Pretrial outlining quality assurance in PIVITOLBoost.

Abstract

50 Background: PIVOTALBoost is a Phase III randomised controlled trial (CRUK/16/018) of radiotherapy to prostate and pelvic nodes versus prostate alone with or without prostate boost. To minimise impact of target volume delineation (TVD) variation on trial outcome, pre-trial radiotherapy quality assurance (RTQA) was implemented to identify and correct potential variations. Methods: Participating centres offering a prostate boost submitted two pre-accrual outlining benchmark cases: one with a central zone boost (GTVpb) only and another with GTVpb (peripheral zone), CTVp/psv and CTVn. A detailed outlining protocol and diagnostic information were provided to centres. Submitted outlines were compared to consensus volumes created by the trial management group (TMG). The TMG deemed the volumes acceptable or as having acceptable or unacceptable variation. Detailed feedback was provided for each submission. Unacceptable variations required resubmission. Results: 32 investigators submitted pre-trial outlines. GTVpb was the most incorrectly outlined volume; 22 (69%) outliners had unacceptable errors for case 2 GTVpb, 17 (53%) for case 1 GTVpb. Most common GTVpb error was inferior extent of lesion followed by incorrect lesion outlined. 12 (38%) of outliners had unacceptable errors for CTVp/psv, most commonly due to delineation at the prostate apex. 8 (25%) outliners had unacceptable CTVn mostly due to incorrect vessel delineation. Of 26 (81%) outliners required to resubmit at least 1 case, 3(12%) required a second resubmission due to unacceptable errors on first resubmission. Conclusions: The majority of pre-trial outlining submissions had unacceptable errors requiring resubmission of at least one case. This was predominantly due to boost delineation error which is a relatively new skill for prostate clinical oncologists in the UK. This suggests robust on-trial RTQA is imperative to minimise further variation. Clinical trial information: ISRCTN80146950.