ESTRO 38 Abstract book

S560 ESTRO 38

Moreover, 73% of the patients started treatment on a Monday (38%) or Tuesday (35%); 16% started on a Wednesday, 10% on a Thursday and 1% on a Friday. Regarding the type of interruption (B= on break; M= machine down; X= canceled, N=no show), 37% of the patients suffered at least one type of unscheduled interruptions (one type 74%; combination of two types 23%; and combination of three types, 3%). Most frequent interruption is M, followed by X. Frequency of type of interruption is shown in Figure II. Also, 52% of the patients suffered scheduled interruptions like preventive machine maintenance or public holidays.

Conclusion For postoperative brain-tumor patients, DECT-derived MonoCT datasets can improve the intra- and inter- observer delineation conformity compared to the currently used SECT. Moreover, they in part led to similar or better results as the gold standard MR. The most suitable image contrast to meet individual delineation requirements of anatomical structures can be chosen after CT acquisition. Future studies need to show whether the advantages can also be translated to other tumor entities and body regions.

Poster: Physics track: Implementation of new technology, techniques, clinical protocols or trials (including QA & audit)

PO-1013 Unscheduled interruptions and total treatment time for VMAT prostate treatments E.M. Ambroa Rey 1 , J. García-Miguel Quiroga 1 , A. Ramirez Muñoz 1 , D. Navarro Giménez 1 , R. Gómez Pardos 1 , M. Colomer Truyols 1 1 Consorci Sanitari de Terrassa, Medical Physics Unit- Radiation Oncology, Terrassa, Spain Purpose or Objective Treatment interruptions during radiotherapy may have a negative effect on patient outcome and uncompensated interruptions increase the risk of local recurrence. The causes of treatment interruptions may be preventive equipment maintenance, local and national public holidays, treatment toxicity, equipment breakdown, and also patient’s private reasons. It is important to account for these interruptions and evaluate if the total treatment time (TTT) is within a reasonable margin. Material and Methods From April 2014 to July 2018, 392 patients with prostate cancer were analyzed for this study. VMAT plans were carried out using Monaco TPS (v5.10). There are 14 local/national holidays each year in our country. Although there is no consensus about what is the ideal treatment time for prostate cancer, most publications recommend not exceeding the TTT by more than 2 to 5 days. Some form of compensation should be introduced where the interruption results in a prolongation of overall treatment time of more than five days. Results Frequency of treatment lengthened is displayed in Figure I. If we consider scheduled treatment time plus 5 days at most, 63% of the treatments were completed on time (only 11% of them were completed with zero days of delay). Meanwhile, 29% had a delay between 6-10 days and approximately an 8% of the patients had a delay of more two weeks. That means that 37% of prostate patients must have treatment compensations.

If we look the ‘Machine down’ histogram (Figure II), 58 patients had only one day of interruption because of a machine breakdown, meanwhile 34 patients had two days of interruption. In the histogram ‘Fraction cancelled’ you can see that 34 patients suffered one day of interruption, meanwhile 8 patients suffered two days of interruption. Conclusion Unscheduled interruptions, like machine breakdown and patient illness, make difficult to complete the treatment in an ideal time. Although our institution has a protocol to deal with these interruptions, from the results we can conclude that this protocol should be reviewed. Also, due to the machine overload, it is difficult to compensate these unscheduled interruptions for every patient. Therefore the best option could be to open the facility to treat patients on weekend days and public holidays to cope with predictable and unpredictable interruptions to normal treatment. PO-1014 Novel independent dosimetry audit based on end-to-end testing in proton beam therapy. A. Carlino 1 , H. Palmans 1,2 , C. Gouldstone 2 , P. Trnkova 3,4 , S. Vatnitsky 1 , M. Stock 1 1 MedAustron Ion Therapy Center, Medical Physics, Wiener Neustadt, Austria ; 2 National Physical Laboratory, Medical Physics, Teddington, United Kingdom ; 3 Erasmus MC, Medical Physics, Rotterdam, The Netherlands ; 4 HollandPTC, Medical Physics, Delft, The Netherlands

Purpose or Objective