Measurement of prompt gamma profiles in inhomogeneous targets with a knife-edge slit camera during proton irradiation

Abstract

Proton and ion beam therapies become increasingly relevant in radiation therapy. To fully exploit the potential of this irradiation technique and to achieve maximum target volume conformality, the verification of particle ranges is highly desirable. Many research activities focus on the measurement of the spatial distributions of prompt gamma rays emitted during irradiation. A passively collimating knife-edge slit camera is a promising option to perform such measurements. In former publications, the feasibility of accurate detection of proton range shifts in homogeneous targets could be shown with such a camera. We present slit camera measurements of prompt gamma depth profiles in inhomogeneous targets. From real treatment plans and their underlying CTs, representative beam paths are selected and assembled as one-dimensional inhomogeneous targets built from tissue equivalent materials. These phantoms have been irradiated with monoenergetic proton pencil beams. The accuracy of range deviation estimation as well as the detectability of range shifts is investigated in different scenarios. In most cases, range deviations can be detected within less than 2 mm. In close vicinity to low-density regions, range detection is challenging. In particular, a minimum beam penetration depth of 7 mm beyond a cavity is required for reliable detection of a cavity filling with the present setup. Dedicated data post-processing methods may be capable of overcoming this limitation.

Benchmarking Geant4 hadronic models for prompt‐γ monitoring in carbon ion therapy

“…These values illustrated the good agreement between the shape of the distributions, showing that the discrepancies between the Monte Carlo and data were more pronounced for the BIC physics list. According to this table, INCL ++ gave the best agreement with the data (especially at 60°with a P-value of 0.97), which can also be seen from the spectra where the 4.43 MeV peak from 12 C was well reproduced.…”

“…Experimental approaches considered so far are based on tracking secondary protons, [2][3][4][5] detecting prompt-c emission, 6,7 or performing online PET gamma reconstruction. [8][9][10] Several modalities for prompt-c imaging have been investigated: collimated cameras, [11][12][13][14][15] compton cameras [16][17][18][19][20][21][22][23] and prompt-c timing. 24 One important parameter is the production yield of secondary particles used in these methods during treatment, as this will affect the accuracy of the reconstructed dose distribution.…”

“…In this paper, which focuses only on the prompt-c modality, two main aims are pursued. First, this work aims to present an experimental measurement of prompt-c yields produced by 12 C interactions in a polymethyl methacrylate (PMMA) target along with their associated energy spectra in order to complete existing data. Indeed, several prompt-c spectra are already available at 12 C ion energies of 80, 95, and 310 MeV/ u.…”

“…First, this work aims to present an experimental measurement of prompt-c yields produced by 12 C interactions in a polymethyl methacrylate (PMMA) target along with their associated energy spectra in order to complete existing data. Indeed, several prompt-c spectra are already available at 12 C ion energies of 80, 95, and 310 MeV/ u. 25,26 As typical clinical energies for 12 C ions for hadrontherapy range between 80 and 480 MeV/u, this experiment was performed with a mean energy of 220 MeV/u.…”

“…Indeed, several prompt-c spectra are already available at 12 C ion energies of 80, 95, and 310 MeV/ u. 25,26 As typical clinical energies for 12 C ions for hadrontherapy range between 80 and 480 MeV/u, this experiment was performed with a mean energy of 220 MeV/u.…”