Optically Stimulated Luminescence Dosimeters Research Articles

Addressing challenges in diagnostic X-ray dosimetry: uncertainties and corrections for Al2O3:C-based optically stimulated luminescent dosimeters.

The use of Al2O3:C-based optically stimulated luminescent dosimeters (OSLDs) in diagnostic X-ray is a challenge because of their energy dependence (ED) and variability of element sensitivity factors (ESFs). This study aims to develop a method to determine ED and ESFs of Landauer nanoDot™ OSLDs for clinical X-ray and investigate the uncertainties associated with ESFand ED correction factors. An area of 2 × 2 cm2 at the central axis of the X-ray field was used to establish the ESFs. A total of 80 OSLDs were categorized into "controlled" (n = 40) and "less-controlled" groups (n = 40). The ESFs of the OSLDs were determined using an 80 kVp X-raybeam quality in free-air geometry. The OSLDs were cross-calibrated with an ion chamber to establish the average calibration coefficient and ESFs. The OSLDs were then irradiated at tube potentials ranging from 50 to 150 kVp to determine their ED. The uniformity of the X-ray field was ± 1.5% at 100cm source-to-surface distance. The batch homogeneities of user-defined ESFs were 2.4% and 8.7% for controlled and less-controlled OSLDs, respectively. The ED of OSLDs ranged from 1.125 to 0.812 as tube potential increased from 50 kVp to 150 kVp. The total uncertainty of OSLDs, without ED correction, could be as high as 16%. After applying ESF and ED correction, the total uncertainties were reduced to 6.3% in controlled OLSDs and 11.6% in less-controlled ones. OSLDs corrected with user-defined ESF and ED can reduce the uncertainty of dose measurements in diagnostic X-rays, particularly in managing less-controlled OSLDs.

Effects of low-dose ionizing radiation on the molecular pathways linking neurogenesis and autism spectrum disorders in zebrafish embryos

Prenatal exposure to environmental factors may play an important role in the aetiopathogenesis of autism spectrum disorder (ASD). We aim to investigate the potential effects of low-dose x-rays from dental diagnostic x-rays on neurodevelopment and molecular mechanisms associated with ASD in developing zebrafish embryos. Zebrafish embryos were divided into four groups and exposed using a dental x-ray unit: control, 0.08, 0.15 and 0.30 seconds, which are exemplary exposure settings for periapical imaging. These exposure times were measured as 7.17, 23.17 and 63.83 mSv using optical stimulated luminescence dosimeters. At the end of 72 hours post-fertilization, locomotor activity, oxidant-antioxidant status, and acetylcholine esterase (AChE) activity were analyzed. Expression of genes related to apoptosis (bax, bcl2a, p53), neurogenesis (α1-tubulin, syn2a, neurog1, elavl3) and ASD (eif4eb, adsl2a, shank3) was determined by RT-PCR. Even at reduced doses, developmental toxicity was observed in three groups as evidenced by pericardial edema, yolk sac edema and scoliosis. Deleterious effects of dental x-rays on neurogenesis through impaired locomotor activity, oxidative stress, apoptosis and alterations in genes associated with neurogenesis and ASD progression were more pronounced in the 0.30s exposure group. Based on these results we suggest that the associations between ASD and low-dose ionizing radiation need a closer look.

Not All Flat-Panel C-Arms Are Created Equal: A Comparison of Three Major Manufacturers.

Introduction: Flat-panel detector C-arms (FCs) are reported to reduce radiation exposure and improve image quality compared with conventional image intensifier C-arms (CCs). The purpose of this study was to compare radiation exposure and image quality between three commonly used FCs. Materials and Methods: A cadaver model was placed in the prone position to simulate percutaneous nephrolithotomy. We compared the following three FCs: OEC Elite CFD from GE HealthCare, Zenition 70 from Philips, and Ziehm Vision RFD from Ziehm Imaging. To measure the radiation dose, optically stimulated luminescence dosimeters (OSLDs) were utilized during five 300-second trials, conducted under three settings: automatic exposure control (AEC), AEC with low dose (LD), and LD with the lowest pulse rate (LDLP). Ten blinded urologists evaluated the image quality. Data were statistically analyzed using the analysis of variance (ANOVA) and Tukey's B post hoc tests. Results: In the AEC setting, the Philips C-arm demonstrated lower ventral OSLD exposure (42,446 mrad) compared with both the GE (51,076 mrad) and Ziehm (83,178 mrad; p < 0.001) C-arms. Similarly, in the LD setting, the Philips C-arm resulted in less ventral OSLD exposure (25,926 mrad) than both the Ziehm (30,956 mrad) and GE (38,209 mrad; p < 0.001) C-arms. Meanwhile, in the LDLP setting, the Ziehm C-arm showed less ventral OSLD exposure (4019 mrad) than both the GE (7418 mrad) and Philips (8229 mrad; p < 0.001) C-arms. All three manufacturers received adequate image quality ratings at the AEC and LD settings. However, at LDLP, the Ziehm C-arm received inadequate ratings in 8% of images, whereas both the GE and Philips C-arms received 100% adequate ratings (p = 0.016). Conclusions: Radiation produced by flat-panel C-arms varies dramatically, with the highest exposure (Ziehm) being almost double the lowest (Philips) in AEC. Improved picture quality at the lowest settings may come at the cost of increased radiation dose. Surgeons should carefully select the machine and settings to minimize radiation exposure while still preserving the image quality.

Impact of beam collimation of z-overscanning on dose to the lens and thyroid gland in paediatric thoracic computed tomography imaging.

Adaptive collimation reduces the dose deposited outside the imaged volume along the z-axis. An increase in the dose deposited outside the imaged volume (to the lens and thyroid) in the z-axis direction is a concern in paediatric computed tomography (CT). To compare the dose deposited outside the imaged volume(tothe lens and thyroid) between 40-mm and 80-mm collimation during thoracic paediatric helical CT. We used anthropomorphic phantoms of newborns and 5-year-olds with 40-mm and 80-mm collimation during helical CT. We compared the measured dose deposited outside the imaged volume using optically stimulated luminescence dosimeters (OSLD) at the surfaces of the lens and thyroid and the image noise between the 40-mm and 80-mm collimations. There were significant differences in the dose deposited outside the imaged volume (to the lens and thyroid) between the 40-mm and 80-mm collimations for both phantoms (P < 0.01). Compared with that observed for 80-mm collimation in helical CTscans of the paediatric thorax, the dose deposited outside the imaged volume (tothe lens and thyroid) was significantly lower in newborns and 5-year-olds with 40-mm collimation.

A Comparative Analysis between SR-Pb Shield and TCM in Eye Dose of Head CT Examination

This study aims to compare the effectivity of silicone rubber-lead (SR-Pb) eye shields and TCM technique during head CT examinations. In this study, a 95-5 wt% SR-Pb eye shield was developed with dimensions of 17 cm ×17 cm ×0.6 cm. This study was carried out at three tube voltages, namely 80, 100, and 120 kV. The measurements were conducted using Optically Stimulated Luminescence Dosimeter (OSLD) as the point dosimeter. Image noise and CT number were measured within specified region of interests (ROIs). These ROIs were positioned in three regions: the right eye, the left eye, and the central area of the head. Comparison of dose and noise was carried out in three conditions: without using SR-Pb and TCM (initial conditions), only using SR-Pb, and only using the TCM technique. From this study, it was found that the use of SR-Pb reduced eye dose as the use of TCM. It was found that a greater dose reduction was obtained when using SR-Pb compared to using TCM. Meanwhile, the use of SR-Pb led to slightly increasing noise and changing the CT number. In conclusion, the use of SR-Pb eye shield can serve as an alternative for eye dose reduction in CT machines that do not support TCM mode.

Assessment of Radiation Dose and Phantom Skin Dose in Transarterial Chemoembolization in a Single Center with 2 Digital Subtraction Angiography Units

Objectives: This study aimed to assess and compare the radiation dose and phantom skin dose in transarterial chemoembolization (TACE) of two digital subtraction angiography (DSA) units (unit A: Philips Allura Xper FD20, unit B: Artis zee biplane)Material and Methods: The dose area product (DAP), reference air kerma (RAK), number of images (NI) and fluoroscopy time (FT) of 240 cases (120 cases/DSA unit) were retrospectively reviewed and collected. To assess skin dose, 28 nanoDot optically stimulated luminescence dosimeters (OSLDs) were placed on the phantom’s back and the TACE procedure was performed with 2 DSA units.Results: The median DAP, RAK, NI, and FT of unit A were 200.49 Gy·cm2, 379.84 mGy, 115 images, and 9.04 minutes, while for unit B were 109.74 Gy·cm2, 276.55 mGy, 121 images, and 10.19 minutes, respectively. Significant differences were observed in DAP, RAK, and FT. The RAK of all patients was less than 2 Gy. The phantom skin dose obtained from unit B was significantly lower than that of unit A in all positions. The peak skin doses of the phantom studies from both units were 973.15 and 658.66 mGy, respectively.Conclusion: The median DAP of the unit A DSA was higher than the national diagnostic reference levels (DRLs). The TACE procedure from both units is safe from skin reaction. To benefit patients, the planning of a dose optimization process of unit A DSA and management of TACE cases using the existing DSA machine must be considered.

Initial Experience with the Commercial Electron FLASH Research Extension

The purpose of this study was to introduce a new commercial electron FLASH system that has the potential to become widely available for FLASH researchers globally. In this study, we first present the initial acceptance and commissioning tests for the FLASH system, and second, we highlight preliminary FLASH effect results from our cell studies. A linear accelerator was converted into a commercial research platform with the FLASH Research Extension, enabling the generation of a powerful 16 MeV electron FLASH beam. The dosimetric and stability tests were conducted using various dosimeters (i.e., radiochromic film, optically stimulated luminescent dosimeters (OSLDs), and a plane-parallel ionization chamber). To evaluate the FLASH effect, normal and cancer cell lines were FLASH irradiated using different pulse repetition frequencies (PRF) of 18 pulses/s and 180 pulses/s. The electron FLASH mode was able to generate over 1 Gy per pulse at the isocenter and a dose rate of up to 690 Gy/s near the accessory mount of the Linac gantry head. The charge collected by the plane-parallel ionization chamber at the highest PRF (i.e., 180 pulses/s) showed a linear relationship with the delivered number of pulses (i.e., 1 to 99 pulses) with a coefficient of determination (R2) of 0.9996. The absorbed dose measured using radiochromic film and OSLDs agreed within 3%, on average, and followed an inverse square law as the source-to-axis distance (SAD) varied for which the R2 values were 0.9972 and 0.9955 for radiochromic film and OSLDs, respectively. The profile of the FLASH beam was symmetrical but was not as flat as the conventional 16 MeV electron beam due to the use of a thinner custom scattering foil to reduce the degradation of the ultra-high dose rate. The depth-dose curve beyond the build-up region for the FLASH beam was similar to the conventional 16 MeV electron beam for which the range at 50% the maximum dose (R50) agreed within 0.5 mm. The FLASH beam output remained consistent over a 4-month period with a variation of 2.5%, on average. The FLASH sparing effect was observed in vitro for healthy human pancreatic cells. Furthermore, we observed that the highest PRF beam (180 pulses/s) was more effective at destroying pancreatic cancerous cells while minimizing damage to healthy cells compared to the lowest PRF beam (18 pulses/s). The novel commercial FLASH Research Extension system was dosimetrically characterized for pre-clinical FLASH research, and preliminary in vitro results demonstrated the FLASH effect. Given the prevalence of linear accelerators, this new commercial system has the potential to greatly increase the access to FLASH research.

Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy.

The integration of 3D-printing technology into radiation therapy (RT) has allowed for a novel method to develop personalized electron field-shaping blocks with improved accuracy. By obviating the need for handling highly toxic Cerrobend molds, the clinical workflow is significantly streamlined. This study aims to expound upon the clinical workflow of 3D-printed electron cutouts in RT and furnish one year of in-vivo dosimetry data. 3D-printed electron cutouts for 6x6 cm, 10x10 cm, and 15x15 cm electron applicators were designed and implemented into the clinical workflow after dosimetric commissioning to ensure congruence with the Cerrobend cutouts. The clinical workflow consisted of four parts: i) the cutout aperture was extracted from the treatment planning system (TPS). A 3D printable cutout was then generated automatically through custom scripts; ii) the cutout was 3D-printed with PLA filament, filled with tungsten ball bearings, and underwent quality assurance (QA) to verify density and dosimetry; iii) in-vivo dosimetry was performed with optically stimulated luminescence dosimeters (OSLDs) for a patient's first treatment and compared to the calculated dose in the TPS; iv) after treatment completion, the 3D-printed cutout was recycled. QA and in-vivo OSLD measurements were conducted (n=40). The electron cutouts produced were 6x6 cm (n=3), 10x10 cm (n=30), and 15x15 cm (n=7). The expected weight of the cutouts differed from the measured weight by 0.4 + 1.1%. The skin dose measured with the OSLDs was compared to the skin dose in the TPS on the central axis. The difference between the measured and TPS doses was 4.0 + 5.2%. The successful clinical implementation of 3D-printed cutouts reduced labor, costs, and removed the use of toxic materials in the workplace while meeting clinical dosimetric standards.

Development of a novel flexible thin PWO(Er)/ZnO(Ag) nanocomposite for ionizing radiation sensing

Radiation dosimetry is an essential aspect of modern radiotherapy. Optically stimulated luminescence (OSL) dosimetry is a promising technique that uses materials to measure radiation doses. However, current OSL dosimeters are limited in their ability to provide comprehensive validation of spatial dose distributions, particularly in flexibility radiation sensitivity. In this regard, a novel flexible PWO(Er)/ZnO(Ag) nanocomposite sensor has been developed by a solvothermal procedure and its ionization radiation responses were investigated under UV, proton, laser 980 nm, and 241Am sources. The calculated alpha detection efficiency showed that the prepared PWO(Er)/ZnO(Ag) sensor is highly sensitive to alpha radiation (99.6 %) with good stability/repeatability and linear response. According to the Photo/Ionoluminescence study, the doped dual nanocomposite sample showed the strongest blue, green, and yellow emissions at room temperature compared with pure and single doped samples with an exciton lifetime of τ = 143.30 ±0.07 μs. The XRD, FTIR, Raman, and EDX results indicated that the prepared pure and doped nanocomposites have two-phase compositions of PWO and ZnO and related chemical compounds/elements in the nanocomposite structure. The morphologies of the PWO and PWO(Er) nanoparticles (NPs) were mostly cubic and heterogeneous with average particle sizes of 125 and 82 nm. ZnO and ZnO(Ag) had hexagonal, spherical, and rod-shaped particles with typical particle diameters of 130 and 90 nm, respectively. Our results indicate the prepared luminescent nanocomposites are transparent, flexible, highly stable, highly sensitive to ionizing radiation, and have the potential for practical use in optoelectronics and medical imaging in the future.

Dosimetric impact of hollow intraoral stents for head and neck cancer radiotherapy: A phantom study.

To investigate the dosimetric impact of the calculation boundaries and dose calculation algorithms of radiotherapy in head and neck cancer patients with an opened oral cavity connected to the exterior by a hollow intraoral positioning stent. A homemade silicone phantom with an opened oral cavity was placed in a CIRS head phantom to model head and neck cancer patients with a hollow intraoral positioning stent. 3D-CRT plans were designed on CT images of the phantom in Monaco and Pinnacle3 treatment planning systems (TPSs) with the same beam parameters. The default boundary and manually extrapolated boundary were both adopted in these two TPSs to explore the dosimetric impact on treatment plans. The nanoDot™ optically stimulated luminescence dosimeters (OSLDs) were chosen to measure the planned dose surrounding the oral cavity of the head phantom after calibration. The doses in the air cavity and two measuring points at the joint area were dramatically changed from 0.0, 92.4 and 148.8 cGy to 177.8, 244.2 and 244.1 cGy in Monaco after adopting the extrapolated boundary. While the calculated doses at the same place were changed from 61.2, 143.7 and 198.3 cGy to 175.4, 234.7 and 233.2 cGy in Pinnacle3 with a similar calculation boundary. For the Monaco TPS, the relative errors compared to the OSLD measured doses were 2.94±1.93%, 0.53±8.64%, 2.65±1.87% and 3.93±1.69% at 4 measuring positions. In contrast, the relative errors 4.03±1.93%, 4.85±8.64%, 7.61±1.87% and 5.61±1.69% were observed in Pinnacle3 . The boundary setting of an opened oral cavity in TPSs has a significant dosimetric impact on head and neck cancer radiotherapy. An extrapolated boundary should be manually set up to include the whole oral cavity in the dose calculation domain to avoid major dose deviations.

Studies of OSL properties of alkali- and rare earth-doped BeO based novel dosimeters for applications in external beam radiotherapy

This study aims to assess the feasibility of a novel Beryllium Oxide (BeO) based ceramics to be used as optically stimulated luminescence (OSL) dosimeters for monitoring of high-energy beams used in radiotherapy. The BeO ceramic dosimeters doped with alkali and rare earth metals (BeO:Na5%,Ce0.005%,Tb0.05%, BeO:Na5%,Ce0.01%,Er0.01%, and BeO:Na5%,Ce0.01%,Dy0.01%) were fabricated in pellet forms, and their luminescence responses were measured at the virtual water phantom interfaces for various field sizes of a 6 MV flattening filter-free photon beam of Varian LINAC. The OSL dosimeter's performance has been confirmed their practical usefulness as in vivo dosimeters in radiotherapy clinics. The provided dose estimates were validated using varying X-ray energies and doses, typically employed for actual medical radiotherapy systems. Our results indicated that the studied dosimeters rendered an almost linear response in the dose range of 0.05 Gy–20 Gy delivered from the 6 MV X-ray beam. Fading of the stored OSL was found to be less than 5% after a short storage period. The dependencies of OSL responses concerning beam energy, dose rate, irradiation angle, depth, and field size are all found to be supportive of the successful utilization of the BeO OSLDs in clinical environments.

Whole body and extremity doses of nuclear medicine personnel involved in manual and semi-automated methods of dispensing liquid iodine-131

This study aimed to evaluate the whole body dose Hp (10) and extremity dose Hp (0.07) of nuclear medicine personnel who administered liquid I-131 by using manual and fabricated semi-automated dispenser system. The semi-automated dispenser system comprises of peristaltic pumps and a motor controller was developed for dispensing liquid I-131. Optically stimulated luminescent dosimeters (OSLD) were used on two radiopharmacists to evaluate the whole body dose HP (10). NanoDot dosimeters were placed on personnel fingers to measure extremity dose HP (0.07). The mean doses were calculated for both manual and automated dispensing techniques. The findings revealed a significant 87.65%–92.31% reduction in both whole body and extremity doses when utilising semi-automated dispenser system compared to manual dispensing. Additionally, the semi-automated dispenser system demonstrated high accuracy with ≤5% error in dispensing the prescribed amount of liquid I-131. The use of the semi-automated system resulted in a significant reduction in whole body and extremity doses due to less contact between personnel and the source, and high accuracy of the prescribed amount of I-131.

Comparing brass mesh to tissue equivalent bolus materials for volumetric modulated arc therapy chest wall irradiation.

To compare the superficial dose when using brass mesh bolus (BMB), no bolus, or 3mm tissue-equivalent bolus with a pseudo-flash volumetric modulated arc therapy (VMAT) breast treatment planning technique. Two different beam arrangements for right-sided irradiation and one beam arrangement for bilateral irradiation were planned on an inhomogeneous thorax phantom in accordance with our clinical practice for VMAT postmastectomy radiotherapy (PMRT). Plans were optimized using pseudo-flash and representative critical organ optimization structures were used to shape the dose. Plans were delivered without bolus, with 3mm tissue-equivalent bolus (TEB), or with one-layer BMB. Optically stimulated luminescence dosimeter (OSLD) and radiochromic film measurements were taken and analyzed to determine the superficial dose in each case and the relative enhancement from the no bolus delivery. Superficial dose measured with OSLDs was found to be 76.4±4.5%, 103.0±6.1%, and 98.1±5.8% of prescription for no physical bolus (NB), TEB, and BMB, respectively. Superficial dose was observed to increase from lateral to medial points when measured with film. However, the relative increase in superficial dose from NB was consistent across the profile with an increase of 43±2.1% and 34±3.3% of prescription for TEB and BMB, respectively. The results are in good agreement with expectations from the literature and the experience with tangential radiotherapy. Three millimeter TEB and one-layer BMB were shown to provide similar enhancement to the superficial dose compared to delivery without bolus. BMB, which does not significantly affect dose at depth and is more conformal to the patient surface, is an acceptable alternative to 3mm TEB for chest wall PMRT patients treated with pseudo-flash PMRT.

Application of OSL strips in CT dosimetry according to the AAPM methodology

Computed tomography (CT) images contribute to high-quality medical diagnosis, but radiation dose can be quite high, requiring accurate assessment. CT dose index (CTDI) was developed for dosimetric purposes, but for scanners operated exclusively in axial mode. Nowadays, CTDI underestimate patient dose in helical CT exams. AAPM report TG111 (2010) suggested a new metric in which the patient's radiation dose is obtained from dose profiles constructed from several measurements made with a small ionization chamber. It is also possible to obtain dose profiles using properly calibrated OSL (optically stimulated luminescence) strips. The main objective of the present work is to contribute to optimizing CT dosimetry, comparing dose profiles obtained with OSL strips with measurements obtained by other authors. In this work, a “pencil” ionization chamber and 20 cm x 0.3 cm OSL strips were X-ray-irradiated, in air and in the holes of two cylindrical CT phantoms, using 100, 120, 140 kV peak voltages, both in lab and in a clinical CT scanner. Irradiated strips were read using an OSL reader built in the GDRFM. OSL profiles were calibrated against ionization chamber. From them, CTDIw and CTDIvol values were determined, differing approximately 3.9% from those of the CT scanner. From the profiles, also the planar equilibrium dose Deq,p (TG111) was evaluated in some CT protocols; Deq,p exceeded the CTDI values from the CT scanner in every case. E.g.: The percentage difference between Deq,p and CTDIvol for the head phantom ranged between 33-25%. Thus, in some cases, it could be advantageous to use calibrated OSL dosimeters instead of ionization chambers to obtain the profiles, saving time, because it is possible to obtain five OSL profiles from a single phantom irradiation.

Radiosurgery dosimetry using CaSO4:Eu OSLD film-a feasibility study.

Recent studies demonstrated that optically stimulated luminescence (OSL) systems allow the evaluation of doses for 2D mapping in a relatively fast and simple way and results show submillimeter resolution. This work presents, for the first time, an optically stimulated luminescence dosemeter (OSLD) in the form of film made with CaSO4:Eu particles embedded in a silicone elastomer matrix. The OSLD film was produced using a low-cost and relatively simple methodology. This film is reusable and the signal can be satisfactorily bleached using blue LEDs. The main dosimetric properties were evaluated using TL/OSL Risø reader with blue stimulation and Hoya U-340 filter. Investigation shows repeatability within 3% when measuring with the same film sample. Regarding the OSLD film homogeneity, nearly 12% sensitivity change was observed within the 5×5cm2 produced film. Additionally, the dose response curve shows linearity from 5 to 25Gy. Fading of the OSL signal is relatively high, about 50% in the first week and then is stable. Nevertheless, a 3×3cm2 OSLD film was successfully used to map dose distribution in radiosurgery (6MV photon beam). This work demonstrates the feasibility of 2D dosimetry using reusable OSLD films based on CaSO4:Eu.

Radiation dose-event relationship after intraoperative radiotherapy as a boost in patients with breast cancer.

Intraoperative radiotherapy (IORT) can be used as a boost in combination with external whole breast irradiation. This study reports the clinical and dosimetric factors associated with IORT-related adverse events (AE). Between 2014 and 2021, 654 patients underwent IORT. A single fraction of 20 Gy was prescribed to the surface of the tumour cavity using the mobile 50-kV X-ray source. For skin dose measurement, at least four optically stimulated luminescent dosimeter (OSLD) chips were annealed and attached to the skin edge in the superior, inferior, medial, and lateral locations during IORT. Logistic regression analyses were conducted to identify factors associated with IORT-related AE. With a median follow-up period of 42 months, 7 patients experienced local recurrence, resulting in a 4-year local failure-free survival rate of 97.9%. The median skin dose measured by OSLD was 3.85 Gy (range, 0.67-10.89 Gy), and a skin dose of > 6 Gy was observed in 38 patients (2%). The most common AE was seroma (90 patients, 13.8%). We also found that 25 patients (3.9%) experienced fat necrosis during follow-up, and among them, 8 patients underwent biopsy or excision to exclude local recurrence. IORT-related late skin injury occurred in 14 patients, and a skin dose > 6 Gy was significantly associated with IORT-induced skin injury (odds ratio 4.942, 95% confidence interval 1.294-18.871, p = 0.019). IORT was safely administered as a boost to various populations of patients with breast cancer. However, several patients may experience severe skin injuries, and for older patients with diabetes, IORT should be performed with caution.

A User-Friendly System for Mailed Dosimetric Audits of 192Ir or 60Co HDR Brachytherapy Sources.

The main goal of this work is to design and characterize a user-friendly methodology to perform mailed dosimetric audits in high dose rate (HDR) brachytherapy for systems using either Iridium-192 (192Ir) or Cobalt-60 (60Co) sources. A solid phantom was designed and manufactured with four catheters and a central slot to place one dosimeter. Irradiations with an Elekta MicroSelectron V2 for 192Ir, and with a BEBIG Multisource for 60Co were performed for its characterization. For the dose measurements, nanoDots, a type of optically stimulated luminescent dosimeters (OSLDs), were characterized. Monte Carlo (MC) simulations were performed to evaluate the scatter conditions of the irradiation set-up and to study differences in the photon spectra of different 192Ir sources (Microselectron V2, Flexisource, BEBIG Ir2.A85-2 and Varisource VS2000) reaching the dosimeter in the irradiation set-up. MC simulations indicate that the surface material on which the phantom is supported during the irradiations does not affect the absorbed dose in the nanoDot. Generally, differences below 5% were found in the photon spectra reaching the detector when comparing the Microselectron V2, the Flexisource and the BEBIG models. However, differences up to 20% are observed between the V2 and the Varisource VS2000 models. The calibration coefficients and the uncertainty in the dose measurement were evaluated. The system described here is able to perform dosimetric audits in HDR brachytherapy for systems using either 192Ir or 60Co sources. No significant differences are observed between the photon spectra reaching the detector for the MicroSelectron V2, the Flexisource and the BEBIG 192Ir sources. For the Varisource VS2000, a higher uncertainty is considered in the dose measurement to allow for the nanoDot response.

Assessment of radiation exposure in a nuclear medicine department of an oncology hospital

BackgroundMedical personnel in nuclear medicine departments are exposed to ionizing radiation which is associated with cancer induction and mortality risks. Examples of such personnel are those working in the hot-areas where radioisotopes for nuclear medicine examinations are prepared. This work aims to estimate the occupational radiation exposure for workers at the Nuclear Medicine department in Da Nang Oncology Hospital, Vietnam. Materials and methodsThe study was conducted from 2020 to 2021. The personal dose equivalents (Hp) were quantified for soft tissues for deep dose (Hp(10)), eye lens dose (Hp(3)), skin dose (and Hp(0.07)) were quantified utilizing optically stimulated luminescence dosimeters (OSLD) crystals. In this study, the dose equivalent at the hot area is measured by 9 OSLD, while that for staff was measured using 16 OSLD. ResultsIn 2020, the annual average Hp(10) was (0.38 mSv ± 1.39); in 2021 Hp(10) was (0.25 mSv ± 1.27). The average Hp(10) was well below the annual occupational dose limits (20 mSv.year−1). Regarding the annual dose, all recorded values were quite low compared to the annual radiation dose limits for radiation staff (20 mSv annual ∼ 1.67 mSv.month−1). Nevertheless, some points of measurement revealed a high-value dose of 5.69 mSv ± 2.83. This suggests that rigorous evaluation of the workplace is essential to ensuring workers' exposure is kept within safe levels. ConclusionsIt is concluded that the Hp(10) and Hp(0.07) for the working environment and radiation workers were below the dose limits from ICRP. In addition, it is recommended that continuous monitoring of the occupational dose in nuclear medicine department is essential to reduce the dosimetric hazards of personnel working in the department.

Abstract P1-10-11: Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes

Abstract BACKGROUND: The role of multi-lumen catheter devices in the delivery of high dose rate (HDR) brachytherapy for adjuvant accelerated partial breast irradiation (APBI) for women with DCIS or early-stage breast cancer has been well established. In vivo dosimetry (IVD) using optically stimulating luminescence dosimeters (OSLD) is a feasible way to detect applicator instability that may cause translational and rotational inaccuracies during HDR brachytherapy delivery. Herein, we evaluate the accuracy and effectiveness of IVD to improve patient outcomes following APBI brachytherapy using the Strut Adjusted Volume Irradiation (SAVI) device. METHODS: Single-institution cohort study piloting the use of OSLD on the patient’s skin during HDR brachytherapy APBI to assess the estimated maximum skin dose (skin Dmax) and the achievable accuracy of OSLD for skin Dmax measurements. Women treated with SAVI-based APBI between November 1, 2018 and October 1, 2021 were eligible to enroll in our study. All patients met the American Society for Radiation Oncology “suitable” or “cautionary” criteria and were treated according to the American Brachytherapy Society consensus treatment planning guidelines. A SAVI preplan was created to estimate the probable point of skin Dmax. During CT simulation, a radiopaque marker was placed on the skin for visualization during treatment planning. Correction factors were applied to account for the OSLD tissue-air interface that is not present in the TG-43 expected dose calculations. Measured and calculated IVD doses were analyzed to assess agreement and cause for discrepancies found. Breast phantom IVD measurements repeated seven times with two independent dose points were analyzed to assess the best accuracy achievable under ideal conditions. RESULTS: We enrolled 41 patients with an average age of 68 years. Table 1 details the brachytherapy treatment delivery and dosimetry data. Higher skin Dmax as a percentage of the radiation prescription was associated with the occurrence of breast volume loss noted on subsequent clinical breast exams (OR 1.84 per each 5% increase in skin Dmax; 95% CI 1.21 – 3.32; p=0.016). The graphically estimated skin Dmax threshold was 80% with all cases of noted breast volume loss occurring above this threshold. The overall level of achievable IVD accuracy was ±3.32% based on breast phantom measurements. Under ideal conditions, all measurements were in the ±7% range. Three of 14 phantom measurement exceeded the 6% discrepancy range. Clinical IVD measurements detected 5 true positive cases (12.2% of cohort) that required intervention due to rotations in the SAVI applicator. For a ±7% tolerance criteria, 90.2% of the patients tested passed IVD. Of the eight patients that failed at the 7% level, IVD detected 3 OSLD placement errors, 2 rotational discrepancy cases, and 1 large air-gap at the point of measurement. CONCLUSIONS: Accuracy and reproducibility are imperative tenets of HDR brachytherapy APBI. IVD utilizing OSLD is an effective method for detecting treatment set-up and delivery errors for patients receiving SAVI-based APBI with dose accuracy within ±3.32%. Errors requiring intervention due to SAVI device rotation were detected in 12.2% of our cohort, and these errors would have likely gone undetected without IVD. Using OSLD as IVD to measure skin Dmax doses that may increase the risk of breast cosmetic defects should be investigated further. Table 1. Brachytherapy treatment delivery and dosimetry data. *PTV-Eval is a uniform 10 mm expansion on the CTV with exclusion of PTV within 5 mm of skin or chest wall. +Percent dose discrepancy refers to difference in dose between APBI plan calculations and IVD measurements. Citation Format: Tyler Gutschenritter, Afua Yorke, Nayak Polissar, Nirnaya Miljacic, Janice Kim, Lori Young. Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-11.

Entrance Skin Dose (ESD) and Bucky Table Induced Backscattered Dose (BTI-BSD) in Abdominal Radiography With nanoDot Optically Stimulated Luminescence Dosimeter (OSLD).

In radiography, inconsistencies in patients' measured entrance skin dose (ESD) exist. There is no published research on the bucky table induced backscattered radiation dose (BTI-BSD). Thus, we aimed to ascertain ESD, calculate the BTI-BSD in abdominal radiography with a nanoDot OSLD, and compare the ESD results with the published data. A Kyoto Kagaku PBU-50 phantom (Kyoto, Japan)in an antero-posterior supine position was exposed, selecting a protocol used for abdominal radiography. The central ray of x-ray beam was pointed at the surface ofabdomen at the navel, where a nanoDot dosimeter was placed to measure ESD. For the BTI-BSD, exit dose (ED) was determined by placing a second dosimeter on the exact opposite side (backside) of the phantom from the dosimeter used to determine (ESD) with and without bucky table at identical exposure parameters. The BTI-BSD was calculated as the difference between ED with and without bucky table. The ESD, ED, and BTI-BSD were measured in milligray (mGy). ESD mean values with and without bucky table were 1.97 mGy and 1.84 mGy, whereas ED values were 0.062 mGy and 0.052 mGy, respectively. Results show 2-26% lowerESD values with nanoDot OSLD. The BTI-BSD mean value was found to be approximately 0.01 mGy. A local dose reference level (LDRL) can be established using ESD data to safeguard patients from unnecessary radiation. In addition, to minimize the risk of BTI-BSD in patients in radiography, the search for the use or fabrication of a new, lower atomic number material for the bucky table is suggested.