Dosimetric and Radiobiological Evaluation of Patient Setup Accuracy in Head-and-neck Radiotherapy Using Daily Computed Tomography-on-rails-based Corrections.

INTRODUCTION:This study evaluates treatment plans aiming at determining the expected impact of daily patient setup corrections on the delivered dose distribution and plan parameters in head-and-neck radiotherapy. MATERIALS AND METHODS:In this study, 10 head-and-neck cancer patients are evaluated. For the evaluation of daily changes of the patient internal anatomy, image-guided radiation therapy based on computed tomography (CT)-on-rails was used. The daily-acquired CT-on-rails images were deformedly registered to the CT scan that was used during treatment planning. Two approaches were used during data analysis ("cascade" and "one-to-all"). The dosimetric and radiobiological differences of the dose distributions with and without patient setup correction were calculated. The evaluation is performed using dose-volume histograms; the biologically effective uniform dose () and the complication-free tumor control probability (P+) were also calculated. The dose-response curves of each target and organ at risk (OAR), as well as the corresponding P+ curves, were calculated. RESULTS:The average difference for the "one-to-all" case is 0.6 ± 1.8 Gy and for the "cascade" case is 0.5 ± 1.8 Gy. The value of P+ was lowest for the cascade case (in 80% of the patients). DISCUSSION:Overall, the lowest PI is observed in the one-to-all cases. Dosimetrically, CT-on-rails data are not worse or better than the planned data. CONCLUSIONS:The differences between the evaluated "one-to-all" and "cascade" dose distributions were small. Although the differences of those doses against the "planned" dose distributions were small for the majority of the patients, they were large for given patients at risk and OAR.