Real-time Dosimeter Research Articles

Experimental study on polystyrene-MWCNT nanocomposite as a radiation dosimeter

Polystyrene-multi-wall carbon nanotube nanocomposite samples were made through a solution processing method and investigated as a real-time dosimeter. Samples were irradiated by 60Co gamma radiation source over the dose-rate of 0.4–160 mGy/min. The current-voltage curve at the constant dose-rate of 75 mGy/min exhibited a linear response in the range of ±1000 V. Current-voltage curve showed that the sample is bias-polarity independent. Other dosimetric characteristics of this sample were accomplished under the bias voltage of 800 V. The results showed that the photocurrent in different dose-rates exhibited a higher sensitivity for the lower dose-rates region of 0.4–12 mGy/min. The maximum change in photocurrent due to angular variation within ±60° compared with incidence beam was measured as 2.8%. The maximum discrepancy of photocurrent in different field sizes was also studied. Reproducibility and repeatability of the results were within 0.4% and 1%, respectively.

New real-time patient radiation dosimeter for use in radiofrequency catheter ablation.

In a previous study, we reported on a novel (prototype) real-time patient dosimeter with non-toxic phosphor sensors. In this study, we developed new types of sensors that were smaller than in the previous prototype, and clarified the clinical feasibility of our newly proposed dosimeter. Patient dose measurements obtained with the newly proposed real-time dosimeter were compared with measurements obtained using a calibrated radiophotoluminescence glass reference dosimeter (RPLD). The reference dosimeters were set at almost the same positions as the new real-time dosimeter sensors. We found excellent correlations between the reference RPLD measurements and those obtained using our new real-time dosimeter (r2 = 0.967). However, the new type of dosimeter was found to underestimate radiation skin dose measurements when compared with an RPLD. The most probable reason for this was the size reduction in the phosphor sensor of the new type of dosimeter. We believe that, as a result of reducing the phosphor sensor size, the backscattered X-ray irradiation was underestimated. However, the new dosimeter can accurately determine the absorbed dose by correcting the measured value with calibration factors. The calibration factor for the new type dosimeter was determined (by linear regression) to be ~1.15. New real-time patient dosimeter design would be an effective tool for the real-time measurement of patient skin doses during interventional radiology treatments.

A Low-Power, Real-Time Displacement Damage Dosimeter

The Naval Research Laboratory has developed a low-power, real-time displacement damage dosimeter (RT3D). RT3D consists of two components; one being the measurement electronics and the second being the actual dosimeter (GaAs diode) exposed to the radiation source. RT3D accumulates displacement damage passively (without power) and the displacement damage dose (DDD) is measured at will with measurement electronics by measuring the GaAs diode dark current at one or more forward bias voltages. The DDD is subsequently determined in real-time from a calibration curve derived from ground-based testing. The dosimeter is capable of measuring approximately three orders of magnitude in DDD. The dosage measurement range of the sensor can be modified by placing an absorber material over the sensor. Proton testing performed in situ yielded an error estimate determination to within 10% for simulated space use.

Experimental evaluation of thermal stability of PS- MWCNT nanocomposite as a real-time dosimeter

Introduction: Carbon nanotubes (CNTs) are ideal reinforcing fillers for a polymer matrix, because of their nanometer size, high aspect ratio and, more importantly, their excellent mechanical strength, and electrical and thermal conductivity. The CNTs are categorized into two groups: SWCNT and MWCNT. MWCNTs would have diameters ranging from 2 to 100 nm and lengths of up to tens of microns, and they exhibited electrical conductivity as high as 105–107 S/m. The most promising theories for explaining electrical behavior in polymer nanocomposites are based on hopping conductivity models developed to understand the charge transport in disordered semiconductors and amorphous solids. The probability of an electron hopping from one localized state to another one depends on temperature. The authors in the previous articles introduced a novel dosimeter applied in diagnostic and therapeutic dosimetry. The objective of this experimental work is to evaluate the thermal stability of PS/MWCNT (0.28 wt%) nanocomposite as a real-time dosimeter for the diagnostic and therapeutic purposes. Materials and Methods: MWCNT with purity of 98 wt%, density of 2.1 g/cm3, outside diameter: 5-15 nm, inside diameter: 3-5 nm, average length: 50 μm, SSA: ~233 m2/g, electrical conductivity greater than 104 S/m was prepared from US Nano Inc, and finally high purity toluene and DCM as the solvents were purchased from Merck Company. PS 1540 with the density 1.05 g/cm3 was supplied by Tabriz Petrochemical Company. Solution processing has been used to prepare 0.28 wt% PS/MWCNT nanocomposite for dosimetry purposes. Results: Electric resistance of the nanocomposites in different temperatures was measured. Results showed that a positive temperature coefficient (PTC) effect from the room temperature until the glass transition temperature (Tg) for the sample was exhibited, and after that, the negative temperature coefficient (NTC) effect was observed. The maximum discrepancy in the resistance for the sample at room temperature until 50°C was 15%. Conclusion: In this experimental work, the variation of electric resistance with temperature for the 0.28 wt% MWCNT-PS nanocomposite at room temperature until 80°C was measured, in which indicated a PTC effect before glass transition temperature of polystyrene and NTC effect after that. It can be concluded that for applying this material in a dosimeter, regarding the temperature dependence of the aforementioned nanocomposite, there is need to insert a temperature correction factor in the extracted data for dosimetry purposes. This research work motivates the investigation in depth of the thermal properties behavior of polymer- CNT nanocomposites as a real-time dosimeter.

Linearity response characterization of Polystyrene/ Graphene oxide nanocomposite as real-time dosimeter for therapeutic purposes

Introduction: In recent years, one of the emerging two dimensional (2D) carbon based nano- materials namely Graphene Oxide has been incorporated into polymeric matrices to enhance the electrical properties of the composites. The electrical conductivity of Graphene Oxide is excellently used in fabricating polymer-based sensors, energy-related systems, biotechnology, anti-statics, microwave absorbers, conductive coatings, and ionizing radiation dosimeters. The objective of this experimental work is to evaluate the linearity response of Polystyrene/Graphene oxide (0.1 wt%) nanocomposite as real-time dosimeter for therapeutic purposes. Materials and Methods: PS 1540 was supplied by Tabriz Petrochemical Company. Graphene oxide (GO) naopowder was prepared from US Nano Inc, and finally high purity toluene and DCM as the solvents were purchased from Merck Company. Solution processing has been used to prepare 0.1 wt% PS/GO nanocomposite for dosimetry purposes. A Picker-V9 60Co gamma-cell installed in the Secondary Standard Dosimetry Laboratory (SSDL) of Iran was used to irradiate the nanocomposite at various dose rates in the range of 98-159 mGy/min. Results: From the SEM images of fractured surfaces of PS/GO nanocomposite, the nano size scale of GOs nanoparticles can be observed as 140 nm. The plot of photocurrent versus dose rate for 0.1 wt% PS/GO was investigated. Results showed that the linearity was obtained in the range of 98-159 mGy/min with R2=1. The I-V measurements of the nanocomposite in a constant dose rate of 75 mGy/min at the SSD=80 cm were exhibited, in which the response was linear within the ±1000 V with R2=0.99, and also repeatability was examined for each measurement with the standard deviation less than 1%. Conclusion: In this experimental research, the linearity of Polystyrene/Graphene oxide nanocomposite as real-time dosimeter was carried out. Results showed that this nanocomposite exhibited a linear response in different dose rates ranging from 98-159 mGy/min that can be used as a real-time dosimeter utilized in therapeutic level.

Photoluminescence Properties of Yb and Ag Co-Doped Ta<sub>2</sub>O<sub>5</sub> Thin Films

We prepared ytterbium and silver co-doped tantalum-oxide (Ta2O5:Yb,Ag) thin films using a simple co-sputtering method and evaluated photoluminescence (PL) properties of the films after annealing. We found that a PL peak at a wavelength of 980 nm due to Yb3+ can be strongly enhanced by Ag doping. From X-ray diffraction measurements, we found that Ag2Ta8O21 and orthorhombic Ta2O5 crystalline phases are very important in order to enhance the 980-nm peak observed from our Ta2O5:Yb,Ag thin films. Because of the human-body transmittability of the 980-nm wavelength, such films are applicable to a novel real-time X-ray dosimeter system.

Effectiveness of a novel real-time dosimeter in interventional radiology: a comparison of new and old radiation sensors

Radiation dose management is important in interventional radiology (IR) procedures, such as percutaneous coronary intervention, to prevent radiation-induced injuries. Therefore, radiation dose should be monitored in real time during IR. This study evaluated the fundamental characteristics of a novel real-time skin dosimeter (RTSD) developed at our institution. In addition, we compared the performance of our new and old radiation sensors and that of a skin dose monitor (SDM), with ion chamber reference values. We evaluated the fundamental characteristics (e.g., energy dependence, dose dependence, and angular dependence) of the RTSD developed by us in the diagnostic X-ray energy range. The performance of our RTSD was similar to that of the SDM. In particular, the new radiation sensor of our RTSD demonstrated better dose rate dependence compared to the old sensor. In addition, the new sensor had the advantage of being small in size and thus minimally affecting the X-ray images compared to the old sensor. Therefore, the developed skin dosimeter and radiation sensor may be useful in real-time measurement of patients' exposure to and multi-channel monitoring of radiation in IR procedures. The new dosimeter system can be recommended for visualization and management of the radiation dose to which the patients' skin is exposed.

Radiation Exposure to Surgeon and Assistant During Flat Panel Mini C-Arm Fluoroscopy in Hand and Wrist Surgical Procedures.

During mini C-arm fluoroscopy, both the patient and surgical team are exposed to scatter radiation. The objective of this study was to quantify body, thyroid, and hand radiation exposure to surgeon and assistant during intraoperative use of flat panel mini C-arm fluoroscopy in hand and wrist surgical procedures. Over 5 months, the surgeon's and assistant's radiation exposure was recorded during all osseous hand and wrist surgical procedures. Whole-body and thyroid radiation exposure were measured with 2 types of dosimeters: a photon thermoluminescence detector and a RaySafe i2 real-time dosimeter. Ring dosimeters were used to quantify hand radiation exposure. Mini C-arm fluoroscopy was used in 94 surgical procedures. Total fluoroscopy time was 1,996 seconds and varied between surgical procedures (range, 1-152 seconds; median, 11 seconds). No thermoluminescence detector photon dosimeter exceeded the threshold limit of 0.1 mSv. The RaySafe i2 real-time dosimeters recorded a cumulated dose of 0.029 mSv for the body and 0.012 mSv for the thyroid position of the surgeon. The assistant received a cumulated dose of 0.011 mSv for the body and 0.011 mSv for the thyroid position. The ring dosimeters showed a cumulated dosage of 1.28 mSv for the surgeon and 0.20 mSv for the assistant. Our results show that the surgeon's and assistant's body, thyroid, and hands were exposed to acceptable levels of scatter radiation during intraoperative use of the flat panel mini C-arm. The surgeon received the highest radiation exposure: 2.9% of the yearly radiation limits for the body, 0.05% for the thyroid position, and 2.56% for the hands. The assistant was exposed to less scatter radiation: 1.1% for the body, 0.04% for the thyroid, and 0.4% for the hands. This study quantified radiation levels to which surgeon and assistant are exposed during mini C-arm fluoroscopy in hand and wrist surgical procedures.

Radiation exposure for the surgical team in a hybrid-operating room.

Hybrid-operating rooms enable the surgeon to acquire intraoperative high-resolution 2- and 3D images and use them for navigation. The radiation dose of the operating personal and the patient remains the major concern. In 9months, 109 pelvic and spine cases were performed using a hybrid operating room. Radiation dose of the surgeon and the assisting nurse was recorded using real-time dosimeters. Lower radiation doses for the main surgeon in navigated dorsal instrumentations of the thoracic spine were recorded. Standing between the C-arm during screw placement increased the radiation dose sixfold. Lumbar dorsal instrumentation showed a similar radiation dose compared to the previous studies in traditional operating room settings. The use of a hybrid-operating room for dorsal spine instrumentation showed no increase in radiation dose compared to traditional settings. Intraoperative navigation can help to reduce the radiation dosage for the operating personnel.

Abstract No. 605 Minimizing the uncertainty when you are expecting the unexpected: monitoring radiation exposure during pregnancy

Women are underrepresented in IR, while maybe partially due to fear of radiation exposure during child-bearing period1. For those who choose IR as a career, they may face the challenge of being able to stay productive during pregnancy and receiving the appropriate support from their colleagues who may lack the in-depth understanding of radiation risks relating to pregnancy. We will review and compare the commonly used dosimeters including the real-time dosimeter to provide comprehensive understanding of their sensitivity, accuracy and consistency in monitoring fetal radiation exposure and to provide additional insights to the appropriate dosimeter choice and radiation protection practice. 1. Literature review of the current commercially available personnel dosimeter types which may be used to monitor fetal and maternal dose during pregnancy. 2. Compare the real-time fetal dosimeter reading to the estimated dose from maternal real-time dosimeter reading during commonly performed IR procedures. 3. Compare the fetal dose report from the standard optically stimulated luminescence dosimeters (OSL) to calculated dose from maternal dose record during pregnancy. 1. Preliminary result demonstrates the high sensitivity of both standard OSL dosimeter and real-time dosimeter wearing under the lead apron for providing fetal dose monitoring. 2. Real-time dosimeter provides instant dose report but is inferior to OSL in consistency and accuracy. Fetal radiation exposure, while negligible per procedure, accumulative dose contributes to stochastic risk. Real-time dosimeter can provide instant awareness of dose rate and minimize unnecessary anxiety and warrants instant modification in radiation safety practice. Standard dosimeters provide accurate however delayed accumulate dose report to ensure compliance with radiation safety guidelines.

Method for determining the half-value layer in computed tomography scans using a real-time dosimeter: Application to dual-source dual-energy acquisition

PurposeWe have proposed a method for determining the half-value layers (HVL) in dual-source dual-energy computed tomography (DS-DECT) scans without the need for the X-ray tubes to be fixed. MethodsA custom-made lead-covered case and an ionizing chamber connected with a multi-function digitizer module (a real-time dosimeter) were used. The chamber was placed in the center of the case, and aluminum or copper filters were placed in front of the aperture. The HVL was measured using aperture widths of 1.0, 2.0, and 3.0 cm for tube potentials of 80, 120, and 150 kV in single-source single-energy CT (SS-SECT) scans and was calculated from the peak air kerma rate (peak method) and the integrated air kerma rate (integrating method); the obtained values were compared with those from a conventional non-rotating method performed using the same procedure. The HVL was then measured using an aperture width of 1.0 cm for tube potential combinations of 70/Sn150 kV and 100/Sn150 kV in DS-DECT scans using the peak method. ResultsIn the SS-SECT scans, the combination of a 1.0-cm aperture and the peak method was adequate due to the small differences in the HVL values obtained for the conventional non-rotating method. The method was also found to be applicable for the DS-DECT scans. ConclusionsOur proposed method can determine the HVL in SS-SE and DS-DECT scans to a good level of accuracy without the need for the X-ray tubes to be fixed. The combination of a 1.0-cm aperture and the peak method was adequate.

Radiation Exposure to the Hand of a Spinal Interventionalist during Fluoroscopically Guided Procedures.

Study DesignProspective study.PurposeDuring fluoroscopically guided spinal procedure, the hands of spinal surgeons are placed close to the field of radiation and may be exposed to ionizing radiation. This study directly measured the radiation exposure to the hand of a spinal interventionalist during fluoroscopically guided procedures.Overview of LiteratureFluoroscopically guided spinal procedures have been reported to be a cause for concern due to the radiation exposure to which their operators are exposed.MethodsThis prospective study evaluated the radiation exposure of the hand of one spinal interventionalist during 52 consecutive fluoroscopic spinal procedures over a 3-month period. The interventionalist wore three real-time dosimeters secured to the right forearm, under the lead apron over the chest, and outside the lead apron over the chest. Additionally, one radiophotoluminescence glass dosimeter was placed under the lead apron over the left chest and one ring radiophotoluminescence glass dosimeter was worn on the right thumb. The duration of exposure and radiation dose were measured for each procedure.ResultsThe average radiation exposure dose per procedure was 14.9 µSv, 125.6 µSv, and 200.1 µSv, inside the lead apron over the chest, outside the lead apron over the chest, and on the right forearm, respectively. Over the 3-month period, the protected radiophotoluminescence glass dosimeter over the left chest recorded less than the minimum reportable dose, whereas the radiophotoluminescence glass ring dosimeter recorded 368 mSv for the thumb.ConclusionsOur findings indicated that the cumulative radiation dose measured at the dominant hand may exceed the annual dose limit specified by the International Commission on Radiological Protection. Spinal interventionalists should take special care to limit the duration of fluoroscopy and radiation exposure.

Operator Radiation and the Efficacy of Ceiling-Suspended Lead Screen Shielding during Coronary Angiography: An Anthropomorphic Phantom Study Using Real-Time Dosimeters

Operator radiation and the radiation protection efficacy of a ceiling-suspended lead screen were assessed during coronary angiography (CA) in a catheterization laboratory. An anthropomorphic phantom was placed under the X-ray beam to simulate patient attenuation in eight CA projections. Using real-time dosimeters, radiation dose rates were measured on models mimicking a primary operator (PO) and an assistant. Subsequently, a ceiling-suspended lead screen was placed in three commonly used positions to compare the radiation protection efficacy. The radiation exposure to the PO was 2.3 to 227.9 (mean: 67.2 ± 49.0) μSv/min, with the left anterior oblique (LAO) 45°/cranial 25° and cranial 25° projections causing the highest and the lowest dose rates, respectively. The assistant experienced significantly less radiation overall (mean: 20.1 ± 19.6 μSv/min, P < 0.003), with the right anterior oblique (RAO) 30° and cranial 25° projections resulting in the highest and lowest exposure levels, respectively. Combined with table-side shielding, the ceiling-suspended lead screen reduced the radiation to the PO by 76.8%, 81.9% and 93.5% when placed close to the patient phantom, at the left side and close to the PO, respectively, and reduced the radiation to the assistant by 70.3%, 76.7% and 90.0%, respectively. When placed close to the PO, a ceiling-suspended lead screen provides substantial radiation protection during CA.

Radiation Exposure to the Surgeon and Patient During a Fluoroscopic Procedure: How High Is the Exposure Dose? A Cadaveric Study.

Using fresh cadavers, real-time dosimeters were used to estimate the radiation exposure dose from C-arm fluoroscopy to surgeons, medical staff, and patients during various procedures. The aim of this study was to evaluate the radiation exposure dose from C-arm fluoroscopy, which is used to generate real-time images of the human body, under a variety of conditions and in different areas. Awareness of the harmful effects of long-term low-dose radiation is rising. There are no all-inclusive reports evaluating the radiation exposure dose to medical staff associated with fluoroscopic procedures that can accurately simulate the real clinical situation. Seven fresh cadavers were irradiated for 1, 3, and 5 minutes with C-arm fluoroscopy. The x-ray source was positioned under the table, over the table, and laterally. Radiation exposure doses were measured at different simulated areas such as the center area, and the surgeon's hand or thyroid gland. There were significant differences in the radiation exposure dose under different conditions and for different irradiated areas. The risk of direct and scatter radiation exposure was the greatest with the lateral position, which increased by more than 200 times and more than 30 times, respectively, compared with that from a position under the table. Direct radiation was attenuated to less than one-hundredth after passing through the body of the cadaver. All radiation exposure doses were positively correlated with total exposure time. Our study revealed the direct and scatter radiation exposure dose from C-arm fluoroscopy to different areas under a variety of conditions when fluoroscopy is used to generate real-time images of the human body. Our results serve as a guide for medical staff to understand the risk of radiation exposure during each fluoroscopic procedure. Medical staff, especially surgeons, should consider how to protect themselves and reduce radiation exposure by using appropriate shielding. 4.

Dosimetry characteristics of HDPE–SWCNT nanocomposite for real time application

In this experimental work, different dosimetric characteristics of high density polyethylene-single wall carbon nanotube nanocomposite were investigated. The nanocomposite samples were prepared with different nanotube contents of 0.22, 0.25, and 0.39 weight percentages which were before, exactly in, and after percolation region of the nanocomposite, respectively. The samples were exposed to 60Co gamma radiation source over the dose rate of 65–214mGy/min, while the applied bias was 100V. A linear response achieved for the sample contained 0.25 nanotube wt% verified that the percolation threshold is the optimum point for dosimetric purposes. The current–voltage characteristics curve measured for 0.25 CNT wt% nanocomposite showed that the behavior of this sample was bias polarity independent. Also, the results showed that the response of this nanocomposite was energy-independent. The maximum discrepancy of photocurrent due to angular variation within 0–90° with respect to beam incidence and the reproducibility of the response were measured as 5.4% and 0.8%, respectively. The stability study showed that this material may be suitable for protection dose level control. Therefore, this kind of nanocomposite requiring calibration can be used as a real-time dosimeter.

B.307 - Personnel real time dosimetry in interventional radiology

Introduction: Personnel real time dosimetry has grown in the past years as an important request to help medical staff to optimize their radiation exposure during interventional radiology and hemodynamics procedures. Often the absorbed dose could be reduced if appropriate modifications of the implementation of procedures could be introduced, based on evidence from collected dose-rate data correlated with medical staff position with respect to the patient. Also real time dose monitoring could help Medical Physicist in their day-by-day dosimetry measurements, allowing automatic data recording and hence simplification of procedures. The INFN RAPID project has developed a real-time dosimeter based on a new sensor, capable of dose-rate measurement with a frequency of few Hz, worn by medical staff during real procedures and calibrated on a certified X-ray beam.

Does Wearing A Real-Time Visual Dosimeter Reduce the Personal Radiation Dose for Interventional Radiology Nurses? An Observational Comparative Study

AimReal-time radiation dosimeters can provide visual display of personal radiation dose as it occurs, potentially providing nurses working in radiation environments with more understanding about their personal radiation protection and safety strategies. This comparative observational study aimed to evaluate if the wearing of a real-time dosimeter with visual display by nurses working in interventional radiology would reduce their personal radiation dose. Materials and methodsPersonal dose data were collected from 10 nurses while working in two interventional radiology suites over two measurement periods. In the first measurement period, the nurses were not provided with any radiation dose information during the interventional procedures. In the second measurement period, the nurses were able to view their personal radiation dose in real time. ResultsNurses working in interventional radiology suites reduced their personal radiology doses when using a real-time radiation dosimeter that provided a real-time display of their personal dose. ConclusionThe results support the use of real-time radiation dosimeters as an occupational radiation protection strategy in interventional radiology suites.

Novel Dosimeter Using a Nontoxic Phosphor for Real-Time Monitoring of Patient Radiation Dose in Interventional Radiology.

To our knowledge, no feasible method exists for real-time measurement of the radiation dose given to the patient during interventional radiology (IR) procedures. Therefore, we produced a prototype of a real-time dosimeter for patients undergoing IR that uses a nontoxic phosphor. The basic characteristics of the real-time dosimeter prototype are comparable to those of the previously used skin dose monitor, with the exception that our prototype has the distinct advantage of including multichannel sensors. The novel real-time dosimeter system is expected to be useful for measuring patient exposure to the radiation dose during IR procedures.

A rapid noninvasive characterization of CT x-ray sources.

The aim of this study is to generate spatially varying half value layers (HVLs) that can be used to construct virtual equivalent source models of computed tomography (CT) x-ray sources for use in Monte Carlo CT dose computations. To measure the spatially varying HVLs, the authors combined a cylindrical HVL measurement technique with the characterization of bowtie filter relative attenuation (COBRA) geometry. An apparatus given the name "HVL Jig" was fabricated to accurately position a real-time dosimeter off-isocenter while surrounded by concentric cylindrical aluminum filters (CAFs). In this geometry, each projection of the rotating x-ray tube is filtered by an identical amount of high-purity (type 1100 H-14) aluminum while the stationary radiation dose probe records an air kerma rate versus time waveform. The CAFs were progressively nested to acquire exposure data at increasing filtrations to calculate the HVL. Using this dose waveform and known setup geometry, each timestamp was related to its corresponding fan angle. Data were acquired using axial CT protocols (i.e., rotating tube and stationary patient table) at energies of 80, 100, and 120 kVp on a single CT scanner. These measurements were validated against the more laborious conventional step-and-shoot approach (stationary x-ray tube). At each energy, HVL data points from the COBRA-cylinder technique were fit to a trendline and compared with the conventional approach. The average relative difference in HVL between the two techniques was 1.3%. There was a systematic overestimation in HVL due to scatter contamination. The described method is a novel, rapid, accurate, and noninvasive approach that allows one to acquire the spatially varying fluence and HVL data using a single experimental setup in a minimum of three scans. These measurements can be used to characterize the CT beam in terms of the angle-dependent fluence and energy spectra along the bowtie filter direction, which can serve as input for accurate CT dose computations.

SU-D-213-03: Towards An Optimized 3D Scintillation Dosimetry Tool for Quality Assurance of Dynamic Radiotherapy Techniques

Purpose: The purpose of this work is to simulate a multi-focus plenoptic camera used as the measuring device in a real-time three-dimensional scintillation dosimeter. Simulating and optimizing this realistic optical system will bridge the technological gap between concept validation and a clinically viable tool that can provide highly efficient, accurate and precise measurements for dynamic radiotherapy techniques. Methods: The experimental prototype, previously developed for proof of concept purposes, uses an off-the-shelf multi-focus plenoptic camera. With an array of interleaved microlenses of different focal lengths, this camera records spatial and angular information of light emitted by a plastic scintillator volume. The three distinct microlens focal lengths were determined experimentally for use as baseline parameters by measuring image-to-object magnification for different distances in object space. A simulated plenoptic system was implemented using the non-sequential ray tracing software Zemax: this tool allows complete simulation of multiple optical paths by modeling interactions at interfaces such as scatter, diffraction, reflection and refraction. The active sensor was modeled based on the camera manufacturer specifications by a 2048×2048, 5 µm-pixel pitch sensor. Planar light sources, simulating the plastic scintillator volume, were employed for ray tracing simulations. Results: The microlens focal lengths were determined to be 384, 327more » and 290 µm. A realistic multi-focus plenoptic system, with independently defined and optimizable specifications, was fully simulated. A f/2.9 and 54 mm-focal length Double Gauss objective was modeled as the system’s main lens. A three-focal length hexagonal microlens array of 250-µm thickness was designed, acting as an image-relay system between the main lens and sensor. Conclusion: Simulation of a fully modeled multi-focus plenoptic camera enables the decoupled optimization of the main lens and microlens specifications. This work leads the way to improving the 3D dosimeter’s achievable resolution, efficiency and build for providing a quality assurance tool fully meeting clinical needs. M.R. is financially supported by a Master’s Canada Graduate Scholarship from the NSERC. This research is also supported by the NSERC Industrial Research Chair in Optical Design.« less