ESTRO 2020 Abstract Book

S816 ESTRO 2020

randomly from all breast cancer patients receiving radiotherapy from 2017 to 2018 at our institution. Patients were prescribed 50 Gy to the CTV. All patients were treated with forward planned tangential and supraclavicular step-and-shoot 6 MV fields and with combined 18 MV fields used for larger breasts. 17 of the patients were treated in deep inspiration breath-hold. For each patient an additional plan was generated, using two 6 MV VMAT fields in a butterfly configuration (each arc spanning 40-70 degrees). A skin flash of 1cm was used to ensure robustness. Dose planning was done in pinnacle 16.0 in the Auto-Planning module. Mean doses to organs at risk, the relative volume receiving 90% of the prescribed dose (V90%) for supraclavicular and IMN region and V95% for breast were compared using paired t-tests. Results Mean doses to the organs at risk and the V90% and V95% to the target areas are shown in the table. The mean dose to Ipsilat lung, contralat lung and contralat breast was statistically significant higher with the automated plans, whereas the heart dose remained similar dose. The automated plans showed statistically significant higher coverage of the all the target volumes. Conclusion The left-sided breast radiotherapy with VMAT plans in Pinnacle with Autoplan allowed plans with good coverage to the target regions. Compared to the manual plans the VMAT plans had statistically significant better coverage to the target regions without introducing significantly higher dose to the heart but with a small significant increased dose to the ipsilat lung dose and contralateral - lung and breast. But all OAR doses were clinically acceptable and meet the dose constraints suggested by DBCG (www.DBCG.dk). PO-1512 VMAT based TBI using a novel rotatable tabletop C. Losert 1 , R. Shpani 1 , R. Kießling 1 , P. Freislederer 1 , M. Li 1 , F. Walter 1 , M. Niyazi 1 , M. Reiner 1 , C. Belka 1 , S. Corradini 1 1 LMU Munich, Department of Radiation Oncology, Munich, Germany Purpose or Objective VMAT techniques have recently been implemented in clinical practice for total-body irradiation (TBI). To date, most techniques still use special couches, translational tables, or other self-made immobilization devices for dose delivery. Aim of the present study was to report the first results of a newly developed rotatable tabletop designed for VMAT-TBI. Material and Methods The VMAT-TBI technique theoretically allows the use of standard equipment in the standard linac room. Nevertheless, the main problem is that patients taller than 120cm cannot be treated in one position due to the limited cranio-caudal couch shift capacities at the linac. Therefore, patients are usually turned from a head-first supine position (HFS) to a feet-first supine position (FFS) to overcome this limitation. The newly developed rotatable tabletop consists completely of carbon fiber, including the ball bearing within the base plate of the rotation unit. The patient can be turned 180° from a HFS to a FFS position within a few seconds, without the need of repositioning.

Results The first 20 patients had a median age of 47 years, and received TBI before bone marrow transplantation for acute myeloid leukaemia. Most patients (13/20) received a TBI dose of 4 Gy in 2 fractions, twice daily. The mean number of applied monitor units (MU) was 6476 MU using a multi- arcs and multi-isocenter VMAT-TBI technique. The tabletop has been successfully used in daily clinical practice and helped to keep the treatment times at an acceptable level. During the first treatment fraction, the mean overall treatment time (OTT) was 57 minutes. Since no additional image guidance was used in fraction 2 of the same day, the OTT could be significantly reduced to 38 minutes in mean.

Conclusion The easy and reproducible rotation of the patient on the treatment couch using the rotatable tabletop, is time- efficient and overcomes the need of repositioning the patient after turning from a HFS to a FFS position during VMAT TBI. Furthermore, it prevents couch-gantry