treatment, while one patient who had refused WBRT developed a local relapse one year after IOERT. In addition two women developed distant metastases.

node negative, ER positive and HER2 negative. The gross tumour volume (GTV) was defined using mammography, ultrasonography and MRI and grown by 5mm to form the clinical target volume (CTV) and a further 10mm for the planning target volume (PTV). Patients were treated with a single 20Gy fraction to the PTV using volumetric arc therapy up to 72 hours prior to partial mastectomy and sentinel node biopsy. Toxicity was assessed, both subjectively and objectively, using the RTOG-EORTC radiation toxicity scale, NCIC CTCAE and EORTC cosmetic scale at baseline, 48 hours, 14 days and 3,6,9 and 12 A total of ten patients with clinical T1N0 invasive ductal carcinomas, with a median age of 69, were treated between October 2016 and March 2018. All patients were planned and treated successfully using pre-defined constraints to a mean PTV of 48.9 cc. Pathological review demonstrated an increase in tumour size by a mean of 2.06mm and all patients were node negative. Four patients had close (<1mm) margins to ductal carcinoma in- situ. Three patients required surgical revision of margins, one of whom chose a subsequent mastectomy and reconstruction following a further close margin. The fourth patient declined surgery and chose to have whole breast radiotherapy (42.56 Gy in 16 fractions). There were no surgical complications, all had grade 1 surgical scar pain and oedema 7 days following theatre but no delays in wound healing were demonstrated. At 3 months, 8 patients reported good (n=7) to excellent (n=1) cosmesis and 2 reported fair results. Six patients reported grade 1 hyperpigmentation and 1 patient had grade 2 and 3 pain and breast oedema respectively. Conclusion The preliminary results demonstrate feasibility and tolerability following a single pre-operative 20Gy fraction for early stage breast cancer. Continued follow-up is required to meet the secondary objectives including cosmesis at 12 months and ipsilateral breast recurrence. EP-1330 Intraoperative electron radiotherapy (IOERT) boost in early breast cancer: toxicity analysis C. Vidali 1 , Z. Pellin 2 , M. Severgnini 3 , S. Scomersi 4 , M. Bortul 5 1 ASUITS, Radiotherapy, Trieste, Italy ; 2 University of Trieste, Surgery, Trieste, Italy ; 3 ASUITS, Medical Physics, Trieste, Italy ; 4 ASUITS, Surgery, Trieste, Italy ; 5 University of Trieste, Surgery - Breast Unit, Trieste, Italy Purpose or Objective The clinical activity with IOERT as an anticipated boost in the treatment of early breast cancer started in October 2012 at the Breast Unit of the ASUITs of Trieste. The aim of this study is to present the results of our experience with particular attention to acute and late toxicity. Material and Methods Patients with an invasive and unifocal breast tumor - cT1or T2 ≤ 2.5 cm -, cN0-N1 who underwent conservative surgery (quadrantectomy and sentinel node biopsy; axillary dissection only in case of macrometastasis) were eligible to IOERT boost, performed with the mobile LINAC Mobetron. Two protocols were applied in our Center: 1) IOERT (dose: 10 Gy max. dose) followed by conventional whole breast radiotherapy (WBRT) (50 Gy in 25 fr.); 2) IOERT (11.1 Gy max. dose) followed by hypofractionated WBRT (40.5 Gy in 15 fr.), as in the HIOB Protocol schedule. Acute toxicity was evaluated after IOERT and at the end of WBRT using the CTCAE 5.0 Toxicity Scoring system and late complications at 6 months and at every further follow-up, using the LENT-SOMA score. Results months. Results

Conclusion In our experience recurrence rate was very low and acceptable acute and late toxicity were observed, especially in the group of patients who received hypofractionated WBRT after the intraoperative boost. Therefore the use of IOERT as an anticipated boost is encouraged in selected low-risk breast cancer women, even off- clinical trials. EP-1331 Accelerated hypofractionated Whole Breast Irradiation with Concurrent TB Boost:Toxicity and cosmesis S. Lasheen 1 , S. Shams El Din 1 , R. Moussa 2 , M. Hassan 1 , F. Hagag 1 1 NEMROCK Center- Kaser Al-AINI- Faculty of Medicine- Cairo University, Department of clinical oncology, Cairo, Egypt ; 2 NEMROCK Center- Kaser Al-AINI- Faculty of Medicine- Cairo University, Department of medical physics, Cairo, Egypt Purpose or Objective The safety and efficacy of accelerated hypofractionated WBI has been validated in several clinical trials, however tumor bed boost -when administered in theses trials- was prescribed sequential to WBI. The safety of concomitant TB boost in this setting and it's impact on cosmetic outcome is of great interest especially in high volume departments to reduce the work load as well as improve patient compliance. The aim of this study is to investigate the use of accelerated hypofractionated WBI with a concomitant TB boost in terms of toxicity and cosmetic outcome. Material and Methods