ESTRO 2023 - Abstract Book

S1291

Digital Posters

ESTRO 2023

Conclusion Both schedules were effective in SCC treatment. The higher OS for the RT30 group is related with a selection bias towards the use of this scheme in patients with better prognosis.

PO-1590 Treatment planning of spine and pelvis using SEMAR-corrected CT sets

D. Ignatius 1 , M. Sabet 2 , P. Rowshanfarzad 3 , Z. Alkhatib 2 , S. Goodall 4 , M. Ibrahim 2 , A. Hirst 3 , R. Croxford 3 , J. Dass 5

1 Liverpool Cancer Therapy Centre, Radiation Oncology Medical Physics, Sydney, Australia; 2 Sir Charles Gairdner Hospital, Radiation Oncology Medical Physics, Perth, Australia; 3 The University of Western Australia, School of Physics, Mathematics and Computing, Perth, Australia; 4 GenesisCare Cancer Centre, Radiation Oncology Medical Physics, Perth, Australia; 5 Sir Charles Gairdner Hospital, Radiation Oncology, Perth, Australia Purpose or Objective Computed tomography (CT) based treatment planning in external beam radiation therapy relies on the electron densities determined by CT numbers in Hounsfield Units. Artifacts from metal implants on CT images produce incorrect CT numbers, which impact the accuracy of patient treatment. Traditional method of manual artifact overriding using surrounding soft tissue density introduces subjectivity, increases cost associated with contour delineation, and may result in incorrect dose calculation. This work evaluates the use of single-energy metal artifact reduction (SEMAR) algorithm for treatment planning of patients with metal implants in spinal and pelvic regions by comparison to the traditional method. Materials and Methods Four phantoms (2 spines and 2 hips) were 3D-printed in-house: one of each had metal insert(s) and the other without metal. Three CT datasets were created for each group: without metal (CT_ref), with metal (CT_no_SEMAR), and with metal reconstructed with SEMAR (CT_SEMAR). CT datasets of two treated patients with metal hip implants were also reconstructed with SEMAR. For each phantom/patient, the clinical VMAT plan (created with manual artifact overrides on CT_no_SEMAR) was calculated on CT_SEMAR and DVH curves were compared. Accuracy of CT number restoration was evaluated by comparison to CTref values. Dosimetric measurements were made in phantoms with metal insert(s) on film (spine) and with ion chamber (hip) and compared with reference films and plan, respectively. Results CT number accuracy improved with the use of SEMAR filter: RMSD from CT_ref reduced by 35.4 and 98.8 in spine and hip, respectively. The plan DVHs and dosimetric measurements showed comparable results with the two methods. Conclusion SEMAR accurately predicted CT numbers and produced plans comparable to those on CT sets with manual artifact overrides in patients with hip and spine implants. Using CT_SEMAR makes planning more efficient with similar clinical outcome.

PO-1591 Pentoxifylline and Vitamin E for radiation-induced fibrosis in breast and head and neck patients

M. Harpsoe 1,2 , C.N. Andreassen 1,2 , B.V. Offersen 3,2,4

1 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 3 Aarhus University Hospital, Experimental Clinical Oncology, Aarhus, Denmark; 4 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark Purpose or Objective Patients treated with radiation therapy (RT) for breast (BC) or head and neck cancer (HNC) have an estimated 10% risk of developing fibrosis in the radiated area at 3 years. Symptoms of fibrosis may develop over years and cause pain, cosmetic deformities and decreased mobility. There is no established treatment of radiation-induced fibrosis (RIF) but pentoxyfylline