ESTRO 38 Abstract book

S617 ESTRO 38

Knowledge-Based Planning (KBP) feedback as part of the Real Time Review (RTR) process for the Stereotactic Prostate Adaptive RT Utilising Kilovoltage Intrafraction Monitoring (SPARK) trial. Material and Methods A knowledge based dose-volume histogram (DVH) estimation model and automated planning routine were created using 34 SPARK RT plans that had previously been submitted as part of the clinical trial QA program. The KBP routine was applied to 6 subsequent patients pre- treatment. A feedback report comparing the KBP generated DVH versus the initial plan was collated using a customised script and sent to the site within 24 hours. Centres were asked to review the report and decide whether they would amend their clinical plan. A patient specific questionnaire (PSQ) was also supplied to each centre to gauge implementation and interpretation of the KBP information. Results Of the 6 patients, 5 were protocol compliant and 1 case was replanned due to a major protocol deviation. As a result of KBP feedback 2/5 (40%) cases which were originally protocol compliant, were nevertheless replanned (Figure 1). Protocol dose constraints for all 6 cases were calculated and an average for each metric was generated. The mean dose-volume metrics were then compared between the initial submission, resubmission and KBP generated plans. Overall, the rectum, bladder, penile bulb and urethra planning risk volume (PRV) demonstrated that an improved dose-volume relationship could be achieved compared to the initial submission and was implemented in practice for the 3 resubmitted cases. Variable results were observed for the femoral heads, demonstrating a potential dose trade off (Table 1).

needle configuration was one of the pre-plan goals. A single dose of 19 Gy was prescribed. Sparing of critical organs (OARs) is a prerequisite, with specific focus on the urethra constraint (max. 17.7 Gy in 10% volume). A slight underdosage of the target was accepted when necessary. When the primary goal of target coverage (100% dose in 95% volume) could not be met, a second requirement (17 Gy in 90% volume) was used. The implantation of needles in the OR was performed using TRUS imaging co-registered with mpMRI / PSMA-PET. In the radiotherapy department a CT scan was obtained for catheter reconstruction and contouring of OARs. The final treatment plan was calculated. Prior to treatment the position of the needles was verified against gold fiducials or seeds from the primary treatment using fluoroscopy. Results The defined workflow has proven to be feasible. The primary coverage goal for the pre-plan was met in 3 out of 8 cases. The secondary coverage requirement for the pre-plan was met in all cases. For the treatment plan these numbers are the same, except for two cases: 1. Primary goal was met at treatment, not for pre-plan; 2. Primary goal was not met; secondary requirement was met for the pre-plan but failed for treatment (13.1 Gy for 90% volume).

Mean urethra dose was 16.8 Gy in 10% volume; mean rectal dose 7.9 Gy in 1 cc. Acute toxicity was limited so far with only one patient needing a catheter for 2 weeks (calculated risk: initial IPSS score 18; Qmax 6ml/s). Conclusion This single fraction treatment of prostate recurrences is feasible using CT only for treatment planning. Dose constraints can be met, tumour coverage is in general adequate and acute toxicity limited. This seems to be a way to delay or even avoid androgen ablation. The treatment effect needs to be evaluated after sufficient follow-up. 1. Zumsteg et al. Eur Urol. 2015;67:1009 2. Maenhout et al. Technol Cancer Res Treat. 2017;16:1194 PO-1111 Knowledge-Based Planning as a Real Time Review QA Feedback Tool in the TROG 1501 SPARK trial O. Cook 1 , A. Moore 1 , R. Kaderka 2 , K. Moore 2 , P. Keall 3 , J. Martin 4 1 TROG Cancer Research, Radiation Therapy Quality Assurance, Newcastle, Australia ; 2 University of California- San Diego, Radiation Medicine and Applied Sciences, California, USA ; 3 University of Sydney, Faculty of Medicine and Health, Sydney, Australia ; 4 Calvary Mater Newcastle, Radiation Oncology, Newcastle, Australia Purpose or Objective Quality assurance (QA) in radiotherapy (RT) clinical trials is essential to ensure protocol compliance, patient safety and trial quality. However, protocol compliance does not necessarily ensure optimal plan generation . This study aimed to demonstrate the feasibility and impact of

The PSQ was completed for 3 patients and open ended email response was received for the remaining 3 cases. All centres indicated that the KBP feedback process was a valuable tool for quality improvement in clinical trials and that the KBP feedback report provided enough information to make meaningful changes to their plans. In 2 cases the centres felt the turn-around time and resources were not sufficient if they were to make the suggested changes. Conclusion KBP feedback was successfully incorporated into the RTR process for the SPARK trial and demonstrated that both improvements to and validation of plan quality for OAR dosimetry could be achieved. KBP feedback was received well with centres seeing value of this novel QA tool. There is potential to continue to build and improve on the model for future SBRT prostate trials, whether it be used as a QA