Design and commissioning of the non‐dedicated scanning proton beamline for ocular treatment at the synchrotron‐based CNAO facility

Abstract

Purpose: Only few centers worldwide treat intraocular tumors with proton therapy, all of them with a dedicated beamline, except in one case in the USA. The Italian National Center for Oncological Hadrontherapy (CNAO) is a synchrotron-based hadrontherapy facility equipped with fixed beamlines and pencil beam scanning modality. Recently, a general-purpose horizontal proton beamline was adapted to treat also ocular diseases. In this work, the conceptual design and main dosimetric properties of this new proton eyeline are presented. Methods: A 28 mm thick water-equivalent range shifter (RS) was placed along the proton beamline to shift the minimum beam penetration at shallower depths. FLUKA Monte Carlo (MC) simulations were performed to optimize the position of the RS and patient-specific collimator, in order to achieve sharp lateral dose gradients. Lateral dose profiles were then measured with radiochromic EBT3 films to evaluate the dose uniformity and lateral penumbra width at several depths. Different beam scanning patterns were tested. Discrete energy levels with 1 mm water-equivalent step within the whole ocular energy range (62.7-89.8 MeV) were used, while fine adjustment of beam range was achieved using thin polymethylmethacrylate additional sheets.Depth-dose distributions (DDDs) were measured with the Peakfinder system. Monoenergetic beam weights to achieve flat spread-out Bragg Peaks (SOBPs) were numerically determined. Absorbed dose to water under reference conditions was measured with an Advanced Markus chamber, following International Atomic Energy Agency (IAEA) Technical Report Series (TRS)-398 Code of Practice. Neutron dose at the contralateral eye was evaluated with passive bubble dosimeters. Results: Monte Carlo simulations and experimental results confirmed that maximizing the air gap between RS and aperture reduces the lateral dose penumbra width of the collimated beam and increases the field transversal dose homogeneity. Therefore, RS and brass collimator were placed at about 98 cm (upstream of the beam monitors) and 7 cm from the isocenter, respectively. The lateral 80%-20% penumbra at middle-SOBP ranged between 1.4 and 1.7 mm depending on field size, while 90%-10% distal fall-off of the DDDs ranged between 1.0 and 1.5 mm, as a function of range. Such values are comparable to those reported for most existing eye-dedicated facilities. Measured SOBP doses were in very good agreement with MC simulations. Mean neutron dose at the contralateral eye was 68 lSv/Gy. Beam delivery time, for 60 Gy relative biological effectiveness (RBE) prescription dose in four fractions, was around 3 min per session. Conclusions: Our adapted scanning proton beamline satisfied the requirements for intraocular tumor treatment. The first ocular treatment was delivered in August 2016 and more than 100 patients successfully completed their treatment in these 2 yr.

Modelling and measurements of distributions in an adult human phantom undergoing proton scanning beam radiotherapy: lung- and prostate-located tumours

“…Hence, the comparison of the results in the present study was extended to the data measured in water phantoms. The data for the bubble detectors placed inside a water tank irradiated with an energy range between 62.7 and 89.8 meV used for eye treatments (Ciocca et al 2019) suggest that H is about ten times lower than those obtained in the present study for a similar primary proton energy used for the lung treatment. Unexpectedly, for a brain tumor of 65 cm 3 volume located inside a paediatric phantom irradiated with proton PBS of energies in the range 70-140 meV (Knežević et al 2018), the H measured with track-etched detectors showed similar values as the ones simulated in the present study for the lung tumour with a target volume twice as large and much lower primary proton energy.…”

Characterization of a MLIC Detector for QA in Scanned Proton and Carbon Ion Beams

“…The capability of the Giraffe device to measure depth-dose profiles and range values of ocular spread-out Bragg peaks (SOBPs) was tested. Collimated fields already delivered for real patients' ocular treatments were selected: those representing the only clinical case of very small field sizes (around 1.5 cm diameter), suitable for Giraffe tests (for the 2 SOBPs used see Table 1) at our facility [20]. The SOBPs used for ocular treatment are built with discrete energy levels, each corresponding to an isoenergetic slice (IES) with 1 mm water-equivalent step within the energy range (62.7 to 89.8 MeV) and a particular beamline configuration to shift the beam penetration at shallower depths.…”

“…The Giraffe outputs were compared with the expected FLUKA Monte Carlo curves [20], performing the scoring within the same diameter as the sensitive volume of the detector. The Omni-Pro Incline software automatically retrieves the distal R 90 for the measured SOBP.…”

Clinical Implementation of a 6D Treatment Chair for Fixed Ion Beam Lines

“…Treatments with patients in a lying posture are most commonly used in radiation therapy and there have been many reports of that clinical experience including setup accuracy and intra-fraction patient movement (8)(9)(10)(11)(12)(13). On the other hand, there have been only a few studies that reported on the experience of radiation treatments using an upright posture, either with x ray or ion beams (14)(15)(16)(17)(18)(19)(20)(21). To the best of our knowledge, beside a preliminary study of intra-faction movement in seated posture by films in 1980s (22), neither the clinical workflow nor the intra-fraction patient movement of the treatment with patients in an upright posture on a chair has been reported after the advent of image guidance.…”