ESTRO 2022 - Abstract Book

S1118

Abstract book

ESTRO 2022

Materials and Methods Two steps are taken to increase the surface dose for IOERT: 1) Introducing a bolus to achieve a maximum surface dose, and 2) re-normalizing in order to allow for the same prescribed dose at the reference depth.

Results By realizing these adaptations, the dose delivery curve approaches that of IOBT in the most superficial millimeters of irradiated tissue. In greater depths, the dose fall-off is steeper than that of IOBT. The effect of this adaptation on local control will be analyzed in five years by comparing patients treated with a historical cohort. We expect no increased toxicity due to this adaptation. Patients treated at the IOBT center have acceptable toxicity despite this high surface dose, and as stated electron dose fall-off remains steeper in comparison to IOBT dose-fall off, possibly resulting in less toxicity with IOERT. Due to the fixed tube used for IOERT, one of the disadvantages of IOERT when compared to IOBT is the relative inability to adapt to the anatomy of the patient. Two possible bevel angles (30 and 45 degrees) can be used, depending on the shape of the target volume. With the use of the bolus and re-normalization, we are able to compensate for differences in anatomy while still being able to deliver a high surface dose with a steep dose fall-off. Conclusion We describe and propose an adaptation of the IOERT technique in order to increase surface dose with the aim of further improving local control. The dosimetric differences between IOERT and IOBT are reduced thanks to this adaptation.

PO-1324 Accelerated hypofractionation with SIB-IMRT in Anal Cancer : assessment of efficacy and toxicity

S. Lucidi 1 , N. Bertini 1 , M. Loi 2 , P. Bonomo 2 , G. Francolini 2 , D. Greto 2 , G. Simontacchi 2 , A. Galardi 2 , L. Marrazzo 3 , A. Allegra 4 , B. Guerrieri 4 , E. Scoccimarro 4 , M. Mariotti 4 , M.G. Carnevale 4 , G. Stocchi 4 , L.P. Ciccone 4 , A. Peruzzi 4 , V. Lorenzetti 4 , C. Talamonti 3 , S. Pallotta 3 , M. Mangoni 4 , L. Livi 4 1 University of Florence, Department of Biomedical, Experimental, and Clinical Sciences M. Serio, Florence, Italy; 2 Azienda Ospedaliero-Universitaria Careggi, Radiation Oncology, Florence, Italy; 3 Azienda Ospedaliero-Universitaria Careggi, Medical Physics Unit, Florence, Italy; 4 University of Florence, Department of Experimental and Clinical Biomedical Sciences '' M. Serio'', Florence, Italy