Radiophotoluminescent Dosimeter Research Articles

Monte Carlo simulated correction factors for high dose rate brachytherapy postal dosimetry audit methodology

Background and PurposeFull-scatter conditions in water are impractical for postal dosimetry audits in brachytherapy. This work presents a method to obtain correction factors that account for deviations from full-scatter water-equivalent conditions for a small plastic phantom Material and MethodsA 16 × 8 × 3 cm phantom (PMMA) with a radiophotoluminescent dosimeter (RPLD) at the centre and two catheters on either side was simulated using Monte Carlo (MC) to calculate correction factors accounting for the lack of scatter, non-water equivalence of the RPLD and phantom, source model and backscatter for HDR 60Co and 192Ir sources. ResultsThe correction factors for non-water equivalence, lack of full scatter, and the use of PMMA were 1.062 ± 0.013, 1.059 ± 0.008 and 0.993 ± 0.009 for 192Ir and 1.129 ± 0.005, 1.009 ± 0.005 and 1.005 ± 0.005 for 60Co respectively. Water-equivalent backscatter thickness of 5 cm was found to be adequate and increasing thickness of backscatter did not have an influence on the RPLD dose. The mean photon energy in the RPLD for four HDR 192Ir sources was 279 ± 2 keV in full scatter conditions and 295 ± 1 keV in the audit conditions. For 60Co source the corresponding mean energies were 989 ± 1 keV and 1022 ± 1 keV respectively. ConclusionsCorrection factors were obtained through the MC simulations for conditions deviating from TG-43, including the amount of back scatter, and the optimum audit set up. Additionally, the influence of different source models on the correction factors was negligible and demonstrates their generic applicability.

Development and international multicentre pilot testing of a postal dosimetry audit methodology for high dose rate brachytherapy

Background and PurposeDosimetry audits are essential for reducing errors in brachytherapy. A postal dosimetry audit methodology was developed and tested in an international multicentre pilot, to assess the accuracy of the Reference Air Kerma Rate of 192Ir and 60Co brachytherapy sources Materials and MethodsA compact phantom made of polymethyl methacrylate was developed to accommodate two catheters, a radiophotoluminescence dosimeter (RPLD) for dose measurements and a Gafchromic (RTQA2) film strip for source position verification. Deviations of the audit setup from TG-43 conditions were quantified experimentally and compared to previous Monte Carlo (MC) simulations. A measurement uncertainty budget was estimated for the RPLD analysis. The methodology was tested in an international pilot study consisting of 59 dosimeter sets among 48 centres from 11 countries. ResultsThe experimental correction factors showed good agreement with previous MC simulations, and the total correction factor accounting for non-water equivalence, lack of scatter and beam quality was found to be 1.029 ± 0.009 for 192Ir and 1.059 ± 0.007 for 60Co sources, to be employed in audit measurement. The total uncertainty budget was estimated to be 2.24 % (k = 1). In the multicentre study, the ratio between measured and reported user dose ranged from 0.968 to 1.049, with all irradiated dosimeter sets within ± 5 %, and 54 out of 59 within ± 3 %. ConclusionsThe methodology was tested in an international multicentre pilot study and has shown good performance validating the uncertainty budget.

An efficient protocol for commissioning radiophotoluminescence dosimeters for radiotherapy dosimetry audits

PurposeThe aim of this study was to develop an efficient protocol for the commissioning of 1000 radiophotoluminescence dosimeters (RPLDs) for use in postal dosimetry audits in radiotherapy. This involved the determination of correction factors necessary to reduce measurement uncertainty and ensure accurate dose measurements. MethodsThe commissioning process started with the RPLDs subjected to a series of controlled irradiations to determine their individual nominal response. Experiments were also conducted to assess the influence of irradiation position, reading position, and ambient temperature on the dosimeter readings all which were accounted for calculating individual sensitivity correction factors (SCFs) for each dosimeter. Statistical analysis was performed to evaluate the variability of SCFs depending on normalization group. An additional investigation simulating different dosimetry audit batches was conducted to study the effect of SCF variability on dosimetry audit measurements. ResultsThe adopted commissioning protocol required irradiation position correction factors (0.990–0.996), readout tray position correction factors (0.992–1.01) and room temperature corrections (∼0.4 % per ° C). This enabled the calculation of SCFs for a batch of 1000 RPLDs and the analysis found the majority of SCFs falling within the range of 0.985–1.015. The standard deviations of the SCF distributions were approximately 1% for all normalization groups. It was observed that SCFs normalized to the entire batch of 1000 dosimeters could be effectively used for smaller audit batches, with an additional uncertainty contribution of up to 0.2%. This minimal increase in uncertainty is acceptable within the context of dosimetry audits. ConclusionsThe developed protocol for commissioning RPLDs provides a reliable method for ensuring accurate dose measurements in postal radiotherapy dosimetry audits. The correction factors applied during the commissioning process were thoroughly described to effectively minimize measurement uncertainty. The findings support the use of SCFs normalized to large dosimeter batches for smaller audit groups, thereby streamlining the dosimetry audit process. Future research should focus on the long-term stability of SCFs to further enhance the reliability of RPLD-based dosimetry audits.

Characterization of Radiophotoluminescence Dosimeters Under X-Ray Irradiation at High Doses

Characterization of Radiophotoluminescence Dosimeters Under X-Ray Irradiation at High Doses

Online and offline Radiation-Induced Attenuation measurements on FD-7 radiophotoluminescence dosimeters irradiated at high X-ray doses

Radiophotoluminescence (RPL) FD-7 glass dosimeters find applications in low to high dose radiation environments. This work presents an experimental characterization of RPL glass dosimeter, irradiated with 100 kV X-ray tubes at room temperature at doses ranging from 1.3 kGy to 0.47 MGy, much higher of their common use range. In this study, a customized set-up has been developed, allowing the online investigation of the glass transmission changes with radiation, known as Radiation-Induced Attenuation (RIA), as well as the recovery and post-mortem characterizations up to 2 months after irradiation. Multi-wavelength analysis was performed, focusing on the range between 200 nm and 800 nm. At 700 nm and 800 nm, RIA increases progressively with dose up to about 5 kGy, and tends to approach saturation (2–3 dB/mm) for doses higher than 50 kGy. Higher attenuation is reported at lower wavelengths: 445-nm light transmission reduces to only about 1% of its initial value after 2 kGy. RIA recovery after irradiation was observed, up to 6% at 700 nm wavelength within 3 h from the irradiation conclusion and up to 26% 2 months after, especially at doses in the kGy range. Both online RIA and its recovery are highly dependent on the selected wavelength and on the total absorbed dose. This information is crucial for the extension of the use of these dosimeters up to high doses, complementary to the RPL signal, traditionally used alone for the determination of doses up to the Gy range.

The IAEA remote audit of small field dosimetry for testing the implementation of the TRS-483 code of practice.

The TRS‑483, an IAEA/AAPM International Code of Practice on dosimetry of small static photon fields, underwent testing via an IAEA coordinated research project (CRP). Alongside small field output factors (OFs) measurements using active dosimeters by CRP participants, the IAEA Dosimetry Laboratory received a mandate to formulate a remote small field dosimetry audit method using its passive dosimetry systems. This work aimed to develop a small field dosimetry audit methodology employing radiophotoluminescent dosimeters (RPLDs) and radiochromic films. The methodology was subsequently evaluated through a multicenter pilot study with CRP participants. The developments included designing and manufacturing a dosimeter holder set and the characterization of an RPLD system for measurements in small photon fields using the new holder. The audit included verification of small field OFs and lateral beam profiles for small fields. At first, treatment planning system (TPS) calculated OFs were checked against a reference data set that was available for conventional linacs. Second, calculated OFs were verified through the RPLD measurement of point doses in a machine-specific reference field, 4cm × 4cm, 2cm × 2cm, and 1cm × 1cm, corresponding size circularfields or nearest achievable field sizes. Lastly, profile checks in in-plane and cross-plane directions were done for the two smallest fields by comparing film measurements with TPS calculations at 20%, 50%, and 80% isodose levels. RPLD correction factors for small field measurements were approximately unity. However, they influenced the dose determination's overall uncertainty in small fields, estimated at 2.30% (k=1 level). Considering the previous experience in auditing reference beam output following the TRS-398 Code of Practice, the acceptance limit of 5% for the ratio of the dose determined by RPLD to the dose calculated by TPS, DRPLD/DTPS, was considered adequate. The multicenter pilot study included 15 participants from 14 countries (39 beams). Consistent with the previous findings, the results of the OF check against the reference data confirmed that TPSs tend to overestimate OFs for the smallest fields included in this exercise. All except three RPLD measurement results were within the acceptance limit, and the spread of results increased for smaller field sizes. The differences between the film measured and TPS calculated dose profiles were within 3mm for most of the beams checked; deviated results revealed problems with TPS commissioning and calibration of the treatment unit collimation systems. The newly developed small field dosimetry audit methodology proved effective and successfully complemented the CRP OF measurements by participants with RPLD audit results.

Radiophotoluminescence response of LiF:Mg,Ti pellets irradiated with clinical proton beams in the 70–200 MeV energy range

Lithium fluoride doped with Mg and Ti (LiF:Mg,Ti) has been used for several decades as thermoluminescent dosimeter material, but recently also its radiophotoluminescence has been investigated for applications in dosimetry. In this work, LiF:Mg,Ti pellets (TLD-100) were irradiated in a water phantom at CNAO (Pavia, Italy) with therapeutic proton beams at five energies from 70 to 200 MeV in the dose range from 2 to 20 Gy. After irradiation, their visible radiophotoluminescence spectra were measured in controlled conditions and the spectrally-integrated red emission response of radiation-induced color centers has been investigated. The radiophotoluminescence signal, excited by a 445 nm continuous wave laser, was integrated within a 50 nm-wide band around the emission peak of the F2 color centers, located around 670 nm in LiF. The spectrally-integrated signal of the samples irradiated at the energy of 147.7 MeV exhibited a linear dependence with dose. Moreover, this radiophotoluminescence response appears independent from Linear Energy Transfer in the range from 0.8 to 1.6 keV/μm in all the samples irradiated at the dose of 5 Gy. Such independence was found up to 10.3 keV/μm in samples irradiated within two spread out Bragg peaks made of 36 energy components in the entire investigated proton energy range. The radiophotoluminescence response of the TLD-100 pellets was compared to that of nominally-pure LiF crystals irradiated in the same conditions, which show a similar behavior. The results are encouraging for the exploitation of TLD-100 pellets as passive solid-state radiophotoluminescent dosimeters for proton therapy.

2316: Energy correction factors for out of field dosimetry with radiophotoluminescent dosimeters

2316: Energy correction factors for out of field dosimetry with radiophotoluminescent dosimeters

Recommendation for reducing the crystalline lens exposure dose by reducing imaging field width in cone-beam computed tomography for image-guided radiation therapy: an anthropomorphic phantom study.

In cone-beam computed tomography (CBCT) for image-guided radiation therapy (IGRT) of the head, we evaluated the exposure dose reduction effect to the crystalline lens and position-matching accuracy by narrowing one side (X2) of the X-ray aperture (blade) in the X-direction. We defined the ocular surface dose of the head phantom as the crystalline lens exposure dose and measured using a radiophotoluminescence dosimeter (RPLD, GD-352M) in the preset field (13.6cm) and in each of the fields when blade X2 aperture was reduced in 0.5cm increments from 10.0 to 5.0cm. Auto-bone matching was performed on CBCT images acquired five times with blade X2 aperture set to 13.6cm and 5.0cm at each position when the head phantom was moved from -5.0 to + 5.0mm in 1.0mm increment. The maximum reduction rate in the crystalline lens exposure dose was -38.7% for the right lens and -13.2% for the left lens when blade X2 aperture was 5.0cm. The maximum difference in the amount of position correction between blade X2 aperture of 13.6cm and 5.0cm was 1mm, and the accuracy of auto-bone matching was similar. In CBCT of the head, reduced blade X2 aperture is a useful technique for reducing the crystalline lens exposure dose while ensuring the accuracy of position matching.

Development of organic radiophotoluminescence dosimeters based on radiation-induced emission-switching mechanism of fluorescein and p-benzoquinone

Organic materials were developed for use as tissue-equivalent dosimeters operating on the principle of organic radiophotoluminescence (ORPL) based on the emission-switching of fluorescein and p-benzoquinone (BQ) in polymethylmethacrylate and propylene carbonate. The BQ-derived radical ions generated by X-ray irradiation open the lactone ring of fluorescein, thereby producing emissive molecules. The fluorescence properties and potential applications of the dosimeters were investigated. At the optimal composition (1 wt% fluorescein and 10 wt% BQ), the linear range was 0–4 Gy. Furthermore, the dose sensitivity in this range was significantly higher than that of Ag-phosphate glass. The sensitivity range and high radiation-dose-sensitivity make the material suitable for use in radiotherapy.

Effect of Al-doping on dosimetric properties of CaF2

In this study, the effect of Al-doping on dosimetric properties of CaF2 was investigated. Al-doped CaF2 showed a radiophotoluminescence (RPL) peak at 750 nm after X-ray irradiation. The RPL intensity decreased with the increase of Al concentration and was less than that of undoped CaF2. The minimum detectable dose as the RPL dosimeter of 0.01% Al-doped CaF2 was 42 mGy. Al-doped CaF2 also indicated thermally stimulated luminescence (TSL) glow peaks at 225, 285, 387, and 436 °C. The wavelengths of TSL were 390 and 500 nm. The minimum detectable dose as the TSL dosimeter of 1% Al-doped CaF2 turned out to be 0.43 μGy which is comparable to commercial dosimeters.

Development of organic RPL dosimeters based on fluorescent products of the radiation-induced reaction of 2′,7′-dichlorofluorescein diacetate

In this study, we achieved a shift in the fluorescence wavelength of the organic molecules by X-ray irradiation and fabricated organic materials for radiation dosimetry, focusing on the radiation-induced radical oxidation of 2′,7′-dichlorofluorescein-diacetate (DCFHDA). We doped DCFHDA into processable and transparent polymers to develop a novel tissue-equivalent dosimeters with 3D measurement capabilities. Photoluminescence spectra of the organic materials were measured before and after X-ray irradiation, and their sensitivities to X-rays were compared based on the changes in their fluorescence intensity. Fluorescent molecules were produced from DCFHDA upon X-ray irradiation, and the material was sensitive to X-rays at doses of up to 6 kGy. Furthermore, trichloroacetic acid doping enhanced the dose sensitivity of the material by promoting the radical reaction, which indicates that it can be used as a sensitizer. These results indicate that the fluorescence wavelengths of DCFHDA switched to those of another fluorescent molecule, i.e., the achievement of radiophotoluminescence (RPL). We achieved an organic RPL (ORPL) and showed the possibility of ORPL that can be utilized in dosimetry in radiotherapy.

Electronics Irradiation With Neutrons at the NEAR Station of the n_TOF Spallation Source at CERN

We study the neutron field at the NEAR station of the neutron time of flight (n_TOF) facility at CERN, through Monte Carlo simulations, well-characterized static random access memories (SRAMs) and radio-photo-luminescence (RPL) dosimeters, with the aim of providing neutrons for electronics irradiation. Particle fluxes and typical quantities relevant for electronics testing were simulated for several test positions at NEAR and compared to those at the CERN high energy accelerator mixed-field facility (CHARM), highlighting similitudes and differences. The SRAM detectors, based on single event upset (SEU) and single event latch-up (SEL) counts, each one with a different energy response, and RPL dosimeters were tested in a reference position and the results were benchmarked to FLUKA simulations. Finally, the neutron spectra at NEAR are compared to those of the most well-known spallation sources and typical environments of interest, for accelerator and atmospheric applications, showing the potential of the facility for electronics irradiation.

CERN Super Proton Synchrotron Radiation Environment and Related Radiation Hardness Assurance Implications

The Super Proton Synchrotron (SPS) is the second largest accelerator at CERN where protons are accelerated between 16 GeV/c and 450 GeV/c. Beam losses, leading to the mixed-field radiation of up to MGy magnitude, pose a threat to the reliability of the electronic equipment and polymer materials located in the tunnel and its vicinity. Particularly in the arc sectors, where both main magnets and radiation sensors are periodically arranged, the Total Ionizing Dose (TID) is of concern for the front-end electronics of A Logarithmic Position System (ALPS). The SPS is equipped with multiple radiation detection systems such as Beam Loss Monitors (BLM), RadMons, and as of 2021, the Distributed Optical Fibre Radiation Sensing (DOFRS), that combined all together provide a very comprehensive picture of both the TID spatial distribution and its time evolution. Within this study, the overview of measured 2021 and 2022 TID levels is presented, together with the demonstration of capabilities offered by the different radiation monitors. The DOFRS, supported by the passive Radio-Photo Luminescence (RPL) dosimeter measurements, is used to assess the TID values directly at the electronic racks, which turned out to be reaching several tens of Gy per year, potentially affecting the ALPS lifetime.

Validation of HDR brachytherapy doses in the treatment of keloid scars using the egs_brachy Monte Carlo application

Objective. Radiotherapy is a well-known alternative in the treatment of keloid scars to reduce the recurrence of scars. The purpose of this study was to investigate the feasibility and accuracy of dose delivered from a high-dose-rate (HDR) afterloaders in keloid scar brachytherapy using Monte Carlo (MC) simulations and measurements. Approach. Treatment doses and central axis dose profiles were measured using radiophotoluminescence dosimeters and radiochromic films, respectively, with two HDR afterloaders, both using an Ir-192 source, in a phantom made of solid water and polycarbonate sheets. The nominal treatment dose calculated by the AAPM Task Group No. 43 (TG-43) dose model was set to 8.5 Gy at a distance of 0.5 cm laterally from the middle of the source line located in a plastic applicator simulating a 15 cm long surgically removed scar treatment with 30 equally spaced (0.5 cm) source positions. The dose profiles were measured at three different distances from the applicator and the absolute doses at four points at different distances. MC simulations were performed using the egs_brachy, which is based on EGSnrc code system. Main results. The measured and simulated dose profiles match well, especially at 10.0 mm (difference <1%) and 15.0 mm depths (difference <4%), and with a small dose difference at 5.0 mm depth (difference <4%). Point dose measurements agreed well in the dose maximum area (difference <7%) with the simulated dose profiles, although the largest difference near the edge of the profile was <30%. The dose differences between the TG-43 dose model and the MC simulation were small (differences <4%). Significance. Simulated and measured dose levels at a depth of 0.5 cm showed that the nominal treatment dose can be achieved with the utilized setup. The measurement results of the absolute dose agree well with the corresponding simulation results.

Radiophotoluminescence Phenomenon of CaF2 Ceramics Doped with Li

The objective of this study is to examine the impact of Li-doping on the radiophotoluminescent (RPL) properties of CaF2. Before ionizing irradiation, Li-doped CaF2 exhibited no photoluminescence (PL) under excitation in the range of 250–700 nm. After ionizing irradiation, Li-doped CaF2 displayed PL at 800 nm when excited at 390 and 610 nm. The decay time constant for this luminescence was determined to be 20 ns, which suggests that it is attributed to (F2+)A centers. All the Li-doped CaF2 showed higher PL intensity than the non-doped CaF2 did, with the highest intensity observed in the 0.5% Li-doped CaF2. The 0.5% Li-doped CaF2 was also found to have a minimum measurable dose of 14 μGy as an RPL dosimeter, and the RPL response monotonically increased to 10 Gy. As for radiation-induced luminescence other than RPL, the scintillation peak and the thermally stimulated luminescence (TSL) glow peak were mainly observed at 300 nm and 140 °C, respectively.

A ratiometric radio-photoluminescence dosimeter based on a radical excimer for X-ray detection.

A novel radio-photoluminescence material featuring fluorochromic responses toward UV or X-ray irradiation has been obtained. Such a unique monomer- to excimer-based luminescence transition allows for dosimetry of ionizing radiation in a ratiometric manner. Rather than quenching the luminescence, the radiation-induced radical species of Th-105 boost the excimer emission, rendering it as a rare material possessing radical-excimers.

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.

Development of a New Radiation Shield for the Face and Neck of IVR Physicians.

Interventional radiology (IVR) procedures are associated with increased radiation exposure and injury risk. Furthermore, radiation eye injury (i.e., cataract) in IVR staff have also been reported. It is crucial to protect the eyes of IVR physicians from X-ray radiation exposure. Many IVR physicians use protective Pb eyeglasses to reduce occupational eye exposure. However, the shielding effects of Pb eyeglasses are inadequate. We developed a novel shield for the face (including eyes) of IVR physicians. The novel shield consists of a neck and face guard (0.25 mm Pb-equivalent rubber sheet, nonlead protective sheet). The face shield is positioned on the left side of the IVR physician. We assessed the shielding effects of the novel shield using a phantom in the IVR X-ray system; a radiophotoluminescence dosimeter was used to measure the radiation exposure. In this phantom study, the effectiveness of the novel device for protecting against radiation was greater than 80% in almost all measurement situations, including in terms of eye lens exposure. A large amount of scattered radiation reaches the left side of IVR physicians. The novel radiation shield effectively protects the left side of the physician from this scattered radiation. Thus, the device can be used to protect the face and eyes of IVR physicians from occupational radiation exposure. The novel device will be useful for protecting the face (including eyes) of IVR physicians from radiation, and thus could reduce the rate of radiation injury. Based on the positive results of this phantom study, we plan to perform a clinical experiment to further test the utility of this novel radiation shield for IVR physicians.

Out-of-Field Doses Produced by a Proton Scanning Beam Inside Pediatric Anthropomorphic Phantoms and Their Comparison With Different Photon Modalities.

Since 2010, EURADOS Working Group 9 (Radiation Dosimetry in Radiotherapy) has been involved in the investigation of secondary and scattered radiation doses in X-ray and proton therapy, especially in the case of pediatric patients. The main goal of this paper is to analyze and compare out-of-field neutron and non-neutron organ doses inside 5- and 10-year-old pediatric anthropomorphic phantoms for the treatment of a 5-cm-diameter brain tumor. Proton irradiations were carried out at the Cyclotron Centre Bronowice in IFJ PAN Krakow Poland using a pencil beam scanning technique (PBS) at a gantry with a dedicated scanning nozzle (IBA Proton Therapy System, Proteus 235). Thermoluminescent and radiophotoluminescent dosimeters were used for non-neutron dose measurements while secondary neutrons were measured with track-etched detectors. Out-of-field doses measured using intensity-modulated proton therapy (IMPT) were compared with previous measurements performed within a WG9 for three different photon radiotherapy techniques: 1) intensity-modulated radiation therapy (IMRT), 2) three-dimensional conformal radiation therapy (3D CDRT) performed on a Varian Clinac 2300 linear accelerator (LINAC) in the Centre of Oncology, Krakow, Poland, and 3) Gamma Knife surgery performed on the Leksell Gamma Knife (GK) at the University Hospital Centre Zagreb, Croatia. Phantoms and detectors used in experiments as well as the target location were the same for both photon and proton modalities. The total organ dose equivalent expressed as the sum of neutron and non-neutron components in IMPT was found to be significantly lower (two to three orders of magnitude) in comparison with the different photon radiotherapy techniques for the same delivered tumor dose. For IMPT, neutron doses are lower than non-neutron doses close to the target but become larger than non-neutron doses further away from the target. Results of WG9 studies have provided out-of-field dose levels required for an extensive set of radiotherapy techniques, including proton therapy, and involving a complete description of organ doses of pediatric patients. Such studies are needed for validating mathematical models and Monte Carlo simulation tools for out-of-field dosimetry which is essential for dedicated epidemiological studies which evaluate the risk of second cancers and other late effects for pediatric patients treated with radiotherapy.