ESTRO 2020 Abstract Book

S1068 ESTRO 2020

fraction was registered and it was defined as the interval between the execution of the first set-up control and the end of the last treatment field. This time was considered in our analyses as a marker of patient compliance. The means of daily periods of the first and last week of treatment were calculated for everyone. A reduction of mean treatment time between the first and the last week was indicative of patient good compliance. Patients were also stratified by age (<60 years old = group A vs . ≥60 years old = group B) because DIBH usually required a good physical performance. Results Almost all patients (38/39, 97%) were able to complete irradiation in DIBH. Only one patient required to switch to a free-breathing IMRT treatment and was excluded from this analyses. Totally 27 patients showed a reduction of mean treatment time and were classified as “compliant”, while 11 experienced an increase and were classified as “not compliant”. In group A, 6 patients (20%) showed a worse time difference (mean= + 2:11 min) while 23 patients (80%) showed an improvement (mean= - 2:15 minutes). In group B, 5 patients (55%) showed a worse time difference (mean = +0:55 minutes), while 4 patients (45%) showed an improvement (mean= -1:55 minutes). The difference in terms of number of “compliant” patients (80% in group A vs. 45% in group B) resulted statistically significant (p-value=0.04). Conclusion Audio coaching, good patient education and patient training are usually useful to increase patient compliance during DIBH radiation treatment. Age is an important parameter to be considered for patient selection, because compliance was significantly worse in patient ≥60 years old. A visual coaching system is probably necessary to guide DIBH in older patients. 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.

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.

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