Optically Stimulated Luminescence Dosimeters Research Articles

Characteristics of optically stimulated luminescent dosimeter of beryllium oxide in BNCT irradiation field

The irradiation fields in boron neutron capture therapy (BNCT) consist of neutrons with a wide energy range and undesired high-intensity γ-rays. As the thermoluminescent dosimeter (TLD) used for BNCT dosimetry is out of production, a new type of γ-ray dosimeter is required for the quality assurance (QA) of the treatment. Therefore, in this study, an optically stimulated luminescent dosimeter (OSLD) made of BeO ceramic was selected and its use in the field of BNCT was investigated. The performance of the dosimeter was tested and the effect of a thermal neutron on the γ-ray dose obtained by the OSLD was measured. The OSLDs had a good γ-ray dose linearity of approximately 300 mGy corresponding to the dose in the quality assurance procedure of BNCT, and the thermal neutron sensitivity of the OSLD was less than that of TLD.

Dose metrology: TLD/OSL dose accuracy and energy response performance

An essential step in evaluating and comparing the performance of two passive radiation dosimeter types, thermosluminescent (TLD) and optically stimulated luminescence (OSL), used by workers in environments with ionizing radiation for individual radiological monitoring and control of external exposure at various times (cumulative dose for 1 month), is to compare the measured dose accuracy, energy response, and coefficient of variation.In fact this performance study consists in determining the accuracy of both R(10) and R(0.07) which are considered as the ratios of the measured dose (Hp(10) or Hp(0.07)) to the delivered dose (Hp(10) or Hp(0.07)) for each photon energy. The validity of the results of this test is based on the acceptance limits of the ICRP and the international standard IEC-62387. The relative energy response used is normalized to the 137Cs 662 keV energy to find which energy response is closest to the ideal case, and the coefficient of variation that allows to determine the statistical fluctuation of the Hp(10) and Hp(0.07) doses.The results of the accuracy test for the OSL and TLD dosimeters are acceptable because they fall within the ICRP limits. For the energy response, the OSL performs better than the TLD for Hp(10) and Hp(0.07), and for the coefficient of variation, the OSL satisfies the requirements of ISO 62387 for both Hp(10) and Hp(0.07), while the TLD satisfies these requirements only for the measurement of Hp (0.07).

Planning and dosimetric evaluation of three total body irradiation techniques: Standard SSD VMAT, Extended SSD VMAT and Extended SSD Field-in-Field.

The aim of this study was to dosimetrically compare three total body irradiation (TBI) techniques which can be delivered by a standard linear accelerator, and to deduce which one is preferable. Specifically, Extended Source to Surface Distance (SSD) Field-in-Field (FiF), Extended SSD Volumetric Modulated Arc Therapy (VMAT), and Standard SSD VMAT TBI techniques were dosimetrically evaluated. Percent depth dose and dose profile measurements were made under treatment conditions for each specified technique. After having generated treatment plans with a treatment planning system (TPS), dose homogeneity and critical organ doses were investigated on a Rando phantom using radiochromic films and optically stimulated luminescence dosimeters (OSLDs). TBI dose of 12Gy in six fractions was prescribed for each technique. The gamma index (5%/5mm) was used for the analysis of radiochromic films. Passing rates for Extended SSD FiF, Extended SSD VMAT and Standard SSD VMAT techniques were found to be 90%, 87% and 94%, respectively. OSLD measurements were within ± 5% agreement with TPS calculations for the first two techniques whereas the agreement was found to be within ± 3% for the Standard SSD VMAT technique. TPS calculations demonstrated that mean lung doses in the first two techniques were around 8.5Gy while it was kept around 7Gy in Standard SSD VMAT. It is concluded that Standard SSD VMAT is superior in sparing the lung tissue while all three TBI techniques are feasible in clinical practice with acceptable dose homogeneity. In the absence of VMAT-based treatment planning, Extended SSD FiF would be a reasonable choice compared to other conventional techniques.

In Vivo Dosimetry for Superficial High Dose Rate Brachytherapy with Optically Stimulated Luminescence Dosimeters: A Comparison Study with Metal-Oxide-Semiconductor Field-Effect Transistors

The purpose of the study was to calibrate and commission optically-stimulated luminescence dosimeters (OSLDs) for in vivo measurements in contact-based 192Ir treatments for superficial high dose rate (HDR) brachytherapy in place of metal-oxide-semiconductor field-effect transistors (MOSFETs). Dose linearity and dose rate dependence were tested by varying source-to-OSLD distance and dwell time. Angular dependence was measured using a solid water phantom setup for OSLD rotation. A group of OSLDs were readout 34 consecutive times to test readout depletion while OSLDs were optically annealed using a mercury lamp for 34.7 h. End-to-end tests were performed using a Freiburg flap and Valencia applicator. OSLD measurements were compared to MOSFETs and treatment planning system (TPS) doses. OSLD response was supralinear for doses above 275 cGy. They were found to be independent of dose rate and dependent on the incident angle in edge-on scenarios. OSLDs exhibited minimal readout depletion and were successfully annealed after 24 h of illumination. Freiburg flap measurements agreed well with the TPS. For the Valencia, OSLDs showed to be the more accurate system over MOSFETs, with a maximum disagreement with the TPS being 0.09%. As such, OSLDs can successfully be used in place of MOSFETs for in vivo dosimetry for superficial HDR brachytherapy.

Al2O3:C optically stimulated luminescence dosimetry for evaluation of potential factors contributing to entrance skin doses received by liver cancer patients undergoing Transarterial Chemoembolization

Transarterial Chemoembolization (TACE) has been accepted as an effective technique that can be practically used for liver cancer treatment due to its outstanding benefits for patients with large, infiltrative, and multifocal tumors that cannot be surgically removed. However, this invasive image-guided technique may potentially result in higher radiation doses than general diagnostic radiology. Radiation-induced skin injury caused by excessive exposure to X-rays during fluoroscopically guided procedures has been previously reported. Therefore, dose assessment during TACE examination is relevant to minimize radiological hazards and reduce patient distress.The study aims to 1) quantify the magnitude of radiation doses received in TACE treatments, 2) evaluate potential factors contributing to an increase of the entrance skin dose, and 3) demonstrate an improved image-guided procedure for reducing radiation doses while maintaining high X-ray image quality. The study was carried out employing an anthropomorphic phantom to determine radiation dose using a standard commercial optically stimulated luminescence dosimeter (OSLD). Experimental data was collected from 370 patients under three specific image-guided techniques. They include 1) abdomen frontal 3 fps procedure where a pathway of blood flow was created using an image acquisition rate of three frames per second (fps), 2) navigation where a blood vessel roadmap was created with subtraction of bones and organs, and 3) fluoroscopy where X-ray beams were continuously delivered to a target for creating real-time images with no interference removed. Analysis of variance was used to demonstrate the difference of the mean entrance skin doses (ESDs) among the three imaging techniques. A multiple regression model was also used to investigate potential factors contributing to the increased ESDs.The study confirms that the ESDs received by TACE patients using these three imaging techniques are not significantly different. Moreover, the statistical-based model shows that the five main factors obtained from the exposure parameters and patient dosimetric data contribute to the patient ESDs. They include 1) the dose area product (DAP), 2) fluoroscopy time, 3) X-ray tube voltage, 4) X-ray tube current, and 5) total diagnostic images. All information is reported based on the machine DICOM-RDSR (Digital Imaging and Communication in Medicine – Radiation Dose Structured Report) data after completed examinations. Finally, the ANOVA test confirms that this simplified model can be used to estimate the radiation doses received by TACE patients, accounting for a 95% confidence interval.

Experimental determination of breast skin dose using volumetric modulated arc therapy and field-in-field treatment techniques

Abstract Introduction: The use of volumetric modulated arc therapy (VMAT) on the breast has several dosimetric advantages but its impact on skin dose should be evaluated and compared to well-established treatment techniques using tangential fields. The aim of this work is to contrast the skin dose for VMAT and field-in-field (FIF) and to estimate the magnitude of the skin dose involved. Method: The skin dose was measured, without build-up, using thermoluminescent dosimeter (TLD) and optically stimulated luminescence dosimeter (OSLD) in breast radiotherapy by an in-house anthropomorphic phantom. Two different treatment techniques were used: FIF and VMAT, based on the planning strategy proposed by Nicolini et al. The dose levels were 4300 cGy, 4600 cGy and 5600 cGy in 20 fractions. In vivo dosimetry with TLD for VMAT was performed for different breast sizes in the same locations as phantom measurements. Results: The ipsilateral phantom breast skin dose using both treatment techniques was equivalent. TLD measured doses by the VMAT technique were up to 5% higher than OSLD, although they agree if we consider the geometry uncertainty of the TLD. In accordance with in vivo dosimetry, the mean dose of the ipsilateral breast skin was 62 ± 6% (51%, 75%) relative to the prescribed dose, regardless of the breast size for the volumes considered with this small population (n = 9) as shown by Mann–Whitney U-test (Z = 1·9, 95% confidence). The uncertainty expected in this region due to geometry (volume) changes is up to 9% higher for volumes from 225·9 cc to 968·8 cc. According to the treatment techniques and in vivo dosimetry, the contralateral breast skin dose was 1·0% in FIF and 2·5% in VMAT concerning the prescribed dose. Conclusion: There is no difference in skin dosimetry between VMAT and FIF techniques on the ipsilateral breast. It provides useful support for the use of VMAT as a planning technique for breast irradiation. The work describes the importance of quantifying potential differences in skin dosimetry.

Effects of Fully Filling Deep Electron/Hole Traps in Optically Stimulated Luminescence Dosimeters in the Kilovoltage Energy Range

Background: This study investigated the characteristics of optically stimulated luminescence dosimeters (OSLDs) with fully filled deep electron/hole traps in the kV energy ranges.Materials and Methods: The experimental group consisted of InLight nanoDots, whose deep electron/hole traps were fully filled with 5 kGy pre-irradiation (OSLD<sub>exp</sub>), whereas the non-preirradiated OSLDs were arranged as a control group (OSLD<sub>cont</sub>). Absorbed doses for 75, 80, 85, 90, 95, 100, and 105 kVp with 200 mA and 40 ms were measured and defined as the unit doses for each energy value. A bleaching device equipped with a 520-nm long-pass filter was used, and the strong beam mode was used to read out signal counts. The characteristics were investigated in terms of fading, dose sensitivities according to the accumulated doses, and dose linearity.Results and Discussion: In OSLD<sub>exp</sub>, the average normalized counts (sensitivities) were 12.7%, 14.0%, 15.0%, 10.2%, 18.0%, 17.9%, and 17.3% higher compared with those in OSLD<sub>cont</sub> for 75, 80, 90, 95, 100, and 105 kVp, respectively. The dose accumulation and bleaching time did not significantly alter the sensitivity, regardless of the filling of deep traps for all radiation qualities. Both OSLD<sub>exp</sub> and OSLD<sub>cont</sub> exhibited good linearity, by showing coefficients determination (R2) > 0.99. The OSL sensitivities can be increased by filling of deep electron/hole traps in the energy ranges between 75 and 105 kVp, and they exhibited no significant variations according to the bleaching time.

Effective dose and radiation risk under 640-slice abdominal computed tomography examination without contrast medium injection

Medical imaging plays a crucial role in modern medicine. In order to provide fast and accurate medical diagnosis, computed tomography (CT) is a commonly used tool in radiological examinations, and 640-slice CT is the most advanced CT imaging modality. To evaluate the radiation dose and the risk under 640-slice abdominal CT examination. Examinations were performed using a 640-slice CT scanner on an Alderson-Rando anthropomorphic phantom. The used scanning acquisition parameters were the same as those used on abdominal examination without contrast medium injection in clinical practice. To measure the absorbed doses, optically stimulated luminescence dosimeters (OSLDs) were put into liver, stomach, bladder, gonads, colon, small intestine, bone marrow, and skin. According to the 1990 Recommendations of the International Commission on Radiological Protection (ICRP Publication 60), the calculated effective doses received from this examination were 0.90 mSv in males and 0.89 mSv in females. According to the 2007 Recommendations of the International Commission on Radiological Protection (ICRP Publication 103), the calculated effective dose received from this examination was 0.83 mSv in both sexes. Radiation doses obtained from the abdominal 640-slice CT examination are lower than the yearly cumulative doses received from natural radiation, revealing there is no deterministic effect and radiation risk is relatively low; therefore, this CT examination is considered safe.

Dy-concentration dependence on dosimetric properties of CaF2 transparent ceramics

In this study, we synthesized Dy-doped CaF2 transparent ceramics with several concentrations and evaluated optical, thermally stimulated luminescence (TSL), and optically stimulated luminescence (OSL) properties. The 0.05, 0.1, and 0.5% Dy-doped samples had diffuse transmittance of approximately 60% at 500 nm, and the absorption band appeared at around 280 nm after X-ray irradiation. The photoluminescence (PL) excitation wavelengths were 255, 295, 325, 350, 360, and 390 nm. When Dy concentration was 0.1%, the PL quantum yield was maximum. The OSL peaks of the Dy-doped samples was observed at 480, 570, and 660 nm by the optical stimulation at 280 nm. The TSL glow curves of the 0.5 and 1.0% Dy-doped samples consisted of the glow peaks at 75, 160, and 200 °C. The minimum detectable dose of the 0.5% Dy-doped sample as the OSL and TSL dosimeters was 15 mGy and 0.28 μGy, respectively.

Challenges in personal and clinical dosimetry using Li2B4O7 and MgB4O7 as TLD and OSLD

Thermoluminescent (TLD) and optically stimulated luminescent dosimeters (OSLD) are essential in radiation dosimetry. Such dosimeters can be easily transported due to their small size and can be used in in vivo dosimetry and anthropomorphic simulations. In this work, the dosimetric properties of Li2B4O7 and MgB4O7 compounds were evaluated based on their response to the applied stimulus, whether thermal or optical. The linear dose response range of the luminescent signal, its fading, the lowest detectable dose, and reproducibility are important parameters in determining a good dosimeter for clinical and personal dosimetry. Therefore, the objective of this work was, based on studies performed by other authors on dosimetric characterizations of doped a codoped Li2B4O7 and MgB4O7, to point out those compounds with the greatest potential for applications in personal and clinical dosimetry using TL and OSL techniques. Considering the results described in other works, the materials that stood out for use in personal and clinical dosimetry were Li2B4O7:Cu and MgB4O7:Dy,Na. In several of the reported studies, no data related to LDD, fading and reproducibility of the luminescent signal of the investigated compounds were found. Therefore, there are many possibilities for investigations into these two types of compounds for the purpose of their use in personal and clinical dosimetry. Further studies will provide a broader scientific basis for choosing appropriate dosimetric materials for these applications.

A direct comparison of the optically stimulated luminescent properties of BeO and Al2O3 for clinical in-vivo dosimetry

Optically stimulated luminescence dosimetry is a relatively recent field of in-vivo dosimetry in clinical radiotherapy, developing over the last 20 years. As a pilot study, this paper presents a direct comparison between the sensitivity variance with use, stability of measurement and linearity of the current clinical standard Al2O3:C and a potential alternative, beryllium oxide. A set of ten optically stimulated luminescence dosimeters (OSLD), including five of each type, were used simultaneously and irradiated on a Versa HD linear accelerator. Having similar sensitivity, while Al2O3:C showed a relatively stable signal response from initial use, BeO was found to have a higher response to the same dose. However, BeO displayed a strong exponential decline from initial signal response following a model of Respons{e}_{BeO}=(0.55pm 0.05){e}^{-left(0.40pm 0.05right)x}+(0.54pm 0.01), reaching stability after approximately 10 irradiation cycles. BeO was shown to have potentially higher accuracy than Al2O3:C, with less variation between individual doses. Both OSLD showed good linearity between 0.2–5.0 Gy. Between these bounds, Al2O3:C demonstrated a strong linear response following the trend Dose_{Al_{2}O_{3}, group(adj)}=(1.00pm 0.09)x-(0.02pm 0.04),{text{Gy}}, however beyond this showed deviation from linearity, resulting in a measured dose of 12.0pm 0.2 Gy at 10.0 Gy dose delivery. BeO showed strong linearity across the full examined range of 0.2–10.0 Gy with following a model of Dos{e}_{BeO, ind}=(0.98pm 0.01)x+(0.04pm 0.01) Gy with a recorded dose at 10.0 Gy delivery as 9.9pm 0.1 Gy. In conclusion, BeO does show large variance in sensitivity between individual OSLD and a considerable initial variance and decline in dose–response, however after pre-conditioning and individual normalisation to offset OSLD specific sensitivity BeO provides not only a viable alternative to Al2O3:C, but potentially provide higher accuracy, precision and reproducibility for in-vivo dosimetry.

Modified irradiation technique for transfusable blood using a clinical linear accelerator

Whole blood irradiation prior to blood transfusion mitigates the risk of Transfusion Associated Graft versus Host Disease (TA-GvHD) to the receiver. This study aimed to improve dose homogeneity, also to benefit from a faster technique and a simplified blood irradiation workflow. An acrylic box accommodating eight units of blood has been fabricated, build-up material being used to ensure dose homogeneity. A linear accelerator dose distribution treatment plan for blood bag irradiations has been evaluated, measurement of dose using nanoDot optically stimulated luminescent dosimeters (OSLD) allowing comparison with calculated dose. By using build-up material, dose distribution was within 95%–107% of the prescribed dose. With all eight units of blood accommodated in the box, an irradiation time of 20 min per box has been needed. Compared to a previously adopted procedure, use of the acrylic box and build-up material maintains dose homogeneity, also simplifying the workflow, the technique also being easy to undertake by the operators.

External Radiation Dose to Owners of Canines Treated with ( 117m Sn) Radiosynoviorthesis for Osteoarthritis.

A novel device in the veterinary market uses a colloid containing radioactive 117mSn to treat osteoarthritis in the synovial joints of canines. The technique of injecting a radioisotope to restore synovia is referred to as radiosynoviorthesis. The outpatient canine procedure uses a maximum administration of 222 MBq of 117mSn injected into one or more joints. Due to the 13.91 d half-life and 158.6 keV gamma output of 117mSn, abiding by the annual public dose limit of 1 mSv is of primary regulatory concern. The therapy protocol starts with a pre-screening questionnaire to establish owner and animal behavior patterns. The questionnaire is used to determine the duration of written time and distance limitations post therapy. In this study, external radiation doses to owners were measured by providing optically stimulated luminescent dosimeters (OSLD) for up to 30 d post-treatment of the pet. Twelve owners were measured over various time frames at two licensed locations independent of each other. In one location, the average (OSLD) measured 0.029 mSv over a 14-d wear period. In the second location, the average (OSLD) measured 0.057 mSv over a 30-d wear period; both values were well below the recommended annual public dose. The overall average extrapolated external radiation dose was estimated at 0.092 mSv, while the maximum dose estimate was 0.25 mSv. The (OSLD) results and extrapolated owner doses provide reasonable assurance that the public dose limits will be met.

Optically stimulated luminescence dosimetry on tissue equivalent LiF: Mg, Cu, Na, Si phosphor

Lithium fluoride (LiF) is one of the best tissue equivalent materials exhibiting good thermoluminescence (TL) properties, however it shows weak optically stimulated luminescence (OSL) response with blue light (470 nm) stimulation. Several research groups are working on improving the OSL properties of LiF phosphor. In an attempt, a thorough investigation on tissue equivalent LiF: Mg,Cu,Na,Si (MCNS) as a possible OSL material has been done in the current work. As the preparation route and particle size can modify the energy levels and optical transitions, the striking improvement is expected by preparing it in nanocrystalline form. The structural and morphological characterization has been done using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The OSL emission is observed in continuous wave mode under blue (460 nm) light stimulation. The OSL decay curve exhibits a significant increase in intensity which is ~2 times higher than LiF based commercial phosphor (TLD-100) irradiated with gamma dose of 0.1 Gy. The phosphor shows a linear dose response in the range of 0.1–20 Gy with almost constant decay rate. The phosphor has shown low residual signal which is good for its repetitive use. The OSL decay curve has been analysed and related parameters such as photoionization cross-section and decay constant are determined. ESR study has been done to identify the defect centres and describing the role of point defects and charge compensators involved in the luminescence process. This reveals the existence of Cu in Cu+ or Cu0 state. Good OSL properties suggests MCNS phosphor has a potential as a OSL dosimeter. The current study adds new knowledge and opens a new window to improve the OSL sensitivity of LiF material.

Preliminary study for dose evaluation depending on dose range with optically stimulated luminescence dosimeter considering individual dosimeter sensitivity.

The purpose of this study was to investigate dose evaluation depending on dose range using optically stimulated luminescence dosimeter (OSLD) and evaluate the possibility of high dose evaluation. This study investigated a commercial OSLD and used a Co-60 gamma irradiator for irradiation. The OSLDs (N = 26) were sampled in total OSLDs (N = 46) depending on the radiation sensitivity for this study. After irradiating doses from 0.5 to 40 Gy at fixed intervals in a standard environment, the dose response of a reference OSLD (N = 5) was determined through the reading process at each dose. The dose-response curves obtained from the reference OSLD were fitted according to the dose. In the dose range below 3 Gy, a linear function was used to determine the relationship between dose and the OSLD response. Quadratic and cubic functions were applied for dose ranges of up to 15 Gy and 40 Gy, respectively. Test OSLDs (N = 21) were evaluated at various doses (2.5 to 30 Gy) using different fitting functions, according to dose ranges. When doses from 0.5 Gy to 3.0 Gy were curve-fitted to the linear function, the relationship was y = 70278.0x − 3125.3 (r2 = 0.999). When doses of up to 15 Gy were curve-fitted to the quadratic function, the relationship was y = 628.6x2 + 70444.6x − 6142.3 (r2 = 0.999). Furthermore, when doses of up to 40 Gy were curve-fitted to the cubic function, the relation was y = −15.5x3 + 527.3x2 + 75059.6x − 16260.3 (r2 = 0.998). Test OSLDs were evaluated for various dose ranges based on the above equation. It was confirmed that the average difference was 0.86 ± 0.27%, and it was evaluated that the largest difference occurred at 30 Gy (2.24 ± 0.24%). In this study, we prove that measurements using the OSLD at various dose ranges, including high doses, will be possible through the application of an in-house software program and a correction process.

A comparative validation of biodosimetry and physical dosimetry techniques for possible triage applications in emergency dosimetry

Large-scale radiological accidents or nuclear terrorist incidents involving radiological or nuclear materials can potentially expose thousands, or hundreds of thousands, of people to unknown radiation doses, requiring prompt dose reconstruction for appropriate triage. Two types of dosimetry methods namely, biodosimetry and physical dosimetry are currently utilized for estimating absorbed radiation dose in humans. Both methods have been tested separately in several inter-laboratory comparison exercises, but a direct comparison of physical dosimetry with biological dosimetry has not been performed to evaluate their dose prediction accuracies. The current work describes the results of the direct comparison of absorbed doses estimated by physical (smartphone components) and biodosimetry (dicentric chromosome assay (DCA) performed in human peripheral blood lymphocytes) methods. For comparison, human peripheral blood samples (biodosimetry) and different components of smartphones, namely surface mount resistors (SMRs), inductors and protective glasses (physical dosimetry) were exposed to different doses of photons (0–4.4 Gy; values refer to dose to blood after correction) and the absorbed radiation doses were reconstructed by biodosimetry (DCA) and physical dosimetry (optically stimulated luminescence (OSL)) methods. Additionally, LiF:Mg,Ti (TLD-100) chips and Al2O3:C (Luxel) films were used as reference TL and OSL dosimeters, respectively. The best coincidence between biodosimetry and physical dosimetry was observed for samples of blood and SMRs exposed to γ-rays. Significant differences were observed in the reconstructed doses by the two dosimetry methods for samples exposed to x-ray photons with energy below 100 keV. The discrepancy is probably due to the energy dependence of mass energy-absorption coefficients of the samples extracted from the phones. Our results of comparative validation of the radiation doses reconstructed by luminescence dosimetry from smartphone components with biodosimetry using DCA from human blood suggest the potential use of smartphone components as an effective emergency triage tool for high photon energies.

Impact of detector selection on commissioning of Leipzig surface applicators with improving immobilization in high-dose-rate brachytherapy

PURPOSECommission and treatment setup of Leipzig surface applicators, because of the steep dose gradient and lack of robust immobilization, is challenging. We aim to improve commissioning reliability by investigating the impact of detector choice on percentage depth dose (PDD) verifications, and to enhance accuracy and reproducibility in calibration/treatment setup through a simple and novel immobilization device. METHODS AND MATERIALSPDD distributions were measured with radiochromic films, optically stimulated luminescent dosimeters (OSLDs), a diode detector, and both cylindrical and parallel plate ionization chambers. The films were aligned to the applicators in parallel and transverse orientations. PDD data from a benchmarking Monte Carlo (MC) study were compared with the measured results, where surface doses were acquired from extrapolation. To improve setup accuracy and reproducibility, a custom-designed immobilization prototype device was made with cost-effective materials using a 3D printer. RESULTSThe measured PDD data with different detectors had an overall good agreement (<±10%). The parallel plate ionization chamber reported unreliable doses for the smallest applicator. There was no remarkable dose difference between the two film setups. The two-in-one prototype device provided a rigid immobilization and a flexible positioning of the applicator. It enhanced accuracy and reproducibility in calibration and treatment setup. CONCLUSIONWe recommend using radiochromic films in the transverse orientation for a reliable and efficient PDD verification. The applicator's clinical applicability has been limited by a lack of robust immobilization. We expect this economical, easy-to-use prototype device can promote the use of Leipzig applicators in surface brachytherapy.

On the analysis of photon arrival time distributions obtained using the pulsed optically stimulated luminescence technique

The objective of this work is to address the analysis of photon arrival time distributions (PATDs) obtained using the pulsed optically stimulated luminescence (POSL) technique in two particular situations: (a) when the interval between pulses is insufficient for the full decay of some of the luminescence components, and (b) in the presence of shallow traps. PATDs are important to characterize the luminescence lifetime of synthetic and natural optically stimulated luminescence (OSL) materials used for dosimetry and in luminescence dating, as well as to separate the OSL components from luminescence centers associated with different luminescence lifetimes. In this study we simulated numerically the PATDs that can be obtained in the presence of fast and slow luminescence centers, where “fast”/“slow” is relative to the pulse width and period, and show that the analysis of these PATDs using semi-empirical equations based on a simple model can lead to wrong results when certain conditions are not satisfied (e.g. full decay of luminescence component between pulses, presence of shallow traps). Modifications to the semi-empirical equations are derived to provide better estimates for the luminescence lifetimes in the conditions simulated. Experimental data on Al2O3:C OSL dosimeters are used to illustrate the relevance of the results.

Small beam dosimetry by using Al2O3 optically stimulated luminescent (OSL) dosimeters at high energy photons and electrons

The study focused on the measurements of depth dose for small beam in the high energy photons and electrons. The percentage depth dose (PDD) was measured in 6 and 10 MV photons and 9 and 12 MeV electrons at 3 × 3 cm field sizes by using the Al2O3 optically stimulated luminescent (OSL) dosimeters. The PDD in OSL dosimeters were compared to those in ionization chamber and Gafchromic EBT3 film dosimeter. The results showed that the PDD in OSL dosimeters in lower photon and electron energies were in good agreement within 4% to ionization chamber and film. The PDD in 10 MV photons however showed gradual increase of deviation up to 10% beyond the depth of maximum dose (dmax). The surface doses in OSL dosimeters were significantly higher compared to those in ionization chamber and film dosimeter. The overall results suggested the suitability of OSL dosimeters to be used as indirect dosimetry works in high energy photons and electrons.

Technical note: Evaluation of a silicone-based custom bolus for radiation therapy of a superficial pelvic tumor.

PurposeUse of standard‐of‐care radiation therapy boluses may result in air‐gaps between the target surface and bolus, as they may not adequately conform to each patient's unique topography. Such air‐gaps can be particularly problematic in cases of superficial pelvic tumor radiation, as the density variation may result in the radiation delivered to the target site being inconsistent with the prescribed dose. To increase bolus fit and thereby dose predictability and homogeneity, we designed and produced a custom silicone bolus for evaluation against the clinical standard.MethodsA custom bolus was created for the pelvic regions of both an anthropomorphic phantom and a pelvic patient with squamous cell carcinoma of the penile shaft. Molds were designed using computed tomography (CT) scans, then 3D‐printed and cast with silicone rubber to yield the boluses. Air‐gap measurements were performed on custom and standard‐of‐care Superflab gel sheet boluses by analyzing total volume between the bolus and target surface, as measured from CT scans. Therapeutic doses of radiation were delivered to both boluses. Radiation dose was measured and compared to the expected dose using nine optically stimulated luminescent dosimeters (OSLDs) placed on the phantom.ResultsMean air‐gap volume between the bolus and phantom was decreased from 314 ± 141 cm3 with the standard bolus to 4.56 ± 1.59 cm3 using the custom device. In the case of the on‐treatment patient, air‐gap volume was reduced from 169 cm3 with the standard bolus to 46.1 cm3 with the custom. Dosimetry testing revealed that the mean absolute difference between expected and received doses was 5.69%±4.56% (15.1% maximum) for the standard bolus and 1.91%±1.31% (3.51% maximum) for the custom device. Areas of greater dose difference corresponded to areas of larger air‐gap.ConclusionsThe custom bolus reduced air‐gap and increased predictability of radiation dose delivered compared to the standard bolus. The custom bolus could increase the certainty of prescribed dose‐delivery of radiation therapy for superficial tumors.