ESTRO 2024 - Abstract Book

S3296

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

In the field of hadrontherapy, instruments aimed to verify the particle range in vivo with a precision of few millimeters are under study [1]. First clinical applications to proton range verification based on Prompt Gamma Imaging (PGI) technique have been recently demonstrated [2] [3]. On the other hand, the use of PGI verification within Carbon Ion Radiation Therapy (CIRT) is a field still quite unexplored.

In this work we explore the PG fall-off retrieval capability with a pixelated knife-edge slit camera with a beam of C ions at clinical energies.

Material/Methods:

First, to evaluate the feasibility of applying PGI technique to CIRT we conducted through FLUKA numerical simulations (a general purpose Monte Carlo code for particle transport [5]) [4].

Specifically, we scored the response of a pixelated knife-edge slit camera to the secondary particles emitted in the 3 7 MeV energy range by a ICRP soft tissue phantom emulating the patient irradiated with a monoenergetic pencil beam of C-ions of 150MeV/u (generic setup in Figure 1). The energy choice fits within the interval of therapeutic energies used in CIRT [6]. Our results suggest that range verification on a spot-by-spot basis is not feasible to achieve the 4 mm accuracy target, due to the small number of ions delivered in a single spot, in the order of . However, a layer-by-layer approach seems possible, where the average number of primary particles delivered in a spill to cover a given layer of the tumor volume is about 5 × ions. Following the MC simulation campaign, we developed a prototype of the detection system used in the simulations (Figure 2 – Top). The detector is based on a 2”x2” pixelated LYSO scintillator (6 mm crystal pitch) coupled 1:1 with FBK NUVHD SiPMs (15μm cell). The readout is based on four 16-channel GAMMA ASICs [7], which read synchronously the light signal oneach SiPM and provide in output to a FPGA-based DAQ system the energy information of the gamma ray.

On May 2023 we conducted an experimental campaign at CNAO (Pavia, IT) to replicate the measurements simulated with FLUKA.

A tissue-equivalent phantom has been irradiated with a clinical beam of 150MeV/u and moved in 5 positions at a 2 mm distance to verify the capability of the setup to measure the Bragg peak shift.

The particle beam structure used for these measurements is composed by 100 spill of 8x10^7 carbon ions for a total of 8x10^9 carbon ions to have high statistics and compensate for the smaller trasversal dimension of the detector.

Figure 1 – Top: Setup of simulations. Bottom: Dose deposition along with PGs profile.