ESTRO 2020 Abstract Book

S506 ESTRO 2020

PO-0947 Dosimetric evaluation of organs at risk in APBI patients treated with multicatheter interstitial BT M. Maçães 1 , S. Pinto 1,2 , A. Pereira 1,2 , J. Lencart 1,2 , P. Fernandes 3 , L. Trigo 3 1 Portuguese Oncology Institute of Porto IPO Porto, Medical Physics, Porto, Portugal ; 2 IPO Porto Research Center CI-IPOP, Medical Physics - Radiobiology and Radiation Protection Group, Porto, Portugal ; 3 Portuguese Oncology Institute of Porto IPO Porto, Brachytherapy Department, Porto, Portugal Purpose or Objective The present work consist of a dosimetric evaluation of organs at risk (OARs) according to the recent GEC-ESTRO recommendations (1) in sixty one APBI patients treated with multicatheter interstitial brachytherapy (MIBT) using Between February 2017 and December 2019, 61 APBI patients (32 patients with left-sided and 29 with right- sided breast tumors) were treated with MIBT technique. After lumpectomy, a post-operative multicatheter implant was performed with a prescription dose of 32Gy (4Gy/fraction in 5 days with a minimum interval between fractions of six hours). After catheter insertion, the patients underwent a CT scan (2mm slices), and treatment plans were obtained with TPS Oncentra MasterPlan v4.1. After the target volumes and the OAR, including skin, lung ipsilateral, ipsilateral non- target breast and heart (in cases of left-sided tumors), were delineated and the dose-volume histograms were evaluated. Results Of 61 patients, 52% had a left sided lesion and 48% had the tumor in the right breast. Regarding the tumor location in breast, we did not find a relation between the quadrant and the dose received by OAR. Table 1 shows the analyzed dose-volume parameters and the recommended limits. a HDR Ir-192 source. Material and Methods

The average of all dose-volume parameters was in conformity with guidelines, however there were patients (16.3%) exceeded some recommendations because of PTV’s location relative to OAR mainly lung, ribs and heart. It is important to take it in consideration the follow-up of patients regarding toxicity. PO-0948 Deep inspiration breath-hold for cardioprotection in patients with left-sided breast cancer O. Micke 1 , R. Mücke 2 , K. Kister 3 , U. Schäfer 4 1 Franziskus Hospital Bielefeld, Departement of Radiotherapy and Radiation Oncology, Bielefeld, Germany ; 2 Radiotherapy RheinMainNahe, Radiotherapy, Bad Kreuznach, Germany ; 3 St. Anna Hospital, Department of Internal Medicine, Herne, Germany ; 4 Lippe Hospital Lemgo, Department of Radiotherapy, Lemgo, Germany Purpose or Objective Radiation therapy (RT) has been widely used for breast cancer (BC) treatments. However, for left sided breast radiotherapy cardiac complication is of concern, because earlier studies did not show an increase in overall survival in breast cancer patients treated with RT because of the increase in non-breast cancer mortality, in particular cardiovascular events. Additional systemic treatment may even enhance this effect. Deep inspiration breath-hold (DIBH) technique can reduce the cardiac dose by increasing the distance between the heart and the breast or chest wall. Material and Methods Overall, 350 patients (ages 30-83) with left-sided BC were enrolled on a prospective quality assurance study from 2016-2019. We treated 150 patients with free breathing (FB) and 200 with DIBH. For treatment application the Catalyst/Sentinel system (C-RAD AB, Uppsala, Sweden) was used and gating control was performed by an audio- visual patient feedback system. CT and surface data were acquired in FB and DIBH. FB patients were significantly older (median: 58 vs. 48.5 years), more likely to have pre- existing heart (11% vs. 1%) and lung disease (13% vs. 4%), and less likely to receive chemotherapy (42% vs. 66%). Treatments were prescribed with 50 Gy in 25-28 fractions. Opposing tangent fields with electronic compensator techniques (field-in-field) were used to improve dose homogeneity. The separation between the heart and the chest wall was standardizedly measured at the 7th thoracic vertebrae and 11 cm anterior to the vertebral body on the scan for each patient. Results The overall treatment time, including patient setup and alignment as well as beam on time, ranged from 7-15 minutes for each fraction. The average time for each treatment field is 11 seconds (ranged for 9.5-15 seconds). The separation between the heart and chest wall for DIBH scans is 6.5 cm (range 5.1-7.8 cm). This is significantly larger than the separation in the FB scans, which is 2.72 cm (range 2-4.25 cm). The maximum dose to the heart is significantly lower for the DIBH scans than the FB scans, 11.0 Gy (range 6.8-21 Gy) vs 35.6 Gy (range 12.8- 45.5 Gy). The mean dose to the heart is lower, 0.93 vs. 2.06 Gy. Conclusion DIBH can significantly benefit the left breast and chest wall patients by separating the heart from the radiation fields. Daily real-time surfacing imaging facilitates patients’ setup and ensures accurate and reproducible positioning for DIBH treatments without additional radiation dose. Patient compliance was good, and treatment durations are clinically acceptable. DIBH with real-time surface monitoring appears to be a viable option to potentially reduce heart dose for left breast cancers patients, and thus may reduce the potential long-term cardiovascular complications.

The mean to all parameters was below of the limits of GEC- ESTRO recommendations, although some patient’s heart, ipsilateral lung and ribs exceeded the dose. The dose heart mean was < 1Gy for all patients, but regarding D 0.1 cm 3 <50% parameter, 3 patients exceeded the limit because the PTV has a very close proximity to the heart. The minimum heart-to-PTV distance was 2mm and cm 3 values were 53.89% and 46.84% respectively, however, 5 patients exceeded dose-volume parameters because of the proximity of PTV-ribs. Of the 61 patients, 9 exceeded the dose-volume parameter D 0.1 cm 3 <60% to lung. Evaluating those cases, we detected that all of them had the 50% isodose curve reaching the lung, opposing the rest of the patients. Doses to skin and ipsilateral non-target breat were low for the maximum distance was 46mm. Regarding the ribs the average D 0.1 cm 3 and D 1.0

all patients. Conclusion