Dosimetric effects within target and organs at risk of interfractional patient mispositioning in left breast cancer radiotherapy

Purpose: To investigate the effects of interfraction setup uncertainties on the dose distribution within the clinical target volume (CTV) and the organs at risk (OAR) of left-sided breast cancer patients undergoing external radiotherapy. Methods and Materials: Interfractional setup errors were assessed by measuring surface control points displacements during 89 irradiation sessions in 4 patients, by means of opto-electronic localization. The measured position deviations were fed back to the treatment planning system for the evaluation of the corresponding dosimetric effects within CTV and OARs (lung, heart). Results: Results revealed errors above 5 mm on some of the control points, but corresponding volumetric variations were on average below 2% for both the CTV within the 95-105% dose range and the OARs receiving more than 50% and 90% of the prescribed dose. A specific sensitivity to the setup errors was found as a function of the treatment plan design, leading to isolated cases exhibiting volumetric variations of CTV and OARs exceeding 2%. Conclusions: This study confirms the potential increase of treatment quality provided by the systematic patient position verification and highlights the role of opto-electronic position detection systems for the real-time check of patient setup errors and the evaluation of the corresponding dosimetric consequences, as a way to achieve consistent dose delivery. (C) 2004 Elsevier Inc.