Modulator Wheel Research Articles

Design, optimization, and testing of ridge filters for proton FLASH radiotherapy at TRIUMF: The HEDGEHOG

TRIUMF has recently developed and implemented a workflow to design and fabricate application-specific ridge filters, which is a key upgrade to enable research using ultra-high (FLASH) dose rate beam delivery at its Proton Therapy Research Centre. These static ridge filters, called HEDGEHOGs, replace the rotating modulator wheels used to create a spread-out Bragg peak (SOBP) during conventional proton radiotherapy beam delivery, which are incompatible with the fast irradiation times of clinical doses at FLASH dose rates at TRIUMF. Initial beam commissioning of HEDGEHOGs demonstrated that they produce spread-out Bragg peaks matching their design parameters. Additional studies of some of the design parameters, including SOBP widths as well as different pin diameters and fabrication options (material, 3D printer technology) have now been completed. Based on those studies, the use of liquid medium printers (resin, jet) instead of filament printers is recommended. These studies also demonstrate that the lateral dose uniformity of the beam at 36.5 cm from the HEDGEHOG location is acceptable even with relatively large 7 mm base-diameter pins. The code base and workflow are made publicly available and can easily be adapted to other facilities. The feasibility of adapting the HEDGEHOG workflow to other beam lines or facilities was validated on a second proton beam line at the same facility at which the HEDGEHOG workflow was developed.

Low-energy protons shallow spread-out Bragg peak imaging with a lithium fluoride crystal

The 35 MeV proton beam produced by a modular linear accelerator was used to irradiate at grazing incidence a LiF crystal through a spinning Mylar multi-sector range modulation wheel and a Pyrex range shifter. Starting from a measured pristine depth dose curve, these energy-modulation devices were designed to plan a test shallow spread-out Bragg peak in water. The irradiation of the LiF crystal produced in its lattice a volume distribution of color centers, which could be visualized in a fluorescence microscope as a fluorescent image under blue-light illumination. Since the intensity of this fluorescent image was proportional point-by-point to the absorbed energy, it was elaborated to obtain an experimental depth dose curve in the LiF crystal, from which the proton beam energy distribution was estimated. This latter was finally used to evaluate the corresponding spread-out Bragg peak that would be obtained in water and compare it to the designed one.

Decomposition of the weight fractions for modelling ridge filters in a proton wobbling nozzle

In proton therapy, the width of a pristine Bragg peak is too narrow to cover the entire tumor volume, and should be spread out using the Spread out Bragg peak (SOBP) techniques such as energy stacking, range modulator wheel and ridge filter. The main purpose of this study was to demonstrate feasibility of using a simple least square technique to decompose the simulated weight fractions of elemental Bragg peaks of ridge filters used in a clinical wobbling beam nozzle. First, initial simulated beam parameters including mean energy and energy spread at the nozzle entrance for all available clinical energies were commissioned against measurements for the open middle wobbling field at the Proton and Radiation Center of the Linkou Chang Gung Memorial Hospital (LCGMH) using the Particle Therapy Simulation Framework (PTSim) Monte Carlo package. Material composition and geometry of nozzle components were provided by the vendor. Depth dose distribution of beam energies from 70 to 230 MeV at 20-MeV increment were simulated and validated with measurement. Curve fitting to those beam parameters was performed to extend simulation energy range to all available clinical energies. For the reconstructed ridge filter simulation, elemental Bragg peaks (BPs) with layer filters corresponding to ridge filter step thicknesses were obtained as bases of the weight factor decomposition. The least square technique was implemented to decompose weight factors for individual ridge filter at a selected beam energy within its applicable energy range. Finally, the reconstructed ridge filters using decomposed weight factors were tested at one other energy to validate the study design. Four different ridge filters (5 cm-LE, 5 cm-HE, 10 cm and 11 cm SOBP) were examined in this study. Commission results for tuned beam parameter settings showed maximum disagreement of BP characteristics, represented by the 80% dose depth (R80d) and width of distal fall-off (W80-20), occurred at 230 MeV and was smaller than 0.2 and 0.5 mm respectively. Furthermore, analyzed outcome for SOBPs from the four ridge filters revealed general improvement of agreement to measurement with decomposition and satisfactory agreement between measurements and those with least square technique. Deviation from measurement of SOBP characteristics evaluated for R90d, W80-20 and SOBP flatness after weight decomposition showed values smaller than 1mm/1%. Similar evaluation of SOBP width generated larger difference with maximum value of 2.7 mm for the 11-cm ridge filter. Results of the validation testes were similar with maximum deviation of 1.4 mm, 0.6 mm, 0.2% and 3.8 mm for R90d, W80-20, flatness and width respectively.

Calculation of secondary radiation absorbed doses due to the proton therapy on breast cancer using MCNPX code

Secondary radiation damage caused by proton radiation therapy can affect other tissues and result in unwanted doses. Therefore, it is necessary to calculate the secondary radiation doses (from scattering processes) for radiation protection issues. In this study, we simulated a proton beam in a 10 cm distance (from source-to-surface distance) was used to irradiate a hypothetical breast tumor at the MIRD phantom under conditions of variable beam radius and energy. Thereafter, absorbed doses to the tumor and scattering radiation doses to the heart, lung, liver, stomach, and spleen were calculated. The results showed that the maximum scattered neutron dose-to-organs close to the breast, such as the heart, lung, liver, stomach and spleen, with 70 MeV proton energy and beam radius of 1 cm are negligible. Finally, the spread-out Bragg peak was obtained using an appropriate weighted combination of beams of different energies which can be replaced as a suitable method instead of modulator wheel design for applying in MCNPX code input program.The evaluated indices in this study are the absorbed tumor doses for single particle and the scattered doses due neutrons and photons. The results showed that the majority of scattered radiation is neutrons. Scattered particle spectral powers for neutrons and photons were also plotted. It was observed that in the photon spectra, the maximum scattered radiation occurs with the beam of 1 cm radius and 70 MeV energy, while the neutron spectra show that scattered radiation is predominantly at low energy. Finally, a spread-out Bragg peak appropriate for a hypothetical tumor with 1.77 cm width was obtained, and the absorbed doses and scattered doses were calculated.

FLASH proton irradiation setup with a modulator wheel for a single mouse eye.

Recent studies indicate that FLASH irradiation, which involves ultra-high dose rates in a short time window (usually >40Gy/s in <500ms), might be equally efficient against tumors but less harmful to healthy tissues, compared to conventional irradiation with the same total dose. Aiming to verify the latter claim for ocular proton radiotherapy, in vivo experiments with mice are being carried out by Charité - Universitätsmedizin Berlin. This work presents the implemented setup for delivering FLASH proton radiation to a single eye of mice at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). The HZB cyclotron is tuned to provide a high-intensity 68MeV focused proton beam. Outside the vacuum beamline, the protons hit a single scatterer, which also serves as range shifter, and a rotating modulator wheel, which produces a flat depth-dose distribution. Two transmission ionization chambers in between, read out by fast electronics, are used as dose monitors for triggering an in-vacuum beam shutter, which blocks the beam once the desired dose has been delivered. A collimating aperture shapes the radiation field at the isocenter, which is measured by a radioluminescent screen and a CCD camera. At the same position, a parallel-plate ionization chamber of type Advanced Markus® is used for absolute dosimetry and characterization of the spread-out Bragg peak inside a water phantom. A thin-foil mirror of adjustable tilt in the beam path assists the correct alignment of the target through side illumination. Radiochromic films of type EBT3 are used to supplement the dosimetry and assist the alignment. A dose rate of 75Gy/s has been measured, delivering within 200ms 15Gy (RBE) with a reproducibility better than ±1%. A depth-dose curve with a range of 5.2mm in water, 0.9mm distal fall-off (90%-10%), and ±2.5% ripple has been demonstrated, with a PTV of 6.3mm diameter, 1.7mm lateral penumbra (90%-10%), 8% uniformity, and 3% symmetry. The implemented setup is able to accommodate ocular irradiation of narcotized mice with protons, targeting selectively the left or the right eye, under conventional and FLASH conditions. Switching between these two modes can be done within half an hour, including the calibration of the dose monitors and the verification of the dose delivery. Further upgrades are planned after the completion of the on-going experiment.

Development and validation of an optimal GATE model for double scattering proton beam delivery

Proton therapy (PT) is an emerging external beam radiation therapy characterized by superior dose distribution compared to conventional modalities. In the present study, an optimal GATE model was developed and then validated for a double scattering proton nozzle based on the previously constructed model. To this aim, a double scattering treatment nozzle was modeled in the GATE platform. To accelerate the GATE simulations, a virtual range modulation wheel (vRMW) and a variance reduction technique (VRT) were implemented. Proton beam flatness, symmetry, and delivery efficiency, secondary neutron dose, and dosimetric performance were characterized through a set of GATE simulations. The findings show that range cutoff value of 0.075 mm provides the best compromise between the simulation accuracy and speed for the simulated geometry. A proton beam flatness of 98.6% was observed at the downstream of the aperture for a 7 × 7 cm2 field size. The beam flatness deteriorates at the edge of the treatment field for the single scattering model while it remains approximately constant for the double scattering one. In comparison to the single scattering delivery, the second scattering model results in a 1.28 times increase in neutron dose for the nickel, as the optimal collimator/aperture material. Furthermore, a flat beam modulation width of 3.50 cm is formed with a distal edge at 7.86 cm in water using both GATE and MCNPX codes. The GATE model agreed with the MCNPX results with a maximum difference of ±6.3% in absorbed dose estimation. The findings demonstrate that the constructed GATE model of double scattering proton nozzle results in a fast and accurate simulation of passive scattering PT.

Simulation of dose distribution and secondary particle production in proton therapy of brain tumor.

The aim of this study is simulation of the proton depth-dose distribution and dose evaluation of secondary particles in proton therapy of brain tumor using the GEANT4 and FLUKA Monte Carlo codes. Proton therapy is a treatment method for variety of tumors such as brain tumor. The most important feature of high energy proton beams is the energy deposition as a Bragg curve and the possibility of creating the spread out Bragg peak (SOBP) for full coverage of the tumor. A spherical tumor with the radius of 1 cm in the brain is considered. A SNYDER head phantom has been irradiated with 30-130 MeV proton beam energy. A PMMA modulator wheel is used for covering the tumor. The simulations are performed using the GEANT4 and FLUKA codes. Using a modulator wheel, the Spread Out Bragg Peak longitudinally and laterally covers the tumor. Flux and absorbed dose of secondary particles produced by nuclear interactions of protons with elements in the head are considerably small compared to protons. Using 76.85 MeV proton beam and a modulator wheel, the tumor can be treated accurately in the 3-D, so that the distribution of proton dose in the surrounding tissues is very low. The results show that more than 99% of the total dose of secondary particles and protons is absorbed in the tumor.

Monte Carlo simulations and dose measurements of 2D range-modulators for scanned particle therapy

This paper introduces the concept of a 2D range-modulator as a static device for generating spread-out Bragg peaks at very small distances to the target. The 2D range-modulator has some distinct advantages that can be highly useful for different research projects in particle therapy facilities. Most importantly, it creates an instantaneous, quasi-static irradiation field with only one energy, thus decreasing irradiation time tremendously. In addition, it can be manufactured fast and cost efficiently and its SOBP width and shape can be adjusted easily for the specific purpose/experiment. As the modulator is a static element, there is no need for rotation (e.g. like in a modulation wheel) or lateral oscillation and due to the small base structure period it can be positioned close to the target.Two different rapid prototyping manufacturing techniques were utilized. The modulation properties of one polymer and one steel modulator were investigated with both simulations and measurements. For this purpose, a sophisticated water phantom system (WERNER), that can perform fast, completely automated and high resolution dose measurements, was developed. Using WERNER, the dose distribution of a modulator can be verified quickly and reliably, both during experiments, as well as in a time constrained clinical environment.The maximum deviation between the Monte Carlo simulations and dose measurements in the spread-out Bragg peak region was 1.4% and 4% for the polymer and steel modulator respectively. They were able to create spread-out Bragg peaks with a high degree of dose homogeneity, thus validating the whole process chain, from the mathematical optimization and modulator development, to manufacturing, MC simulations and dose measurements.Combining the convenience, flexibility and cost-effectiveness of rapid prototyping with the advantages of highly customizable modulators, that can be adapted for different experiments, the 2D range-modulator is considered a very useful tool for a variety of research objectives. Moreover, we have successfully shown that the manufacturing of 2D modulators with high quality and high degree of homogeneity is possible, paving the way for the further development of the more complex 3D range-modulators, which are considered a viable option for the very fast treatment of moving targets and/or FLASH irradiation.

Design of a compact proton beam energy modulator for imaging

Proton beam therapy is the current state of the art for irradiation of cancerous tumors near vital organs. Proton imaging is a new technology that images tumors with the same particle interaction as proton therapy, promising more accurate treatment preparation compared to traditional computerized tomography scans. A specific proton imaging technique in development at Massachusetts General Hospital requires an energy modulator that can fit inside the gantry nozzle. This work presents the design of a compact proton beam energy modulator required for such imaging applications. A combination of steel and lead wedges was used to create a balanced modulation wheel, with an axis of rotation perpendicular to the incident beam. The mechanical design also allows interchangeable disks and precise position control. The modulator design was verified by testing on a proton beam line. The final device achieved a wide range of energy modulation (21 cm water-equivalent thickness) while maintaining a constant exiting beam angular spread meeting device requirements. This compact design facilitates proton imaging to be practically incorporated into future gantry systems, which will advance proton treatment for tumors near vital organs.

An Iterating Method to Calculate the Geometry of Range Modulation Wheel in Passive Proton Therapy

In the passive method of proton therapy, range modulation wheel is used to scatter the single energy proton beam. It rounds and scatters the single energy proton beam to the spectrum of particles that covers cancerous tissue by a change in penetration depth. Geant4 is a Monte Carlo simulation platform for studying particles behaviour in a matter. We simulated proton therapy nozzle with Geant4. Geometric properties of this nozzle have some effects on this beam absorption plot. Concerning the relation between penetration depth and proton particle energy, we have designed a range modulation wheel to have an approximately flat plot of absorption energy. An iterative algorithm programming helped us to calculate the weight and thickness of each sector of range modulation wheel. Flatness and practical range are calculated for resulting spread-out Bragg peak.

Research on spectral reflectance reconstruction based on compressive sensing by a gradual modulation wheel

The spectral reflectance of an object can show the color of an object from its intrinsic properties. As a result, it is very important to reconstruct the spectral reflectance of the object. In this paper, a method of spectral reflectance reconstruction based on compressive sensing by a gradual modulation wheel is proposed. After a light source is modulated by a grating and a gradual modulation wheel, it is irradiated onto an object, and the spectral reflectance is received by a single pixel detector. Different experimental devices are set up for a color block and a multispectral image. The spectral reflectance of the multispectral image is further modulated by a spatial modulator, and then the multispectral image is received by a single pixel detector. In the simulation experiment, the effect of different transformation cycles on the gradual modulation wheel is investigated and the objective evaluations are structural similarity, peak signal to noise ratio, and root mean square error, which has allowed the exact conditions to be determined for the best spectral reflectance reconstruction and accurate copying of the multispectral image.

Higher order analysis of time-resolved proton radiographs

We demonstrate the potential of analyzing the higher order moments of time-resolved proton radiographic signals to generate images that show internal structures not visible in standard water-equivalent thickness (WET) images. Using a single detector distal to the patient, proton transmission images were acquired using a scintillating screen coupled to a CCD camera, with the beam range modulated using a small dedicated range modulator wheel. The variation of dose with time to a given pixel is referred to as the dose rate function, DRF. The width of the DRF can be correlated to the WET of the material and the shape of the DRF is representative of heterogeneities. The shape of the DRF can be described by the higher order functions, skewness and kurtosis. A number of phantoms were imaged to assess the usability of the higher order images: the Gammex 467 phantom; a step phantom; thin plastic squares at shallow and deep depths of solid water; an anthropomorphic foot phantom; and an anthropomorphic head phantom. In all cases the higher order moment images highlighted regions of heterogeneities, and in many cases such heterogeneities were not visible in the standard WET image. Such heterogeneities could be either composed of changes in thickness of the same material or changes due to different materials. As well as having the potential as a useful imaging protocol in its own right, the higher order images offer the potential to discriminate which pixels can be relied on in the WET map and which pixels are likely to be subject to range mixing. In this work we demonstrate that these higher order images can be used to create a mask to remove pixels that are potentially subject to range mixing and potentially have unreliable WET values.

Research on spectral reflectance reconstruction based on compressive sensing by gradual modulation wheel

Research on spectral reflectance reconstruction based on compressive sensing by gradual modulation wheel

Periodic Measurements of Passive Proton Beam Width Using Radiochromic Film in Fixed Gantry System

Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel is used to create a spread-out Bragg peak, but the distribution at the patient position may change due to positional deviation of the incident beam. Therefore, assessment of the incident position of the beam is very important even in the scattering method. To investigate the width and distribution of the proton beam before entering the RMW, a radiochromic film was installed at the outlet of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport pipe and the entrance of the monitor detector were measured using films. The beam width was measured from the full width at half maximum of the profile obtained from the distribution. Measurements were conducted every month for 10 months. Results: Beams of widths ranging from 1.82 to 2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction were outputted from the exit of the transport pipe. Beams of widths ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31 mm in the vertical direction were outputted from the entrance of the monitor detector. The maximum width fluctuation for 10 months was 0.55 mm in the horizontal direction and 1.26 mm in the vertical direction at the entrance of the monitor detector. Conclusions: The distribution was obtained before the proton beam was scattered by the scatterer, and then we propose a method to periodically measure and monitor the changes in the beam distributions every month.

A quality assurance for respiratory gated proton irradiation with range modulation wheel.

The purpose of this study was to provide periodic quality assurance (QA) methods for respiratory‐gated proton beam with a range modulation wheel (RMW) and to clarify the characteristics and long‐term stability of the respiratory‐gated proton beam. A two‐dimensional detector array and a solid water phantom were used to measure absolute dose, spread‐out Bragg peak (SOBP) width and proton range for monthly QA. SOBP width and proton range were measured using an oblique incidence beam to the lateral side of a solid water phantom and compared between with and without a gating proton beam. To measure the delay time of beam‐on/off for annual QA, we collected the beam‐on/off signals and the dose monitor‐detected pulse. We analyzed the results of monthly QA over a 15‐month period and investigated the delay time by machine signal analysis. The dose deviations at proximal, SOBP center and distal points were −0.083 ± 0.25%, 0.026 ± 0.20%, and −0.083 ± 0.35%, respectively. The maximum dose deviation between with and without respiratory gating was −0.95% at the distal point and other deviations were within ±0.5%. Proximal and SOBP center doses showed the same trend over a 15‐month period. Delay times of beam‐on/off for 200 MeV/SOBP 16 cm were 140.5 ± 0.8 ms and 22.3 ± 13.0 ms, respectively. Delay times for 160 MeV/SOBP 10 cm were 167.5 ± 15.1 ms and 19.1 ± 9.8 ms. Our beam delivery system with the RMW showed sufficient stability for respiratory‐gated proton therapy and the system did not show dependency on the energy and the respiratory wave form. The delay times of beam‐on/off were within expectations. The proposed QA methods will be useful for managing the quality of respiratory‐gated proton beams and other beam delivery systems.

Timing resolution for an optical fibre-based detector in a 74 MeV proton therapy beam

A Terbium activated Gadolinium Oxysulfide (Gd2O2S:Tb)-filled optical fibre sensor was developed and tested as a proton therapy beam dosimeter on a 74 MeV proton beam. Tests were carried out at the TRIUMF proton therapy centre, where a passively scattered beam is used for treatment. To create a clinically relevant spread-out Bragg peak, a modulator wheel with steps of varying thickness is employed. To determine the sensor’s response in a 23 mm spread out Bragg peak, the sensor signal was sampled at depth intervals of 0.79 mm along the beam axis in a water phantom. The resulting data showed a periodic variation in the signal corresponding to the rotation of the modulator wheel and related to the depth in water of the detector. This timing resolution in the sensor response could find application in quality assurance for modulated proton beams.

Erratum to: Depth Dose Measurement using a Scintillating Fiber Optic Dosimeter for Proton Therapy Beam of the Passive-Scattering Mode Having Range Modulator Wheel

The affiliation of Ui-Jung Hwang was incorrect. It should be corrected as “Department of Radiation Oncology, Chungnam National University Hospital, Daejeon 35015, Korea”.

Depth Dose Measurement using a Scintillating Fiber Optic Dosimeter for Proton Therapy Beam of the Passive-Scattering Mode Having Range Modulator Wheel

To apply a scintillating fiber dosimetry system to measure the range of a proton therapy beam, a new method was proposed to correct for the quenching effect on measuring an spread out Bragg peak (SOBP) proton beam whose range is modulated by a range modulator wheel. The scintillating fiber dosimetry system was composed of a plastic scintillating fiber (BCF-12), optical fiber (SH 2001), photo multiplier tube (H7546), and data acquisition system (PXI6221 and SCC68). The proton beam was generated by a cyclotron (Proteus-235) in the National Cancer Center in Korea. It operated in the double-scattering mode and the spread out of the Bragg peak was achieved by a spinning range modulation wheel. Bragg peak beams and SOBP beams of various ranges were measured, corrected, and compared to the ion chamber data. For the Bragg peak beam, quenching equation was used to correct the quenching effect. On the proposed process of correcting SOBP beams, the measured data using a scintillating fiber were separated by the Bragg peaks that the SOBP beam contained, and then recomposed again to reconstruct an SOBP after correcting for each Bragg peak. The measured depth-dose curve for the single Bragg peak beam was well corrected by using a simple quenching equation. Correction for SOBP beam was conducted with a newly proposed method. The corrected SOBP signal was in accordance with the results measured with an ion chamber. We propose a new method to correct for the SOBP beam from the quenching effect in a scintillating fiber dosimetry system. This method can be applied to other scintillator dosimetry for radiation beams in which the quenching effect is shown in the scintillator.

Technical Note: An approach to building a Monte Carlo simulation model for a double scattering proton beam system.

The purpose of this study was to demonstrate and develop a Monte Carlo (MC) simulation model for a passive double scattering compact proton therapy system based on limited information of the mechanical components. We built a virtual machine source model (VMSM) which included a detailed definition of each beam-modifying component in the nozzle. Conceptually, it is similar to the conventional virtual analytical source model (VASM), except that the numerical machine nozzle or beamline is constructed in the VMSM, whereas in the VASM analytical parameters characterizing the energy spectrum and source fluence distribution are sought. All major beam shaping components were included in the VMSM and the model simulates interactions of the beam with a rotating range modulation wheel (RMW) combined with the beam current modulation. The RMWs, the first and second scatterer in the system were generated and tuned to reproduce measurement data as closely as possible. To validate the model, we compared the percent depth dose curves, spread out Bragg peaks (SOBPs) and lateral profiles against measured commissioning beam data. The agreement of beam range between the MC calculation and measurement was within 1 mm for all beam options. The distal-falloff length was in good agreement as well (<1 mm for the large and deep groups, <1.5 mm for the small group). Agreement to within 2.5 mm of measured SOBP widths was obtained for all MC calculations. For lateral profiles, differences were found to be less than 2 mm. We demonstrated that with limited geometrical information it is possible to build an acceptable source model for MC simulations of a passive double scattering compact proton therapy system. The agreement between the measurements and the MC model provides validation for use of the model for further studies of the dosimetric effects in patient treatments.

Time-resolved diode dosimetry calibration through Monte Carlo modeling for invivo passive scattered proton therapy range verification.

PurposeOur group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water‐equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam‐specific response to WEPL fit for the selected ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water‐equivalent plastic. This necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time‐resolved diode dosimetry technique.MethodsMeasurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The ‘scout’ beams were then applied in the simulation environment to simulated water‐equivalent plastic, a CT of water‐equivalent plastic, and a patient CT data set to assess uncertainty.ResultsSimulated detector response in water‐equivalent plastic was validated against measurements for ‘scout’ spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie.ConclusionFeasibility has been shown for performing the calibration of the detector response for three ‘scout’ beams through simulation for the time‐resolved diode dosimetry technique in passive scattered proton delivery.