ESTRO 2022 - Abstract Book

S1473

Abstract book

ESTRO 2022

.

Conclusion Target coverage was superior in the adapted plans as compared to the scheduled plans, even in cases with decreased target volume when the scheduled plan would be deemed sufficient. Therefore shape changes of the target volume play an important role, which cannot be corrected for using an IGRT or plan of the day approach. Further analysis with more patients is ongoing.

PO-1674 Going from planar kV-MV to kV-kV setup images in image-guided radiotherapy of breast cancer

S.N. Bekke 1 , K. Andersen 1 , C. Behrens 1 , D. Sjöström 1 , P. Sibolt 1 , S. Damkjær 1

1 Copenhagen University Hospital – Herlev and Gentofte, Dept of Oncology, Copenhagen, Denmark

Purpose or Objective In routine IGRT of patients with breast cancer, positioning is often based on a tangential MV and an orthogonal kV image (kV-MV setup) prior to treatment delivery. It is convincing to see the target (breast) in the beams-eye view with the MV image, but it can be challenging to interpret setup difficulties in the form of e.g. rotations or arm position based on a kV- MV setup. In the present study a setup based on an anterior-posterior (AP) kV image and a lateral kV image (kV-kV setup) is evaluated using MV images acquired during treatment delivery for patients treated in Free-Breathing (FB) or Deep Inspiration Breath-Hold (DIBH). In addition, the yaw rotation setup error is quantified. Materials and Methods The analysis was based on 84 fractions from 11 patients treated with 3D conformal radiotherapy with tangential fields after breast conserving surgery, with and without lymph node involvement. The DIBH technique was used for 7 patients. To evaluate the setup deviations in the AP direction (vertical) between the kV-kV setup and MV images, MV images were acquired during treatment delivery for the two open tangential fields (n = 168). The setup deviations between the two unpaired groups treated with FB or DIBH was compared using a Wilcoxon rank sum test. Furthermore, the yaw setup correction from the initial patient position, based on in-room lasers and tatoo marks, were retrospecitvly collected based on the kV-kV setup. Yaw setup corrections above 3 degrees requires repositioning in the clinical setting in our institution.