ESTRO 2020 Abstract Book

S1069 ESTRO 2020

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 the MV image with that of the DRR generated after treatment planning. Results The new application of Medusa for patient monitoring during radiation therapy asked for solutions for camera positioning and zoom function, room illumination and interference of images due to scattered radiation. We included all this in a project aimed at implementing respiratory control for breast cancer patients avoiding the need for an active system like spirometry. Analysis of the visible pulmonary margin in the tangential beam shows no significant difference between "medusa" patients and "spirometry" patients (unpaired student test p = 0.35).

PO-1917 Pre-trial plan selection training - is it sufficient for optimal plan selections online? A. Webster 1 , S. Hafeez 2,3 , H. McNair 3,4 , V.N. Hansen 5 , C. Griffin 6 , R. Lewis 6 , E. Hall 6 , R. Huddart 3,7 1 National Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre, London, United Kingdom ; 2 Institute of Cancer Research, Department of Radiotherapy and Imaging, London, United Kingdom ; 3 The Royal Marsden NHS Foundation Trust, Department of Radiotherapy, London, United Kingdom ; 4 Institute of Cancer Research, Translational Therapeutic Radiography Team, London, United Kingdom ; 5 Odense University Hospital, Department of Radiotherapy Physics, Odense, Denmark ; 6 Institute of Cancer Research, Clinical Trials and Statistics Unit, London, United Kingdom ; 7 Institute of Cancer Research, Clinical Academic Radiotherapy Team, London, United Kingdom Purpose or Objective HYBRID (CRUK/12/055) and RAIDER (CRUK/14/016) are two randomised phase II multicentre bladder trials evaluating plan of the day (PoD) radiotherapy. Previously we reported the introduction of a pre-trial PoD Quality Assurance (QA) programme (ESTRO 36 OC-0351) and the initial guideline compliance in on-trial PoD selections for RAIDER (ESTRO 38 OC-0634). Here we aim to compare the difference in compliance between pre-trial and on-trial PoD selections, reported and unreported, to determine QA requirements. Material and Methods The pre-trial QA programme initially included: • A video overview of PoD • A PoD selection guidance document • 12 training cases • 12 test cases The PoD selections for the 12 test cases were compared to the gold-standard consensus selection. The on-trial QA programme initially consisted of retrospective data collection of CBCTs and PoD selections. The PoD selections for the on-trial patients were compared to the offline gold-standard expert reviewer selection. For each patient, i.e. submission, a guideline compliance score was calculated = number of compliant PoD selections/total number of PoD selections. Differences in PoD selection compliance scores between pre-trial and on- trial submissions, trials, PoD experience, centre size and recruitment rate were tested using Mann-Whitney U and Kruskal-Wallis tests. Results 8,286 PoD selections from 35 centres were reviewed, equating to 1,339 PoD submissions, Table 1.

Conclusion In a series of patients treated using spirometry, we confirmed the utility of Medusa to check both the amplitude and the reproducibility of the inspiration. The RTT’s, using skin-drawn marks visualised by the Medusa screen, can guide the patient to the required inspiration during the pre-treatment CT-scan and subsequently throughout the entire treatment series to verify and maintain a stable extent of apnoea.

The compliance score of PoD selections pre-trial was significantly higher than PoD selections on-trial ( P <.001), Table 2. Thus, the PoD selections online were less compliant than PoD selections offline. Compliance scores differed by centre size (p=.01) and recruitment rate