Optimization of a general-purpose, actively scanned proton beamline for ocular treatments: Geant4 simulations.

Pierluigi Piersimoni,Cristina Riccardi,Silvia Molinelli,Michele Pirola,Adele Rimoldi,Mario Ciocca

doi:10.1120/jacmp.v16i2.5227

Abstract

The Italian National Center for Hadrontherapy (CNAO, Centro Nazionale di Adroterapia Oncologica), a synchrotron‐based hospital facility, started the treatment of patients within selected clinical trials in late 2011 and 2012 with actively scanned proton and carbon ion beams, respectively. The activation of a new clinical protocol for the irradiation of uveal melanoma using the existing general‐purpose proton beamline is foreseen for late 2014. Beam characteristics and patient treatment setup need to be tuned to meet the specific requirements for such a type of treatment technique. The aim of this study is to optimize the CNAO transport beamline by adding passive components and minimizing air gap to achieve the optimal conditions for ocular tumor irradiation. The CNAO setup with the active and passive components along the transport beamline, as well as a human eye‐modeled detector also including a realistic target volume, were simulated using the Monte Carlo Geant4 toolkit. The strong reduction of the air gap between the nozzle and patient skin, as well as the insertion of a range shifter plus a patient‐specific brass collimator at a short distance from the eye, were found to be effective tools to be implemented. In perspective, this simulation toolkit could also be used as a benchmark for future developments and testing purposes on commercial treatment planning systems.PACS numbers: 21.30Fe, 24.10.Lx, 29.20.dk, 29.27.Eg, 29.85.Fj

Highlights

The ocular melanoma is currently the most common early intraocular tumor in adulthood, with a relatively low incidence rate per year
Uveal melanoma is a malignant tumor which tends to grow both inside the bulb, invading and disrupting the intraocular tissues, and outside it, infiltrating the sclera and orbital tissues
Projectile charged particles are accelerated in the Centro Nazionale di Adroterapia Oncologica (CNAO) synchrotron ring, travel in a long extraction vacuum beam pipe, crossing the magnetic field generated by two orthogonal deflecting magnets

Summary

Introduction

The ocular melanoma is currently the most common early intraocular tumor in adulthood, with a relatively low incidence rate per year. With regard to the radiation treatment options for this disease, proton therapy and brachytherapy with plaques are both considered today valid and conservative alternatives to radical eye surgery enucleation, and offer the patient the possibility to maintain a good quality of life These types of treatments allow, in most cases, the retention of residual visual capacity of the eye involved by the neoplasia. Proton radiotherapy for ocular melanoma results in an overall very satisfying local control of 97% at 5 yrs, 96% at 10 yrs, 94% at 15 yrs, and overall tumor specific survival rates of 91% at 5 yrs, 83% at 10 yrs, and 79% at 15 yrs. Differentiated outcome analysis shows that age, tumor size (diameter and thickness), localization, and relation to other structures (optic disc, ciliary body, iris) have the strongest influence on local failure, enucleation rate, and survival.[1,2]

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