Dose Imaging in radiotherapy photon fields with Fricke and Normoxic-polymer Gels

Fricke gel xylenol orange dosimeter layers for stereotactic radiosurgery: A preliminary approach

Investigations regarding the feasibility, reliability, and accuracy of Fricke gel dosimeter layers for stereotactic radiosurgery are presented. A representative radiosurgery plan consisting of two targets has been investigated. Absorbed dose distributions measured using radiochromic films and gelatin Fricke Gel dosimetry in layers have been compared with dose distributions calculated by using a treatment planning system and Monte Carlo simulations. The different dose distributions have been compared by means of the gamma index demonstrating that gelatin Fricke gel dosimeter layers showed agreements of 100%, 100%, and 93%, with dose and distance tolerances of 2% and 2 mm, with respect to film dosimetry, treatment planning system and Monte Carlo simulations, respectively. The capability of the developed system for three-dimensional dose mapping was shown, obtaining promising results when compared with well-established dosimetry methods. The obtained results support the viability of Fricke gel dosimeter layers analyzed by optical methods for stereotactic radiosurgery.

Characterization of ferrous-agarose-xylenol gel dosimeter at 60Co γ-rays beam therapy unit

Fricke gel dosimetry is a valuable technique used for recording 3D dose distribution in radiotherapy. Herein, we present the dosimetric characteristics of a synthesized ferrous-agarose-xylenol orange gel dosimeter in a clinical ⁶⁰Co beam. Experimental data were obtained using a secondary standards dosimetry laboratory ⁶⁰Co therapy unit. The dosimeter was calibrated using the ionization chamber as a reference, and its total mass attenuation coefficient, absorption spectrum, optical density-dose relationship, sensitivity, and dose rate dependency were evaluated. The potentiality of the ferrous-agarose-xylenol gel dosimeter was investigated to measure output factors for different field sizes. The gel dosimeter readings were measured using a spectrophotometer. The ferrous-agarose-xylenol gel dosimeter exhibited a linearity in the range of 3-15 Gy, indicating that the dosimeter is tissue-equivalent and dose rate-independent and yield reproducible results. The measured output factors and those published in the literature showed good agreement.

Parameter estimation and mathematical modeling of the diffusion process of a benzoic acid infused Fricke gel dosimeter

This work presents a mathematical model implementation for studying the diffusion process of ferric ions in post-irradiated Fricke gel dosimeters. Fricke gel samples were manufactured in layers for their analysis by optical transmission imaging and benzoic acid was incorporated to improve their radiosensitivity. The developed method consists on designing the dosimeters with a suitable composition for their optical analysis which allows accurate measurements in a wide dose range with noticeable linear responses with an average linear correlation coefficient of r²=0.993. The developed algorithm calculates the diffusion coefficient by means of an inverse problem formulation. Moreover, the proposed method is capable of modeling time-dependent physical properties and evolution over time of the irradiated dosimeters accurately and comparable with experimentally measured data. The obtained results evince the complexity of the diffusion phenomena in this type of materials and the capacity of the proposed method to provide a reliable quantification of the diffusion coefficient as a scalar approximation of the diffusion tensor. The obtained diffusion coefficient varies from 1.21 to 1.61 mm²/h with uncertainties lower than 2%. The model is also transferable to other diffusion driven systems and the numerical solving method can also be adapted to solve diffusion calculation based on other theoretical approaches.

Fricke gel dosimeter with improved sensitivity for low-dose-level measurements

Fricke solution has a wide range of applications as radiation detector and dosimetry. It is particularly appreciated in terms of relevant comparative advantages, like tissue‐equivalence when prepared in aqueous media like gel matrix, continuous mapping capability, independence of dose rate and incident direction, as well as linear dose response. This work presents the development and characterization of an improved Fricke gel system, based on modified chemical compositions, making possible its application in clinical radiology due to its improved sensitivity. Properties of standard Fricke gel dosimeter for high‐dose levels are used as a starting point, and suitable chemical modifications are introduced and carefully investigated in order to attain high resolution for low‐dose ranges, like those corresponding to radiology interventions. The developed Fricke gel radiation dosimeter system achieves the expected typical dose‐dependency, showing linear response in the dose range from 20 up to 4000 mGy. Systematic investigations including several chemical compositions are carried out in order to obtain an adequate dosimeter response for low‐dose levels. A suitable composition from among those studied is selected as a good candidate for low‐dose‐level radiation dosimetry consisting of a modified Fricke solution fixed to a gel matrix containing benzoic acid along with sulfuric acid, ferrous sulfate, Xylenol orange, and tridistilled water. Dosimeter samples are prepared in standard vials for in‐phantom irradiation and further characterization by spectrophotometry measuring visible light transmission and absorbance before and after irradiation. Samples are irradiated using typical X‐ray tubes for radiology and calibrated Farmer‐type ionization chamber is used as reference to measure dose rates inside phantoms at vial locations. Once sensitive material composition is optimized, dose‐response curves show significant improvement regarding overall sensitivity for low dose levels. The aim of this work consists of implementing the optimized gel dosimeter to perform direct measurements of absorbed dose in samples irradiated during microcomputed tomography scanning in order to preliminary assess dose levels for further scanning of small animals for further applications in veterinary and paleontology. As a first attempt, dose distributions were measured in water‐equivalent phantoms having dimensions comparable to small animals, 100 to 1000 cm³, approximately. According to the obtained results, it is found that the proposed method shows satisfactory reliability and adequate performance for a promising gel dosimetry system.

PACS number(s): 87.53.Bn, 87.57.uq, 87.59.‐e