ESTRO 2022 - Abstract Book

S1352

Abstract book

ESTRO 2022

PO-1570 Instrumented solid-water phantom for quick and high-resolution PDD measurement

P. PITTET 1 , A. Zouaoui 2 , J. Esteves 3 , J. Ribouton 4 , P. Jalade 5 , F. Blanc 6 , G. Haefeli 7 , J. Galvan 8 , G. Lu 9

1 Institut des Nanotechnologies de Lyon, CNRS - Université Lyon 1, Villeurbanne, France; 2 Institut des Nanotechnologies de Lyon, CNRS Unversité Lyon 1, Villeurbanne , France; 3 Institut des Nanotechnologies de Lyon , CNRS université Lyon 1, Villeurbanne, France; 4 Hospices Civils de Lyon - Centre Hospitalier Lyon Sud, Service de Physique medicale - Radioprotection, Peirre Bénite, France; 5 Hospices Civils de Lyon - Centre Hospitalier Lyon Sud, Service de Physique medicale - Radioprotection, Pierre Bénite, France; 6 Ecole Polytechnique Fédérale de Lausanne - EPFL, Laboratoire de Physique des Hautes Energies - LPHE, Lausanne, Switzerland; 7 Ecole Polytechnique Fédérale de Lausanne - EPFL, Laboratoire de Physique des Hautes Energies - EPFL, Lausanne, Switzerland; 8 Institut des Nanotechnologies de Lyon , CNRS - CPE Lyon, Villerbanne, France; 9 Institut des Nanotechnologies de Lyon , CNRS- Université Lyon 1, Vlleurbanne, France Purpose or Objective Percentage Depth Dose curve (PDD) measurement is an important step of the QA process in radiotherapy[1]. It is routinely implemented by using computer-controlled water phantoms, which need a time-consuming set-up. To facilitate this task, we propose an instrumented solid-water phantom to allow a quick and highly resolved PDD measurement or check without using a water tank. Its high depth resolution also makes it possible to measure PDD in heterogeneous cavity conditions. Materials and Methods The proposed PDD phantom is shown in figure 1. It consists of a plastic scintillating fibre ribbon (SciFi) inserted into a RW3 water-equivalent block. The scintillating fibre outputs are coupled to three arrays of 256 silicon photodiodes, with signal readout and processing modules. Each detected signal from fibre ribbon outputs corresponds to integrated dose over the irraidated fiber segment length. The relationship between signal readout and integrated dose has been established by testing. Signal processing allows on-axis PDD retrievment. The RW3 phantom has one air cavity that extends on either side of the fibre ribbon and can be fitted with inserts made of RW3 or other materials equivalent to cortical bone or lung, respectively. The designed and fabricated PDD phantom has been tested at university hospital of Lyon on a 6MV photon beam delivered by a Novalis TRUBEAM STX Linac. The obtained results have been compared with measurements from computer-controlled water phantom (equipped with a PinPoint Ion Chamber). On the other, primo MC simulations have been performed and compared.

Results The designed phantom provides a 250 µ m depth resolution, which is suitable for measurements in built-up areas close to surface or near a heterogeneous cavity. Fig.2 compares simulated and measured PDD curves in homogeneous (with an RW3 insert) and heterogenous (with an air cavity) conditions, respectively.