ESTRO 38 Abstract book

S166 ESTRO 38

Purpose or Objective This study aims to quantify the dosimetric reduction to the heart and lung when comparing WBEBRT with MCABPI for early stage left sided breast cancer. Material and Methods Planning CT data sets of 15 patients with left breast cancer receiving multicatheter brachytherapy after breast conserving surgery were used to create two independent treatment plans – WBEBRT prescribed to 50Gy/25# and MCABPI prescribed to 34Gy/10#. The dose parameters for (i) ipsilateral lung, (ii) heart, and (iii) left anterior descending artery(LAD) were calculated, recorded and compared between the two treatment modalities. Results Upon Equivalent Dose in 2 Gy fractions(EQD2) conversion, and comparing MCAPBI with WBEBRT, the largest dose reduction was for the LAD artery whose mean dose differed by a factor of 7.7. This was followed by the ipsilateral lung and heart with a factor of 4.6 and 2.6 respectively. Compared to WBEBRT, the mean MCAPBI LAD was significantly lower compared to WBEBRT (6.0 Gy vs 45.9 Gy; p < 0.01). The mean MCAPBI heart D0.1cc (representing the dose received by the most highly exposed 0.1 cc of the risk organ, i.e. the dose peak) was significantly lower (16.3 Gy vs 50.6 Gy; p < 0.01). Likewise, the mean heart dose (MHD) was significantly lower (2.3 Gy vs 6.0 Gy; p < 0.01). Peak dose and mean lung dose (MLD) for ipsilateral lung was also lower for MCAPBI compared to WBEBRT (Peak dose: 22.2 Gy vs 52.0 Gy; p < 0.01; MLD: 2.3 Gy vs 10.7 Gy; p < 0.01). Conclusion MCAPBI demonstrated a significant reduction in radiation dose to the heart, LAD and lung when compared to WBEBRT. This potentially translates into better cardiac and pulmonary toxicities for patients undergoing MCAPBI. OC-0321 Phase I-II multicenter trial Very Accelerated Partial Breast Irradiation (VAPBI): early effects J. Guinot 1 , V. Gonzalez-Perez 2 , N. Meszaros 3 , C. Polgar 3 , T. Major 3 , M.A. Santos 1 , D. Najjari 4 , C. Gutierrez 4 1 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Valencia, Spain ; 2 Fundación Instituto Valenciano de Oncologia, Department of Radiation Physics, Valencia, Spain ; 3 National Cancer Institute., Department of Radiation Oncology, Budapest, Hungary ; 4 Catalan Institute of Oncology, Department of Radiation Oncology, Barcelona, Spain Purpose or Objective Accelerated partial breast irradiation (APBI) is a standard treatment for early breast carcinoma after conserving surgery. High dose rate (HDR) with multi-catheter interstitial brachytherapy (MIBT) is used twice a day (3.4Gy x 10, 4Gy x 8 or 4.3Gy x 7 fractions), to a total irradiation time of 4-5 days. We present the preliminary results of the first part of a Phase I-II trial endorsed by the GEC-ESTRO Breast Working Group, using a very accelerated scheme (VAPBI) with HDR-MIBT in 4 fractions, to decrease the total time of treatment to 2-3 days. Material and Methods The criteria to include patients were the same as the APBI GEC-ESTRO Phase III trial, only invasive carcinomas were included. Between August 2017 and July 2018, 31 patients from three centers, with low risk early invasive breast carcinoma have been treated with 4 fractions of 6.25Gy. The total dose was 25Gy prescribed to the CTV. Ten patients have been implanted perioperatively (32%), during the surgical procedure, and 22 postoperatively using CT or US-guided implantation of plastic tubes. 22 cases (71%) have been treated in two days. Mean age was 64 (51-87). Pathology showed invasive ductal carcinoma in 27 cases, invasive lobular carcinoma 2, tubular carcinoma 1 and colloid carcinoma in 1 case. All were with negative sentinel node, free margins 2mm or greater. Luminal A: 23 This abstract is part of the media programme a d will be released on the day of its presentation

cases, Luminal B: 8. Grade 1: 20, G 2:10, G3: 1 case. Mean time between surgery and MIBT was 67 days (39-104) in postoperative cases. Median number of plastic tubes was 13 (range 7-24) implanted in a median of 3 planes (2-5). Regarding the dosimetry, mean V100 was 86cc (19.5- 171cc) mean V150 was 24.2cc (6-41cc); mean D90: 105.4% (96-112.4%); mean DNR: 0.29 (0.23-0.41). Results The technique is the same as used for the GEC-ESTRO Phase III trial, and no differences have been recorded during the implantation and removal. Temporary hematoma developed in 7 cases (5 after perioperative implantations). Pain was referred in one third of cases, well managed with painkillers, and the tolerance was good. No case of infection. With a median follow-up of 7 months, and minimum of three months, slight pigmentation changes (G1) in the entrance of tubes were described in 26%, but with progressive attenuation with longer follow-up. Slight induration or fibrosis (G1) in 16%. Conclusion VAPBI with MIBT using four fractions of 6.25Gy in two or three days is feasible. No differences have been observed after a median follow-up of six months (minimum three months), compared with the previous experience of the APBI Phase III trial. Acute effects are similar. A longer follow up is needed to evaluate chronic effects. The shorter total time is beneficial for the patients and reduces the workload of the Brachytherapy unit. OC-0322 HDR Skin applicator fabrication for clinical cases: handmade vs digitally designed and 3D printed S. Nic A Bhaird 1 , R. Caines 1 , C. Lee 1 1 Clatterbridge Cancer Centre, Department of Physics, Liverpool, United Kingdom Purpose or Objective Several studies have demonstrated feasibility of digitally designed 3D-printed HDR skin applicators [1-2], but none have systematically compared this process against traditional hand-formed methods. This study compared five clinical hand-formed applicators previously used for treatment to digitally designed 3D-printed applicators retrospectively created for the same cases. Geometric and dosimetric measurements were performed. Material and Methods The traditional applicators compromised of a thermoplastic shell, hand-formed wax stand-off and catheters for source transfer. These applicators were constructed to meet specifications for skin-catheter distances and catheter-catheter distances. A process was developed to design these applicators digitally in the contouring module of an EBRT treatment planning system (TPS) (Eclipse v13.6, Varian Medical Systems, CA). The thermoplastic shell of the original applicators was used as a base for the 3D printed applicators. Applicator designs were exported and printed locally with the Axiom 20 3D printer (Airwolf3D, CA). All applicators were CT scanned at high resolution and over 3,800 geometric measurements made in the TPS. Skin-catheter and catheter-catheter distances were inspected and for each applicator type the proportion of measurements within a 1 mm tolerance determined. Treatment planning and delivery was performed for both applicator types according to local protocol. Dosimetry at the centre of each treatment area was verified by TLD. Results Skin-catheter distances: The proportion of geometrical measurements within 1 mm of specification was 0.56 [95% CI: 0.53–0.59] for the hand-formed applicators compared with 0.69 [95% CI: 0.67–0.72] for the 3D-prints (p<0.01,Fig. 1) Catheter-catheter distances: The proportion of geometrical measurements within 1 mm of specification was 0.58 [95% CI: 0.55–0.61] for the hand-formed