microStar Reader Research Articles

LONG-TERM PERFORMANCE OF AN OPTICALLY STIMULATED LUMINESCENT SYSTEM FOR DOSE EQUIVALENT HP(10) MEASUREMENT.

The performance of an optically stimulated luminescent (OSL) passive dosimetry system named MicroStar reader manufactured by Landauer Inc and acquired in 2011 is assessed in this study. The assessment carried out is based on the results of the intercomparison (IC) exercises organised by the International Atomic Energy Agency in 2013 and 2021. The IC results show that this OSL reader can maintain good performance after long-term usage provided adequate maintenance and calibration operations are carried out. Moreover, this assessment also reveals the importance of using a higher number of measurements per data point for the non-linearity test of the IEC 62387 standard.

Anthropomorphic phantom organ dose assessment using optically stimulated luminescence dosimeters unified in multi-detector computed tomography

This organ dose profile investigation is based on a technology that allows for the acquisition of densely sampled dose data, obtained using modified nanoDot™ OSLDs and a typical anthropomorphic Alderson Radiation Therapy phantom (ARTM 1092 model). The CT scan parameters were based on adult chest-abdomen and head region CT procedures, which were performed using a Siemens Somatom Definition AS+ at Hospital Sultanah Aminah in Johor. In studying the scanned region, the tube voltage and exposure duration values were considerably altered, with modulation approaches significantly altering the dosage distribution. In the head-neck procedure, the average absorbed dose per slice for the brain and thyroid was 3.469–33.645 mGy and 3.372–34.528 mGy, respectively. The distribution of chest-abdomen region organ dose mapping explains that the lungs received the highest organ dose, receiving a dose of 20.795 mGy from protocol P4, a setting of 140 kV tube voltage in the CT chest-abdomen protocol. The organ dosage levels in this investigation varied from 2.277 to 20.794 mGy, depending on tube voltage, tube current, and exposure period, as well as the organ composition, location, and surrounding anatomic structures. The average absorbed dosage in the lungs per slice varied from 3.439 to 20.794 mGy. The most significant coefficient of variation (CoV) for dosage samples of the lungs inside separate slices was 13%. The radiation dose patterns are consistent with similar tests and modalities, with variations dependent on tube voltage, exposure period, tube current, slice collimation, and pitch factor. The LED and CAL measured data (Mean ± SD) were determined to be an average of 4657 ± 563 and 1677 ± 31 counts, respectively. The supplied data is evidence of the microStar reader's superior performance.

SABR pre-treatment checks using alanine and nanoDot dosimeters.

Stereotactic Ablative Radiotherapy (SABR) remains one of the preferred treatment techniques for early-stage cancer. It can be extended to more treatment locales involving the sternum, scapula and spine. This work investigates SABR checks using Alanine and nanoDot dosimeter for three treatment sites, including sternum, spine and scapula. Alanine and nanoDot dosimeters' performances were verified using a 6 MV photon beam before SABR pretreatment verifications. Each dosimeter was placed inside customized designed inserts into a Rod Phantom (in-house phantom) made of Perspex that mimics the human body for a SABR check. Electron Paramagnetic Resonance (EPR) spectrometer, Bruker EleXsys E500 (9.5GHz) and Microstar (Landauer Inc.) Reader was employed to acquire the irradiated alanine and nanoDot dosimeters' signal, respectively. Both dosimeters treatment sites are expressed as mean ± standard deviation (SD) of the measured and Eclipse calculated dose Alanine (19.59 ± 0.24, 17.98 ± 0.15, 17.95 ± 0.18) and nanoDot (19.70 ± 0.43, 17.05 ± 0.08, 17.95 ± 0.98) for spine, scapula and sternum, respectively. The percentage difference between alanine and nanoDot dosimeters was within 2% for sternum and scapula but 2.4% for spine cases. These results demonstrate Alanine and nanoDot dosimeters' potential usefulness for SABR pretreatment quality assurance (QA).

COMPARISON OF THE PERFORMANCE OF TWO OSL READERS FOR THE PERSONAL DOSE EQUIVALENT HP(10) MEASUREMENT.

Technical performances of two optically stimulated luminescence readers including, a microStar reader and an Auto 200 reader both manufactured by Landauer, Inc. were studied by the National Radiation Protection Agency Dosimetry Laboratory using manufacturer and International Electrotechnical Commission requirements. The two reader tools demonstrated satisfactory results as they metall the requirements. The two readers showed similar performance for the overall uncertainty and the Coefficient of Variation tests. The microStar reader showed better performances for the linearity and quality control tests, whereas the Auto 200 reader has a lower limit of detection. Moreover, an average shift of 0.08mSv exists when measuring the doses with the two readers.

Use of Commercially Available Optically Stimulated Luminescence Dosimeter As Extremity Dose Estimator.

In 2009, Idaho National Laboratory (INL) transitioned to an external dosimetry program using optically stimulated luminescent (OSL) technology. This process led to the introduction of the Landauer, Inc., nanoDot dosimeter and MicroStar reader to INL's radiological control program. At the time, a small, self-contained, single chip OSL dosimeter that could be easily read in the field was recognized as having many potential applications for a radiological control program. The ability to achieve a realistic extremity-dose estimate in the field shortly following work where significant exposure is expected is a much sought-after capability at INL. It was proposed to employ the Landauer nanoDot dosimeter as a supplemental extremity monitor as an alternative to time-motion dose analyses based on direct radiation measurements, which had proven to be inaccurate and operationally inefficient. Additionally, this process does not involve the nanoDot in the US Department of Energy Laboratory Accreditation Program (DOELAP) process, which significantly reduces operational complexity. A dose conversion value for the nanoDot dosimeter was derived from direct comparisons with a DOELAP-accredited extremity dosimeter. The geometry or placement of the nanoDot relative to the accredited extremity dosimeter was kept as proximate as possible to best replicate the expected results from the accredited extremity dosimeter. Upon implementation, the nanoDot has proven to be effective in providing reasonable and timely extremity-dose estimates for operational control.

Fluoroscopy-guided intervention procedure norms for occupational eye radiation dose: An overall evaluation

The main objective of radiation management in interventional radiology is to minimise the unnecessary use of radiation. Fluoroscopically guided interventional procedures (FGI) are performed with increasing frequency in operating theatre for a growing number of procedures. In this view, we evaluate the occupational eye dose of an interventional radiologist (IR) for different dosimeter positions commonly utilised in the FGI procedures. Herein, one IR was examined for a period of three months while performing the 65 FGI procedures of different types. Eye doses of the IR were measured using the optically-stimulated luminescence dosimeters called the nanoDots (Landauer, Inc.). The IR wore the protective lead glasses equipped with the nanoDots (on the left and right eye) during the observations period. All the nanoDot measurements were conducted using the microStar reader system (Landauer Inc.). The eye dose of the IR per dose area product (DAP) was discerned to be 0.85 ± 0.13 μSv.Gy−1.cm−2 for the left eye with the protection. The estimated annual eye dose of 18.32 mSv.y−1 was below the recommended dose limit (20 mSv.y−1). The mean eye dose and DAP correlation was observed to be significant and insignificantly related to the fluoroscopy time (p < 0.05). The observed lower dose for the right eye than that of the left one was attributed to the specific position of the IR with respect to the patient. Present strategy on the occupational eye dose measurement was shown to be effective for determining the risk of the eye lens dose level in the absence of the protective lead glasses. It is established that the eye dose limit can easily exceed the recommended standard if the IR does not use the protective lead glasses with other safety equipment during the treatment.

Direct and indirect entrance surface dose measurement in X-ray diagnostics using nanoDot OSL dosimeters

This study investigated the suitability of nanoDot optically stimulated luminescence (OSL) dosimeters for entrance surface dose (ESD) measurements in common X-ray diagnostics. OSL dosimetry system supplied by Landauer Inc, (Glenwood, IL, USA) consisting of nanoDot OSL dosimeters and microStar reader were used. ESDs were measured with nanoDots placed on whole-body anthropomorphic phantom (for direct measurements) and in free air without backscatter material (for indirect measurements) in accordance with the IAEA Technical Report Series No. 457. Measurements were carried out in five X-ray projections including AP abdomen, AP chest, PA chest, AP thoracic spine and AP skull. The mean ESD for each projection was evaluated from multiple measurements with three different field sizes. Mean ESDs (direct measurements) for AP abdomen, AP chest, PA chest, AP thoracic spine and AP skull were 4.3 mGy, 0.7 mGy, 0.3 mGy, 6.8 mGy and 2.8 mGy respectively. While in the case of indirect measurements, the corresponding mean ESD values were 4.8 mGy, 0.7 mGy, 0.2 mGy, 7.2 mGy and 3.7 mGy respectively. The results were found to be within IAEA and European Commission (EC) diagnostic reference levels (DRLs) range. The percentage difference of the ESDs measured by direct and indirect methods in all projections were between 0 to 40%. It was affirmed that nanoDot OSL dosimeter is a good candidate for ESD measurement in common radiographic examinations, while taking into account the effect of energy dependence.

Response of optically stimulated luminescence dosimeters subjected to X-rays in diagnostic energy range

The use of optically stimulated luminescence (OSL) for dosimetry applications has recently increased considerably due to availability of commercial OSL dosimeters (nanoDots) for clinical use. The OSL dosimeter has a great potential to be used in clinical dosimetry because of its prevailing advantages in both handling and application. However, utilising nanoDot OSLDs for dose measurement in diagnostic radiology can only be guaranteed when the performance and characteristics of the dosimeters are apposite. In the present work, we examined the response of commercially available nanoDot OSLD (Al2O3:C) subjected to X-rays in general radiography. The nanoDots response with respect to reproducibility, dose linearity and signal depletion were analysed using microStar reader (Landauer, Inc., Glenwood, IL). Irradiations were performed free-in-air using 70, 80 and 120 kV tube voltages and tube currents ranging from 10 – 100 mAs. The results showed that the nanoDots exhibit good linearity and reproducibility when subjected to diagnostic X-rays, with coefficient of variations (CV) ranging between 2.3% to 3.5% representing a good reproducibility. The results also indicated average of 1% signal reduction per readout. Hence, the nanoDots showed a promising potential for dose measurement in general X-ray procedure.

Angular dependence of dose sensitivity of nanoDot optically stimulated luminescent dosimeters in different radiation geometries.

A type of in vivo dosimeter, an optically stimulated luminescent dosimeter, OSLD, may have dose sensitivity that depends on the angle of incidence of radiation. This work measures how angular dependence of a nanoDot changes with the geometry of the phantom in which irradiation occurs and with the intrinsic structure of the nanoDot. The OSLDs used in this work were nanoDot dosimeters (Landauer, Inc., Glenwood, IL), which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). Dose to the OSLDs was delivered by 6 MV x-rays. NanoDots with various intrinsic sensitivities were irradiated in numerous phantoms that had geometric shapes of cylinders, rectangles, and a cube. No angular dependence was seen in cylindrical phantoms, cubic phantoms, or rectangular phantoms with a thickness to width ratio of 0.3 or 1.5. An angular dependence of 1% was observed in rectangular phantoms with a thickness to width of 0.433-0.633. A group of nanoDots had sensitive layers with mass density of 2.42-2.58 g/cm(3) and relative sensitivity of 0.92-1.09 and no difference in their angular dependence. Within experimental uncertainty, nanoDot measurements agree with a parallel-plate ion chamber at a depth of maximum dose. When irradiated in cylindrical, rectangular, and cubic phantoms, nanoDots show a maximum angular dependence of 1% or less at an incidence angle of 90°. For a sample of 78 new nanoDots, the range of their relative intrinsic sensitivity is 0.92-1.09. For a sample of ten nanoDots, on average, the mass in the sensitive layer is 73.1% Al2O3:C and 26.9% polyester. The mass density of the sensitive layer of a nanoDot disc is between 2.42 and 2.58 g/cm(3). The angular dependence is not related to Al2O3:C loading of the nanoDot disc. The nanoDot at the depth of maximum dose has no more angular dependence than a parallel-plate ion chamber.

SU-E-T-173: Evaluation of the MicroSTAR Reader for the OSLD System for Remote Dosimetry Audits at the IROC HQAC

Purpose: Analysis of the performance of the microSTARii reader for optically stimulated luminescence dosimeters (OSLD) used by the IROC Houston Quality Assurance Center (IROC HQAC) for external audits compare to the characteristics of the Microstar reader. Methods: The IROC HQAC uses the Microstar reader for the OSLD program for verification of output of photon, electron and proton beams. The calculation of dose from the OSLD system is based on a group of factors defined at time of the commissioning of a batch of detectors. Factors like system sensitivity (SS), depletion (KD), element correction factor (ECF), linearity (KL), energy correction (KE). The new microSTARii unit presents many hardware and software upgrades that were considered useful for this program. Based on these changes many factors, that were considered reader dependent, were revised in order to analyze the effect of the new reading process. The SS, KD, ECF and KL were evaluated and compared with data defined based on reading done on Microstar reader. Results: The SS is reader specific and specified at 100 cGy dose level. This value is define per reading session and monitored over time. The KD factor was found to be different because of reading procedure are different. Themore » ECF values changed for a group of nano dots compare to values defined based on reading done on the Microstar reader. The KL was defined for the reader. Conclusion: The new microSTARii reader presents new features that improve the efficiency of the OSLD program at the IROC HQAC. New characterization is needed before final implementation is done to match the requirements of the existing OSLD system defined for the Microstar reader. Changes in uncertainty of the results has not been analized.« less

SU‐E‐T‐315: The Change of Optically Stimulated Luminescent Dosimeters (OSLDs) Sensitivity by Accumulated Dose and High Dose

Purpose:The objective of this study is to evaluate radiation sensitivity of optical stimulated luminance dosimeters (OSLDs) by accumulated dose and high dose.Methods:This study was carried out in Co‐60 unit (Theratron 780, AECL, and Canada) and used InLight MicroStar reader (Landauer, Inc., Glenwood, IL) for reading. We annealed for 30 min using optical annealing system which contained fluorescent lamps (Osram lumilux, 24 W, 280 ∼780 nm). To evaluate change of OSLDs sensitivity by repeated irradiation, the dosimeters were repeatedly irradiated with 1 Gy. And whenever a repeated irradiation, we evaluated OSLDs sensitivity. To evaluate OSLDs sensitivity after accumulated dose with 5 Gy, We irradiated dose accumulatively (from 1 Gy to 5 Gy) without annealing. And OSLDs was also irradiated with 15, 20, 30 Gy to certify change of OSLDs sensitivity after high dose irradiation. After annealing them, they were irradiated with 1Gy, repeatedly.Results:The OSLDs sensitivity increased up to 3% during irradiating seven times and decreased continuously above 8 times. That dropped by about 0.35 Gy per an irradiation. Finally, after 30 times irradiation, OSLDs sensitivity decreased by about 7%. For accumulated dose from 1 Gy to 5 Gy, OSLDs sensitivity about 1 Gy increased until 4.4% after second times accumulated dose compared with before that. OSLDs sensitivity about 1 Gy decreased by 1.6% in five times irradiation. When OSLDs were irradiated ten times with 1Gy after irradiating high dose (10, 15, 20 Gy), OSLDs sensitivity decreased until 6%, 9%, 12% compared with it before high dose irradiation, respectively.Conclusion:This study certified OSLDs sensitivity by accumulated dose and high dose. When irradiated with 1Gy, repeatedly, OSLDs sensitivity decreased linearly and the reduction rate of OSLDs sensitivity after high dose irradiation had dependence on irradiated dose.

A comparison of dosimetric properties of three solid state dosimetry systems for dosimetry audit in radiotherapy

Published Article,The purpose of this study is to investigate and compare characteristics of three solid state dosimetry systems in order to determine working parameters and corrections needed for remote dosimetry audits of high energy photon and electron beams. The following systems were investigated: a thermo luminescent dosimetry (TLD) system (TLD-100, PCL3 reader), an optically stimulated luminescent dosimetry (OSLD) system (nanoDots, microStar reader) and a radiophoto luminescent dosimetry (RPLD) system (GD 302M, FGD-1000 reader).

SU‐E‐T‐28: Commissioning of OSLDs as An In‐Vivo Dosimeter in INTRABEAM Radiotherapy for Early Stage Breast Cancer

Purpose: To commission OSLDs for estimating skin dose for patients undergoing INTRABEAM radiation therapy for early stage breast cancer. Methods: Intrabeam system, using low energy X‐rays of 20keV effective energy, 0.64mm of Al HVL, deliver 20Gy to the spherical applicator surface. Optically Stimulated Luminescence Dosimeters (OSLDs Landauer screened nanoDOTs) were used for this study. OSLDs were water proofed using 3M Tegaderm film and held by a custom made solid water holder. OSLDs were irradiated in water at distances from the applicator surface ranging from 5mm up to 40mm. Measurements were repeated three times for each depth. Depth dose data in water as provided by the manufacturer is applied for estimating the delivered dose to OSLDs. Irradiated OSLDs were analyzed using microStar reader after giving a minimum 10 minutes delay to allow suppression of ambient phosphorescence. Calibration curves (Dose vs Counts) were generated for each applicator/probe combination and validated by performing comparisons in plastic water using PTW MARKUS planeparallel Ionization chamber and virgin OSLDs. Results: Calibration curves were generated for spherical applicators with diameters ranging from 2.5cm to 5cm. OSLD calibration curves were validated by performing a set of measurements in plastic water using ionization chamber &amp; OSLDs. The results were within ±6% as expected based on the OSDL sensitivity uncertainty and OSLD positioning uncertainty. The reproducibility of OSLD measurements were ±2% (1σ). Conclusion: OSLDs can be used for in vivo dosimetry for intrabeam therapy and can accurately measure skin dose for patients receiving INTRABEAM therapy. Immediate reading and the ease of use provide added advantages to use OSLDs as an in vivo dosimeter. This calibration method incorporates the energy spectrum change with depth and hence the change in OSLD sensitivity with energy.

SU-E-I-07: The Effect of Different Beam Filters On the KV CBCT Image Dose Response Curves of NanoDot OSL Dosimeters

Purpose: To evaluate the effect of different beam filters on the dose response curves of nanoDot OSL dosimeters at kV CBCT energy. Methods: The InLight™ OSL dosimetry system (Landauer,Inc., Glenwood, IL, USA) consisting of nanoDot dosimeters and MicroStar reader was calibrated using the X-ray Volume Imager (XVI) mounted on the Elekta Synergy (Elekta, Crawley, UK) linac and the On Board Imager(OBI) mounted on the Varian True Beam (Varian Medical systems, Palo Alto, CA) linac. Doses ranged between 0 and 12 cGy were delivered to nanoDot OSLDs on 5 cm thick PMMA slab using 120kVp F0(no filter) and F1(Bowtie filter)XVI CBCT beams, 125 kVp half fan (HF) and full fan (FF) OBI beams. Dose points were correlated to absolute air kerma levels measured in air using the 0.6 cc Farmer ionization chamber and converted to dose in water at the phantom surface according to AAPM TG61. Results: Dose response curves for all imaging settings were linear. The dose response curves for the 120 kVp F0 and F1 VXI CBCT beams differed by 8 to 9 %. The dose response curves for the 125 kVp FF and HF OBI CBCT beams also differed by 7 to 8 %. These results suggest that nanoDot dosimeters are sensitive not only to differences in kVp of the beam but also to differences in spectra resulted from the use of different filters. Conclusion: Dose response curves of nanoDot OSLDs for photon beams of same kVp but filtered with different filters are different. Hence,the use of correction factors (based solely on differences in the response of the OSLDs at different kVps) to allow the reading of the MicroStar reader to be converted from one set of reference condition to another is not sufficient to ensure accurate estimation of measured doses.It is important to create dose response curve at every irradiation setting. This project is funded, in part, under a grant with the Pennsylvania Department of Health. The Department specifically declaims responsibility for any analyses, interpretations or conclusions

SU-E-T-49: Implementation of Optically Stimulated Luminescent Detectors in the Clinical Setting

Purpose: To perform experiments to determine how Optically Stimulated Luminescent Detectors (OSLDs) can be used for in vivo dosimetry in the clinical environment. For clinical use, OSLDs should have stable, reproducible behavior in measuring dose and be easy to use. Methods: OSLDs were placed in solid water at dmax, with 12cm of solid water below for backscatter, and were irradiated with a TG51 calibrated linac at 10MV, 100SSD and with a 10x10 cm2 field. The OSLDs were of the Nanodot type from Landauer; the Landauer microStar reader was used to measure photomultiplier counts. No modifications were made to the reader, e.g., use of special filters. OSLDs were irradiated to a variety of dose levels which could be encountered in the clinic, as well as levels of 200Gy or more. OSLDs were bleached after each irradiation with a compact fluorescent light source. Results: Without preirradiation to relatively high doses, OSLDs displayed non-stabilized supralinear behavior in plots of counts versus dose; dosing histories where cumulative dose is acquired solely in amounts comparable to clinical levels, e.g., <10Gy per irradiation, do not yield useful detectors; the counts versus dose curve continues to change significantly with acquired cumulative irradiation until cumulative dose reaches 250Gy or more. However, irradiation of OSLDs to as little as 200Gy before use yields stable detectors that followed supralinear behavior characterized with a quadratic polynomial fit. Pre-irradiation of 1kGy or more, as reported by Jursinic*, is not needed to yield stable detector performance. Conclusion: Nanodot OSLDs can be used in a clinical setting after receiving one shot preirradiations of ∼200Gy. Dose measuring performance is stable after the preirradiation treatment. One shot irradiations of 1kGy or more are not needed to obtain stable counts versus dose performance.* P. Jursinic, Med. Phys. 37, p. 132 to 140 (2010)

SU‐E‐T‐210: An Investigation for the Use of OSLDs for in Vivo Patient‐Specific Quality Assurance for Patients Requiring Bolus

Purpose: For treatments that require addition of bolus, dose to the skin and superficial regions must be known for adequate plan evaluation. Dose calculation inaccuracies in these regions may occur because they are in the build‐up region, as well as a Results of the IMRT/VMAT optimization algorithm ignoring the bolus during optimization. In this study, we evaluated the routine use of optically‐stimulated luminescent dosimeters (OSLDs) as a means of in vivo quality assurance for superficial dosimetry in patients requiring bolus during treatment. Methods: Landauer nanoDot OSLDs were used to perform measurements on 11 patients (total 13 sites) including head and neck, anal, groin, and breast. Treatment techniques included RapidArc, IMRT, and 3D‐CRT. All patients were treated with nominal energy 6MV. One OSLD was placed on the patient's skin, under the prescribed bolus, for one fraction. Bolus thickness was 0.5 cm. Each OSLD was read using the Landauer MicroStar reader, which operates in cw mode with a 1‐s read period, and corrected for sensitivity. Three readings were taken and the average calculated. Readings that were out of tolerance (15 percent) were repeated. OSLD readings were compared with TPS(Eclipse) calculations at a depth of 4mm (corresponding to the inherent OSLD build‐up). Results: 10 sites passed with less than 10 percent deviation (measurement accuracy of standard nanoDot). 6 Sites showed less than 3 percent deviation, 8 sites showed less than 5 percent deviation. 1 Site showed greater than 13 percent deviation. 2 sites showed greater than 25 percent deviation, and upon repetition, yielded similar results. Large deviations correlated to treatment sites with irregular surfaces (tracheotomy, skin creases). Conclusion: OSLDs are a quick and efficient way to perform in vivo quality assurance of doses in the superficial regions in patients requiring bolus for treatments. For simple geometries studied, TPS calculations show sufficient accuracy.

Comparative dose evaluations between XVI and OBI cone beam CT systems using Gafchromic XRQA2 film and nanoDot optical stimulated luminescence dosimeters

To investigate the effect of energy (kVp) and filters (no filter, half Bowtie, and full Bowtie) on the dose response curves of the Gafchromic XRQA2 film and nanoDot optical stimulated luminescence dosimeters (OSLDs) in CBCT dose fields. To measure surface and internal doses received during x-ray volume imager (XVI) (Version R4.5) and on board imager (OBI) (Version 1.5) CBCT imaging protocols using these two types of dosimeters. Gafchromic XRQA2 film and nanoDot OSLD dose response curves were generated at different kV imaging settings used by XVI (software version R4.5) and OBI (software version 1.5) CBCT systems. The settings for the XVI system were: 100 kVp∕F0 (no filter), 120 kVp∕F0, and 120 kVp∕F1 (Bowtie filter), and for the OBI system were: 100 kVp∕full fan, 125 kVp∕full fan, and 125 kVp∕half fan. XRQA2 film was calibrated in air to air kerma levels between 0 and 11 cGy and scanned using reflection scanning mode with the Epson Expression 10000 XL flat-bed document scanner. NanoDot OSLDs were calibrated on phantom to surface dose levels between 0 and 14 cGy and read using the inLight(TM) MicroStar reader. Both dosimeters were used to measure in field surface and internal doses in a male Alderson Rando Phantom. Dose response curves of XRQA2 film and nanoDot OSLDs at different XVI and OBI CBCT settings were reported. For XVI system, the surface dose ranged between 0.02 cGy in head region during fast head and neck scan and 4.99 cGy in the chest region during symmetry scan. On the other hand, the internal dose ranged between 0.02 cGy in the head region during fast head and neck scan and 3.17 cGy in the chest region during chest M20 scan. The average (internal and external) dose ranged between 0.05 cGy in the head region during fast head and neck scan and 2.41 cGy in the chest region during chest M20 scan. For OBI system, the surface dose ranged between 0.19 cGy in head region during head scan and 4.55 cGy in the pelvis region during spot light scan. However, the internal dose ranged between 0.47 cGy in the head region during head scan and 5.55 cGy in the pelvis region during spot light scan. The average (internal and external) dose ranged between 0.45 cGy in the head region during head scan and 3.59 cGy in the pelvis region during spot light scan. Both Gafchromic XRQA2 film and nanoDot OSLDs gave close estimation of dose (within uncertainties) in many cases. Though, discrepancies of up to 20%-30% were observed in some cases. Dose response curves of Gafchromic XRQA2 film and nanoDot OSLDs indicated that the dose responses of these two dosimeters were different even at the same photon energy when different filters were used. Uncertainty levels of both dosimetry systems were below 6% at doses above 1 cGy. Both dosimetry systems gave almost similar estimation of doses (within uncertainties) in many cases, with exceptions of some cases when the discrepancy was around 20%-30%. New versions of the CBCT systems (investigated in this study) resulted in lower imaging doses compared with doses reported on earlier versions in previous studies.

Determining the Applicability of the Landauer nanoDot as a General Public Dosimeter in a Research Imaging Facility

The Research Imaging Institute (RII) building at the University of Texas Health Science Center at San Antonio (UTHSCSA) houses two cyclotron particle accelerators, positron emission tomography (PET) machines, and a fluoroscopic unit. As part of the radiation protection program (RPP) and meeting the standard for achieving ALARA (as low as reasonably achievable), it is essential to minimize the ionizing radiation exposure to the general public through the use of controlled areas and area dose monitoring. Currently, thirty-four whole body Luxel+ dosimeters, manufactured by Landauer, are being used in various locations within the RII to monitor dose to the general public. The intent of this research was to determine if the nanoDot, a single point dosimeter, can be used as a general public dosimeter in a diagnostic facility. This was tested by first verifying characteristics of the nanoDot dosimeter including dose linearity, dose rate dependence, angular dependence, and energy dependence. Then, the response of the nanoDot dosimeter to the Luxel+ dosimeter when placed in a continuous, low dose environment was investigated. Finally, the nanoDot was checked for appropriate response in an acute, high dose environment. Based on the results, the current recommendation is that the nanoDot should not replace the Luxel+ dosimeter without further work to determine the energy spectra in the RII building and without considering the limitation of the microStar reader, portable on-site OSL reader, at doses below 0.1 mGy (10 mrad).

The effect of different bleaching wavelengths on the sensitivity of Al2O3:C optically stimulated luminescence detectors (OSLDs) exposed to 6 MV photon beams

To determine the effect of different bleaching wavelengths on the response of Al(2)O(3):C optically stimulated luminescence detectors (OSLDs) exposed to accumulated doses of 6 MV photon beams. In this study the authors used nanoDot OSLDs readout with a MicroStar reader. The authors first characterized the dose-response, fading, and OSL signal loss of OSLDs exposed to doses from 0.5 to 10 Gy. To determine the effect of different bleaching wavelengths on the OSLDs' response, the authors optically treated the OSLDs with 26 W fluorescent lamps in two modes: (i) directly under the lamps for 10, 120, and 600 min and (ii) with a long-pass filter for 55, 600, and 2000 min. Changes in the OSLDs' sensitivity were determined for an irradiation-readout-bleaching-readout cycle after irradiations with 1 and 10 Gy dose fractions. The OSLDs presented supralinearity for doses of 2 Gy and above. The signal loss rates for sequential readouts were (0.287 ± 0.007)% per readout in the reader's strong-stimulation mode, and (0.019 ± 0.002)% and (0.035 ± 0.007)% per readout for doses of 0.2 and 10 Gy, respectively, in the reader's weak-stimulation mode. Fading half-life values ranged from (0.98 ± 0.14) min to (1.77 ± 0.24) min and fading showed dose dependence for the first 10-min interval. For 10 and 55 min bleaching using modes (i) and (ii), the OSL signal increased 14% for an accumulated dose of 7 Gy (1 Gy fractions). For OSLDs exposed to 10 Gy fractions, the OSL signal increased 30% and 25% for bleaching modes (i) and (ii) and accumulated dose of 70 Gy, respectively. For 120 and 600 min bleaching using modes (i) and (ii), the OSL signal increased 2.7% and 1.5% for an accumulated dose of 7 Gy (1 Gy fractions), respectively. For 10 Gy fractions, the signal increased 14% for bleaching mode (i) (120 min bleaching) and decreased 1.3% for bleaching mode (ii) (600 min bleaching) for an accumulated dose of 70 Gy. For 600 and 2000 min bleaching using modes (i) and (ii), the signal increased 2.3% and 1.8% for an accumulated dose of 7 Gy (1 Gy fractions), respectively. For 10 Gy fractions, the signal increased 10% for mode (i) (600 min bleaching) and decreased 2.5% for mode (ii) (2000 min bleaching) for an accumulated dose of 70 Gy. The dose-response of nanoDot OSLDs read using the MicroStar reader presented supralinearity for doses of 2 Gy and above. The signal loss as a function of sequential readouts depended on dose. Fading also depended on dose for the first 10-min interval. For dose fractions of 1 and 10 Gy, OSLDs may be reused within 3% and 5% accuracies up to the maximum accumulated dose of 7 and 70 Gy investigated in this study, respectively. These accuracies were obtained after the OSLDs were bleached with a light source with wavelengths above about 495 nm. The authors also concluded that changes in sensitivity of OSLDs depended on bleaching time, accumulated dose, and wavelength spectrum of the bleaching source.

PTOSL response of commercial Al2O3:C detectors to ultraviolet radiation

The photo-transferred optically stimulated luminescence (PTOSL) technique using Al2O3:C detectors has been suggested as a good option for ultraviolet (UV) radiation dosimetry. The objective of this work was to study the PTOSL response of Al2O3:C InLight detectors and the OSL microStar reader of Landauer. The parameters such as radiation pre-dose, optical treatment time and UV illumination time were determined. The detectors presented a satisfactory stimulus of PTOSL signals when they were subjected to a preconditioning procedure with gamma radiation (1 Gy pre-dose), 30 min of optical treatment (to empty the shallow traps) and 30 min of UV illumination from an artificial source.