Purpose: Peer review is an essential component of radiation therapy quality assurance (RT QA). Deviating from RT QA standards is associated with poor outcomes in cancer patients. We previously published on the importance of prospective peer review on all patients receiving radiation across our multi-center radiation medicine department. Herein, we more closely analyzed the reasons for RT QA deviations.

Methodology: All cases within our department are treated per a uniform set of system-wide directives. Once contoured, cases undergo prospective peer review with each case assigned a grade (A, B, or C). “A” cases are considered per protocol (i.e. directive) and require no changes, “B” cases require minor modification, and “C” cases require major modification before treatment planning. All radiation cases with curative intent from 2017-2022 were reviewed. Chi-Square Test of Independence was performed to determine associations between the proportion of B scores, reasons for error, and the anatomical sites treated.

Results: 13,901 curative cases were peer-reviewed from 2017-2022. 58.6% of cases were scored as A, 41.3% were scored as B, and 0.1% were scored as C. Of the cases receiving a B score, 52.2% were due to contour modifications (of either the target or an organ at risk), 37.4% were due to directive variance (discrepancy between the prescription and treatment directive), and 10.4% were due to other errors. The 10 anatomical sites with the highest proportion of B scores (out of the total number of cases treated for that site) were vulva (69.0%), anal (64.6%), cervix (56.2%), head and neck (55.6%), endometrial (53.9%), bladder (53.4%), pancreas (53.4%), esophagus (49.6%), lymphoma (49.1%), and sarcoma (46.0%). Gynecological cases were more likely to receive a B score than non-gynecological cases (56.5% of gynecological cases received B score vs. 38.9% of non-gynecological cases received B score, p<0.0001). Contour modifications accounted for the majority of B scores for 8 of the 10 top sites, including all gynecological sites. The proportion of cases that received a B score due to contour modifications did not differ by site type (51.8% of gynecological sites received B score due to contour modifications vs. 52.1% of non-gynecological sites received B score due to contour modifications, p=0.899).

Conclusions: In this large study on peer review, we found that 41% of cases treated in our department had protocol deviations. While the plurality of cases receiving a B score were gynecological, errors were found across disease sites and most were due to a contour modification, highlighting the importance of prospective peer-review upstream of treatment planning for all patients receiving radiation therapy as part of RT QA. Implementing methods to mitigate contouring and clerical errors is important to enhance patient safety and should be considered routine for current radiation therapy.