ESTRO 2023 - Abstract Book

S1656

Digital Posters

ESTRO 2023

Conclusion This study verifies that the dosimetric error of ITV-based IMRT due to the tumor motion was larger in VMAT than in Tomo. Also, Tomo can be considered to be more suitable than the conventional LINAC-based VMAT method in terms of the dosimetric accuracy of ITV-based IMRT for the treatment of a moving tumor.

Poster (Digital): Inter-fraction motion management and offline adaptive radiotherapy

PO-1908 Simulation of dose with reduction of tissue in breast radiotherapy

M. Kjeldsen 1 , M. Berg 2 , H. Nissen 1 , E. Maae 1

1 Vejle Hospital, Oncology, Vejle, Denmark; 2 Vejle Hospital, Oncology, Vejle , Denmark

Purpose or Objective In breast radiotherapy (RT), the delivery of dose is planned from a ‘snapshot’ CT-scan. A major challenge is the changes in patient anatomy, mobility and positioning during treatment. Significant changes in tissue volume in the beam path are seen on daily cone-beam CTs and may result in unacceptable changes in the dose distribution. We have previously examined added tissue and are introducing a region of interest (ROI) in our clinic for daily CBCT evaluation of added tissue. The consequence of reduced tissue depth is less investigated. Decisions regarding missing tissue during treatment would benefit from a corresponding ROI, and should be equally considered to avoid risks of side effects in modern RT. Here we have undertaken a systematic dose calculation of tissue reduction, in order to clarify the treatments consequences. Materials and Methods Twenty left-sided lumpectomy patients receiving 3D conformal RT were consecutively enrolled. All patients received irradiation to the breast and the loco-regional lymph nodes. Delineations were according to ESTRO guidelines. Treatment plans were made in Raystation 9 (RaySearch Laboratories AB, Sweden) according to the guidelines of the Danish Breast Cancer Group (DBCG) and local guidelines. During planning V105%=2% and V107%=2% was used as objective and constraint for the breast, respectively. For comparison, plans with other fractionations were converted to 40 Gy in 15 fractions by scaling the dose. Isotropic reduction of patient outer contours with 3, 4, 5, 7 and 10 mm reduction in turn was simulated,