ESTRO 37 Abstract book
ESTRO 37
S607
Conclusion In this limited group, it has been shown that replanning is required in only 10% of cases. This makes the introduction of a decision protocol for plan adaptation using daily CBCT possible, without risk of stress or large increases in overall treatment times. Once the training in the decision protocol is complete, IGART lung can be safely introduced clinically.
limit is 6 mm. Above these levels dose degradation may be significant, and the plan should be re-evaluated. These action levels are straight forward to implement in clinical practice as part of the daily CBCT based positioning and now serve as standard practice regarding the need for re-scanning and re-planning in our Clinic. PO-1077 Feasibility of a CBCT decision protocol for high precision radiotherapy of advanced lung tumors C. Semmekrot 1 , A. Rupert 1 , D. Daal 1 , J. Verdonk 1 , D. Woutersen 1 , E. Van Dieren 1 1 Medisch Spectrum Twente, Radiotherapy, Enschede, The Netherlands Purpose or Objective The radiotherapy department in MST has recently started introducing a new technique called Image Guided Adaptive Radiotherapy (IGART), for patients treated for advanced stage lung tumors. Using a Cone Beam CT (CBCT) before treatment, anatomical changes can be observed and action can be taken to adapt treatment, if required. Evidence elsewhere indicates that this IGART protocol may increase local control for stage III lung cancer patients. Using CBCT, many changes are observed, which may lead to the conclusion the replanning is almost required at a daily basis. However, adaption of a plan is time consuming and potentially delays delivery of remaining fractions, which is undesirable if the adaption proves to be limited. Therefore, the criteria used to decide when to replan have to be optimized. The aim of this retrospective study is to find these criteria, to limit the number of replans. Material and Methods A retrospective analysis was performed using a group of 30 T3 lung tumor patients, imaged using CBCT on a weekly basis. Of this group, 10 patients were excluded because of pacemaker, pneumectomy, scolioses, or precurring atelectase. For the remaining group, each CBCT was compared to planCT. For the match, changes in position of carina, oesophagus, myelum, and CTV-tumor (primairy and lymph nodes) were scored. Results were divided into three groups: <0> no change (0-2.5mm), <1> limited (2.5-5), or <2> large change (more than 5 mm). In addition, occurence of atelectase in each CBCT was scored, as <0> (none), <1> (limited), <2> (large). Plans were recomputed using the CBCT, segmented to water and lung HU, and Eclipse with SmartAdapt (V13.6) to deformably match contours to CBCT. Recomputation was performed for 3 patients with no change, and 7 patients with largest changes. For the PTV, both the Original and the deformed contour was used. DVHs of original (planned DVH) and recomputed (given DVH) were compared and scored in at 85%, 95%, and 95% DVH level for PTVs. In addition, change in Dmax myelum was scored. For the remaining contours, changes in DVH graphs were compared between
Poster: RTT track: Motion management and adaptive strategies
PO-1078 CBCT guided adaptive radiotherapy for cervix cancer:Uncertainty of the choice of the plan of the day M. Gobeli 1 , B. Rigaud 2 , C. Charra-Brunaud 3 , S. Renard 3 , G. De Rauglaudre 4 , V. Beneyton 5 , S. Racadot 5 , K. Peignaux 6 , J. Leseur 7 , D. Williaume 7 , N. Rannou 7 , A. Simon 8 , C. Lafond 7 , N. Jaksic 7 , K. Gnep 7 , C. Herve 7 , F. Riet 9 , I. Pougnet 4 , R. De Crevoisier 7 1 Centre Eugene Marquis, Radiotherapy Department-, Rennes, France 2 University of Rennes 1, LTSI, Rennes, France 3 Institut de cancérologie de Lorraine, Radiotherapy Department, Nancy, France 4 Institut Sainte Catherine, Radiotherapy Department, Avignon, France 5 Centre Leon Berard, Radiotherapy Department, Lyon, France 6 Centre George François Leclerc, Radiotherapy Department, Dijon, France 7 Centre Eugene Marquis, Radiotherapy Department, Rennes, France 8 INSERM- U1099, Campus de Beaulieu, Rennes, France 9 Hôpital Universitaire Pitié Salpêtrière, Radiotherapy Department, Paris, France Purpose or Objective Adaptive radiotherapy (ART) using a pre-treatment plan library (PPL) in locally advanced cervix cancer is a novel strategy who need to be evaluated before is implementation for clinical application. This approach implies a crucial decision to choose the best plan of the day (PoD) on the CBCT. This study though to evaluate the Fifteen patients had a PPL based on three planning CTs with three bladder filling (empty, intermediate and full) allowing to generate three PTVs. Twenty-four CBCTs images were retrospectively selected. The CTV was manually contoured on CBCT images by one expert. The PPL was bone registered on CBCT to simulate the PoD choice. The Dice score between the CTVs of the planning CTs and the CTV of the CBCT were calculated (overlapping index). The best PoD was identified as providing the highest Dice score (maximum CTV overlap). A total of 26 operators (13 medical doctors and 13 technicians) belonging to 6 institutions participated to the study. The user had to choose one of the 3 PTV visualized on CBCT imaging, using a web application (dline ®). The pertinence of the PoD choice was analysed by calculating the proportion of users having chosen the best PoD. A correlation was finally searched between the choice of the PoD and the Dice range (DR). The DR was defined on the PPL as the difference between the highest and the lowest Dice (Figure 1). pertinence PoD choice. Material and Methods
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