A setting approach for tolerance table of couch position in record and verify system

Abstract

Objective To evaluate the effect of the tolerance table of different couch positions in the record and verify system (R&V system) upon the setup accuracy. Methods Clinical data of 715 patients (15 743 fractions of treatment) were extracted from the R&V system database and assigned into four categories including thorax and abdomen, head and neck, breast, and rectum based on the disease site and immobilization device. The first day couch position (FstD) and cumulative average couch position (CumA) were utilized as the references to analyze the couch setup of each faction of treatment, and to establish the tolerance tables of different sites. The sensitivity and specificity of two methods were evaluated by the actual clinical treatment record of the patients. Results For the FstD as the reference, the couch tolerance in the breast was significantly higher than those in other parts. When the CumA was used as the reference, the couch tolerance tended to be stable after a certain fractions of treatment, and the tolerance of all sites was less than that of the FstD.The tolerance tables significantly differed between these two methods (P=0.000). Both two methods possessed high specificity, whereas the CumA method yielded higher sensitivity than the FstD approach. Conclusion Setting a reasonable tolerance table of couch position can effectively improve the setup accuracy. Key words: Record and verify system; Couch tolerance; Setup error