A systematic review of clinical applications of polymer gel dosimeters in radiotherapy

Abstract: Radiotherapy has rapidly improved because of the use of new equipment and techniques. Hence, the appeal for a feasible and accurate three-dimensional (3D) dosimetry system has increased. In this regard, gel dosimetry systems are accurate 3D dosimeters with high resolution. This systematic review evaluates the clinical applications of polymer gel dosimeters in radiotherapy. To find the clinical applications of polymer gel dosimeters in radiotherapy, a full systematic literature search was performed on the basis of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in electronic databases up to January 31, 2017, with use of search-related terms in the titles and abstracts of articles. A total of 765 articles were screened in accordance with our inclusion and exclusion criteria. Eventually, 53 articles were included in the study. The findings show that most clinical applications of polymer gel dosimeters relate to external radiotherapy. Most of the gel dosimeters studied have acceptable dose accuracy as a 3D dosimeter with high resolution. It is difficult to judge which is the best polymer gel dosimeter to use in a clinical setting, because each gel dosimeter has advantages and limitations. For example, methacrylic acid–based gel dosimeters have high dose sensitivity and low toxicity, while their dose response is beam energy dependent; in contrast, N-isopropylacrylamide gel dosimeters have low dose resolution, but their sensitivity is lower and they are relatively toxic. Keywords: Polymer gel dosimetry Clinical application Radiotherapy Brachytherapy Neutron capture therap

Diode calibration for dose determination in total body irradiation

Background: Total Body Irradiation (TBI) is different from standard radiotherapy in many aspects, so it is not easy to predict the delivered dose to the patient under TBI treatment. Diode dosimetry procedures for surface dose reading can help to define variations of the actually delivered dose from the prescribed one. The aim of this study was to describe the measurements made to calibrate diodes in order to implement as a dosimeter for TBI tratment. An algorithm was also proposed based on diode dosimetry in order to determine the midplane dose. Materials and Methods: In this study, four p-type diodes connected to a MULTIDOSE electrometer were implemented as dosimeter. For diode calibration a water phantom with dimension of 30�30�32cm3 along with a 0.6 cc Farmer ion chamber were used. Directional dependence of diodes, the effects of thickness correction factor and complete backscatter factor were studied. Three algorithms, arithmetic, geometric mean and proposed algorithm were used to investigate midplane dose determination in TBI condition. Results: It was found by measurements that the effect of angle incident on diode response was significant and should have been taken into account. Variation in thickness correction factor was found about 0.7. The accuracy in midplane dose determination in the arithmetic, geometric mean and proposed algorithm was about 3.8, 12.5 and 3.3, respectively. Conclusion: Diode dosimetry is very useful as a check of midplane dose delivered to patients under TBI treatment. When the calibration and correction factors are carefully determined, high precision can be obtained. The proposed algorithm by this study seems to be useful in order to midplane dose determination in TBI condition

Different Methods of Measuring Neutron Dose/Fluence Generated During Radiation Therapy with Megavoltage Beams

Medical linear accelerators (linacs) are the most frequently applied radiation therapy machines in the locoregional treatment of cancers by producing either high-energy electron or photon beams. However, with high-energy photons (>8 MeV), interaction of these photons with different high-Z nuclei of materials in components of the linac head unavoidably generates neutrons. On the other hand, the average energy of these generated neutrons has almost the highest radiation-weighting factor. Therefore, the produced neutrons should not be neglected. There are various tools for the measurement of neutron dose/fluence generated in a megavoltage linac, including thermoluminescent dosimeters, solid-state nuclear track detectors, bubble detectors, activation foils, Bonner sphere systems, and ionization chamber pairs. In this review article, each of the above-mentioned dosimetric methods will be described in detail

Thorax organ dose estimation in computed tomography based on patient CT data using Monte Carlo simulation

Background: This study presents pati ent specific and organ dose esti mati on in computed tomography (CT) imaging of thorax directly from pati ent CT image using Monte Carlo simulati on. Pati ent's CT image is considered as the pati ent specific phantom and the best representati ve of pati ent physical index in order to calculate specific organ dose. Materials and Methods: EGSnrc/BEAMnrc Monte Carlo (MC) System was used for CT scanner simulati on and DOSXYZnrc was used in order to produce pati ent specific phantom and irradiati on of photons to phantom in step and shoot mode (axial mode). In order to calculate pati ent thorax organ dose, pati ent CT image of thorax as voxelized phantom was divided to a 64x64x20 matrix and 6.25 x 6.25 x 6.25 mm3 voxel size and this phantom was imported to DOSXYZnrc code. MC results in unit of Gy/parti cle were converted to absorbed dose in unit of mGy by a conversion factor (CF). We calculated pati ent thorax organ dose in MC simulati on from all irradiated slices, in 120 kV and 80 kV photon energies. Results: Effecti ve dose was obtained from organ dose and organ weighti ng factor. Esophagus and spinal cord received the lowest, and bone received the highest dose. In our study, effecti ve dose in CT of thorax was 7.4 mSV and 1.8 mSv in 120 and 80 kV, respecti vely. Conclusion: The results of this study might be used to provide the actual pati ent organ dose in CT imaging and calculati on of real effecti ve dose based on organ dose

Physical and dosimetric aspect of euromechanics add-on multileaf collimator on varian clinac 2100 C/D

Background: Before treatment planning and dose delivery, quality assurance of multi-leaf collimator (MLC) has an important role in intensity-modulated radiation therapy (IMRT) due to the creation of multiple segments from optimization process. Objective: The purpose of this study is to assess the quality control of MLC leaves using EBT3 Gafchromic films. Material and Methods: Leaf Position accuracy and leaf gap reproducibility were checked with Garden fence test. The garden fence test consists of 5 thin bands A) 0.2 Cm width spaced at 2 Cm intervals and B) 1 Cm width spaced at 1 Cm intervals. Each leaf accuracy was analyzed with measuring the full-width half-maximum (FWHM). Maximum and average leaf transmission were measured with gafchromic EBT3 films from Ashland for both 6 MV and 18 MV beams. Results: Leaf positions were found to be in a range between 1.78 � 2.53 mm, instead of nominal 2 mm for the test A and between 9.09 � 10.36 mm, instead of nominal 10 mm for the test B. The Average radiation transmission of the MLC was noted 1.79 and 1.98 of the open 10x10 Cm 2 field at isocenter for 6 MV and 18 MV beams, respectively. Maximum radiation transmission was noted 4.1 and 4.4 for 6 MV and 18 MV beams, respectively. Conclusion: In this study, application of gafchromic EBT3 films for the quality assurance of Euromechanics multileaf collimator was studied. Our results showed that the average leaf leakage and positional accuracy of this type of MLC were in the acceptance level based on the Protocols. © 2019, Shiraz University of Medical Sciences. All rights reserved

A novel investigation of the effect of different concentrations of methacrylic acid on the dose response of MAGAT gel dosimeter in intraoperative radiotherapy

Purpose: High dose prescription in one treatment session of intraoperative radiotherapy (IORT) requires precise monitoring of the delivered dose. Methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel with superior dose sensitivity and dose resolution seems to be a suitable tool for 3 dimensional dose verification of IORT. In the current study, the dose response of MAGAT gel dosimeter with varying concentrations of methacrylic acid (MAA) was investigated. Finally, the MAGAT with optimal concentration was subjected to dose rate and energy dependency measurements. Methods: MAGAT gel with different concentrations of 3, 5, 6, 8 and 10 was manufactured and irradiated with 50 keV produced by IORT. Gel vials were read out by MRI and R-2 responses were plotted against dose. Dose rate and energy dependency of optimum MAGAT gel were assessed by irradiation by a VARIAN linear accelerator using various dose rates of 30, 40 and 50 cGy/min and diverse photon energies of 6 and 18 MV as well as 50 keV of IORT. Results: MAGAT with a concentration of 8 MAA, exhibited a high-dose response and dose sensitivity of 5.16 Gy(-1) s(-1) in irradiation by IORT. Moreover, its response was independent of low dose rates (30, 40 and 50 cGy/min) and mega-voltage energies (p > 0.05). However, there was a significant difference between the R-2-dose response of MAGAT irradiated by mega-voltage (6 and 18 MV) and 50 keV energy of IORT. Conclusion: MAGAT is an effective tool to investigate three dimensional dose distributions of IORT independent of dose rates used in X-ray IORT. Moreover, its response is energy independent over mega-voltage energies.

Comparison of CCC and ETAR dose calculation algorithms in pituitary adenoma radiation treatment planning; Monte Carlo evaluation

Aims To verify the accuracy of two common absorbed dose calculation algorithms in comparison to Monte Carlo (MC) simulation for the planning of the pituitary adenoma radiation treatment. Materials and methods After validation of Linac's head modelling by MC in water phantom, it was verified in Rando phantom as a heterogeneous medium for pituitary gland irradiation. Then, equivalent tissue-Air ratio (ETAR) and collapsed cone convolution (CCC) algorithms were compared for a conventional three small non-coplanar field technique. This technique uses 30 degree physical wedge and 18 MV photon beams. Results Dose distribution findings showed significant difference between ETAR and CCC of delivered dose in pituitary irradiation. The differences between MC and dose calculation algorithms were 6.40 ± 3.44 for CCC and 10.36 ± 4.37 for ETAR. None of the algorithms could predict actual dose in air cavity areas in comparison to the MC method. Conclusions Difference between calculation and true dose value affects radiation treatment outcome and normal tissue complication probability. It is of prime concern to select appropriate treatment planning system according to our clinical situation. It is further emphasised that MC can be the method of choice for clinical dose calculation algorithms verification. Copyright © 2014 Cambridge University Press

Incidence and mortality of various cancers in Iran and compare to other countries: A review article

Abstract Background: Iran in recent years had the rapid development of industrialization and modernity, and changes in the people’s lifestyles and environment, these changes may affect epidemiological patterns of various types of cancers. In this review, incidence and mortality of various cancers (skin, gastric, esophageal, breast, and prostate) in Iran have been reported. Methods: The related data about Iran and other countries were collected from databases such as Google Scholar, Scopus, PubMed, EMBASE, and Web of Science. All included studies were published before Jun 2017. Results: There is an increment trend of incidence and mortality rate for most cancers in Iran. Conclusion: The plan for control and prevention of cancers must be a high priority for health policy in Iran as well as it is suggested that earlier screening is need for high-risk population. Keywords: Cancer, Incidence, Mortality, Risk factor, Ira

Bismuth oxide nanoparticles as agents of radiation dose enhancement in intraoperative radiotherapy

Purpose Intraoperative radiotherapy (IORT) technique is an advanced radio therapeutic method used for delivery of a single high-dose radiation during surgery while removing healthy tissues from the radiation field. Nowadays, growing attention is being paid to IORT for its low-energy (kilovoltage) delivery as it requires less radiation protection, but suffers several disadvantages, including high-dose delivery and prolonged treatment time. The application of nanoparticles with high atomic number and high attenuation coefficients in kilovoltage energy may help overcome the mentioned shortcomings. This study was designed to investigate and quantify the mean dose enhancement factor (DEF) in the presence of nanoparticles using IORT method. Methods Bismuth oxide nanoparticles (Bi(2)O(3)NPs), both in sheet and spherical formats, were synthesized using a novel hydrothermal method and characterized with x-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. Genipin-gelatin gel dosimeter (GENIPIN) was produced in three batches of pure with sheet and with spherical nanoparticles in concentration of 46.596 mu g/ml, and irradiated with 50 kV x-rays. Results Samples were scanned by a spectrophotometer, which indicated a DEF of 3.28 +/- 0.37 and 2.50 +/- 0.23 for sheet and spherical NPs, respectively. According to the results of this study, GENIPIN is a suitable dosimeter for the evaluation of three-dimensional dose distribution in the presence Bi2O3 NPs. Conclusion As a result, IORT along with Bi2O3 NPs has the potential to reduce treatment time and/or normal tissue dose; moreover, it could provide localized dose enhancement

Evaluation of ferrous benzoic methylthymol-blue gel as a dosimeter via magnetic resonance imaging

PURPOSE: In previous studies, methylthymol-blue and benzoic acid have been introduced as a diffuser limiter and sensitivity enhancer in the gel dosimeter composition, respectively. This work focused on analyzing a formulation of the Fricke gel dosimeter consisting of methylthymol-blue and benzoic acid through magnetic resonance imaging. METHODS: The gel dosimeter samples were irradiated using 6, 10, and 15 MV photons with different levels of doses and read using a 1.5 T scanner in order to evaluate the dose-response sensitivity and to study the effect of benzoic acid concentration, diffusion coefficient and temperature and to determine the temporal stability of the gel dosimeter. RESULTS: Inspection of radiological properties revealed that this gel dosimeter can be considered as a tissue equivalent medium. Within the dose range 0 to 1000 cGy, the R1 sensitivity and R2 sensitivity of the gel dosimeter equaled 0.058 +/- 0.003 and 0.092 +/- 0.004 s(-1)Gy(-1), respectively. The diffusion coefficient was less than 0.85 +/- 0.02mm(2)h(-1) for doses higher than 200 cGy. In addition, by changing the temperature from 15C to 25, the R1 sensitivity and R2 sensitivity decreased about 5 and 11, respectively. Further, no significant energy and dose rate dependence were observed over photon energies of 6, 10, and 15 MV and over the range 65 to 525 cGy min(-1). CONCLUSIONS: Based on our observation, the ferrous benzoic acid methylthymol-blue gel dosimeter can be suggested to measure the dose distribution. Further analysis is required to clarify its performance in clinical situations