Dosimetric accuracy of a treatment planning system for actively scanned proton beams and small target volumes: Monte Carlo and experimental validation

Magro, Giuseppe; Molinelli, S.; Mairani, A.; Mirandola, A.; Panizza, D.; Russo, Stefania; Ferrari, A.; Valvo, Francesca; Fossati, Piero; Ciocca, Mario

doi:10.1088/0031-9155/60/17/6865

Cited by 20 publications

(24 citation statements)

References 17 publications

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“…These results show that beyond the accurate transport of particles in the target, the initial conditions of the beam are also fundamental. This observation is consistent with the results of Magro et al ( 11 ) between the same TPS and MC simulations for small targets at shallow depths. Beamline approximations used for MC simulations are giving, in general, good results, as shown in Bauer et al ( 8 ) for the MC framework, where the differences between simulations and measurements are in average below 3%, or in Grassberger et al ( 12 ) where their model compared to a full beamline propagation show differences inferior to 1% in the middle of a SOBP.…”

Section: Discussionsupporting

confidence: 93%

“…A challenging clinical entity has been selected for testing the PS application: an arterio-venous malformation (AVM) that is a small target inferior to 20 ml in most of the cases and below 3 ml in our study, treated at HIT with protons in one fraction of 18 Gy RBE at the isodose 80%. Magro et al ( 11 ) found for small targets at shallow depth discrepancies between TPS and measurements in water up to ~19%.…”

Section: Methodsmentioning

confidence: 99%

“…The use of modeled beamlines in MC applications has been described in many works for beam delivery with active energy selection ( 5 , 9 – 11 ), for passive energy selection with pencil-beam scanning ( 12 , 13 ), or for passive scattering ( 14 , 15 ). In our case, due to confidential issues with the beamline geometry, the model is not available for external users in need of precise simulation, neither for data analysis comparisons after irradiation at HIT nor for simulation-related researches.…”

Section: Introductionmentioning

confidence: 99%

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Phase Space Generation for Proton and Carbon Ion Beams for External Users’ Applications at the Heidelberg Ion Therapy Center

et al. 2016

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In the field of radiation therapy, accurate and robust dose calculation is required. For this purpose, precise modeling of the irradiation system and reliable computational platforms are needed. At the Heidelberg Ion Therapy Center (HIT), the beamline has been already modeled in the FLUKA Monte Carlo (MC) code. However, this model was kept confidential for disclosure reasons and was not available for any external team. The main goal of this study was to create efficiently phase space (PS) files for proton and carbon ion beams, for all energies and foci available at HIT. PSs are representing the characteristics of each particle recorded (charge, mass, energy, coordinates, direction cosines, generation) at a certain position along the beam path. In order to achieve this goal, keeping a reasonable data size but maintaining the requested accuracy for the calculation, we developed a new approach of beam PS generation with the MC code FLUKA. The generated PSs were obtained using an infinitely narrow beam and recording the desired quantities after the last element of the beamline, with a discrimination of primaries or secondaries. In this way, a unique PS can be used for each energy to accommodate the different foci by combining the narrow-beam scenario with a random sampling of its theoretical Gaussian beam in vacuum. PS can also reproduce the different patterns from the delivery system, when properly combined with the beam scanning information. MC simulations using PS have been compared to simulations, including the full beamline geometry and have been found in very good agreement for several cases (depth dose distributions, lateral dose profiles), with relative dose differences below 0.5%. This approach has also been compared with measured data of ion beams with different energies and foci, resulting in a very satisfactory agreement. Hence, the proposed approach was able to fulfill the different requirements and has demonstrated its capability for application to clinical treatment fields. It also offers a powerful tool to perform investigations on the contribution of primary and secondary particles produced in the beamline. These PSs are already made available to external teams upon request, to support interpretation of their measurements.

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Section: Discussionsupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phase Space Generation for Proton and Carbon Ion Beams for External Users’ Applications at the Heidelberg Ion Therapy Center

et al. 2016

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“…One of the main benefits of proton therapy is the ability to control the distal range of the treatment field by taking advantage of the Bragg Peak. This allows for the treatment of target volumes located proximal to normal tissue or organs at risk with little dosimetric detriment to the non‐target volumes . When target volumes are located relatively deep in the patient, the accuracy of the TPS is sufficient .…”

Section: Introductionmentioning

confidence: 99%

Quantifying the effect of air gap, depth, and range shifter thickness on TPS dosimetric accuracy in superficial PBS proton therapy

Shirey

2017

J Applied Clin Med Phys

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This study quantifies the dosimetric accuracy of a commercial treatment planning system as functions of treatment depth, air gap, and range shifter thickness for superficial pencil beam scanning proton therapy treatments. The RayStation 6 pencil beam and Monte Carlo dose engines were each used to calculate the dose distributions for a single treatment plan with varying range shifter air gaps. Central axis dose values extracted from each of the calculated plans were compared to dose values measured with a calibrated PTW Markus chamber at various depths in RW3 solid water. Dose was measured at 12 depths, ranging from the surface to 5 cm, for each of the 18 different air gaps, which ranged from 0.5 to 28 cm. TPS dosimetric accuracy, defined as the ratio of calculated dose relative to the measured dose, was plotted as functions of depth and air gap for the pencil beam and Monte Carlo dose algorithms. The accuracy of the TPS pencil beam dose algorithm was found to be clinically unacceptable at depths shallower than 3 cm with air gaps wider than 10 cm, and increased range shifter thickness only added to the dosimetric inaccuracy of the pencil beam algorithm. Each configuration calculated with Monte Carlo was determined to be clinically acceptable. Further comparisons of the Monte Carlo dose algorithm to the measured spread‐out Bragg Peaks of multiple fields used during machine commissioning verified the dosimetric accuracy of Monte Carlo in a variety of beam energies and field sizes. Discrepancies between measured and TPS calculated dose values can mainly be attributed to the ability (or lack thereof) of the TPS pencil beam dose algorithm to properly model secondary proton scatter generated in the range shifter.

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“…Of particular concern is the dose deposition in highly inhomogeneous patient regions, that is, in the presence of metal implants, thick bones, or cavities. The treatment of small volumes requiring the use of small fields, or the treatment of shallow regions requiring the use of range shifters and large air gaps are also not accurately modeled by commercial TPSs. In these cases, Monte Carlo simulations are a valuable instrument to obtain more reliable dose maps .…”

Section: Introductionmentioning

confidence: 99%

Technical Note: Defining cyclotron‐based clinical scanning proton machines in a FLUKA Monte Carlo system

2017

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Purpose: Cyclotron-based pencil beam scanning (PBS) proton machines represent nowadays the majority and most affordable choice for proton therapy facilities, however, their representation in Monte Carlo (MC) codes is more complex than passively scattered proton system-or synchrotronbased PBS machines. This is because degraders are used to decrease the energy from the cyclotron maximum energy to the desired energy, resulting in a unique spot size, divergence, and energy spread depending on the amount of degradation. This manuscript outlines a generalized methodology to characterize a cyclotron-based PBS machine in a general-purpose MC code. The code can then be used to generate clinically relevant plans starting from commercial TPS plans. Methods: The described beam is produced at the Provision Proton Therapy Center (Knoxville, TN, USA) using a cyclotron-based IBA Proteus Plus equipment. We characterized the Provision beam in the MC FLUKA using the experimental commissioning data. The code was then validated using experimental data in water phantoms for single pencil beams and larger irregular fields. Comparisons with RayStation TPS plans are also presented. Results: Comparisons of experimental, simulated, and planned dose depositions in water plans show that same doses are calculated by both programs inside the target areas, while penumbrae differences are found at the field edges. These differences are lower for the MC, with a c(3%-3 mm) index never below 95%. Conclusions: Extensive explanations on how MC codes can be adapted to simulate cyclotron-based scanning proton machines are given with the aim of using the MC as a TPS verification tool to check and improve clinical plans. For all the tested cases, we showed that dose differences with experimental data are lower for the MC than TPS, implying that the created FLUKA beam model is better able to describe the experimental beam.

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Dosimetric accuracy of a treatment planning system for actively scanned proton beams and small target volumes: Monte Carlo and experimental validation

Cited by 20 publications

References 17 publications

Phase Space Generation for Proton and Carbon Ion Beams for External Users’ Applications at the Heidelberg Ion Therapy Center

Phase Space Generation for Proton and Carbon Ion Beams for External Users’ Applications at the Heidelberg Ion Therapy Center

Quantifying the effect of air gap, depth, and range shifter thickness on TPS dosimetric accuracy in superficial PBS proton therapy

Technical Note: Defining cyclotron‐based clinical scanning proton machines in a FLUKA Monte Carlo system

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