Proton Beam Line Research Articles

Synthesis and luminescent properties of Gd3Ga2Al3O12 phosphors doped with Eu3+ or Ce3+

Eu3+-or Ce3+-doped gadolinium gallium aluminum garnet (GGAG), Gd3Ga2Al3O12, phosphors are fabricated using solid-state reactions with Gd2O3, Ga2O3, Al2O3, CeO2 and Eu2O3 powders. The Eu3+-or Ce3+-doped Gd3Ga2Al3O12 phosphors are sintered at 1300 °C or 1600 °C for 5 hours by using an electric furnace under normal atmosphere. X-ray diffraction and field-emission scanning electron microscopy studies are carried out in order to analyze the physical properties of these materials, and their luminescence properties are also measured by using UV and X-ray sources. The Eu3+-or Ce3+-doped Gd3Ga2Al3O12 phosphors show higher light yields in comparison to commercial phosphors such as Gd2O2S:Tb (gadox). This indicates that Gd3Ga2Al3O12:Eu3+ phosphors are promising materials for use in X-ray imaging and dose monitoring at proton beamlines.

Proton pencil beam scanning for mediastinal lymphoma: treatment planning and robustness assessment

ABSTRACTBackground: Modern radiotherapy (RT) for lymphoma is highly personalized. While advanced imaging is largely employed to define limited treatment volumes, the use of proton pencil beam scanning (PBS) for highly conformal lymphoma RT is still in its infancy. Here, we assess the dosimetric benefits and feasibility of PBS for mediastinal lymphoma (ML).Materials and methods: Ten patients were planned using PBS for involved-site RT. The initial plans were calculated on the average four-dimensional computed tomography (4D-CT). PBS plans were compared with 3D conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and proton double scattering (DS). In order to evaluate the feasibility of PBS and the plan robustness against inter- and intra-fractional uncertainties, the 4D dose was calculated on initial and verification CTs. The deviation of planned dose from delivered dose was measured. The same proton beamline was used for all patients, while another beamline with larger spots was employed for patients with large motion perpendicular to the beam.Results: PBS provided the lowest mean lung dose (MLD) and mean heart dose (MHD) for all patients in comparison with 3D-CRT, IMRT, and DS. For eight patients, internal target volume (ITV) D98% was degraded by <3%; and the MLD and MHD deviated by <10% of prescription over the course of treatment when the PBS field was painted twice in each session. For one patient with target motion perpendicular to the beam (>5 mm), the degradation of ITV D98% was 9%, which was effectively mitigated by employing large spots. One patient exhibited large dose degradation due to pericardial effusion, which required replanning across all modalities.Conclusions: This study demonstrates that PBS plans significantly reduce MLD and MHD relative to 3D-CRT, IMRT, and DS and identifies requirements for robust free-breathing ML PBS treatments, showing that PBS plan robustness can be maintained with repainting and/or large spots.

SU‐F‐T‐163: Improve Proton Therapy Efficiency: Report of a Workshop

Purpose:The technology of proton therapy, especially the pencil beam scanning technique, is evolving very quickly. However, the efficiency of proton therapy seems to lag behind conventional photon therapy. The purpose of the abstract is to report on the findings of a workshop on improvement of QA, planning and treatment efficiency in proton therapy.Methods:A panel of physicists, clinicians, and vendor representatives from over 18 institutions in the United States and internationally were convened in Knoxville, Tennessee in November, 2015. The panel discussed several topics on how to improve proton therapy efficiency, including 1) lean principle and failure mode and effects analysis, 2) commissioning and machine QA, 3) treatment planning, optimization and evaluation, 4) patient positioning and IGRT, 5) vendor liaison and machine availability, and 6) staffing, education and training.Results:The relative time needed for machine QA, treatment planning &amp; check in proton therapy was found to range from 1 to 2.5 times of that in photon therapy. Current status in proton QA, planning and treatment was assessed. Key areas for efficiency improvement, such as elimination of unnecessary QA items or steps and development of efficient software or hardware tools, were identified. A white paper to summarize our findings is being written.Conclusion:It is critical to improve efficiency by developing reliable proton beam lines, efficient software tools on treatment planning, optimization and evaluation, and dedicated proton QA device. Conscious efforts and collaborations from both industry leaders and proton therapy centers are needed to achieve this goal and further advance the technology of proton therapy.

Benchmarking Monte Carlo simulations against experimental data in clinically relevant passive scattering proton therapy beamline configurations

Monte Carlo simulations are widely used to calculate secondary neutron doses in proton therapy. When using the passive scattering technique, a small variation in the tumor size or location requires a full adjustment of the beamline configuration. This work thus focuses on modeling all possible beamline elements of the local facility with the MCNPX code while covering the entire clinical range of proton beam energies. This paper documents the experimental validation of realistic beamline configurations dedicated to intracranial tumor treatments, with different sources and beamline elements. Simulations were compared against measurements and treatment planning system (TPS) data considering percentage depth dose distributions (PDD) and relative lateral dose profiles. The results show that simulated and measured PDD distributions differ by no more than 1.6 mm on the proton beam range (tolerance set at 2 mm/2%) for the 162 MeV configuration. Meanwhile, for the modulated lateral dose profiles, the 219 MeV configuration presented the largest difference for the in-plane field width at 90% with 2 mm difference in measurements. The modeled proton sources and beamline elements were validated, and the new realistic geometries can be used to calculate secondary neutron doses to healthy tissues.

SPES and the neutron facilities at Laboratori Nazionali di Legnaro

The SPES Radioactive Ion Beam (RIB) facility, now in the construction phase at INFN-LNL, has the aim to provide high-intensity and high-quality beams of neutron-rich nuclei for nuclear physics research as well as to develop an interdisciplinary research center based on the cyclotron proton beam. The SPES system is based on a dual-exit high-current cyclotron, with tunable proton beam energy 35-70MeV and 0.20-0.75mA. The first exit is used as proton driver to supply an ISOL system with an UCx Direct Target able to sustain a power of 10kW. The expected fission rate in the target is of the order of \( 10^{13}\) fissions per second. The exotic isotopes will be re-accelerated by the ALPI superconducting LINAC at energies of 10 A MeV and higher, for masses around \( A=130\) amu, with an expected beam intensity of \( 10^7\) - \( 10^9\) pps. The second exit will be used for applied physics: radioisotope production for medicine and neutrons for material studies. Fast neutron spectra will be produced by the proton beam interaction with a conversion target. A production rate in excess of \( 10^{14}\) n/s can be achieved: this opens up the prospect of a high-flux neutron irradiation facility (NEPIR) to produce both discrete and continuous energy neutrons. A direct proton beam line is also envisaged. NEPIR and the direct proton line would dramatically increase the wide range of irradiation facilities presently available at LNL. We also present LENOS, a proposed project dedicated to accurate neutron cross-sections measurements using intense, well-characterized, broad energy neutron beams. Other activities already in operation at LNL are briefly reviewed: the SIRAD facility for proton and heavy-ion irradiation at the TANDEM-ALPI accelerator and the BELINA test facility at CN van de Graaff accelerator.

An empirical model for calculation of the collimator contamination dose in therapeutic proton beams

Collimators are used as lateral beam shaping devices in proton therapy with passive scattering beam lines. The dose contamination due to collimator scattering can be as high as 10% of the maximum dose and influences calculation of the output factor or monitor units (MU). To date, commercial treatment planning systems generally use a zero-thickness collimator approximation ignoring edge scattering in the aperture collimator and few analytical models have been proposed to take scattering effects into account, mainly limited to the inner collimator face component. The aim of this study was to characterize and model aperture contamination by means of a fast and accurate analytical model. The entrance face collimator scatter distribution was modeled as a 3D secondary dose source. Predicted dose contaminations were compared to measurements and Monte Carlo simulations. Measurements were performed on two different proton beam lines (a fixed horizontal beam line and a gantry beam line) with divergent apertures and for several field sizes and energies. Discrepancies between analytical algorithm dose prediction and measurements were decreased from 10% to 2% using the proposed model. Gamma-index (2%/1 mm) was respected for more than 90% of pixels. The proposed analytical algorithm increases the accuracy of analytical dose calculations with reasonable computation times.

Design, Construction, Installation, Mapping and Shimming for a 416 ton Compact Cyclotron Magnet

The construction of a 100-MeV high-intensity cyclotron, from which proton beam will be extracted through stripping to several proton beam lines for different users, has been completed at China Institute of Atomic Energy. Given that it is the H-ions that are to be accelerated in the machine, the peak field is only 1.35 T. To simplify the fabrication, the pole adopts straight sector instead of the spiral one. Meanwhile, vertical focusing should be sufficiently high to obtain high-current proton beam. All these demands make it particularly difficult for the design and fabrication of the main magnet, which is heavy in weight and challenging to meet precision requirement in fabrication. In the process, we have developed a high-performance parallel computation PIC code for beam dynamics of high-current cyclotrons and for FFAGs, which can be used for beam dynamic simulation at a very precise level. The result is then applied to guide the design, fabrication, installation, magnetic mapping, and shimming of the 416-ton main magnet with a precision requirement up to 0.05 mm. Another challenge is due to the deformations of the magnet without/with the vacuum. The whole map measured in the vacuum has to be completed in such a big machine for the first time in the world. The result shows that all requirements, including the isochronous field, vertical focusing, and imperfection fields, have been satisfied properly. The first beam and the stable beam for an 8-h commissioning test had been achieved on July 4 and July 25, 2014, respectively.

Measured Neutron Spectra and Dose Equivalents From a Mevion Single-Room, Passively Scattered Proton System Used for Craniospinal Irradiation

To measure, in the setting of typical passively scattered proton craniospinal irradiation (CSI) treatment, the secondary neutron spectra, and use these spectra to calculate dose equivalents for both internal and external neutrons delivered via a Mevion single-room compact proton system. Secondary neutron spectra were measured using extended-range Bonner spheres for whole brain, upper spine, and lower spine proton fields. The detector used can discriminate neutrons over the entire range of the energy spectrum encountered in proton therapy. To separately assess internally and externally generated neutrons, each of the fields was delivered with and without a phantom. Average neutron energy, total neutron fluence, and ambient dose equivalent [H* (10)] were calculated for each spectrum. Neutron dose equivalents as a function of depth were estimated by applying published neutron depth-dose data to in-air H* (10) values. For CSI fields, neutron spectra were similar, with a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate continuum between the evaporation and thermal peaks. Neutrons in the evaporation peak made the largest contribution to dose equivalent. Internal neutrons had a very low to negligible contribution to dose equivalent compared with external neutrons, largely attributed to the measurement location being far outside the primary proton beam. Average energies ranged from 8.6 to 14.5 MeV, whereas fluences ranged from 6.91 × 10(6) to 1.04 × 10(7) n/cm(2)/Gy, and H* (10) ranged from 2.27 to 3.92 mSv/Gy. For CSI treatments delivered with a Mevion single-gantry proton therapy system, we found measured neutron dose was consistent with dose equivalents reported for CSI with other proton beamlines.

Design and simulation of the nuSTORM pion beamline

The nuSTORM (neutrinos from STORed Muons) proposal presents a detailed design for a neutrino facility based on a muon storage ring, with muon decay in the production straight section of the ring providing well defined neutrino beams. The facility includes a primary high-energy proton beam line, a target station with pion production and collection, and a pion beamline for pion transportation and injection into a muon decay ring. The nuSTORM design uses “stochastic injection”, in which pions are directed by a chicane, referred to as the Orbit Combination Section (OCS), into the production straight section of the storage ring. Pions that decay within that straight section provide muons within the circulating acceptance of the ring. The design enables injection without kickers or a separate pion decay transport line. The beam line that the pions traverse before being extracted from the decay ring is referred to as the pion beamline. This paper describes the design and simulation of the pion beamline, and includes full beam dynamics simulations of the system.

WE‐EF‐BRA‐06: Feasibility of Spatially Modulated Proton Beams for Small Animal Research

Purpose:To investigate the feasibility of proton minibeam radiotherapy (pMBRT) for small animal research. The motivation is to explore with protons the extraordinary normal tissue sparing effects to spatially modulated beams as observed on high flux synchrotron beam lines. We hypothesized that we can design a multi‐slit collimator for our proton beam line to produce planar‐parallel dose profiles with high modulation in the entrance region and homogenous dose coverage in the overlap of the Bragg peaks.Methods:The high dose rate 50 MeV research proton beamline at the University of Washington was modeled using the TOol for PArticle Simulation (TOPAS) Monte Carlo package. A brass collimator was implemented to generate proton minibeams. The collimator consists of an array of 2 cm long slits to cover an area of 2×2 cm2. The slit widths (0.1–1 mm), center‐to‐center (ctc) distances (1–3 mm) and collimator thickness (1–7 cm) were varied to evaluate the effect on dose rate, the peak‐to‐valley dose ratios (PVDR) and the change of penumbra and peak width (FWHM) with depth.Results:The Bragg peak was at a depth of ∼21 mm. The penumbra and FWHM remained relatively constant to a depth of about 10–15 mm. The PVDR ranged from 1.6 to 26 and the dose rate dropped exponentially with collimator thickness. A uniform dose can be achieved at depth with slightly compromised PVDRs and dose rate.Conclusion:The technical realization of pMBRT is feasible. The simulations have shown that it is possible to obtain uniform dose at depth while modulation is maintained on the entrance side. While the simulated beam widths are larger than on synchrotron generated microbeams the dosimetric advantage could avoid having to interlace two microbeams to achieve uniform dose in the target. The next steps are to build a collimator and verify the simulations experimentally.

A graphical approach to radio frequency quadrupole design

The design of a radio frequency quadrupole, an important section of all ion accelerators, and the calculation of its beam dynamics properties can be achieved using the existing computational tools. These programs, originally designed in 1980s, show effects of aging in their user interfaces and in their output. The authors believe there is room for improvement in both design techniques using a graphical approach and in the amount of analytical calculations before going into CPU burning finite element analysis techniques. Additionally an emphasis on the graphical method of controlling the evolution of the relevant parameters using the drag-to-change paradigm is bound to be beneficial to the designer. A computer code, named DEMIRCI, has been written in C++ to demonstrate these ideas. This tool has been used in the design of Turkish Atomic Energy Authority (TAEK)’s 1.5 MeV proton beamline at Saraykoy Nuclear Research and Training Center (SANAEM). DEMIRCI starts with a simple analytical model, calculates the RFQ behavior and produces 3D design files that can be fed to a milling machine. The paper discusses the experience gained during design process of SANAEM Project Prometheus (SPP) RFQ and underlines some of DEMIRCI’s capabilities.

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

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

Design study of the ESS-Bilbao 50 MeV proton beam line for radiobiological studies

The ESS-Bilbao proton accelerator facility has been designed fulfilling the European Spallation Source (ESS) specifications to serve as the Spanish contribution to the ESS construction. Furthermore, several applications of the ESS-Bilbao proton beam are being considered in order to contribute to the knowledge in the field of radiobiology, materials and aerospace components. Understanding of the interaction of radiation with biological systems is of vital importance as it affects important applications such as cancer treatment with ion beam therapy among others. ESS-Bilbao plans to house a facility exclusively dedicated to radiobiological experiments with protons up to 50MeV. Beam line design, optimisation and initial calculations of flux densities and absorbed doses were undertaken using the Monte Carlo simulation package FLUKA. A proton beam with a flux density of about 106protons/cm2s reaches the water sample with a flat lateral distribution of the dose. The absorbed dose at the pristine Bragg peak calculated with FLUKA is 2.4±0.1Gy in 1min of irradiation time. This value agrees with the clinically meaningful dose rates, i.e. around 2Gy/min, used in hadrontherapy. Optimisation and validation studies in the ESS-Bilbao line for radiobiological experiments are detailed in this article.

Dosimetric characterization of a synthetic single crystal diamond detector in a clinical 62 MeV ocular therapy proton beam

A synthetic single crystal diamond based Schottky photodiode was tested at INFN-LNS on the proton beam line (62MeV) dedicated to the radiation treatment of ocular disease. The diamond detector response was studied in terms of pre-irradiation dose, linearity with dose and dose rate, and angular dependence. Depth dose curves were measured for the 62MeV pristine proton beam and for three unmodulated range-shifted proton beams; furthermore, the spread-out Bragg peak was measured for a modulated therapeutic proton beam. Beam parameters, recommended by the ICRU report 78, were evaluated to analyze depth-dose curves from diamond detector. Measured dose distributions were compared with the corresponding dose distributions acquired with reference plane-parallel ionization chambers. Field size dependence of the output factor (dose per monitor unit) in a therapeutic modulated proton beam was measured with the diamond detector over the range of ocular proton therapy collimator diameters (5–30mm). Output factors measured with the diamond detector were compared to the ones by a Markus ionization chamber, a Scanditronix Hi-p Si stereotactic diode and a radiochromic EBT2 film. Signal stability within 0.5% was demonstrated for the diamond detector with no need of any pre-irradiation dose. Dose and dose rate dependence of the diamond response was measured: deviations from linearity resulted to be within ±0.5% over the investigated ranges of 0.5–40.0Gy and 0.3–30.0Gy/min respectively. Output factors from diamond detector measured with the smallest collimator (5mm in diameter) showed a maximum deviation of about 3% with respect to the high resolution radiochromic EBT2 film. Depth-dose curves measured by diamond for unmodulated and modulated beams were in good agreement with those from the reference plane-parallel Markus chamber, with relative differences lower than ±1% in peak-to-plateau ratios, well within experimental uncertainties. A 2.5% variation in diamond detector response was observed in angular dependence measurements carried-out by varying the proton beam incidence angle in the polar direction. The dosimetric characterization of the tested synthetic single crystal diamond detector clearly indicates its suitability for relative dosimetry in ocular therapy proton beams, with no need of any correction factors accounting for dose rate and linear energy transfer dependence.

TH‐A‐19A‐01: An Open Source Software for Proton Treatment Planning in Heterogeneous Medium

Purpose:Due to its success in Radiation Oncology during the last decade, interest in proton therapy is on the rise. Unfortunately, despite the global enthusiasm in the field, there is presently no free, multiplatform and customizable Treatment Planning System (TPS) providing proton dose distributions in heterogenous medium. This restricts substantially the progress of clinical research for groups without access to a commercial Proton TPS. The latest implementation of our pencil beam dose calculation algorithm for proton beams within the 3D Slicer open‐source environment fulfills all the conditions described above.Methods:The core dose calculation algorithm is based on the Hong algorithm (1), which was upgraded with the Kanematsu theory describing the evolution of the lateral scattering of proton beamlets in heterogeneous medium. This algorithm deals with both mono‐energetic beams and Spread Out Bragg Peak (SOBP). In order to be user‐friendly, we provide a graphical user interface implemented with the Qt libraries, and visualization with the 3D Slicer medical image analysis software. Two different pencil beam algorithms were developed, and the clinical proton beam line at our facility was modeled.Results:The dose distributions provided by our algorithms were compared to dose distributions coming from both commercialized XiO TPS and literature (dose measurements, GEANT4 and MCNPx) and turned out to be in a good agreement, with maximum dose discrepancies of 5% in homogeneous phantoms and 10% in heterogeneous phantoms. The algorithm of SOBP creation from an optimized weigthing of mono‐energetic beams results in flat SOBP.Conclusion:We hope that our efforts in implementing this new, open‐source proton TPS will help the research groups to have a free access to a useful, reliable proton dose calculation software.(1) L. Hong et al., A pencil beam algorithm for proton dose calculations, Phys. Med. Biol. 41 (1996) 1305–1330.This project is paid for by NCI/MGH Federal share as a research grant.

A Monte Carlo study for the calculation of the average linear energy transfer (LET) distributions for a clinical proton beam line and a radiobiological carbon ion beam line

Fluence, depth absorbed dose and linear energy transfer (LET) distributions of proton and carbon ion beams have been investigated using the Monte Carlo code Geant4 (GEometry ANd Tracking). An open source application was developed with the aim to simulate two typical transport beam lines, one used for ocular therapy and cell irradiations with protons and the other for cell irradiations with carbon ions. This tool allows evaluation of the primary and total dose averaged LET and predict their spatial distribution in voxelized or sliced geometries. In order to reproduce the LET distributions in a realistic way, and also the secondary particles’ contributions due to nuclear interactions were considered in the computations. Pristine and spread-out Bragg peaks were taken into account both for proton and carbon ion beams, with the maximum energy of 62 MeV/n. Depth dose distributions were compared with experimental data, showing good agreement. Primary and total LET distributions were analysed in order to study the influence of contributions of secondary particles in regions at different depths. A non-negligible influence of high-LET components was found in the entrance channel for proton beams, determining the total dose averaged LET by the factor 3 higher than the primary one. A completely different situation was obtained for carbon ions. In this case, secondary particles mainly contributed in the tail that is after the peak. The results showed how the weight of light and heavy secondary ions can considerably influence the computation of LET depth distributions. This has an important role in the interpretation of results coming from radiobiological experiments and, therefore, in hadron treatment planning procedures.

Commissioning of a compact laser-based proton beam line for high intensity bunches around 10 MeV

We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than ${10}^{9}$ particles in less than 10 ns and with tunable energy spread down to 2.7% ($\mathrm{\ensuremath{\Delta}}\mathrm{E}/{\mathrm{E}}_{0}$ at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of $\ensuremath{-}90\text{ }\text{ }\mathrm{deg}$. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

The QMN Beam Line of the Neutron-induced Single Event Effects Facility at the 70 MeV Cyclotron of LNL-INFN

The SPES project, based on a variable energy high current proton cyclotron (35-70 MeV; 750μA), soon to be operational at LNL, foresees a neutron irradiation facility for Single Event Effects (SEE) studies on microelectronic components and systems. The proposed facility will comprise both a beam line with continuous energy atmospheric-like neutron production targets, and a Quasi Mono-energetic Neutron (QMN) beam line. A direct proton beam line is also foreseen. Here we describe the general features of the proposed QMN beam line. The quasi mono-energetic neutrons will be produced in various thin Be and Li targets and the spent proton beam will be magnetically deflected towards a beam dump. The layout of the facility with a multi-angle collimator scheme for tail corrections is presented and the proton currents necessary to deliver high neutron fluxes using thin Be targets are estimated.

A Neutron-induced Single Event Effects Facility at the 70 MeV Cyclotron of LNL-INFN

We describe a proposed neutron irradiation facility for studyi ng neutron-i nduced Single Event Effects (SEE) in microelectronic components and systems at the new variable energy high current proton cyclotron (35-70 MeV; 750μA) soon to be operational at LNL. We descri be the progress in designing two neutron production targets to furnish continuous atmospheric-like neutron differential spectra: a W-based thick target (to stop 70 MeV protons), and an innovative composite target made of Beryllium and Tantal um or Lead. We also describe the layout of the facility that will also house quasi-monoenergetic neutron (QMN) and direct proton beam lines. The thick target beam line could be available as soon as the new cyclotron is commissioned. The composite target and QMN beam lines, to be designed in concert, would be completed soon after.

Dosimetric properties of a proton beamline dedicated to the treatment of ocular disease

A commercial proton eyeline has been developed to treat ocular disease. Radiotherapy of intraocular lesions (e.g., uveal melanoma, age-related macular degeneration) requires sharp dose gradients to avoid critical structures like the macula and optic disc. A high dose rate is needed to limit patient gazing times during delivery of large fractional dose. Dose delivery needs to be accurate and predictable, not in the least because current treatment planning algorithms have limited dose modeling capabilities. The purpose of this paper is to determine the dosimetric properties of a new proton eyeline. These properties are compared to those of existing systems and evaluated in the context of the specific clinical requirements of ocular treatments. The eyeline is part of a high-energy, cyclotron-based proton therapy system. The energy at the entrance of the eyeline is 105 MeV. A range modulator (RM) wheel generates the spread-out Bragg peak, while a variable range shifter system adjusts the range and spreads the beam laterally. The range can be adjusted from 0.5 up to 3.4 g/cm(2); the modulation width can be varied in steps of 0.3 g/cm(2) or less. Maximum field diameter is 2.5 cm. All fields can be delivered with a dose rate of 30 Gy/min or more. The eyeline is calibrated according to the IAEA TRS-398 protocol using a cylindrical ionization chamber. Depth dose distributions and dose/MU are measured with a parallel-plate ionization chamber; lateral profiles with radiochromic film. The dose/MU is modeled as a function of range, modulation width, and instantaneous MU rate with fit parameters determined per option (RM wheel). The distal fall-off of the spread-out Bragg peak is 0.3 g/cm(2), larger than for most existing systems. The lateral penumbra varies between 0.9 and 1.4 mm, except for fully modulated fields that have a larger penumbra at skin. The source-to-axis distance is found to be 169 cm. The dose/MU shows a strong dependence on range (up to 4%/mm). A linear increase in dose/MU as a function of instantaneous MU rate is observed. The dose/MU model describes the measurements with an accuracy of ± 2%. Neutron dose is found to be 146 ± 102 μSv/Gy at the contralateral eye and 19 ± 13 μSv/Gy at the chest. Measurements show the proton eyeline meets the requirements to effectively treat ocular disease.