Radiophotoluminescent Glass Dosimeter Research Articles

Dose measurements with radiophotoluminescent glass dosimeters (GD- 352M and GD-302M) in therapeutic proton beams

Radiophotoluminescent glass dosimeters (RPLDs) are increasingly used, especially to measure the doses in therapeutic beams, but the reported data are mainly related to photon and electron beams, while the data for proton beams are limited and not always consistent.In this study, dose measurements were performed with two types of RPLDs: GD-352M and GD-302 M (Asahi Techno Glass Corporation). The dose dependence, long-term fading and response in different Spread out Bragg Peak (SOBP) configurations were evaluated. The dose dependence was measured in the middle of the SOBP for doses ranging from 1 Gy to 120 Gy and a linear dose response was shown for both types of RPLDs. The long-term fading of RPLDs irradiated with proton beams determined under normal ambient conditions over a period of one year is negligible. The GD-352M and GD-302M responses were evaluated in different configurations of the SOPB. The fluence-averaged (LETf) and dose-averaged (LETd) LET values at the positions of the dosimeters were calculated using the PHITS Monte Carlo code. GD-302 M results showed a small under-response compared to the doses provided by treatment planning system (TPS) (within 1.9 %). GD-352M showed an under-response compared to TPS doses for all investigated ranges and modulations with an average under-response of 20 %, indicating the need for correction factors. Both types showed a slight decrease in the response with an increase in the LET.

Effect of backscatter radiation on the occupational eye-lens dose.

We quantified the level of backscatter radiation generated from physicians' heads using a phantom. We also evaluated the shielding rate of the protective eyewear and optimal placement of the eye-dedicated dosimeter (skin surface or behind the Pb-eyewear). We performed diagnostic X-rays of two head phantoms: Styrofoam (negligible backscatter radiation) and anthropomorphic (included backscatter radiation). Radiophotoluminescence glass dosimeters were used to measure the eye-lens dose, with or without 0.07-mm Pb-equivalent protective eyewear. We used tube voltages of 50, 65 and 80kV because the scattered radiation has a lower mean energy than the primary X-ray beam. The backscatter radiation accounted for 17.3-22.3% of the eye-lens dose, with the percentage increasing with increasing tube voltage. Furthermore, the shielding rate of the protective eyewear was overestimated, and the eye-lens dose was underestimated when the eye-dedicated dosimeter was placed behind the protective eyewear. We quantified the backscatter radiation generated from physicians' heads. To account for the effect of backscatter radiation, an anthropomorphic, rather than Styrofoam, phantom should be used. Close contact of the dosimeter with the skin surface is essential for accurate evaluation of backscatter radiation from physician's own heads. To assess the eye-lens dose accurately, the dosimeter should be placed near the eye. If the dosimeter is placed behind the lens of the protective eyewear, we recommend using a backscatter radiation calibration factor of 1.2-1.3.

Accurate gamma-ray dose measurement up to 10 MeV by glass dosimeter with a sensitivity control filter for BNCT

Glass dosimeters are very useful and convenient detection elements in radiation dosimetry. In this study, this glass dosimeter was applied to a BNCT treatment field. Boron Neutron Capture Therapy (BNCT) is a next-generation radiation therapy that can selectively kill only cancer cells. In the BNCT treatment field, both neutrons and secondary gamma-rays are generated. In other words, it is a mixed radiation field of neutrons and gamma-rays. We thus proposed a novel method to measure only gamma-ray dose in the mixed field using two RPLGD (Radiophoto-luminescence Glass Dosimeter) and two sensitivity control filters in order to control the dose response of the filtered RPLGD to be proportional to the air kerma coefficients, even if the gamma-ray energy spectrum is unknown. As the filter material iron was selected, and it was finally confirmed that reproduction of the air kerma coefficients was excellent within an error of 5.3% in the entire energy range up to 10 MeV. In order to validate this method, irradiation experiments were carried out using standard gamma-ray sources. As the result, the measured doses were in acceptably good agreement with the theoretical calculation results by PHITS. In the irradiation experiment with a volume source in a nuclear fuel storage room, the measured dose rates showed larger compared with survey meter values. In conclusion, the results of the standard sources showed the feasibility of this method, however for the volume source the dependence of the gamma-ray incident angle on the dosimeter was found to be not neglected. In the next step, it will be necessary to design a thinner filter in order to suppress the effect of the incident angle.

Evaluation of a New Method for CyberKnife Treatment for Central Lung and Mediastinal Tumors by Tracheobronchial Tracking.

CyberKnife treatment for central lung tumors and mediastinal tumors can be difficult to perform with marker less. We aimed to evaluate a novel tracheobronchial-based method (ie, tracheobronchial tracking) for the purpose of minimally invasive CyberKnife treatment for central lung and mediastinal tumors. Five verification plans were created using an in-house phantom. Each plan included five irradiation sessions. The reference plan irradiated and tracked the simulated tumor (using the target tracking volume, TTV). Trachea plans tracked the simulated tracheo-bronchus and irradiated the simulated tumor and included two types of subplans: correlated plans in which the displacement of the simulated tracheobronchial and the simulated tumor were correlated, and non-correlated plans in which these factors were not correlated. Moreover, 15 mm and 25 mm TTVs were evaluated for each plan. The sin waveform and the patient's respiratory waveform were prepared as the respiratory model. Evaluations were performed by calculating the dose difference between the radiophotoluminescent glass dosimeter (RPLD)-generated mean dose values (generated by the treatment planning system, TPS) and the actual absorbed RPLD dose. Statistical analyses were performed to evaluate findings for each plan. Correlation and prediction errors were calculated for each axis of each plan using log files to evaluate tracking accuracy. Dose differences were statistically significant only in comparisons with the non-correlated plan. When evaluated using the sin waveform, the mean values for correlation and prediction errors in each axis and for all plans were less than 0.6 mm and 0.1 mm, respectively. In the same manner, they were less than 1.1 mm and 0.2 mm when evaluated using the patient's respiratory waveform. Our newly-developed tracheobronchial tracking method would be useful in facilitating minimally invasive CyberKnife treatment in certain cases of central lung and mediastinal tumors.

Eye lens dose in spine surgeons during myelography procedures: a dosimetry study

To determine the eye lens dose (3 mm dose equivalent [Hp(3)]) received by spine surgeons during myelography and evaluate the effectiveness of radiation-protective glasses and x-ray tube system positioning in reducing radiation exposure. This study included spine surgeons who performed myelography using over- or under-table x-ray tube systems. Hp(3) was measured for each examination using a radio-photoluminescence glass dosimeter (GD-352M) mounted on radiation-protective glass. This study identified significantly high Hp(3) levels, especially in the right eye lens in spinal surgeons. The median Hp(3) values in the right eye were 524 (391–719) and 58 (42–83) μSv/examination for over- and under-table x-ray tube systems, respectively. Further, Hp(3)AK, which was obtained by dividing the cumulative air kerma from Hp(3), was 8.09 (6.69–10.21) and 5.11 (4.06–6.31) μSv mGy−1 for the over- and under-table x-ray tube systems, respectively. Implementing radiation-protective glasses resulted in dose reduction rates of 54% (50%–57%) and 54% (51%–60%) for the over- and under-table x-ray tube systems, respectively. The use of radiation protection glasses significantly reduced the radiation dose in the eye lens during myelography, with the most effective measures being the combination of using radiation protection glasses and an under-table x-ray tube system.

Relative efficiency of radiophotoluminescent glass dosimeters in a scanning pencil proton beam

The increasing role of hadron therapy, and particularly of proton therapy, in cancer treatment requires dosimetric characterization of luminescent detectors in heavy charged particle beams. The ionization density, which is related to the linear energy transfer (LET), is changing when heavy charged particle is penetrating through a material. Therefore, it is crucial to evaluate how efficiency of the used dosimeters depends on the change in LET.The aim of this study was to evaluate relative efficiency of radiophotoluminescent (RPL) glass dosimeters (type GD-352M) in a clinical scanning pencil proton beam of 100 MeV and compare it to the results obtained with thermoluminescent (TL) dosimeters (type TLD-100). LETf and LETd at the selected dosimeter's position were evaluated and compared by two Monte Carlo codes (MCNP and PHITS). Linear dose response is precondition for the evaluation of dosimeter efficiency and first, dose response in proton beam was evaluated and compared with those in 60Co gamma ray field.Linear dose response up to 9 Gy was confirmed for RPLs in proton beam, and gamma ray field. For TLDs, supralinearity from about 5 Gy was observed. A constant relative efficiency is observed along the plateau (corresponding to LETf from 0.7 keV/μm to 1.7 keV/μm) of non-modulated proton beam with an average value 1.00 ± 0.02 for RPL and 0.97 ± 0.02 for TL dosimeters. Relative efficiency decrease of 10 % is observed for RPLs within the Bragg peak with LETf = 2.3 keV/μm. Future work will be focused on the evaluation of the efficiency for higher LET values using more energetic proton beams and precise positioning along the Bragg peak.

Radiation exposure in cone beam CT measured using a MOSFET and RPLGD dosimeter and Monte Carlo simulation in phantom.

Due to the wide application of the cone beam computed tomography (CBCT) in clinical practice, it is important to assess radiation dose of CBCT more accurately and efficiently in different clinical applications. This study aims to calculate effective and absorbed doses in CBCT measured in an anthropomorphic phantom using computer-based Monte Carlo (PCXMC) software, and to conduct comparative evaluations of MOSFET (metal- oxide- semiconductor field-effect transistor) and radiophotoluminescence glass dosimeters (RPLGD). Effective and absorbed organ doses are compared with those obtained using MOSFET and RPLGD dosimetry in an anthropomorphic phantom given the same exposure settings. Effective and absorbed organ doses from CBCT during scout and main projections are calculated using PCXMC and PCXMCRotation software, respectively. The mean effective dose from CBCT calculated using PCXMC software is 233.8μSv, while the doses calculated using dosimetry (MOSFET and RPLGD) are 266.67μSv and 268.78μSv, respectively. The X-ray source variation is 0.79%. The prescription limits based on the Friedman test for MOSFET and RPLGD pre-points (i.e., in an analytical analysis of diagnostic names in CBCT) are not statistically significant. The calculated correlation coefficient between MOSFET- and RPLGD-derived absorbed dose values with respect to a field of view CBCT parameter of 17×13.5 mm is r = 0.8623. The study demonstrates that the PCXMC software may be used as an alternative to MOSFET and RPLGD dosimetry for effective and absorbed organ dose estimation in CBCT conducted with a large FOV in an anthropomorphic phantom.

Dosimetric impact of deformable image registration using radiophotoluminescent glass dosimeters with a physical geometric phantom.

To study the dosimetry impact of deformable image registration (DIR) using radiophotoluminescent glass dosimeter (RPLD) and custom developed phantom with various inserts. The phantom was developed to facilitate simultaneous evaluation of geometric and dosimetric accuracy of DIR. Four computed tomography (CT) images of the phantom were acquired with four different configurations. Four volumetric modulated arc therapy (VMAT) plans were computed for different phantom. Two different patterns were applied to combination of four phantom configurations. RPLD dose measurement was combined between corresponding two phantom configurations. DIR-based dose accumulation was calculated between corresponding two CT images with two commercial DIR software and various DIR parameter settings, and an open source software. Accumulated dose calculated using DIR was then compared with measured dose using RPLD. The mean±standard deviation (SD) of dose difference was 2.71±0.23% (range, 2.22%-3.01%) for tumor-proxy and 3.74±0.79% (range, 1.56%-4.83%) for rectum-proxy. The mean±SD of target registration error (TRE) was 1.66±1.36mm (range, 0.03-4.43mm) for tumor-proxy and 6.87±5.49mm (range, 0.54-17.47mm) for rectum-proxy. These results suggested that DIR accuracy had wide range among DIR parameter setting. The dose difference observed in our study was 3% for tumor-proxy and within 5% for rectum-proxy. The custom developed physical phantom with inserts showed potential for accurate evaluation of DIR-based dose accumulation. The prospect of simultaneous evaluation of geometric and dosimetric DIR accuracy in a single phantom may be useful for validation of DIR for clinical use.

Silver-Neodymium Codoped Lithium Aluminum Metaphosphate Glasses for Radio-Photoluminescence Dosimeter.

Commercial radio-photoluminescence (RPL) glass dosimeters generally use Ag single-doped phosphate glass as a single-wavelength sensor. Now, a novel type of Ag–Nd-codoped phosphate glass has been developed, which can be applied to dual-wavelength or multi-wavelength RPL sensors, and can thus improve the accuracy and stability of RPL dosimeters. An anhydrous 99.5 (0.7LiPO3–0.3Al (PO3)3) −0.25Ag2O–0.25Nd2O3 glass was prepared and irradiated at different doses, and then the absorption, fluorescence, infrared transmission spectra, as well as fluorescence lifetimes were tested and analyzed. The results show that there is an energy transfer between the Ag defect center and Nd3+ ions, and the transfer efficiency using 380 nm excitation is greater than that using 310 nm excitation. Aside from the 650 nm fluorescence of the Ag defect center, strong 882 nm and 1054 nm fluorescences of Nd ions are exhibited. It is possible that these fluorescences would allow the developed Ag–Nd-codoped phosphate glass to be applied to new RPL glass sensors and dosimeters.

Design and fabrication of indigenous multi-rotational thorax phantom for patient-specific quality assurance of IMRT and VMAT

Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) are commonly used treatment modalities in external beam radiotherapy. Precise quality assurance is required for the clinical implementation of IMRT and VMAT to ensure the correct treatment delivery. Square slab phantom is used commonly in developing countries to measure the pre-treatment point dose measurements. The limitation of the slab phantom was that the detector was positioned on the central axis of the beam which caused difficulty in positioning of the chamber at off-axis of the beam and peripheral regions. The new indigenously multi-purpose multi-rotational phantom was fabricated with various chamber provisions in order to address the above challenge. Innovative devices always play a crucial role in radiotherapy to bring significant technological advancement to the field. The quality assurance Multi-Rotational Thorax (MRT) Phantom designing involved slice-wise modelling of an average adult thorax using Poly-methyl methacrylate (PMMA) to perform point dose absolute dosimetry using an ionization chamber and Radio-Photo-Luminescence Glass Dosimeter (RPLGD). The phantom consisted of 35 slices of PMMA material in an axial direction. Each slice had a dimension of 1 cm thickness, 35 cm length and 20 cm height. The phantom had provisions in the target region and multiple provisions in the lungs, heart, surface and spine. The unique manual rotation system was provided on the lungs as well as in the heart. The provisions were capable of holding the detectors such as ionization chambers and RPLGD. The response of the phantom to open the beam in various gantry angles was initially accessed with multiple gantry angles and then pre-treatment verification of IMRT and VMAT plans was also checked. The results showed that the MRT phantom had good capabilities for absolute point dosimetry. In the case of an open beam, multiple gantry angles, the maximum variations for both the detectors were within −1.9% when compared with the TPS dose. The maximum percentage variation on isocentre (T) for IMRT and VMAT between TPS and Semiflex chamber was 1.85%. Similarly, the maximum percentage variation was 1.92% between TPS and RPLGD on isocentre. For Semiflex chamber, maximum percentage variation on peripheral region was 2.68%. Similarly, for RPLGD maximum percentage variation was 2.76%. The overall difference between the measured values for both the detectors were less than 3%. The present dosimetric study concluded that the MRT phantom with a RPLGD and Semiflex chamber was suitable for routine IMRT and VMAT patient-specific QA purposes.

Analysis of the uncertainties in the dose audit system using radiophotoluminescent glass dosimeters in Japanese radiotherapy units

A dosimetry audit of radiotherapy units in Japan was performed using radiophotoluminescent glass dosimeters (RPLDs). This study analyses the uncertainties associated with the procedure for determining the absorbed dose by an RPLD from a high-energy photon beam in radiotherapy units. The absorbed dose is derived using six parameters: the indicated value given by the RPLD, the individual dosimeter sensitivity correction factor for each element, the calibration coefficient for the reference radiation quality, the correction factor for the radiation quality, the correction factor for the phantom material, and the correction factor of nonlinearity. The uncertainty of each parameter was estimated based on the ISO standard methodology, “Guide to the Expression of Uncertainty in Measurement.” The estimated combined standard uncertainty of the dose measured by RPLD was 1.4% under the reference condition. This value was compared to the standard deviation of the difference between the measured and intended doses obtained from the actual audit results (4447 beams from 577 hospitals) over 13 years. The average percentage difference between the measured and calculated doses under the reference condition was 0.4%, with a standard deviation (k = 1) of 1.3%. The results were consistent with the uncertainty estimated by this report and demonstrate the reliability of the RPLD dosimetry method.

Evaluation of a new acrylic-lead shielding device for peripheral dose reduction during cone-beam computed tomography.

To clarify the peripheral dose changes, especially in the eye lens and thyroid gland regions, using an acrylic-lead shield in cone-beam computed tomography (CBCT). The acrylic-lead shield consists of system walls and a system mat. The radiophotoluminescence glass dosemeter was set on the eye lens and thyroid gland regions on the RANDO phantom. The system mat was laid under the RANDO phantom ranging from the top of the head to the shoulders, and then, the system walls shielded the phantom's head. Additionally, the phantom was covered anteriorly with a band that had the same shielding ability as the system mat to cover the thyroid gland region. Protocols for CBCT imaging of the thoracic or pelvic region in clinical practice were used. The measurement was performed with and without the acrylic-lead shield. The dose to the eye lens region was reduced by 45% using the system wall. Conversely, the dose to the thyroid gland was unchanged. The use of the system mat reduced the dose to the thyroid gland region by 47%, and the dose to the eye lens was reduced by 22%. The dose to the eye lens region decreased to the background level using the system walls and mat. The newly proposed device using an acrylic-lead shield reduced the peripheral dose in CBCT imaging. Attention is focused on managing peripheral dose in image-guided radiation therapy. The peripheral dose reduction using the acrylic-lead shield is a new proposal in radiotherapy that has never been studied.

Geometrical effects on luminescent dosimeter energy response

Luminescent dosimeters are widely used in medical applications. For an optimal use of these dosimeters, comparative studies of their characteristics, under clinical radiations, are very useful. The purpose of this study is to establish the effect of dosimeter geometry on the luminescent dosimeter energy response for different clinical radiation beams. Monte Carlo simulations were used to calculate the energy response of three kinds of non-commercialized luminescent dosimeters. The dosimeters are: a) radiophotoluminescent glass dosimeter (RPLGD, typeFD-7 glass), b) thermoluminescent dosimeter (TLD, type LiF:Mg,Ti) and c) optically stimulated dosimeter (OSLD, type Al2O3:C).The studied dosimeters have cylindrical geometry with a thickness of 2mm and diameters ranging from 1 to 13 mm. The radiation beams were 70 kV X-ray beam, clinical photon beam of 15 MV and clinical electron beam of 9 MeV. This study confirms a non-negligible effect on the dosimeter geometry on its energy response for these beams.

Estimation of Eye Lens Dose during the Handling of Radiopharmaceuticals and Using X-ray Protective Goggles for Dose Reduction in Nuclear Medicine

The purposes of this study were to estimate the eye lens dose during the handling of radiopharmaceuticals and to validate the requirement of X-ray protective goggles in nuclear medicine. Simulated eye lens radiation exposure (3-mm dose equivalent rate) was measured using a radiophotoluminescent glass dosimeter (RPLD) positioned at distances of 30 and 60 cm from 99mTc, 111In, and 123I radiation sources. Reduction rates were evaluated for the following means of radiation protection: X-ray protective goggles (0.07-, 0.50-, and 0.75-mm lead equivalent), a syringe shield, and a lead glass plate. 3-mm dose equivalent rates without protection were obtained at 6.13±0.13 µSv/min/GBq for 99mTc, 23.08±0.19 µSv/min/GBq for 111In, and 11.07±0.11 µSv/min/GBq for 123I. Reduction rates for each source were over 90% for the syringe shield and the lead glass plate. The 0.75-mm lead equivalent X-ray protective goggles decreased the 3-mm dose equivalent rate by 68.8% for 99mTc, 60.6% for 111In, and 68.1% for 123I. Although the estimated eye lens equivalent dose during the handling of radiopharmaceuticals did not exceed the threshold dose, our results suggest that 0.75-mm lead equivalent X-ray protective goggles are needed to reduce the exposure of the lens while handling 99mTc, 111In, and 123I radiation sources.

In vivo dosimetry for testicular and scalp shielding in total skin electron therapy using a radiophotoluminescence glass dosimeter

Mycosis fungoides (MF) is a common, low-grade non-Hodgkin’s lymphoma of skin-homing T lymphocytes that can be treated via skin-directed radiotherapy. Our institution has implemented total skin electron therapy (TSET) with a 4.3 m source-to-surface distance (SSD) and 6 MeV electron beams with a beam spoiler. A 35-year-old male undergoing TSET desired to avoid radiotherapy-induced hair loss and temporary infertility; therefore, leakage dose to scalp and testicles was reduced with a special radiation shield composed of stacked lead sheets. The shields for the scalp and scrotal were of 3 mm and 6 mm, respectively. To assess leakage doses, a radiophotoluminescence glass dosimeter (RPLD) was placed at every fraction. The difference dose between the measured and prescribed dose at the calibration point was 2%. The top of the head and scrotal surface exhibited 18 cGy and 10 cGy, respectively. Thus, the dose to the scrotal surface was not beyond the testicular tolerance dose of 20 cGy. Results of semen analysis two months postradiotherapy were normal. There was no hair loss during or after radiation therapy. Therefore, the RPLD is a useful in vivo dosimeter that provides technical information on radiation shielding to allow for completion of TSET without hair loss or temporary infertility.

Use of optically stimulated luminescence dosimeter and radiophotoliminescent glass dosimeter for dose measurement in dual-source dual-energy computed tomography.

We aimed to evaluate properties of optically stimulated luminescence dosimeters (OSLDs) and radiophotoluminescent glass dosimeters (RPLDs) used in dual-source dual-energy (DE) computed tomography (DECT) dosimetry. Energy dependence was evaluated in single-energy (SE) and DE modes, and their relative dose responses differed by 3.8% and 6.6% under equivalent effective energy with OSLD and RPLD, respectively. Dose variation was evaluated using coefficients of variation of dose values from 10 dosimeters, and dose variation of OSLD and RPLD in SE mode ranged from 2.1 to 3.0% and from 2.1 to 2.8%, and those in the DE mode were 1.8 and 2.6%, respectively. Dose linearity was evaluated from 1 to 150mGy, and linear relationships of dose response were observed between the dosimeters and the ionization chamber (correlation coefficients ≥ 0.9991). Angular dependence was evaluated from - 90° to + 90°, and it was smaller in DE mode than in SE mode for OSLD. The normalized response of RPLD was higher at ± 30° and ± 60° and lower at - 90° in SE and DE modes. This study demonstrated both OSLD and RPLD can perform dosimetry in dual-source DECT with small influence of the properties of the dosimeters compared with that in SECT.

Measurement uncertainty analysis of radiophotoluminescent glass dosimeter reader system based on GD-352M for estimation of protection quantity

At the Korea Institute of Radiological and Medical Sciences, physical human phantoms were developed to evaluate various radiation protection quantities, based on the mesh-type reference computational phantoms of the International Commission on Radiological Protection. The physical human phantoms were fabricated such that a radiophotoluminescent glass dosimeter (RPLGD) with a Tin filter, namely GD-352M, could be inserted into them. A Tin filter is used to eliminate the overestimated signals in low-energy photons below 100 keV. The measurement uncertainty of the RPLGD reader system based on GD-352M should be analyzed for obtaining reliable protection quantities before using it for practical applications. Generally, the measurement uncertainty of RPLGD systems without Tin filters is analyzed for quality assurance of radiotherapy units using a high-energy photon beam. However, in this study, the measurement uncertainty of GD-352M was analyzed for evaluating the protection quantities. The measurement uncertainty factors in the RPLGD include the reference irradiation, regression curve, reproducibility, uniformity, energy dependence, and angular dependence, as described by the International Organization for Standardization (ISO). These factors were calculated using the Guide to the Expression of Uncertainty in Measurement method, applying ISO/ASTM standards 51261(2013), 51707(2015), and SS-ISO 22127(2019). The measurement uncertainties of the RPLGD reader system with a coverage factor of k = 2 were calculated to be 9.26% from 0.005 to 1 Gy and 8.16% from 1 to 10 Gy. A blind test was conducted to validate the RPLGD reader system, which demonstrated that the readout doses included blind doses of 0.1, 1, 2, and 5 Gy. Overall, the En values were considered satisfactory.

Determination of field output correction factors of radiophotoluminescence glass dosimeter and CC01 ionization chamber and validation against IAEA-AAPM TRS-483 code of practice.

To determine the field output correction factors of the radiophotoluminescence glass dosimeter (RPLGD) in parallel and perpendicular orientations with reference to CC01, the ionization chamber. The dose to a small water volume and the sensitive volume of the RPLGD and the IBA-CC01 were determined for 6-MV, 100-cm SAD, 10-cm depth using egs_chamber user-code. The RPLGD in perpendicular and parallel orientations to the beam axis were studied. The field output correction factors of each detector for 0.5×0.5 to 10×10cm2 field sizes were determined. These field output correction factors were validated by comparing field output factors against data determined from IAEA-AAPM TRS-483 code of practice. The field output correction factors of all detectors were within 5% for field sizes down to 0.8×0.8cm2. For 0.5×0.5cm2, the field output correction factors of CC01, RPLGD in perpendicular and parallel orientations differed from unity by 14%, 19%, and 5%, respectively. The percentage difference between field output factors determined using RPLGD and CC01 data, corrected using the field output correction factors determined in this work and measurements with CC01 data corrected using TRS-483, was less than 3% for all field sizes, except for the smallest field size of RPLGD in perpendicular orientation and the CC01. The field output correction factors of RPLGD and CC01 are reported. The validation proves that RPLGD in parallel orientation combined with the field output correction factors is the most suitable for determining the field output factors for the smallest field used in this study.

Dose response of a radiophotoluminescent glass dosimeter for TomoTherapy, CyberKnife, and flattening-filter-free linear accelerator output measurements in dosimetry audit.

We experimentally determined the radiophotoluminescent glass dosimeter (RPLD) dose responses for TomoTherapy, CyberKnife, and flattening-filter-free (FFF) linear accelerator (linac) outputs for dosimetry audits in Japan. A custom-made solid phantom with a narrow central-axis spacing of three RPLD elements was used for output measurement to minimise the dose-gradient effect of the non-flattening filter beams. For RPLD dose estimation, we used the ISO 22127 formalism. Additional unit-specific correction factors were introduced and determined via the measured data. For TomoTherapy (7 units) and CyberKnife (4 units), the doses were measured under machine-specific reference fields. For FFF linac (5 units), in addition to the reference condition, we obtained the field-size effects for the range from 5×5cm to 25×25cm. The correction factors were estimated as 1.008 and 0.999 for TomoTherapy and CyberKnife, respectively. For FFF linac, they ranged from 1.011 to 0.988 for 6 MV and from 1.011 to 0.997 for 10 MV as a function of the side length of the square field from 5 to 25cm. The estimated uncertainties of the absorbed dose to water measured by RPLD for the units were 1.32%, 1.35%, and 1.30% for TomoTherapy, CyberKnife, and FFF linac, respectively. A summary of the dosimetry audits of these treatment units using the obtained correction factors is also presented. The average percentage differences between the measured and hospital-stated doses were<1% under all conditions. RPLD can be successfully used as a dosimetry audit tool for modern treatment units.

Evaluation of radiophotoluminescent glass dosimeter response for therapeutic spot scanning proton beam: suggestion of linear energy transfer-based correction.

A radiophotoluminescent glass dosimeter (RGD) is used for a postal audit of a photon beam because of its various excellent characteristics. However, it has not been used for scanning proton beams because its response characteristics have not been verified. In this study, the response of RGD to scanning protons was investigated to develop a dosimetry protocol using the linear energy transfer (LET)‐based correction factor. The responses of RGD to four maximum‐range‐energy‐pattern proton beams were verified by comparing it with ionization chamber (IC) dosimetry. The LET at each measurement depth was calculated via Monte Carlo (MC) simulation. The LET correction factor (kLETRGD) was the ratio between the uncorrected RGD dose (DrawRGD) and the IC dose at each measurement depth. kLETRGD can be represented as a function of LET using the following equation: kLETRGDLET=‐0.035LET+1.090. DrawRGD showed a linear under‐response with increasing LET, and the maximum dose difference between the IC dose and DrawRGD was 15.2% at an LET of 6.07 keV/μm. The LET‐based correction dose (DLETRGD) conformed within 3.6% of the IC dose. The mean dose difference (±SD) of DrawRGD and DLETRGD was –2.5 ± 6.9% and 0.0 ± 1.6%, respectively. To achieve accurate dose verification for scanning proton beams using RGD, we derived a linear regression equation based on LET. The results show that with appropriate LET correction, RGD can be used for dose verification of scanning proton beams.