Dosimetric System Research Articles

Response to Neutrons and γ-rays of Two Liquid Scintillators

This work aims to evaluate a dosimetric system composed of green malachite supported in agarose. Previous work showed that solutions of green malachite irradiated at 1 to 40 kGy present a linear behavior. This system is a gel composed of green malachite (2.5×10–3 M), sodium benzoate (1%),and agarose (1%) that was exposed tovarious doses of gamma irradiation. The irradiated systems were measured with a UV-V is spectrophotometer at 619 nm. Experimental parameters (such as dose rate, doses, and temperature) were controlled and optimized for reproducible and reliable results. More studies are needed to propose a dosimeter in the system in the range of 1.8 to 4.0 kGy.

Fraction-specific post-treatment quality assurance for active breath-hold radiation therapy

AbstractPurposeThe purpose of this study is to evaluate variation in the treatment hold pattern and quantify its dosimetric impact in breath-hold radiotherapy, using fraction-specific post-treatment quality assurance.Material and MethodsA patient with lung mets treated using intensity-modulated radiation therapy (IMRT) with active breath coordinator (ABC) was recruited for the study. Treatment beam hold conditions were recorded for all the 25 fractions. The linearity and reproducibility of the dosimetric system were measured. Variation in the dose output of unmodulated open beam with beam hold was studied. Patient-specific quality assurance (PSQA) was performed with and without beam hold, and the results were compared to quantify the dosimetric impact of beam hold.ResultsThere was a considerable amount of variation observed in the number of beam hold for the given field and the monitor unit at which the beam held. Linearity and reproducibility of the dosimetric system were found within the acceptable limits. The average difference over the 25 measurements was 0·044% (0·557 to −0·318%) with standard deviation of 0·248.ConclusionPatient comfort with the ABC system and responsiveness to the therapist communication help to maintain consistent breathing pattern, in turn consistent treatment delivery pattern. However, the magnitude of dosimetric error is much less than the acceptable limits recommended by IROC. The dosimetric error induced by the beam hold is over and above the dose difference observed in conventional PSQA.

Dosimetric characterization of LiMgPO4:Tb,B phosphor for its application in food irradiation

Optically stimulated luminescence (OSL) intensity versus dose response of indigenously developed LiMgPO4:Tb,B (LMP) disks is linear in the range of 1 mGy–1 kGy. Currently, no other synthetic OSL phosphor is available, which covers such a large dose range. In order to assess the feasibility of using the phosphor in low-dose food irradiation dosimetry (up to 1 kGy), dosimetric characterization of LMP-based OSL dosimeter was carried out under both, gamma and electron beam irradiation. The doses estimated by LMP and routine dosimeters match well in the field trials. Hence, this phosphor has the potential to be used in phytosanitary application using radiation, where delivered doses are of the order of 0.01–1 kGy. Practical applications Food irradiation dosimetry, in India, is being carried out using chemical dosimeters such as Fricke, Ceric-cerous sulphate, and Alanine-electron paramagnetic resonance. The former two are liquid dosimeters kept in glass tubes and therefore need to be handled delicately during irradiation. The complex chemical preparation, sensitive to environmental conditions (temperature, humidity, etc.) and temperature changes, sensitive to UV radiation and the high sensitivity to impurities make these dosimetry systems inconvenient for routine applications. The OSL intensity versus dose response of indigenously developed LiMgPO4:Tb,B (LMP) has been observed to be linear up to 1 kGy. Apart from good dosimetric qualities, other qualities of the dosimeter system are quick readout, ease of handling, automated readout mechanisms, and integrity in harsh environments. The above-discussed attributes make LMP-based OSL dosimeter a potential candidate to carry out dosimetry during phytosanitary application of radiation in low-dose range (0.01–1 kGy). This range includes irradiation of mangoes, onions, potatoes, etc.

Energy and air kerma dependence of response of a photodiode-based dosimetric system for radioprotection

Low-level X-ray dose measurements are carried out to characterize a portable photodiode-based dosimetric system. In this paper, the energy and air kerma dependence of response is evaluated. The developed system is capable of real-time direct-reading radiation-dose measurement for radioprotection (occupational monitoring) or radiodiagnostic (patient dosimetry). The system can be configured to use various remote portable dosimeters and a computer server for data processing and display. The communication between the portable dosimeter and the server can be carried out in two modes: wireless or USB. The wireless connection is the standard usage mode, and the USB connection is for configuration or testing. The communication protocol is custom-made. For occupational monitoring, ISO 4037–1 was applied, and the following radioprotection qualities were tested: N40, N60, N80, N100, and N120. It was also tested in the following radiodiagnostic qualities: RQR3, RQR5, RQR8, and RQR10, as defined by IEC 61267. Besides X-rays, the developed dosimeter was evaluated for gamma ray energies of Cs-137 and Co-60. It is observed that the dosimeter sensitivity response displays a standard deviation less than 10% within a coefficient of variation of 1% in the reproducibility tests. The system is considered closely linear for air kerma dependence in the radiation qualities investigated. Goodness of fit was evaluated with the reduced chi-squared test.

Basic evaluation of the Eu:BaFBr and Ce:CaF2 hybrid type optical fiber based dosimeter system for correction of quenching effect under carbon ion irradiation

Basic evaluation of the Eu:BaFBr and Ce:CaF2 hybrid type optical fiber based dosimeter system for correction of quenching effect under carbon ion irradiation

Evaluation of Gold Nanoparticle Size Effect on Dose Enhancement Factor in Megavoltage Beam Radiotherapy Using MAGICA Polymer Gel Dosimeter

Background: Gold nanoparticles (GNPs) are among the most promising radiosensitive materials in radiotherapy. Studying the effective sensitizing factors such as nanoparticle size, concentration, surface features, radiation energy and cell type can help to optimize the effect and possible clinical application of GNPs in radiation therapy. In this study, the radiation sensitive polymer gel was used to investigate the dosimetric effect of GNP size in megavoltage (MV) photon beam radiotherapy.Material and Methods: GNPs with the size of 30nm, 50nm and 100nm in diameter were used. Transmission electron microscope (TEM) and dynamic light scattering (DLS) were applied to analyze the size of nanoparticles. The MAGICA polymer gel was synthesized and impregnated with different sizes of GNPs. The samples were irradiated with 6MV photon beam and 24 hours after irradiation, they were read using a Magnetic Resonance Imaging (MRI) scanner. Macroscopic Dose Enhancement Factor (DEF) was measured to compare the effect of GNP size. The MAGICA response of the 6MV x-ray beam was verified comparing Percentage Depth Dose (PDD) curve extracted from polymer gel dosimetry and Treatment Planning System (TPS).Results: MAGICA polymer gel dose response curve was linear in the range of 0 to 10 Gy. DEFs by adding 30nm, 50nm and 100nm GNPs were 1.1, 1.17 and 1.12, respectively. PDD curves of polymer gel dosimeter and treatment planning system were in good agreement.Conclusion: The results indicated a substantial increase in DEF uses a MV photon beam in combination with GNPs of different sizes and it was inconsistent with previous radiobiological studies. The maximum DEF was achieved for 50nm GNPs in comparison with 30nm and 100nm leading to the assumption of self-absorption effect by larger diameters. According to the outcomes of this work, MAGICA polymer gel can be recommended as a reliable dosimeter to investigate the dosimetric effect of GNP size and also a useful method to validate the current radiobiological and simulation studies.

Дозиметрическая оценка различных методик сочетанной лучевой терапии больных раком шейки матки

Purpose: Carrying out dosimetric investigation of possibility to replace a traditional combined radiation therapy of cervical cancer by combinations only external irradiation, without change of total course dose and number of fractions. Material and Methods: Eleven patients with a diagnosis of cervical cancer (stages T2bNxM0 and T3NxM0) who received a course of combined radiotherapy (CRT) have been considered in this study. The combination of dose delivery techniques 3D-CRT + high dose rate brachytherapy (HDR) was used as a basic one. The following fractionation regimes for CRT were simulated: external beam RT (EBRT) of the first stage – total dose 50 Gy and fraction dose 2 Gy (25 fractions), the second stage – total dose 28 Gy and fraction dose 7 Gy (4 fractions). Total CRT course dose was 89.7 Gy EQD2. Dosimetric planning of EBRT using conventional radiography and 3D-CRT has been carried out using XIO dosimetry planning system. Dosimetric planning of first-stage EBRT and second-stage EBRT using the VMAT technique has been performed in the Monaco dosimetry planning system. HDR of the second stage has been planned using the HDRplus dosimetric planning system for the Multisource HDR unit with a 60Co source. Results: Coverage of the clinical volume of the tumor using HDR, on average, was equal to 95 % of the prescribed dose at 91.8 % of the volume, 110 % of the dose – 75.7 % of the volume. 60Co + VMAT results in the coverage level 95 % of the dose at 97.1 % of the volume and 110 % of the dose at 2.1 % of the volume. 3D-CRT + VMAT provide the coverage level of 95 % of the dose at 98 % of the volume and 110 % of the dose at 2.6 % of the volume. Using the combination VMAT + VMAT allows achieving the average coverage of the target at the level of 98 % of the dose at 97 % of the volume, 110 % of the dose at 8.8 % of the volume. The maximum dose per volume of the organs at risk equal to 2 cm3 did not exceed their tolerant levels both for the bladder and for the rectum. Conclusion: At present, there is a technical possibility to replace the second stage of CRT cervical cancer by EBRT using the VMAT technique. Implementation of the VMAT technique allows to increase the uniformity of irradiated volume coverage comparing with traditional HDR. While using VMAT technique the tolerant levels of organs at risk are not exceeded.

Study of the optimal thresholds of gamma passing rate in VMAT plan verification for cervical cancer

Objective To investigate the optimal thresholds of the passing rate with different gamma measurement criteria (percent dose difference/DTA) based on the Delta 4 three-dimensional dosimetric verification system in the verification of volumetric modulated arc-therapy (VMAT) plan for cervical cancer. Methods Thirty clinically-approved dual-arc VMAT plans using the RapidArcTM (Varian Medical Systems Inc.) for cervical cancer were randomly selected. The gamma analysis and dose-volume histogram (DVH) evaluation were performed using Delta 4. All the plans were classified according to the following two criteria: 1. If the absolute percentage dose errors of all specific dosimetry indices on the DVH were less than 5%, the plan was regarded as clinically acceptable. 2. If the gamma passing rate was 90% or 95% under the criteria of 2%/2 mm and 3%/3 mm, the plan was regarded as acceptable. The sensitivity and specificity analyses were conducted based on the classification results and the receiver operating characteristic (ROC) curve was plotted. By calculating the Youden Index, the optimal thresholds under different Gamma criteria (global and local 2%/2 mm and 3%/3 mm) were investigated. Finally, the ability of distinguishing the plan was clinically acceptable or not between the conventional and optimal thresholds was quantitatively compared according to the sensitivity and specificity analyses. Results The optimal thresholds under the global 3%/3 mm and 2%/2 mm criteria were 98.3% and 87.05%; and 97.55%、86.05% for the local gamma analysis. Compared with the conventional thresholds, the sensitivity of the optimal thresholds was 0.93 by using the global and local gamma analyses under the 3%/3 mm criterion. Under the 2%/2 mm criterion, the sensitivity of the optimal thresholds was 0.65 and the specificity was 0.49 by using the global gamma analysis. The sensitivity was 0.7 and the specificity was 0.46 by using the local gamma analysis, suggesting that the sensitivity and the specificity were more balanced under the 2%/2 mm criterion. Conclusions Application of the optimal thresholds in the verification of VMAT plans can maintain the balance between the sensitivity and specificity, prevent the harm of clinically unacceptable plans to patients to certain extent and reduce the probability of increasing the daily work load for physicists due to the misjudgement of clinically acceptable plans. Key words: Volumetric modulated arc-therapy; Plan verification; Receiver operating characteristic curve; Optimal threshold

Evaluation of Gold Nanoparticle Size Effect on Dose Enhancement Factor in Megavoltage Beam Radiotherapy Using MAGICA Polymer Gel Dosimeter

Gold nanoparticles (GNPs) are among the most promising radiosensitive materials in radiotherapy. Studying the effective sensitizing factors such as nanoparticle size, concentration, surface features, radiation energy and cell type can help to optimize the effect and possible clinical application of GNPs in radiation therapy. In this study, the radiation sensitive polymer gel was used to investigate the dosimetric effect of GNP size in megavoltage (MV) photon beam radiotherapy. GNPs with the size of 30nm, 50nm and 100nm in diameter were used. Transmission electron microscope (TEM) and dynamic light scattering (DLS) were applied to analyze the size of nanoparticles. The MAGICA polymer gel was synthesized and impregnated with different sizes of GNPs. The samples were irradiated with 6MV photon beam and 24 hours after irradiation, they were read using a Magnetic Resonance Imaging (MRI) scanner. Macroscopic Dose Enhancement Factor (DEF) was measured to compare the effect of GNP size. The MAGICA response of the 6MV x-ray beam was verified comparing Percentage Depth Dose (PDD) curve extracted from polymer gel dosimetry and Treatment Planning System (TPS). MAGICA polymer gel dose response curve was linear in the range of 0 to 10 Gy. DEFs by adding 30nm, 50nm and 100nm GNPs were 1.1, 1.17 and 1.12, respectively. PDD curves of polymer gel dosimeter and treatment planning system were in good agreement. The results indicated a substantial increase in DEF uses a MV photon beam in combination with GNPs of different sizes and it was inconsistent with previous radiobiological studies. The maximum DEF was achieved for 50nm GNPs in comparison with 30nm and 100nm leading to the assumption of self-absorption effect by larger diameters. According to the outcomes of this work, MAGICA polymer gel can be recommended as a reliable dosimeter to investigate the dosimetric effect of GNP size and also a useful method to validate the current radiobiological and simulation studies.

A simple method to monitor the dose rate of secondary cosmic radiation at altitude

Monitoring the ambient dose equivalent rate at aviation altitudes is an ambitious task, which requires sophisticated dosemeter systems and the possibility to carry out such measurements on board aircraft. A rather simple approach has been investigated in this study: soundings with weather balloons up to an altitude of 30 km. This paper summarises the measurements carried out between 2011 and 2016. The results indicate that annual measurements of the ambient dose equivalent rate at altitudes of around 20 km are a reliable tool to monitor the variation of the dose rate in the atmosphere owing to the solar activity.

337. Analysis of radiation exposure of the medical staff from interventional radiology procedures and evaluation of the RaySafe i2 dosimetric system

Purpose To analyze the radiation exposure of the medical staff from various interventional radiology procedures and to evaluate the RaySafe i2 real time dosimetric system. Methods A two-stage multicentric study was conducted for about six months and involved four hospital centers. Data were collected from the RaySafe i2 dosimetric system on radiation doses absorbed by medical interventionists, nurses and patients in interventions of coronary angiography, coronary angiography followed by percutaneous transluminal coronary (PTCA), PTCA, transcatheter aortic valve implantation (TAVI) and implantation or pacemaker replacement (PM). In the first phase of the study, the RaySafe system monitor was not in the interventionist radiology room, on the contrary, in the second phase. At the end of the study, a satisfaction questionnaire was provided to the medical staff. A descriptive statistic analysis of the individual doses and the sum of the doses (both normalized with respect to the patient’s total Dose Area Product (DAP)) was carried out using the STATA software. Moreover, ANOVA test and Mann–Whitney–Wilcoxon test were performed to compare the various data samples. Results Concerning the radiation doses and the sum of the radiation doses (both normalized with respect to the patient’s total DAP), Raysafe i2 doesn’t led to a statistically significant reduction of the values for all evaluated operation types. Regarding the fiftieth percentile of dose samples, the variation ranges recorded between all centres are reported in Table 1. Conclusions The recorded differences between the two phases of this multicentric study aren’t statistically significant, probably due to the reduced number of samples. However, the medical staff has positively evaluated RaySafe i2 in optimizing its way of working and provided useful suggestions on how to use the system.

Total skin electron therapy (TSET): Monte Carlo Simulation and implementation

Introduction: Total skin electron irradiation technique is used in treatment of the mycosis fungoid. The implementation of this technique requires non-standard measurements and complex dosimetry methods. Operating procedures for total skin electron irradiation and its dosimetry vary in different radiation therapy centers in the world. In this article, validation of TSET technique dosimetry data by Monte Carlo simulation is done. Materials and Methods: The electron beam characteristic of RTSEI for the only electron accelerator, located at the radiation center of the Seyed Alshohada Hospital of Isfahan (NEPTUN 10PC) determined by performing Monte Carlo simulations and using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). For the best uniformity of the vertical profile, the optimal angle of gantry was defined at SSD=300 cm. The effect of the degrader plane that is located at a distance of 20 cm from the patient surface, was evaluated on the amount of energy reduction of the beam, the opening of the electron beam field and the homogeneity of the dose distribution. The transversal dose distribution from the whole treatment with Rotational technique was simulated in a CT- based anthropomorphic phantom. Also, the percentage depth dose in the head, neck, thorax, abdomen and legs was obtained for RTSET technique. TSET dosimetry requires measurements in nonreference conditions. Because of the complexity of the required measurements for the commissioning process of this technique, different dosimetric systems were employed such as radiochromic films (EBT3) and an ionization chamber. In particular, for dual-field beams irradiation, the optimal tilt angle was investigated and the dose distribution in the treatment plane was measured by radiochromic films. Dose distributions and percentage depth dose measurements for a total skin electron therapy were measured in an anthropomorphic phantom. Results: The optimal angle of 20o would give the most uniform total profile and the use of a 0.8 cm PMMA degrader in front of the patient leads to a homogeneous distribution of the dose in all directions (the mean relative dose value was 97%±5%, normalizing to 100% at the calibration point level). The percentage depth dose curves in different organs of anthropomorphic phantom for RTSEI indicates that the depth of maximum dose is on the surface of the phantom, Isodose curve of 80% is formed at a depth less than 4 mm and at the depth less than 1.5 mm, the dose decreases to 20% of the maximum dose. Conclusion: The main purpose of this study was to commission and optimize a TSET technique for the treatment of mycosis fungiodes with the NEPTUN 10PC linear accelerator. This was done through an extensive set of measurements and a large number of MC simulations. The results of Monte Carlo calculations were found to be in general agreement with the measurements, providing a promising tool for further studies of dose distribution calculations in TSEI.

A Specific Patient Quality Assurance (PSQA) procedure for a Co-60 source based High Dose Rate Brachytherapy

Introduction: In radiation therapy, accurate dose determination and precise dose delivery to the tumor are directly associated with better treatment outcomes in terms of higher tumor control and lower post radiation therapy complications. The current study aims the development and clinical application of the Patient Specific Quality Assurance (PSQA) procedures for nasopharyngeal and Tongue cancer treated using a cobalt-60 based high-dose rate brachytherapy. Materials and Methods: In this study, patient-specific quality assurance tools for brachytherapy in nasopharyngeal and Tongue cancers were utilized using a radiometric film dosimeter system through a gamma index for comparison. Also, with the association of dose distribution measured at surface area, and applying a reverse method, the calculated dose distribution at the region of interest were compared with those resulted from a treatment planning system. All results were also compared with those achieved by a Monte Carlo simulation classified as gold standard for the project. We also designed and evaluated two phantoms in this study. The first phantom designed based on the BALTAS phantom and the second one was created as a special phantom for brachytherapy applicators used for Nasopharyngeal and Tongue cancers. The same passing criteria used for external beam QA (3%/3mm), were applied. Finally, the PSQA system’s sensitivity to source positional errors was investigated by introducing intentional and controlled mistakes on selected patient’s plans. Results: Results presented in this study demonstrated that radiochromic film dosimetry based PSQA for brachytherapy can be used not only for patient specific quality assurance, but also as a part of the commissioning process and periodic QA . Conclusion: Patient Specific Quality Assurance tasks should be extended for all Radiotherapy tasks including Brachytherapy.

140. Characterization of a 2D chamber array for high modulated VMAT plan verification

PurposeHigh modulated VMAT plan can be achieved by the last generation of Treatment Planning System (TPS). The aim of this study is to evaluate if a 2D chamber array is adequate to check this complex plans. The response function of the ion chamber and the spatial frequency of the dose distribution are analyzed to quantify the loose of information due to the aliasing effect [1]. Methods and materialsAlmost 200 VMAT plans of different anatomic district (Table 1) were performed with TPS Monaco; the plans were delivered with Elekta agility LINAC and for the patient pre-treatment QA a PTW OCTAVIUS Detector 729 was employed [2]. Gafchromic EBT3 were used as reference dosimetric system due to the higher spatial resolution. A home made program in Matlab was elaborated to analyze the spatial frequency of each line and column of the dose distribution maps. ResultsEach patient plan was recalculate in a specific phantom for pre-treatment verification. This method often involves a loss of spatial frequencies (Fig. 1). The highest detectable spatial frequency that can be obtained with the “OCTAVIUS Detector729” is 0.05 mm−1 (single acquisition). The large sampling distance may result in under-sampling of VMAT fields with high frequency contents. Head & Neck and Lung stereotactic treatment maps show frequency contribution beyond the limit 0.05 mm−1 with loss of information and possible artefacts in case of reconstructed distribution (aliasing). ConclusionThe 2D Array is a dosimetrically accurate and sensitive tool when used for QA and verification of most clinical radiotherapy beams. However, verification for Head and Neck or SBRT treatment plans require more closely spaced ion chambers or multiple merged acquisition should be considered in order to fulfil Nyquist theorem.

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.

Residual Optically Stimulated Luminescent (OSL) Signals for Al2O3: C and a Readout System With Reproducible Partial Signal Clearance.

Optically stimulated luminescent dosimeters are devices that, when stimulated with light, emit light in proportion to the integrated ionizing radiation dose. The stimulation of optically stimulated luminescent material results in the loss of a small fraction of signal stored within the dosimetric traps. Previous studies have investigated the signal loss due to readout stimulation and the optical annealing of optically stimulated luminescent dosimeters. This study builds on former research by examining the behavior of optically stimulated luminescent signals after annealing, exploring the functionality of a previously developed signal loss model, and comparing uncertainties for dosimeters reused with or without annealing. For a completely annealed dosimeter, the minimum signal level was 56 ± 8 counts, and readings followed a Gaussian distribution. For dosimeters above this signal level, the fractional signal loss due to the reading process has a linear relationship with the calculated signal. At low signal levels (below 20,000 counts) in this optically stimulated luminescent dosimeter system, calculated signal percent errors increase significantly but otherwise are on average 0.72 ± 0.27%, 0.40 ± 0.19%, 0.33 ± 0.12%, and 0.24 ± 0.07% for 30, 75, 150, and 300 readings, respectively. Theoretical calculations of uncertainties showed that annealing before reusing dosimeters allows for dose errors below 1% with as few as 30 readings. Reusing dosimeters multiple times increases the dose errors especially with low numbers of readouts, so theoretically around 300 readings would be necessary to achieve errors around 1% or below in most scenarios. Note that these dose errors do not include the error associated with the signal-to-dose conversion factor.

The Development of New Dosimetry System using an Optic-Disk Radiation Sensor for Pencil Beam Scanning Mode

A measurement of integral depth dose profile (IDD) for the pencil beam scanning (PBS) is very important for the accurate delivery of dose to the target volume with a good conformity. In the beam commissioning process for PBS treatment method, the IDD profiles are commonly acquired for the beam modeling of treatment planning system. In this study, we fabricated an optic-disk radiation sensor (ODRS) and characterized the photoluminescence signal generated from an optical disk as fundamental research for the development and evaluation of a new dosimetric system for pencil beam proton therapy using an ODRS system. The relative IDD curve of proton beam was obtained by ODRS system and analyzed with it measured by ion chamber. We proposed an innovative method using a signal generated in clear plastic optic disk. We fabricated the ODRS system for measuring the photoluminescence signal induced by therapeutic pencil beam proton beams, respectively. Homemade phantoms based optic disk made of poly methyl methacrylate were fabricated to allow the optic disk to be exposed in the direction of the beam inside a water phantom capable of 3D operation. The photoluminescence signal generated from the optic disk by the proton beam was converted to an electric signal by a multi-anode photomultiplier tube (MAPMT: H7546, Hamamatsu Photonics, Shizuoka, Japan) connected to the plastic optic fiber surrounding the disk, NI-DAQ system, which allows us to check in real time through a notebook computer. The basic characteristics as the dosimetry sensor for this system based optic disk are described. The linearity relationship between the output according to the dose and dose rate measured using the ion chamber and the photoluminescence signal obtained by this system was confirmed, and the result was shown to be linear. The calibration factor for the energy was found to be close to zero, and it was confirmed that the energy dependence on the optic disk need not be considered. The relative IDD profiles were obtained using the photoluminescence signal generated by the pencil beam irradiation with two energies of 99.9 and 162.1 MeV in this system, which was compared with the curve measured by the Bragg chamber. The IDD results obtained by optic disk radiation sensor indicated good agreement without any correction process with the one by Bragg chamber. In this study, we developed a clear optic disk-based system to evaluate the characteristics for PBS beam dosimetry. An advantage of this system is that it can be easily extended to a two-dimensional array system for application in the PBS beam dosimetry. As a further study, we are developing the ODRS system which can measure the depth dose at each depth in 2 mm increments with respect to the direction of the PBS beam using a 2 mm thick disk array.

Use of radiochromic film dosimetry in radiobiology experiments

In radiobiology experiments, that usually entail unique irradiation geometries, it is necessary to know properly the absorbed doses involved. It is difficult to find them out, due to the differences between these irradiation conditions and the reference conditions in which the absorbed dose is measured by the usual ionometric procedures.The aim of this study is to check the EBT3 radiochromic film as a dosimetric system for x-ray beams used in radiobiology experiments. The film has been calibrated in different energy photon beams, so its energy independence has been proved. Afterwards it has been used to evaluate the absorbed dose in two radiobiology experiments: first one required the irradiation of flowers, while in the second, mice with implanted tumors were irradiated. In both cases EBT3 radiochromic film has shown to be a suitable tool for measuring the absorbed dose in this kind of experiments.

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.

Surface Dose Measurements on an Indigenously Made Inhomogeneous Female Pelvic Phantom Using Metal-Oxide-Semiconductor-Field-Effect-Transistor Based Dosimetric System

Introduction: Megavoltage X-ray beams are used to treat cervix cancer due to their skin-sparing effect. Preferably, the radiation surface doses should be negligible; however, it increases due to electron contamination produced by various field parameters. Therefore, it is essential to provide proper knowledge about the effect of different field parameters on radiation doses. This study sought to find out the effect of various physical parameters on the surface doses. Materials and Methods: The effects of field size, source-to-surface distance, and open or acrylic block tray fields on surface doses were determined. Metal-Oxide-Semiconductor-Field-Effect-Transistor based dosimetric system was used for dose measurements for 6 MV photon beam. The directly measured radiation surface doses on pelvic phantom were compared to surface dose values computed by treatment planning system in the similar field parameters. Results: The measured results for the percentage depth dose (PDD0) in field size of 10x10 cm2 were 13.32%, 12.95% and 13.87% for open field and 36.87%, 36.31% and 35.88% for acrylic block tray field. In addition, the computed doses were 7.83%, 7.73% and 7.65% for open field and 16.33%, 16.12% and 15.88% for acrylic block tray field at 80 cm, 100 cm, and 120 cm SSDs, respectively. Conclusion: The surface dose increases along with the size of the field and decreases with increasing SSD. The surface doses in acrylic block tray fields were significantly higher than the open ones. The treatment planning system computed a lesser radiation doses in same field parameters.