ESTRO 2024 - Abstract Book

S4743

Physics - Quality assurance and auditing

ESTRO 2024

HUQ, M. Saiful, et al. The report of Task Group 100 of the AAPM: Application of risk analysis methods to radiation therapy quality management. Medical physics, 2016, vol. 43, no 7, p. 4209-4262.

FERRER, Carlos, et al. Dosimetric characterization of a novel commercial plastic scintillation detector with an MR ‐ Linac. Medical Physics, 2023, vol. 50, no 4, p. 2525-2539.

233

Mini-Oral

Multicentre dose accumulation study for reirradiation: radiobiology outweighs DIR algorithm

Isak Wahlstedt 1 , Rasmus L Christiansen 2 , Ulrik V Elstrøm 3 , Kenneth Jensen 3 , Laura P Kaplan 4 , Mikkel D Lund 5 , Martin S Nielsen 6 , Tine B Nyeng 7 , Wiviann Ottoson 8 , Raúl Argota-Pérez 8 , Simon N Thomsen 7 , Rebecca J Tobin 1 , Esben S Worm 7 , Lone Hoffmann 7 1 Copenhagen University Hospital - Rigshospitalet, Copenhagen, Department of Oncology, Copenhagen, Denmark. 2 Odense University Hospital, Department of Oncology, Odense, Denmark. 3 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark. 4 Zealand University Hospital, Department of Oncology, Næstved, Denmark. 5 Vejle Hospital, University Hospital of Southern Denmark, Department of Oncology, Vejle, Denmark. 6 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark. 7 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark. 8 Copenhagen University Hospital - Herlev and Gentofte, Radiotherapy Research Unit, Herlev, Denmark

Purpose/Objective:

3D dose accumulation based on deformable image registration (DIR) can be used to assess the safety of reirradiation in head and cancer. However, there are several uncertainties in the dose accumulation, both due to (i) local clinical radiobiological dose considerations and (ii) DIR algorithm uncertainties. This study investigated the dosimetric impact of both radiobiological dose considerations and DIR algorithm uncertainties among eight Danish centers for one head and neck cancer patient.

Material/Methods:

A male head and neck cancer patient received photon radiotherapy (RT) of 68 Gy in 34 fractions to the primary CTV of a right-sided oropharynx cancer in 2012 (Figure 1A) and was reirradiated against a tumor in the base of tongue in 2020 according to the DAHANCA 37 protocol, i.e. 60 GyRBE to the CTV in 50 proton RT fractions (Figure 1B). The patient was mandibulectomised in 2017, i.e. between the two treatment courses (red square in Figure 1B). All centers in this study performed a DIR with their clinically used DIR algorithm between the planning CT scans. The resulting deformation was then used to transfer the dose from the older to the more recent CT scan. Subsequently, the doses were accumulated. For the dose accumulation, each center used their local clinical radiobiological dose corrections. Furthermore, we performed dose accumulations without radiobiological dose corrections to assess the impact of DIR algorithm differences alone. We evaluated differences in accumulated dose among the centers for all clinically delineated structures on the most recent CT scan.