ESTRO 2022 - Abstract Book

S1510

Abstract book

ESTRO 2022

The intrafraction motion evaluation was performed by investigating the residual isocenter shifts during beam on time for the lateral, longitudinal and vertical directions for each treatment fraction. Mean and SD of the residual isocenter shifts over all the treatment fractions of each patient were calculated. Plan robustness was evaluated, for each patient, by calculating the perturbed dose for the single-fraction plan in accordance with the daily residual isocenter shift. Perturbed plans were then accumulated in the overall “shifted” treatment plan. Shifted and original plans were compared in terms of the main DVH goals for target coverage and OARs doses. Statistical significance of dosimetric data was analysed using a Wilcoxon signed-rank test considered significant if p<0.05. Results The residual isocenter shifts during beam on time for 160 treatment fractions were calculated. Intra-fraction mean isocenter shifts over all the patients were 0.1±0.7 mm, -0.6±0.9 mm, 0.3±0.2 mm and 2.4±0.5 mm for lateral, longitudinal, vertical, and deviation respectively with a maximum-minimum range of -1.1÷1.3 mm, -2.2÷1.1 mm, -1.3÷0.4 mm and 1.6÷3.3 mm respectively. In fig. 1 is reported an example of the shifts investigation for a single patient: both the average shift vector for each fraction and the cumulative residual shifts distributions are shown. The average DVH variations due to residual isocenter shifts over all the patients were: 0.0±0.4% for PTV 95% coverage; 0.02±0.06Gy and 0.9±1.9Gy for the mean and maximum(1cc) Heart dose respectively; 0.2±0.3Gy and 0.5±0.8Gy for the mean and maximum LAD PRV dose respectively and 0.4±0.5% for Sx Lung 20Gy volume. For each DVH goals any significant dosimetric difference between the shifted and the original plan was found, this indicating that the technique and its planning and margin definition strategy is robust. An example of the daily and total plan DVH variation for a single patient is reported in fig. 2.

Conclusion DIBH procedure guided by optical systems for left breast irradiation is a reproducible and stable technique with a limited intra-fraction DIBH variability. Residual isocenter shifts do not produce significant dosimetric variations, assessing the robustness of the treatment strategy.

PO-1711 Accurate FLASH delivery requires motion monitoring – SGRT is a feasible option for canine patients

A. Mannerberg 1 , E. Konradsson 1 , A. Edvardsson 2 , M. Kügele 1,2 , M. Kadhim 2 , C. Ceberg 1 , K. Petersson 2,3 , H. Thomasson 2 , M.L. Arendt 4 , B. Børresen 4 , K. Bastholm Jensen 5 1 Lund University, Medical Radiation Physics, Lund, Sweden; 2 Skåne University Hospital, Department of Hematology- Oncology and Radiation Physics, Lund, Sweden; 3 University of Oxford, MRC Oxford Institute for Radiation Oncology, Department of Oncology, Oxford, United Kingdom; 4 University of Copenhagen, Department of Veterinary Clinical Sciences, Fredriksberg, Denmark; 5 Veterinärhuset Öresund, Limhamn, Malmö, Sweden

Purpose or Objective