ESTRO 2023 - Abstract Book

S1575

Digital Posters

ESTRO 2023

Conclusion For the first case, DPF seems to be a reliable predictor for adaptive leaf position changes (DLP). However, the correlation must be evaluated quantitatively - for many complex cases. In a second step, prediction rules have to be established and the reliability of the procedures has to be investigated. Control mechanisms could be part of the DPF-DLP-comparison. Then, FBP could prepare the way for very fast adaptive processes, like for early CT.

PO-1840 Implementation of rotational total skin electron therapy with an in-house-built flattening filter

L. Marrazzo 1 , D. Chilà 1 , G. Simontacchi 2 , M. Casati 3 , M. Zani 4 , C. Arilli 4 , A. Compagnucci 4 , C. Talamonti 1 , L. Livi 1 , S. Pallotta 1

1 University of Florence, Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Firenze, Italy; 2 Careggi University Hospital, Radiation Oncology, Firenze, Italy; 3 Careggi University Hospital, Medical Physics , Firenze, Italy; 4 Careggi University Hospital, Medical Physics, Firenze, Italy Purpose or Objective Total Skin Electron Therapy (TSET) is a technique aiming at the irradiation of the whole skin. In our Institution, an old fashioned six dual fields technique has been employed for the last 13 years. Recently a new linac was installed and commissioned and this drove us toward the development of a new rotational technique (to potentially improve patient dose homogeneity, patient comfort and treatment delivery) with a specifically designed flattening filter (to avoid the necessity for a dual field). Materials and Methods The developed technique was inspired by the work of Reynard [1]. A rotating platform, able to rotate at variable speed, was designed and manufactured. Two different energies delivered with high dose rate (HDR) modality were tested and commissioned (6MeV and 8MeV electrons) with the aim of having different treatment depth according to patients’ disease features. Several configurations of the flattening filter were tested to improve beam homogeneity, as well as different source-to-surface distances (SSD) to select the best beam penetration according to the clinical requirements. PDDs and profiles were measured with EBT3 films. Once the best combination of parameters was selected, the absolute delivered dose per Monitor Unit (MU) was measured by using an Advanced Markus plane parallel ionization chamber. To calculate MUs to be delivered on the rotating patient, the ratio between the static output, measured in a cylindric phantom (30cm diameter) with EBT3 films placed on the phantom surface, and the rotational output (same measurement but with rotating phantom), was assessed. Finally, an end-to-end test was accomplished using an Alderson Rando Phantom. The end-to-end test was repeated twice to test repeatability.

Results The rotating platform was set to rotate with a speed of 3rpm, which was considered comfortable to the patient and at the same time allowing enough rotations to guarantee dosimetric independence of start and stop positions. In Figure 1 the comparison between horizontal and vertical profiles with and without filter (6 MeV HDRE, SSD=390cm) is reported.