ESTRO 36 Abstract Book

S126 ESTRO 36 _______________________________________________________________________________________________

oncology in Canada, namely, reduction in waiting times for radiotherapy, and peer-review of radiation oncology treatment planning. Both are highly relevant to the overall strategy for quality improvement in Canada. Health care system performance on both wait times and peer-review are key quality indicators for radiotherapy treatment programs in Canada. Wait times for radiotherapy - known to be associated with treatment outcomes - have improved in some dimensions, but remain a problem in others, particularly when overall wait times from diagnosis to first treatment are considered. Trends in wait times and current strategies to reduce wait times will be discussed. Peer review of treatment planning consists of a radiation plan being reviewed by at least one independent radiation oncologist (preferably in a multi- disciplinary setting). Radiation planning peer review is endorsed as a critical component of a radiation oncology quality assurance program. The presentation will describe a pan-Canadian initiative that was launched in 2012 with the intent to disseminate the uptake and to improve the conduct of peer review activities. The components of the initiative include a national base-line survey of current practice and attitudes, strategies to promote the uptake of peer review, quantitative evaluations of peer review findings, qualitative assessments of peer review activities in radiation oncology programs, and development of “best practice” guidelines for practitioners and radiation programs for selected common radiotherapy treatment scenarios. SP-0250 Waiting time in radiotherapy, an overlooked problem J.Overgaard 9 Aarhus University Hospital, Dept Expt. Clin. Oncology, Aarhus C, Denmark OC-0251 Late toxicity in HYPRO randomized trial analyzed by automated planning and intrinsic NTCP- modelling A.W.M. Sharfo 1 , M.L.P. Dirkx 1 , R.G. Bijman 1 , W. Schillemans 1 , S. Breedveld 1 , S. Aluwini 1 , F. Pos 2 , L. Incrocci 1 , B.J.M. Heijmen 1 1 Erasmus MC Cancer Institute, Radiation Oncology, Rotterdam, The Netherlands 2 Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective To analyze delivered OAR doses and NTCPs in the HYPRO multicenter randomized hypofractionation trial for prostate cancer patients (Lancet Oncology 2015, 2016) using automated VMAT planning (autoVMAT). The applied multivariate NTCP models were derived by correlating clinically observed complications in the HYPRO trial with clinical and dosimetric parameters. Material and Methods 820 prostate cancer patients were included in the HYPRO trial, randomly assigned to standard fractionation (39x2 Gy, 5 fr/wk) or hypofractionation (19x3.4 Gy, 3 fr/wk). Our platform for fully automated multi-criterial treatment planning was used to generate for each patient an autoVMAT plan. Achieving adequate PTV coverage had the highest priority, followed by minimization of the dose to the rectum, anus, bladder and hips. Plans were compared with respect to PTV dose coverage, rectum D mean , V 65Gy and V 75Gy , mean doses in anus and bladder, and maximum doses in the femoral heads. Moreover, comparisons were Abstract not received Proffered Papers: Automated and robust treatment planning

performed using NTCP models derived from the HYPRO database for grade ≥ 2 late Gastro Intestinal (GI) toxicity, stool incontinence, stool frequency, rectal bleeding, and proctitis. For a subgroup of patients, autoIMRT plans with the clinically used beam angles were generated as well. For the analyses, all OAR doses in both fractionation schemes were converted to EQD 2Gy assuming α/β=3 Gy. Results So far, 430 patients (215 in each arm) were analyzed. Compared to the clinically applied plans, autoVMAT plans had similar or higher PTV coverage. Large and highly significant enhanced OAR sparing was observed with autoVMAT for both treatment arms (see figure 1). Compared to the clinical plans, the autoVMAT plans showed reductions in mean doses in the rectum, anus and bladder of 6.9±4.4 Gy, 7.2±6.2 Gy and 4.1±2.7 Gy (p<0.001), respectively. Rectum V 65Gy and V 75Gy were reduced by 3.3% (relative difference 23.4%±19.7%) and 1.3% (relative difference 27.5%±51.9%) (p<0.001), respectively. Maximum doses in the left and right femoral heads were also reduced by 29% and 32% on average. Figure 2 compares clinical and autoVMAT plans regarding NTCPs for the studied GI symptoms. Significant reductions in rectal NTCPs with autoVMAT were observed with a relative reduction of 10.5% in late GI grade ≥2, 16.8% in stool incontinence, and 18.7% in rectal bleeding (p<0.001). Plan quality improvements with autoIMRT relative to clinical plans were similar as those observed for autoVMAT, showing that enhanced plan quality was not related to the use of VMAT instead of IMRT.

Conclusion Automatically generated VMAT and IMRT plans resulted in large plan quality improvements compared to the clinically applied IMRT plans with significant NTCP reductions. The enhanced plan quality results from improved planning, possibly related to improvements in the treatment planning system (TPS) and/or automation of planning. OC-0252 Acceptance rates of automatically generated treatment plans for breast cancer G. Van der Veen 1 , A. Duijn 1 , J. Trinks 1 , A. Scholten 1 , R. Harmsen 1 , G. Wortel 1 , R. De Graaf 1 , D. Den Boer 1 , E. Damen 1 1 Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands