Purpose: The IAEA TRS-398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ). Pencil beam scanning (PBS) systems cannot approximate reference conditions using a single spot. However, dose distributions requested in TRS-398 can be reproduced with PBS using a combination of spots. This study aims to demonstrate, using Monte Carlo (MC) simulations, that kQ factors computed/measured for broad beams can be used with scanned beams for similar reference dose distributions with no additional significant uncertainty. Methods: We consider the Alfonso formalism 13 usually employed for nonstandard photon beams. To approach reference conditions similar as IAEA TRS-398 and the associated dose distributions, PBS must combine many pencil beams with range or energy modulation and shaping techniques that differ from those used in passive systems (broad beams). In order to evaluate the impact of these differences on kQ factors, ionization chamber responses are computed with MC (Geant4 9.6) in three different proton beams, with their corresponding quality factors (Q), producing a 10 9 10 cm 2 field with a flat dose distribution for (a) a dedicated scanned pencil beam (Q(pbs)), (b) a hypothetical proton source (Qhyp), and (c) a double-scattering beam (Q(ds)). The tested ionization chamber cavities are a 2 x 2 x 0.2 mm 3 air cavity, a Roos-type ionization chamber, and a Farmer-type ionization chamber. Results and Discussion: Ranges of Q(pbs), Qhyp, and Qds are consistent within 0.4 mm. Flatnesses of dose distributions are better than 0.5%. Calculated k fpbs; fref Q(pbs); Q(hyp) is 0.999 + 0.002 for the air cavity and the Farmer-type ionization chamber and 1.001 + 0.002 for the Roos-type ionization chamber. The quality correction factors k fpbs; fref Q(pbs); Q(ds) is 0.999 + 0.002 for the Farmer-type and Roos-type ionization chambers and 1.001 + 0.001 for the Roos-type ionization chamber. Conclusion: The Alfonso formalism was applied to scanned proton beams. In our MC simulations, neither the difference in the beam profiles (scanned beam vs hypothetical beam) nor the different incident beam energies influenced significantly the beam correction factors. This suggests that ionization chamber quality correction factors in scanned or broad proton beams are indistinguishable within the calculation uncertainties provided dose distributions achieved by both modalities are similar and compliant with the TRS-398 reference conditions. (C) 2017 American Association of Physicists in Medicine

Proton ranges in water between 145 MeV to 227 MeV initial energy have been measured at a clinical superconducting synchrocyclotron using the acoustic signal induced by the ion dose deposition (ionoacoustic effect). Detection of ultrasound waves was performed by a very sensitive hydrophone and signals were stored in a digital oscilloscope triggered by secondary prompt gammas. The ionoacoustic range measurements were compared to existing range data from a calibrated range detector setup on-site and agreement of better than 1 mm was found at a Bragg peak dose of about 10 Gy for 220 MeV initial proton energy, compatible with the experimental errors. Ionoacoustics has thus the potential to measure the Bragg peak position with submillimeter accuracy during proton therapy, possibly correlated with ultrasound tissue imaging.

S66ICTR-PHE 2016 quantification the proper attenuation, scatter and partial volume corrections need to be applied.If organ or lesion dosimetry is performed, precise determination of organ/lesion volumes is necessary.Care has to be taken for an appropriate calibration of the imaging system. b) BiokineticsThis requires the determination of a correct temporal sampling and the use of ad hoc procedures to integrate the activity within time to obtain the total number of decays occurring in the source organs and thus the time-integrated activity coefficients (TIACs). c) Absorbed dose CalculationIf the TIACs of the relevant structures are known, a calculation of the absorbed doses can be performed by applying, in most cases, the "MIRD formalism": D = Ã*S D: the mean absorbed dose to a voxel or a target region from the cumulated activity in a source region.Ã: the cumulated activity (i.e. the integral of the time-activity curve) S: S factor (= mean absorbed dose per unit cumulated activity in the voxel or the target region).Different dose calculation approaches exist: These may either be based on tabulated S factors (with mass correction) of anthropomorphic phantoms, on convolution kernels or on Monte-Carlo simulations.Results: The most successful pairs of isotopes for theranostics are I-123/I-124/I-131 [2] and Ga-68/Lu-177/Y-90 [3].In addition, Y-90 PET/CT provides a good estimate of the absorbed doses in selective internal radiotherapy for locoregional liver treatment [4].Conclusion: Although many new radiopharmaceuticals are available for imaging and molecular radiotherapy it is still a challenge to establish reliable dose-response relationships.

Purpose:The IAEA TRS‐398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ). Pencil beam scanning (PBS) requires multiple spots to reproduce the reference conditions. The objective is to demonstrate, using Monte Carlo (MC) calculations, that kQ factors for broad beams can be used for scanned beams under the same reference conditions with no significant additional uncertainty. We consider hereafter the general Alfonso formalism (Alfonso et al, 2008) for non‐standard beam.Methods:To approach the reference conditions and the associated dose distributions, PBS must combine many pencil beams with range modulation and shaping techniques different than those used in passive systems (broad beams). This might lead to a different energy spectrum at the measurement point. In order to evaluate the impact of these differences on kQ factors, ion chamber responses are computed with MC (Geant4 9.6) in a dedicated scanned pencil beam (Q_pcsr) producing a 10×10cm2 composite field with a flat dose distribution from 10 to 16 cm depth. Ion chamber responses are also computed by MC in a broad beam with quality Q_ds (double scattering). The dose distribution of Q _pcsr matches the dose distribution of Q_ds. k_(Q_pcsr,Q_ds) is computed for a 2×2×0.2cm3 idealized air cavity and a realistic plane‐parallel ion chamber (IC).Results:Under reference conditions, quality correction factors for a scanned composite field versus a broad beam are the same for air cavity dose response, k_(Q_pcsr,Q_ds) =1.001±0.001 and for a Roos IC, k_(Q_pcsr,Q_ds) =0.999±0.005.Conclusion:Quality correction factors for ion chamber response in scanned and broad proton therapy beams are identical under reference conditions within the calculation uncertainties. The results indicate that quality correction factors published in IAEA TRS‐398 can be used for scanned beams in the SOBP of a high‐energy proton beam.Jefferson Sorriaux is financed by the Walloon Region under the convention 1217662. Jefferson Sorriaux is sponsored by a public‐private partnership IBA ‐ Walloon Region

Conclusions: Fast and accurate MC tools allow range uncertainties to be reduced and random errors to be integrated efficiently into robustness evaluation.In proton therapy, robust optimization is preferred to traditional PTV margins, which do not suffice to ensure homogeneous coverage of the CTV in case of uncertainties.

The calculation algorithm of a modern treatment planning system for ion-beam radiotherapy should ideally be able to deal with different ion species (e.g. protons and carbon ions), to provide relative biological effectiveness (RBE) evaluations and to describe different beam lines. In this work we propose a new approach for ion irradiation outcomes computations, the beamlet superposition (BS) model, which satisfies these requirements. This model applies and extends the concepts of previous fluence-weighted pencil-beam algorithms to quantities of radiobiological interest other than dose, i.e. RBE- and LET-related quantities. It describes an ion beam through a beam-line specific, weighted superposition of universal beamlets. The universal physical and radiobiological irradiation effect of the beamlets on a representative set of water-like tissues is evaluated once, coupling the per-track information derived from FLUKA Monte Carlo simulations with the radiobiological effectiveness provided by the microdosimetric kinetic model and the local effect model. Thanks to an extension of the superposition concept, the beamlet irradiation action superposition is applicable for the evaluation of dose, RBE and LET distributions. The weight function for the beamlets superposition is derived from the beam phase space density at the patient entrance. A general beam model commissioning procedure is proposed, which has successfully been tested on the CNAO beam line. The BS model provides the evaluation of different irradiation quantities for different ions, the adaptability permitted by weight functions and the evaluation speed of analitical approaches. Benchmarking plans in simple geometries and clinical plans are shown to demonstrate the model capabilities.

Purpose: In current practice, most proton therapy centers apply IAEA TRS‐398 reference dosimetry protocol. Quality correction factors (kQ) take into account in the dose determination process the differences in beam qualities used for calibration unit and for treatment unit. These quality correction factors are valid for specific reference conditions. TRS‐398 reference conditions should be achievable in both scattered proton beams (i.e. DS) and scanned proton beams (i.e. PBS). However, it is not a priori clear if TRS‐398 kQ data, which are based on Monte Carlo (MC) calculations in scattered beams, can be used for scanned beams. Using TOPAS‐Geant4 MC simulations, the study aims to determine whether broad beam quality correction factors calculated in TRS‐398 can be directly applied to PBS delivery modality. Methods: As reference conditions, we consider a 10×10×10 cm 3 homogeneous dose distribution delivered by PBS system in a water phantom (32/10 cm range/modulation) and an air cavity placed at the center of the spread‐out‐Bragg‐peak. In order to isolate beam differences, a hypothetical broad beam is simulated. This hypothetical beam reproduces exactly the same range modulation, and uses the same energy layers than the PBS field. Ion chamber responses are computed for the PBS and hypothetical beams and then compared. Results: For an air cavity of 2×2×0.2 cm 3 , the ratio of ion chamber responses for the PBS and hypothetical beam qualities is 0.9991 ± 0.0016. Conclusion: Quality correction factors are insensitive to the delivery pattern of the beam (broad beam or PBS), as long as similar dose distributions are achieved. This investigation, for an air cavity, suggests that broad beam quality correction factors published in TRS‐398 can be applied for scanned beams. J. Sorriaux is financially supported by a public‐private partnership involving the company Ion Beam Applications (IBA).

Developments in hadron therapy require efforts to improve the accuracy of the dose delivered to a target volume. Here, the determination of the absorbed dose under reference conditions was analysed. Based on the International Atomic Energy Agency TRS-398 code of practice, for hadron beams, the combined standard uncertainty on absorbed dose to water under reference conditions, derived from ionisation chambers, is too large. This uncertainty is dominated by the beam quality correction factors, [Formula: see text], mainly due to the mean energy to produce one ion pair in air, wair. A method to reduce this uncertainty is to carry out primary dosimetry, using calorimetry. A [Formula: see text]-value can be derived from a direct comparison between calorimetry and ionometry. Here, this comparison is performed using a graphite calorimeter in an 80-MeV A(-1) carbon ion beam. Assuming recommended TRS-398 values of water-to-graphite stopping power ratio and the perturbation factor for an ionisation chamber, preliminary results indicate a wair-value of 35.5 ± 0.9 J C(-1).

Purpose: To reduce the uncertainty of the beam quality correction factor kQ,Q0, for scattered proton beams (SPB). This factor is used in dosimetry protocols, to determine absorbed dose-to-water with ionization chambers. For the Roos plane parallel chambers (RPPICs), the IAEA TRS-398 protocol estimates kQ,Q0-factor to be 1.004(for a beam quality Rres=2 g.cm2), with an uncertainty of 2.1%. Methods: A graphite calorimeter (GCal), a water calorimeter (WCal) and RPPICs were exposed, in a single experiment, to a 60 MeV non-modulated SPB. RPPICs were calibrated in terms of absorbed dose-to-water in a 20 MeV electron beam. The calibration coefficient is traceable to NPL's absorbed dose standards. Chamber measurements were corrected for environmental conditions, recombination and polarity. The WCal corrections include heat loss, heat defect and vessel perturbation. The GCal corrections include heat loss and absorbed dose conversion. Except for heat loss correction and its uncertainty in the WCal system, all major corrections were included in the analysis. Other minor corrections, such as beam profile non-uniformity, are still to be evaluated. Experimental kQ,Q0-factors were derived by comparing the results obtained with both calorimeters and ionometry. Results: The absorbed dose-to-water from both calorimeters was found to be within 1.3% with an uncertainty of 1.2%. kQ,Q0-factor for a RPPIC was found to be 0.998 and 1.011, with a standard uncertainty of 1.4% and 0.9% when the dose is based on the GCal and the WCal, respectively. Conclusion: Results suggest the possibility to determine kQ,Q0-values for PPICs in SPB with a lower uncertainty than specified in the TRS-398 thereby helping to reduce uncertainty on absorbed dose-to-water. The agreement between calorimeters confirms the possibility to use GCal or WCal as primary standard in SPB. Because of the dose conversion, the use of GCal may lead to slightly higher uncertainty, but is, at present, considerably easier to operate.

Purpose: To evaluate the uncertainties and characteristics of radiochromic film-based dosimetry system using the EBT3 model Gafchromic (R) film in therapy photon, electron and proton beams.Material and methods: EBT3 films were read using an EPSON Expression 10000XL/PRO scanner. They were irradiated in five beams, an Elekta SL25 6 MV and 18 MV photon beam, an IBA 100 MeV 5 x 5 cm(2) proton beam delivered by pencil-beam scanning, a 60 MeV fixed proton beam and an Elekta SL25 6 MeV electron beam. Reference dosimetry was performed using a FC65-G chamber (Elekta beam), a PPC05 (IBA beam) and both Markus 1916 and PPC40 Roos ion-chambers (60 MeV proton beam). Calibration curves of the radiochromic film dosimetry system were acquired and compared within a dose range of 0.4-10 Gy. An uncertainty budget was estimated on films irradiated by Elekta SL25 by measuring intra-film and inter-film reproducibility and uniformity; scanner uniformity and reproducibility; room light and film reading delay influences.Results: The global uncertainty on acquired optical densities was within 0.55% and could be reduced to 0.1% by placing films consistently at the center of the scanner. For all beam types, the calibration curves are within uncertainties of measured dose and optical densities. The total uncertainties on calibration curve due to film reading and fitting were within 1.5% for photon and proton beams. For electrons, the uncertainty was within 2% for dose superior to 0.8 Gy.Conclusions: The low combined uncertainty observed and low beam and energy-dependence make EBT3 suitable for dosimetry in various applications. (C) 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Purpose/Objective To validate experimentally a GATE/GEANT4-based(G4) Monte Carlo (MC) model in heterogeneous media for dedicated pencil beam scanning in proton therapy. Comparisons between measurements and MC simulations using G4 and PENELOPE-proton are presented. A comparison against analytical modeling from commercial TPS is also investigated. This work evaluates the impact of heterogeneities on range prediction, beam shape and depth dose changes. Materials and Methods The MC model for pencil beam based on G4 has been validated in water and PMMA phantoms (Grevillot et al Phys. Med. Biol.(2011)) reproducing pristine Bragg peaks for a series of individual energies (from 100 to 226.7 MeV) with 0.7 mm range and 0.2 mm spot size accuracy. The same optical model was implemented in PENELOPE-proton. In order to validate the beam model in heterogeneous media, phantoms made of stacked slabs with different densities and known compositions were used. Two experimental test cases including solid water (SW), lung (LN-300) and bone (SB3) tissue-equivalent material were investigated. Depth-dose distributions for a monoenergetic single spot and 10x10cm² composite fields were measured using Gafchromic EBT3 films and the ionization chamber (IC) PPC05 in all configurations. To measure accurately the Bragg peak position, a stack of films of 2x2cm² was inserted in the last centimeter of the proton range. Results Figure 1 shows results for one heterogeneous configuration. All doses-to-medium were converted to dose to water using stopping power ratios. Dose distributions were arbitrarily normalized in the middle of the second SW region. Bragg peak positions are reproduced by MC simulations within 1mm in both configurations (Table 1). IC measurements, G4 (binary-cascade) and PENELOPE-proton simulations are within 2%/2 mm. Point-to-point mean difference of 1.2% is observed between G4 (precompound) and measurement in the first 15 cm of the phantom and increased to 7.2% after bone insert until 286.5mm depth. In lung and bone slabs, EBT3 films and G4 binary-cascade are inagreement within 0.77% while a mean point-to-point difference up to 1.26% is observed with G4 precompound model. The uncertainty (1σ) on EBT3 films was evaluated to be at 2.75% which included readout process and dose calibration against IC (TRS-398). A statistical uncertainty of 0.1% was achieved for MC simulations. Conclusions The Bragg peak position is predicted with 1mm precision for all MC simulations, even though ionization potential values for phantom slabs were calculated using classical additive rules. G4/GATE beam model reproduce depth-dose behavior of proton transport regarding both IC and EBT3 measurement in heterogeneities.

Purpose: IAEA TRS‐398 provides recipes and formulas to compute ion recombination correction factors for continuous and pulsed broad proton beams. However, those formulas may not be optimal for pencil beam scanning modalities (PBS). This work aims at evaluating appropriately ion recombination correction for different ionization chamber types for PBS delivery. Methods: Ion chamber measurements were performed in a water phantom (BluePhantom2, IBA Dosimetry GmbH) irradiated by a 10×10 cm2 uniform field (2.5mm spot spacing, IBA PBS dedicated nozzle) for Extradin T1, FC65‐G, CC01 and PPC05 at different beam energies, beam current and polarizing voltages. The Boutillon formalism was used in order to separate the contributions from initial and general recombination. The recombination correction factor was computed using the two‐voltage method for continuous, pulsed, and pulsed‐scanned beams as well. Chamber‐dependent conditions such as depth and relative position to spot mapping were also evaluated. Results: The formulas for continuous beams in TRS‐398 lead to an underestimation of the correction factors (ks) of 0.4% compared to Boutillon analysis for EXTRADIN T1. An overestimation of 0.2% is observed considering the beam as pulsed. For PPC05 using the two‐voltage methods, (ks) difference of 0.3% is found compared to Boutillon's value. For FC65‐G using the two‐voltage correction (ks) is 0.4% underestimated in continuous beam and can be 3% overestimated using pulsed beam formula. (ks) values is computed for various depth positions, energies and beam currents. Plotting inverse ionizing charge versus inverse squared voltage shows that initial recombination is not negligible for Extradin T1, FC65‐G and PPC05 at low residual range. Conclusion: We have determined recombination correction factors for 4 ion chambers using various practical and yet accurate methods in the specific case of PBS delivery. Significant differences in recombination correction factors can appear if recipes from IAEA TRS‐398 are applied blindly for proton PBS delivery. Jefferson Sorriaux is financed by the Walloon Region under the project name InVivoIGT, convention number 1017266. Jefferson Sorriaux is sponsored by a public‐private partnership IBA ‐ Walloon Region

Purpose: Comparison between the response of a primary standard graphite calorimeter and the response of an ionization chamber (IC) allows the estimations of values of the beam quality correction factor, kQ,Q0, for the IC. This factor is used in the IAEA TRS‐398 dosimetric protocol to derive the absorbed dose‐to‐water using an IC. It depends on three parameters, one of which is the average energy required to produce an ion pair in dry air (Wair). The aim of this work is the experimental determination of the Wair‐value for an 80 MeV/A carbon ion beam. Methods: The dose measured with a graphite calorimeter, after correction for heat transfer between different parts of the calorimeter, must be converted to dose‐to‐water. This conversion needs knowledge of the water‐to‐graphite stopping power ratio and the fluence correction factor. These have been determined experimentally and numerically using Geant4 Monte Carlo simulations. In addition to these calorimetric corrections, the determination of kQ,Q0‐values needs the IC reading to be corrected for ion recombination. Results: The water‐to‐graphite stopping power ratio has been determined numerically to be 1.115 while the fluence correction factor has been determined experimentally and numerically to vary linearly between 0.9996 at the phantom surface and 1.0063 before the Bragg peak. The analysis of the ion recombination correction measurements is still ongoing. Two experimental campaigns with the graphite calorimeter and several IC's have been performed. Based on recommended data from TRS‐398, we derived preliminary Wair‐values of 36. J/C and 34.85 J/C for each campaign. These results are under investigation. Conclusion: These results demonstrate the feasibility of graphite calorimetry in an 80 MeV/A carbon ion beam and are encouraging for our future work: a direct comparison between water and graphite calorimetry in a clinical carbon ion beam. Funding support for Severine Rossomme: BioWin program of the Walloon Government (Belgium); Funding support for NPL people: Acoustics and Ionising Radiation Metrology Programme of the National Measurement System (UK)

Based on experiments and numerical simulations, a study is carried out pertaining to the conversion of dose-to-graphite to dose-to-water in a carbon ion beam. This conversion is needed to establish graphite calorimeters as primary standards of absorbed dose in these beams. It is governed by the water-to-graphite mass collision stopping power ratio and fluence correction factors, which depend on the particle fluence distributions in each of the two media. The paper focuses on the experimental and numerical determination of this fluence correction factor for an 80 MeV/A carbon ion beam. Measurements have been performed in the nuclear physics laboratory INFN-LNS in Catania (Sicily, Italy). The numerical simulations have been made with a Geant4 Monte Carlo code through the GATE simulation platform. The experimental data are in good agreement with the simulated results for the fluence correction factors and are found to be close to unity. The experimental values increase with depth reaching 1.010 before the Bragg peak region. They have been determined with an uncertainty of 0.25%. Different numerical results are obtained depending on the level of approximation made in calculating the fluence correction factors. When considering carbon ions only, the difference between measured and calculated values is maximal just before the Bragg peak, but its value is less than 1.005. The numerical value is close to unity at the surface and increases to 1.005 near the Bragg peak. When the fluence of all charged particles is considered, the fluence correction factors are lower than unity at the surface and increase with depth up to 1.025 before the Bragg peak. Besides carbon ions, secondary particles created due to nuclear interactions have to be included in the analysis: boron ions ((10)B and (11)B), beryllium ions ((7)Be), alpha particles and protons. At the conclusion of this work, we have the conversion of dose-to-graphite to dose-to-water to apply to the response of a graphite calorimeter in an 80 MeV/A carbon ion beam. This conversion consists of the product of two contributions: the water-to-graphite electronic mass collision stopping power ratio, which is equal to 1.115, and the fluence correction factor which varies linearly with depth, as k(fl, all) = 0.9995 + 0.0048(zw-eq). The latter has been determined on the basis of experiments and numerical simulations.

PURPOSE:The IAEA TRS-398 code of practice can be applied for the measurement of absorbed dose to water under reference conditions with an ionization chamber. For protons, the combined relative standard uncertainty on those measurements is less than 2% while for light-ion beams, it is considerably larger, i.e. 3.2%, mainly due to the higher uncertainty contributions for the water to air stopping power ration and the W air-value on the beam quality correction factors kQ,Q0 . To decrease this uncertainty, a quantification of kQ,Q0 is proposed using a primary standard level graphite calorimeter. This work includes numerical and experimental determinations of dose conversion factors to derive dose to water from graphite calorimetry. It also reports on the first experimental data obtained with the graphite calorimeter in proton, alpha and carbon ion beams.METHODS:Firstly, the dose conversion has been calculated with by Geant4 Monte-Carlo simulations through the determination of the water to graphite stopping power ratio and the fluence correction factor. The latter factor was also derived by comparison of measured ionization curves in graphite and water. Secondly, kQ,Q0 was obtained by comparison of the dose response of ionization chambers with that of the calorimeter.RESULTS:Stopping power ratios are found to vary by no more than 0.35% up to the Bragg peak, while fluence correction factors are shown to increase slightly above unity close to the Bragg peak. The comparison of the calorimeter with ionization chambers is currently under analysis. For the modulated proton beam, preliminary results on W air confirm the value recommended in TRS-398. Data in both the non-modulated proton and light-ion beams indicate higher values but further investigation of heat loss corrections is needed.CONCLUSIONS:The application of graphite calorimetry to proton, alpha and carbon ion beams has been demonstrated successfully. Other experimental campaigns will be held in 2012. This work is supported by the BioWin program of the Wallon Government.

Active scanning delivery systems take full advantage of ion beams to best conform to the tumor and to spare surrounding healthy tissues; however, it is also a challenging technique for quality assurance. In this perspective, we upgraded the GATE/GEANT4 Monte Carlo platform in order to recalculate the treatment planning system (TPS) dose distributions for active scanning systems. A method that allows evaluating the TPS dose distributions with the GATE Monte Carlo platform has been developed and applied to the XiO TPS (Elekta), for the IBA proton pencil beam scanning (PBS) system. First, we evaluated the specificities of each dose engine. A dose-conversion scheme that allows one to convert dose to medium into dose to water was implemented within GATE. Specific test cases in homogeneous and heterogeneous configurations allowed for the estimation of the differences between the beam models implemented in XiO and GATE. Finally, dose distributions of a prostate treatment plan were compared. In homogeneous media, a satisfactory agreement was generally obtained between XiO and GATE. The maximum stopping power difference of 3% occurred in a human tissue of 0.9 g cm(3) density and led to a significant range shift. Comparisons in heterogeneous configurations pointed out the limits of the TPS dose calculation accuracy and the superiority of Monte Carlo simulations. The necessity of computing dose to water in our Monte Carlo code for comparisons with TPSs is also presented. Finally, the new capabilities of the platform are applied to a prostate treatment plan and dose differences between both dose engines are analyzed in detail. This work presents a generic method to compare TPS dose distributions with the GATE Monte Carlo platform. It is noteworthy that GATE is also a convenient tool for imaging applications, therefore opening new research possibilities for the PBS modality.

PURPOSE:To measure the calibration curves of EBT3 dosimetry films in photon and proton beams and to quantify the related uncertainties from one beam type to another.METHODS:EBT3 Gafchromic films have similar properties than EBT2 with a symmetric construction and a matte polyester substrate to prevent Newton's ring artefacts. Films from a same batch were exposed in three different beam qualities, an Elekta SL25 6 MV photon beam, a 100 MeV 5×5cm2 proton beam delivered by pencil-beam scanning dedicated system from IBA and a 60 MeV fixed proton beam (2.5cm in diameter) at Clatterbridge Center for Oncology (CCO), UK. The films were read using an EPSON 10000 XL/PRO scanner. Film calibration curves were acquired for all modalities within a range of 0.05 to 20 Gy. Influence of increasing linear-energy transfer (LET) on film response was investigated by comparing dose measured by EBT3 to a silicon diode detector in depth for a fully-modulated beam using the CCO beam line (homogeneous dose with distal end at 3.1cm in water). A comprehensive uncertainty budget (reproducibility, uniformity'¦) was estimated on films irradiated by Elekta SL25.RESULTS:The main source of uncertainty was the non-uniformity of the scanner response. By placing all the irradiated films at the center of the scanner, the uncertainty could be reduced from 5.8% to 1.9% (1 sigma). For all beams and energies, the calibration curves were matched within uncertainties. Along the fully-modulated depth dose curve, diode and EBT3 measurement were in a 4% agreement point-to-point, indicating films weak dependence with LET.CONCLUSIONS:The weak influence of LET, beam type and energy on film response as well as its small uncertainty make EBT3 suitable for relative dosimetry and a promising candidate for measuring correction factors (quality, recombination,'¦) for reference dosimetry with ion chambers of non-standard beams (e.g pencil-beam scanning proton-therapy). “This work is supported by the Walloon Region under the project name InVivoIGT, convention number 1017266.â€.