ESTRO 2020 Abstract book

S1122 ESTRO 2020

PO-1915 Dosimetric impact of non-compliance/VCD failure in left breast rt treatments in DIBH G. Gómez de Segura Melcón 1 , S. Bermejo Martínez 2 , A. Coral Gallart 1 , N. Espinosa López 1 , X. Nolla Nieto 1 , N. Ventosa Lli 2 , P. Carrasco de Fez 1 1 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain ; 2 Hospital de la Santa Creu i Sant Pau, Servei d'Oncologia Radioteràpica, Barcelona, Spain Purpose or Objective During a former study on the stability of internal geometry for left breast radiotherapy treatments performed in Deep Inspiration Breath-Hold (DIBH), we recorded two main types of incidents: 1) Patient non-compliance during CBCT acquisition in DIBH, leading to CBCT studies acquired in free breathing, and 2) Failure of the Video Coaching Device (VCD). The present study was aimed at analysing the impact of these incidents on some clinically relevant dosimetrical indices as calculated on CBCTs. Material and Methods For 33 patients treated of left breast cancer with external beam radiotherapy performed in DIBH we acquired between 3 and 4 CBCT studies, leading to 94 CBCT studies. DIBH was triggered by RPM system(Varian) and guided by a VCD consisting on googles connected to the video output of the RPM station. Lung and heart structures were segmented on each CBCT study, that had been registered on-line. The treatment plan was copied onto CBCT studies and the following clinically-relevant parameters were recorded: V 30 , V 25 y D mean for heart and V 20 for lung. These indices were compared against those calculated on the planning CT study. We also recorded any incidence happening during the treatment. The main incidences were: failures of the VCD (7 studies) and patient non-compliance (3 studies). Other few minor incidences, not analysed herein, were non- stabilities of the breath-hold and registration based on bone structures. Results Tables I and II show statistics of differences between the clinically relevant parameters calculated on CBCTs and those calculated on planning CTs for those cases of patient non-compliance with DIBH instructions (Table I), and for those cases of failure of the VCD (Table II). Table I shows that noncompliance translated on an average increase of around 2% on for the heart V 30 and V 25 with a maximum difference of 4%. However, differences on lung V 20 were negligible.

The quality of image of CBCTs was not as good as that of planning CTs. This translates in an extra source of uncertainty when delineating OARs on different days that could explain a part of the standard deviations we observed. Conclusion Compliance with DIBH instructions is the key factor for assuring internal geometry stability and correct irradiation of left breast treatments in DIBH as large deviations were observed for cases of non-compliance with DIBH instructions. DIBH for left cancer treatment irradiation can guarantee the same dosimetric accuracy performed with or without VCD provided that those patients had been previously well trained. This enables centers not having a VCD in each treatment unit to keep the treatment ongoing on another treatment unit during scheduled maintenance or in case of failure events. PO-1916 Applications of the Medusa surface tracking system for respiratory control in breast cancer patients H. Collela-Fleury 1 , S. Pallier-Boiteau 1 , P. Beauzac 1 , C. Pechmagre 1 , A. De Oliveira 1 , J. Assuli 1 , E. Brot 1 , P. Poortmans 1 , E. Costa 1 , S. Wakrim 1 , Le Corre. Romane (1) 1 Institut Curie Ensemble Hospitalier, RADIOTHERAPY, Paris cedex 05, France Purpose or Objective Respiratory control for especially left-sided breast cancer is becoming a standard approach to decrease the dose to the heart and, to a lesser extent, the lungs. Several systems are used to verify breath hold stability during treatment. We evaluated our in-house developed surface tracking system for this purpose. Material and Methods Medusa was originally developed for proton therapy and is in routine use at our department since 2010. It consists of a camera system providing a view on the patient’s mask to guide positioning on the treatment table. There are two modes of operation: automatic contouring and manual contouring. For intracranial treatments, the operator contours on the Medusa screen both the holes of the mask and the visible places of the face. For ophthalmic treatments, we delineate the corneal limbus and the eyelids. The camera system allows us to verify positioning of the patient during the whole treatment session. Given our positive experience concerning the reliability and ease of use of the system, and in the face of new technologies requiring high positioning accuracy, we decided to extend the use of Medusa to other clinical applications. We studied the reproducibility of the level of inspiration of 17 patients guided with medusa and 12 patients treated using a spirometer. A kV registration on orthogonal bundles was performed for each patient in inspiration breath hold before treatment delivery. The amplitude of the apnea was further evaluated using an MV image of a tangential beam acquired before the treatment. We measured and compared the distance of the visible pulmonary margin on

Table II shows that the impact of sporadic failure of the VCD was limited, as mean differences were well below 1%.It must be kept in mind that those patients that suffered a failure of the VCD had been trained and had already been treated several times in DIBH before the failure.