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A New Method to Reconstruct in 3D the Emission Position of the Prompt Gamma Rays following Proton Beam Irradiation.

ABSTRACT: A new technique for range verification in proton beam therapy has been developed. It is based on the detection of the prompt ? rays that are emitted naturally during the delivery of the treatment. A spectrometer comprising 16 LaBr₃(Ce) detectors in a symmetrical configuration is employed to record the prompt ? rays emitted along the proton path. An algorithm has been developed that takes as inputs the LaBr₃(Ce) detector signals and reconstructs the maximum ?-ray intensity peak position, in full 3 dimensions. For a spectrometer radius of 8?cm, which could accommodate a paediatric head and neck case, the prompt ?-ray origin can be determined from the width of the detected peak with a ? of 4.17?mm for a 180?MeV proton beam impinging a water phantom. For spectrometer radii of 15 and 25?cm to accommodate larger volumes this value increases to 5.65 and 6.36?mm. For a 8?cm radius, with a 5 and 10?mm undershoot, the ? is 4.31 and 5.47?mm. These uncertainties are comparable to the range uncertainties incorporated in treatment planning. This work represents the first step towards a new accurate, real-time, 3D range verification device for spot-scanning proton beam therapy.

SUBMITTER: Panaino CMV

PROVIDER: S-EPMC6906450 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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A New Method to Reconstruct in 3D the Emission Position of the Prompt Gamma Rays following Proton Beam Irradiation.

Panaino Costanza M V CMV Mackay Ranald I RI Kirkby Karen J KJ Taylor Michael J MJ

Scientific reports 20191211 1

A new technique for range verification in proton beam therapy has been developed. It is based on the detection of the prompt γ rays that are emitted naturally during the delivery of the treatment. A spectrometer comprising 16 LaBr<sub>3</sub>(Ce) detectors in a symmetrical configuration is employed to record the prompt γ rays emitted along the proton path. An algorithm has been developed that takes as inputs the LaBr<sub>3</sub>(Ce) detector signals and reconstructs the maximum γ-ray intensity p ...[more]

PMID: 31827167

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Project description:ImportanceAlthough radiotherapy has been used more frequently in past decades for the management of large melanomas, long-term efficacy of proton beam irradiation (PBI) of large choroidal melanomas has not been reported.ObjectiveTo evaluate long-term outcomes in patients who underwent PBI for the treatment of large choroidal melanomas.Design, setting, and participantsData were obtained at a single Boston, Massachusetts, academic tertiary referral practice for this retrospective cohort study. In total, 336 patients with large tumors treated over a 13-year period from January 1, 1985, to December 31, 1997, and followed up until the end points were reached or until December 31, 2008, were included. Data analyses were initially completed in February 2017 and finalized in July 2017. Large tumors were those with a height 10 mm or greater or a longest linear diameter greater than 16 mm or a height greater than 8 mm when the optic nerve was involved.InterventionProton beam irradiation (total 70 Gy) delivered in 5 equal fractions.Main outcomes and measuresThe primary outcomes of rates of visual acuity retention, eye retention, tumor recurrence, and melanoma-related mortality were calculated using Kaplan-Meier estimates, and Cox proportional hazards regression analyses were completed to evaluate risk factors for tumor recurrence and melanoma-related mortality.ResultsIn this cohort of 336 patients with large tumors, 150 were women and 329 were white; mean (SD) age was 60.0 (14.0) years. Of 178 patients without optic nerve involvement (tumor >1 disc diameter from optic nerve), the mean (SD) largest basal diameter was 18.1 (1.9) mm and mean height was 8.2 (2.7) mm. Optic nerve involvement and tumors greater than 8 mm were observed in 109 patients (32.4% of the cohort). Baseline visual acuity of 20/200 or better was observed in 244 patients (72.6%), and worse than 20/800 in 52 (15.5%). Ten-year rates of visual acuity retention were 8.7% (95% CI, 4.1%-15.6%) for at least 20/200 and 22.4% (95% CI, 15.4%-30.4%) for at least counting fingers. Ten years after PBI therapy, the eye was retained (70.4%; 95% CI, 61.5%-77.6%) and tumor controlled (87.5%; 95% CI, 76.8%-93.5%) in most patients. The 10-year all-cause mortality rate was 60.7% (95% CI, 55.5%-65.9%). Approximately half of the patients died of metastatic uveal melanoma (10-year rate, 48.5%; 95% CI, 43.0%-54.4%).Conclusions and relevanceThis study demonstrates that eye conservation is possible in most cases, with ambulatory vision retained in a small proportion of patients 10 years after PBI. Tumor recurrence rates were low and mortality rates were comparable to those observed after enucleation.

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A New Method to Reconstruct in 3D the Emission Position of the Prompt Gamma Rays following Proton Beam Irradiation.

Publications

A New Method to Reconstruct in 3D the Emission Position of the Prompt Gamma Rays following Proton Beam Irradiation.

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