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This study aimed to clarify the dosimetric impact of calibration beam quality for calibration coefficients of the absorbed dose to water for an ionization chamber in an on-site dosimetry audit. Institution-measured doses of 200 photon and 184 electron beams were compared with the measured dose using one year data before and after the calibration of the ionization chamber used. For photon and electron reference dosimetry, the agreements of the institution-measured dose against two measured doses in this audit were evaluated using the calibration coefficients determined using 60Co (${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$) and linear accelerator (linac) (${N}_{D,\mathrm{w},Q}$) beams. For electron reference dosimetry, the agreement of two institution-measured doses against the measured dose was evaluated using${N}_{D,\mathrm{w},Q}$. Institution-measured doses were evaluated using direct- and cross-calibration coefficients. For photon reference dosimetry, the mean differences and standard deviation (SD) of institution-measured dose against the measured dose using ${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$ and ${N}_{D,\mathrm{w},Q}$ were -0.1% ± 0.4% and -0.3% ± 0.4%, respectively. For electron reference dosimetry, the mean differences and SD of institution-measured dose using the direct-calibration coefficient against the measured dose using ${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$ and ${N}_{D,\mathrm{w},Q}$ were 1.3% ± 0.8% and 0.8% ± 0.8%, respectively. Further, the mean differences and SD of institution-measured dose using the cross-calibration coefficient against the measured dose using ${N}_{D,\mathrm{w},Q}$ were -0.1% ± 0.6%. For photon beams, the dosimetric impact of introducing calibration coefficients determined using linac beams was small. For electron beams, it was larger, and the measured dose using ${N}_{D,\mathrm{w},Q}$ was most consistent with the institution-measured dose, which was evaluated using a cross-calibration coefficient.

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BACKGROUND: The C Q $C_Q$ formalism proposed by Watson et al. allows users of the INTRABEAM (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy system to accurately determine the absorbed dose to water, in the absence of a primary dosimetry standard. However, all published C Q $C_Q$ values are for PTW 34013 ionization chambers calibrated in a TW30 reference beam, traceable to PTB (Germany). For North American users, it would be advantageous to have C Q $C_Q$ data for chambers calibrated in a kV reference beam maintained by the National Institute of Standards and Technology (NIST). PURPOSE: In this work, we determine C Q $C_Q$ for a PTW 34013 chamber calibrated in three NIST-traceable reference beams: M30, L40, and L50. METHODS: Using available photon spectra data for M30, L40, and L50 reference beam qualities, Monte Carlo simulations using EGSnrc were performed to calculate the ratio of the absorbed dose to the PTW 34013 chamber air cavity to air-kerma ( D gas / K a $D_{\textrm {gas}}/K_a$ ) for these beams. From this ratio, C Q $C_Q$ as a function of depth in water was determined. The effect of the use of a buildup foil was also investigated. An uncertainty analysis considering both the Type A and Type B uncertainties in the calculation of C Q $C_Q$ was performed. RESULTS: The largest difference in C Q $C_Q$ was found between L50 and TW30, with a relative decrease of 1.4% (no buildup) to 1.6% (buildup). For M30 and L40, the differences were minimal compared with measurement uncertainties. CONCLUSIONS: We report C Q $C_Q$ values for three NIST-traceable kV reference beams. This study reinforces the feasibility of adapting the Watson et al. methodology using different kV reference beams, facilitating the use of INTRABEAM in North America and ensuring the continuity and accuracy of dosimetry standards in intraoperative radiation therapy.

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BACKGROUND/AIM: There are only a few studies on dosimetry with ultrahigh-dose-rate (uHDR) scanned carbon-ion beams. This study investigated the characteristics of four types of ionization chambers for the uHDR beam. MATERIALS AND METHODS: We employed a newly developed large-plane parallel chamber to monitor a 208.3-MeV/u uHDR scanned carbon-ion beam with a 110-Gy/s average dose rate. The ionization chambers used were the Advanced Markus chamber (AMC), PinPoint 3D chamber (PPC), Farmer chamber (FC), and large-plane parallel chamber (StingRay). The AMC and StingRay surfaces and the PPC and FC geometric centers were aligned to the radiation isocenter using treatment room lasers. Using the voltage range stated in the instruction manuals, we obtained the saturation curves of the chambers. From these curves, we obtained the ion recombination correction factors using the two-voltage and three-voltage linear methods. The dose linearity was evaluated using five measurement points, and the chamber repeatability was verified by conducting repeated measurements for different dose values. RESULTS: Although all chambers, except for AMC, reached saturation when specified voltages were applied, they exhibited excellent linearity for different dose values. The ion recombination correction factors of the AMC obtained using the aforementioned linear methods were nearly 1. Additionally, all chambers exhibited excellent repeatability. Although the standard deviation of the PPC for the lowest dose was ~1.5%, those of all the other chambers were <1.0%. CONCLUSION: All ionization chambers can be used for measuring the relative dose, and absolute dose can be conveniently measured using the AMC with an uHDR carbon-ion scanned beam.

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Objective. To enhance the investigations on MC calculated beam quality correction factors of thimble ionization chambers from high-energy brachytherapy sources and to develop reliable reference conditions in source and detector setups in water.Approach. The response of five different ionization chambers from PTW-Freiburg and Standard Imaging was investigated for irradiation by a high dose rate Ir-192 Flexisource in water. For a setup in a Beamscan water phantom, Monte Carlo simulations were performed to calculate correction factors for the chamber readings. After exact positioning of source and detector the absorbed dose rate at the TG-43 reference point at one centimeter nominal distance from the source was measured using these factors and compared to the specification of the calibration certificate. The Monte Carlo calculations were performed using the restricted cema formalism to gain further insight into the chamber response. Calculations were performed for the sensitive volume of the chambers, determined by the methods currently used in investigations of dosimetry in magnetic fields.Main results. Measured dose rates and values from the calibration certificate agreed within the combined uncertainty (k= 2) for all chambers except for one case in which the full air cavity was simulated. The chambers showed a distinct directional dependence. With the restricted cema formalism calculations it was possible to examine volume averaging and energy dependence of the perturbation factors contributing to the beam quality correction factor also differential in energy.Significance. This work determined beam quality correction factors to measure the absorbed dose rate from a brachytherapy source in terms of absorbed dose to water for a variety of ionization chambers. For the accurate dosimetry of brachytherapy sources with ionization chambers it is advisable to use correction factors based on the sensitive volume of the chambers and to take account for the directional dependence of chamber response.

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Objective.Accurate reference dosimetry with ionization chambers (ICs) relies on correcting for various influencing factors, including ion recombination. Theoretical frameworks, such as the Boag and Jaffe theories, are conventionally used to describe the ion recombination correction factors. Experimental methods are time consuming, the applicability may be limited and, in some cases, impractical to be used in clinical routine. The development of simulation tools becomes necessary to enhance the understanding of recombination under circumstances that may differ from conventional use. Before progressing, it is crucial to benchmark novel approaches to calculate ion recombination losses under known conditions. In this study, we introduce and validate a versatile simulation tool based on a Monte Carlo scheme for calculating initial and volume ion recombination correction factors in air-filled ICs exposed to ion beams with clinical dose rates.Approach. The simulation includes gaussian distribution of ion positions to model the distribution of charge carriers along the chamber volume. It accounts for various physical transport effects, including drift, diffusion, space charge screening and free electron fraction. To compute ion recombination, a Monte Carlo scheme is used due to its versatility in multiple geometries, without exhibiting convergence problems associated with numerically solved procedures.Main results. The code is validated in conventional dose rates against Jaffe's theory for initial recombination and Boag's theory for volume recombination based on parameters derived from experimental data including proton, helium and carbon ion beams measured with a plane parallel IC.Significance. The simulation demonstrates excellent agreement, typically 0.05% or less relative difference with the theoretical and experimental data. The current code successfully predicts ion recombination correction factors, in a large variety of ion beams, including different temporal beam structures.

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An Addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water is presented for electron beams with energies between 4 MeV and 22 MeV ( 1.70 cm ≤ R 50 ≤ 8.70 cm $1.70\nobreakspace {\rm cm} \le R_{\text{50}} \le 8.70\nobreakspace {\rm cm}$ ). This updated formalism allows simplified calibration procedures, including the use of calibrated cylindrical ionization chambers in all electron beams without the use of a gradient correction. New k Q $k_{Q}$ data are provided for electron beams based on Monte Carlo simulations. Implementation guidance is provided. Components of the uncertainty budget in determining absorbed dose to water at the reference depth are discussed. Specifications for a reference-class chamber in electron beams include chamber stability, settling, ion recombination behavior, and polarity dependence. Progress in electron beam reference dosimetry is reviewed. Although this report introduces some major changes (e.g., gradient corrections are implicitly included in the electron beam quality conversion factors), they serve to simplify the calibration procedure. Results for absorbed dose per linac monitor unit are expected to be up to approximately 2 % higher using this Addendum compared to using the original TG-51 protocol.

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224Ra (t1/2 = 3.6 d) has been widely used as a tracer in environmental water research. Here, we present a new method for measuring 224Ra in natural waters using a pulsed ionization chamber (PIC)-based radon detector. This method is based on the measurement of the 224Ra daughter isotope 220Rn (thoron) after reaching secular equilibrium within 7 min. Radium isotopes are concentrated on ''Mn-fibers'' before measurement of 220Rn, which can be distinguished from 222Rn by the difference in their half-lives. The measurement efficiency of the method is 0.20 ± 0.01 cps/Bq at an optimum airflow rate of 1.0 L/min and a water/Mn-fiber weight ratio of 1.0. Results from natural water samples obtained by this method agree well with analysis via RaDeCC, an established technique for 224Ra assessments. Since the PIC system is lighter compared to RaDeCC, easier to operate, and does not require the usage of helium carrier gas and desiccant, this method is recommended for in-situ 224Ra measurement in long-term fieldwork with limited logistical support.

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Objectives.To derive a collection efficiency formula,fGauss, for cylindrical ionization chambers in pulsed radiation beams from a volume recombination model of Boaget al(1996Phys. Med. Biol.41885-97) including free electrons. To validatefGaussand a parallel plate chamber formulafexpusing an ion transport code and calculate changes in collection efficiencies caused by electric field charge screening at 0.1-100 mGy doses-per-pulse. And to determine collection efficienciesCE∞predicted at infinite voltage in the absence of avalanche effects by fitting scaled formulae to efficiencies computed for 100-400 V chamber voltages and 10 and 100 mGy doses-per-pulse.Approach.Calculations were performed for an idealized parallel plate chamber with 2 mm electrode separationd, and for an idealized cylindrical chamber with 0.5 and 2.333 mm inner and electrode radiirinandrout.Main results.fGaussandfexppredict the same collection efficiencies for cylindrical and parallel plate chambers satisfyingd2=(rout2-rin2)ln(rout/rin)/2, an equivalence condition met by the chambers studied. Without charge screening, efficiencies computed using the code equalledfGaussandfexp. With screening, efficiencies changed by ⩽0.03%, ⩽1.1% and ⩽21.3% at 1, 10 and 100 mGy doses-per-pulse, and differed between the chambers by ⩽0.9% and ⩽19.6% at ⩽10 and 100 mGy dose-per-pulse. For fits offexpandfGauss,CE∞values were ⩽1.2% and ⩽17.6% from unity at 10 and 100 mGy per pulse respectively, closer than for other formulae tested.Significance.Allowing for screening,fGaussandfexpdescribed computed collection efficiencies to within 0.03%, 1.1% and 21.3% at doses-per-pulse ⩽1, 10 and 100 mGy. Equivalence of the two chambers broke down at 100 mGy per pulse. Departures ofCE∞values from unity suggest that collection efficiencies determined experimentally by fittingfGaussorfexpto readings made at multiple voltages will be accurate to within 1.2% and 17.6% at 10 and 100 mGy per pulse respectively.

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A new 90Y SIR-Spheres delivery kit (SIROS D-vial and shield) has been introduced with a different physical form from the legacy V-Vial kit. Here, we establish the dose calibrator settings and exposure-rate-to-activity conversion factor to assay 90Y SIR-Spheres activity in the new SIROS kit. Methods: Eight D-vials with initial 90Y activities from 1.2 to 6.6 GBq within acrylic shields were assayed with dose calibrators and exposure-rate meters until activities decayed to approximately 0.1 GBq. The dose calibrator settings resulting in the lowest median activity errors and the best-fit slope of exposure rate versus activity were identified. Results: SIROS D-vial 90Y activity can be accurately and reliably estimated directly using setting 51 × 10 on both the CRC-15R and the CRC-55tR dose calibrators (errors within ±0.5%) and indirectly with an exposure-rate reading at 30 cm using conversion factor 0.664 ± 0.003 GBq/(mR/h) (R 2 = 0.985). Conclusion: Dose calibrator settings and exposure-rate-to-activity conversion factor for 90Y activity assays with new SIROS kit should be updated from legacy V-Vial parameters to avoid an approximately 10% underestimation.

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Reliable dosimetry systems are crucial for radiobiological experiments either to quantify the biological consequences of ionizing radiation or to reproduce results by other laboratories. Also, they are essential for didactic purposes in the field of radiation research. Professional dosemeters are expensive and difficult to use in exposure facilities with closed exposure chambers. Consequently, a simple, inexpensive, battery-driven dosemeter was developed that can be easily built using readily available components. Measurements were performed to validate its readout with photons of different energy and dose rate and to demonstrate the applicability of the dosemeter. It turned out that the accuracy of the dose measurements using the developed dosemeter was better than 10%, which is satisfactory for radiobiological experiments. It is concluded that this dosemeter can be used both for determining the dose rates of an exposure facility and for educational purposes.

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PURPOSE: To develop and characterize a large-area multi-strip ionization chamber (MSIC) for efficient measurement of proton beam spot size and position at a synchrotron-based proton therapy facility. METHODS AND MATERIALS: A 420 mm x 320 mm MSIC was designed with 240 vertical strips and 180 horizontal strips at 1.75 mm pitch. The MSIC was characterized by irradiating a grid of proton spots across 17 energies from 73.5 MeV to 235 MeV and comparing to simultaneous measurements made with a reference Gafchromic EBT3 film. Beam profiles, spot sizes, and positions were analyzed. Short term measurement stability and sensitivity were evaluated. RESULTS: Excellent agreement was demonstrated between the MSIC and EBT3 film for both spot size and position measurements. Spot sizes agreed within ± 0.18 mm for all energies tested. Measured beam spot positions agreed within ± 0.17 mm. The detector showed good short term measurement stability and low noise performance. CONCLUSION: The large-area MSIC enables efficient and accurate proton beam spot characterization across the clinical energy range. The results indicate the MSIC is suitable for pencil beam scanning proton therapy commissioning and quality assurance applications requiring fast spot size and position quantification.

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Objective. In current clinical practice for quality assurance (QA), intensity modulated proton therapy (IMPT) fields are verified by measuring planar dose distributions at one or a few selected depths in a phantom. A QA device that measures full 3D dose distributions at high spatiotemporal resolution would be highly beneficial for existing as well as emerging proton therapy techniques such as FLASH radiotherapy. Our objective is to demonstrate feasibility of 3D dose measurement for IMPT fields using a dedicated multi-layer strip ionization chamber (MLSIC) device.Approach.Our developed MLSIC comprises a total of 66 layers of strip ion chamber (IC) plates arranged, alternatively, in thexandydirection. The first two layers each has 128 channels in 2 mm spacing, and the following 64 layers each has 32/33 IC strips in 8 mm spacing which are interconnected every eight channels. A total of 768-channel IC signals are integrated and sampled at a speed of 6 kfps. The MLSIC has a total of 19.2 cm water equivalent thickness and is capable of measurement over a 25 × 25 cm2field size. A reconstruction algorithm is developed to reconstruct 3D dose distribution for each spot at all depths by considering a double-Gaussian-Cauchy-Lorentz model. The 3D dose distribution of each beam is obtained by summing all spots. The performance of our MLSIC is evaluated for a clinical pencil beam scanning (PBS) plan.Main results.The dose distributions for each proton spot can be successfully reconstructed from the ionization current measurement of the strip ICs at different depths, which can be further summed up to a 3D dose distribution for the beam. 3D Gamma Index analysis indicates acceptable agreement between the measured and expected dose distributions from simulation, Zebra and MatriXX.Significance.The dedicated MLSIC is the first pseudo-3D QA device that can measure 3D dose distribution in PBS proton fields spot-by-spot.

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A set of nozzle equipment for proton therapy is currently under development at China Institute of Atomic Energy (CIAE). To facilitate the off-line commissioning of the whole equipment, a set of ionization chamber signal generation system, known as the test electronics, was designed. The results showed that the system can simulate the beam position, beam fluence (which exhibits a positive correlation with the dose), and other related analog signals generated by the proton beam when it traverses the ionization chamber. Moreover, the accuracy of the simulated beam position is within ± 0.33 mm, and the accuracy of the simulated beam fluence signal is within ± 1%. The test electronics can output analog signals representing environmental parameters. The test electronics meets the design requirements, which can be used for the commissioning of the nozzle system as well as the treatment control system without the presence of the proton beam.

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BACKGROUND: Ionization chambers play an essential role in dosimetry measurements for kilovoltage (kV) x-ray beams. Despite their widespread use, there is limited data on the absolute values for the polarity correction factors across a range of commonly employed ionization chambers. PURPOSE: This study aimed to investigate the polarity effects for five different ionization chambers in kV x-ray beams. METHODS: Two plane-parallel chambers being the Advanced Markus and Roos and three cylindrical chambers; 3D PinPoint, Semiflex and Farmer chamber (PTW, Freiburg, Germany), were employed to measure the polarity correction factors. The kV x-ray beams were produced from an Xstrahl 300 unit (Xstrahl Ltd., UK). All measurements were acquired at 2 cm depth in a PTW-MP1 water tank for beams between 60 kVp (HVL 1.29 mm Al) and 300 kVp (HVL 3.08 mm Cu), and field sizes of 2-10 cm diameter for 30 cm focus-source distance (FSD) and 4 × 4 cm2 - 20 × 20 cm2 for 50 cm FSD. The ionization chambers were connected to a PTW-UNIDOS electrometer, and the polarity effect was determined using the AAPM TG-61 code of practice methodology. RESULTS: The study revealed significant polarity effects in ionization chambers, especially in those with smaller volumes. For the plane-parallel chambers, the Advanced Markus chamber exhibited a maximum polarity effect of 2.5%, whereas the Roos chamber showed 0.3% at 150 KVp with the 10 cm circular diameter open-ended applicator. Among the cylindrical chambers at the same beam energy and applicator, the Pinpoint chamber exhibited a 3% polarity effect, followed by Semiflex with 1.7%, and Farmer with 0.4%. However, as the beam energy increased to 300 kVp, the polarity effect significantly increased reaching 8.5% for the Advanced Markus chamber and 13.5% for the PinPoint chamber at a 20 × 20 cm2 field size. Notably, the magnitude of the polarity effect increased with both the field size and beam energy, and was significantly influenced by the size of the chamber's sensitive volume. CONCLUSIONS: The findings demonstrate that ionization chambers can exhibit substantial polarity effects in kV x-ray beams, particularly for those chambers with smaller volumes. Therefore, it is important to account for polarity corrections when conducting relative dose measurements in kV x-ray beams to enhance the dosimetry accuracy and improve patient dose calculations.

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Objective. In this experimental work we compared the determination of absorbed dose to water using four ionization chambers (ICs), a PTW-34045 Advanced Markus, a PTW-34001 Roos, an IBA-PPC05 and a PTW-30012 Farmer, irradiated under the same conditions in one continuous- and in two pulsed-scanned proton beams.Approach. The ICs were positioned at 2 cm depth in a water phantom in four square-field single-energy scanned-proton beams with nominal energies between 80 and 220 MeV and in the middle of 10 × 10 × 10 cm3dose cubes centered at 10 cm or 12.5 cm depth in water. The water-equivalent thickness (WET) of the entrance window and the effective point of measurement was considered when positioning the plane parallel (PP) ICs and the cylindrical ICs, respectively. To reduce uncertainties, all ICs were calibrated at the same primary standards laboratory. We used the beam quality (kQ) correction factors for the ICs under investigation from IAEA TRS-398, the newly calculated Monte Carlo (MC) values and the anticipated IAEA TRS-398 updated recommendations.Main results. Dose differences among the four ICs ranged between 1.5% and 3.7% using both the TRS-398 and the newly recommendedkQvalues. The spread among the chambers is reduced with the newlykQvalues. The largest differences were observed between the rest of the ICs and the IBA-PPC05 IC, obtaining lower dose with the IBA-PPC05.Significance. We provide experimental data comparing different types of chambers in different proton beam qualities. The observed dose differences between the ICs appear to be related to inconsistencies in the determination of thekQvalues. For PP ICs, MC studies account for the physical thickness of the entrance window rather than the WET. The additional energy loss that the wall material invokes is not negligible for the IBA-PPC05 and might partially explain the lowkQvalues determined for this IC. To resolve this inconsistency and to benchmark MC values,kQvalues measured using calorimetry are needed.

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Background and purpose: For dosimetry in magnetic resonance (MR) guided radiotherapy, assessing the magnetic field correction factors of air-vented ionization chambers is crucial. Novel MR-optimized chambers reduce MR-imaging artefacts, enhancing their quality assurance utility. This study aimed to characterize two new MR-optimized ionization chambers with sensitive volumes of 0.07 and 0.016 cm3 regarding magnetic field correction factors and intra-type variation and compare them to their conventional counterparts. Material and methods: Five chambers of each type were evaluated in a water phantom, using a clinical linear accelerator and an electromagnet, as well as a 1.5 T MR-linac system. The magnetic field correction factor kB→,Q, addressing the change of response caused by a magnetic field, was assessed together with its intra-type variation. MR-optimized and conventional chambers were compared using a Mann-Whitney U-Test. Results: Considering 1.5 T and a perpendicular chamber orientation, we observed significant differences in the magnetic field-induced change in chamber reading between the two 0.016 cm3 chamber versions (p = 0.03). For a 7 MV beam, MR-optimized chambers (0.016/0.07 cm3) showed kB→,Q values of 1.0426(66) and 1.0463(44), compared to 1.0319(53) and 1.0480(41) of their conventional counterparts. In anti-parallel orientation, kB→,Q was 1.0012(69) and 0.9863(49) for the MR-optimized chambers. The average intra-type variation of kB→,Q over all chamber types was 0.3%. Conclusion: Magnetic field correction factors were successfully determined for four ionization chamber types, including two new MR-optimized versions, allowing their use in MR-linac absolute dosimetry. Evaluation of the intra-type variation enabled the assessment of their contribution to the uncertainty of tabulated kB→,Q.

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A parallel-plate ionization chamber (PPC) with a nominal volume of 8.16 cm³ was developed based on theoretically simulated design parameters. Its purpose is to serve as a transfer standard for dosimetry in a beta radiation field. The entrance window of the PPC consists of an aluminized Mylar sheet with a thickness of 1.4 mg/cm2. The collecting and guard electrodes are created by applying a graphite coating on a Poly Methyl Methacrylate (PMMA) substrate with a thickness of 5 mm. The nominal sheet resistance of the graphite-coated PMMA substrate was measured using a four-probe technique and found to be approximately 800 Ω per square (Ω/□). Dosimetric characterization of the PPC was performed in the ISO 6980 reference beta radiation field, utilizing 90Sr-90Y and 85Kr beta radiation sources. The assessment included studies on short-term stability, linearity, current-to-voltage characteristics, stabilization time, and leakage current. The PPC was calibrated and established as a transfer standard using the 'Extrapolation Ionization Chamber,' recognized as an absolute standard for dose to tissue in 90Sr-90Y and 85Kr beta sources within the laboratory. The calibration coefficient of the PPC indicates an energy dependence of 0.6 % for 90Sr-90Y and 85Kr beta sources.

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The time response characteristic of the detector is crucial in radiation imaging systems. Unfortunately, existing parallel plate ionization chamber detectors have a slow response time, which leads to blurry radiation images. To enhance imaging quality, the electrode structure of the detector must be modified to reduce the response time. This paper proposes a gas detector with a grid structure that has a fast response time. In this study, the detector electrostatic field was calculated using COMSOL, while Garfield++ was utilized to simulate the detector's output signal. To validate the accuracy of simulation results, the experimental ionization chamber was tested on the experimental platform. The results revealed that the average electric field intensity in the induced region of the grid detector was increased by at least 33%. The detector response time was reduced to 27% -38% of that of the parallel plate detector, while the sensitivity of the detector was only reduced by 10%. Therefore, incorporating a grid structure within the parallel plate detector can significantly improve the time response characteristics of the gas detector, providing an insight for future detector enhancements.

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The reference dose for clinical proton beam therapy is based on ionization chamber dosimetry. However, data on uncertainties in proton dosimetry are lacking, and multifaceted studies are required. Monte Carlo simulations are useful tools for calculating ionization chamber dosimetry in radiation fields and are sensitive to the transport algorithm parameters when particles are transported in a heterogeneous region. We aimed to evaluate the proton transport algorithm of the Particle and Heavy Ion Transport Code System (PHITS) using the Fano test. The response of the ionization chamber f Q and beam quality correction factors k Q were calculated using the same parameters as those in the Fano test and compared with those of other Monte Carlo codes for verification. The geometry of the Fano test consisted of a cylindrical gas-filled cavity sandwiched between two cylindrical walls. f Q was calculated as the ratio of the absorbed dose in water to the dose in the cavity in the chamber. We compared the f Q calculated using PHITS with that of a previous study, which was calculated using other Monte Carlo codes (Geant4, FULKA, and PENH) under similar conditions. The flight mesh, a parameter for charged particle transport, passed the Fano test within 0.15%. This was shown to be sufficiently accurate compared with that observed in previous studies. The f Q calculated using PHITS were 1.116 ± 0.002 and 1.124 ± 0.003 for NACP-02 and PTW-30013, respectively, and the k Q were 0.981 ± 0.008 and 1.027 ± 0.008, respectively, at 150 MeV. Our results indicate that PHITS can calculate the f Q and k Q with high precision.

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The response time of a detector stands as a critical parameter in radiation imaging systems. However, the existing parallel plate ionization chamber detector manifests a noteworthy delay in response time, leading to the production of blurred radiation images. To enhance the image quality of radiation imaging systems, it becomes imperative to modify the electrode structure of the detector and consequently reduce the response time. We propose a gas ionization chamber detector incorporating a glass plate, resulting in a notably swift response time. The COMSOL software is employed to calculate the electric and weighting fields within the detector, while Garfield++ software is utilized to derive the output signal, including information on the response time. To validate the simulation data, an experimental ionization chamber underwent testing on a dedicated platform to acquire the output signal. The results revealed that the average electric field intensity in the induced region of the grid detector was increased by at least 10%. The detector response time was reduced to 50%-28% of that of the parallel plate detector. However, this improvement comes at the cost of a decrease in the detector's sensitivity. The incorporation of glass plates in a parallel plate detector offers a substantial improvement in the time response characteristics of a gas ionization chamber detector, thereby suggesting a valuable direction for future advancements in ionization chamber technology.