Basic features of VIC-T dosimeter with spiral CT readout, CT scanning conditions and data processing with a new polyGeVero-CT software package

On the Use of the Fricke-Pluronic F-127 Gel Dosimeter for Radiation Isocenter Testing of a Medical Linear Accelerator

This work presents a Fricke-XO-Pluronic F-127 2D radiochromic dosimeter with a flat-bed scanner for 2D reading and a dedicated data processing software package as a tool for performing coincidence testing of the radiation and mechanical isocenter of a medical accelerator. The optimal irradiation parameters were determined as follows: monitor units per beam and multi-leaf collimator gap, which are ≤750-≤2500 MU and 2-5 mm, respectively, for a cuboidal container with dimensions of 12 × 12 × 0.3 cm3. Despite the diffusion of Fe3+ ions occurring during irradiation, 2D reading can be performed at least 3 h after irradiation, without affecting the calculation performance of the coincidence test. The test was successfully performed for various irradiation settings. Overall, the Fricke-XO-Pluronic F-127 dosimeter has proven to be a potential tool for the coincidence testing of medical accelerators.

Validation of complex radiotherapy techniques using polymer gel dosimetry

Modern radiotherapy delivers highly conformal dose distributions to irregularly shaped target volumes while sparing the surrounding normal tissue. Due to the complex planning and delivery techniques, dose verification and validation of the whole treatment workflow by end-to-end tests became much more important and polymer gel dosimeters are one of the few possibilities to capture the delivered dose distribution in 3D. The basic principles and formulations of gel dosimetry and its evaluation methods are described and the available studies validating device-specific geometrical parameters as well as the dose delivery by advanced radiotherapy techniques, such as 3D-CRT/IMRT and stereotactic radiosurgery treatments, the treatment of moving targets, online-adaptive magnetic resonance-guided radiotherapy as well as proton and ion beam treatments, are reviewed. The present status and limitations as well as future challenges of polymer gel dosimetry for the validation of complex radiotherapy techniques are discussed.

Flexible Cotton Fabric-Based Ionizing Radiation Dosimeter for 2D Dose Distribution Measurements over a Wide Dose Range at High Dose Rates

This work presents an ecological, flexible 2D radiochromic dosimeter for measuring ionizing radiation in the kilogray dose range. Cotton woven fabric made of cellulose was volume-modified with nitrotetrazolium blue chloride as a radiation-sensitive compound. Its features include a color change during exposure from yellowish to purple-brown and flexibility that allows it to adapt to various shapes. It was found that (i) the dose response is up to ~80 kGy, (ii) it is independent of the dose rate for 1.1-73.1 kGy/min, (iii) it can be measured in 2D using a flatbed scanner, (iv) the acquired images can be filtered using a mean filter, which improves its dose resolution, (v) the dose resolution is -0.07 to -0.4 kGy for ~0.6 to ~75.7 kGy for filtered images, and (vi) two linear dose subranges can be distinguished: ~0.6 to ~7.6 kGy and ~9.9 to ~62.0 kGy. The dosimeter combined with flatbed scanner reading and data processing using dedicated software packages constitutes a comprehensive system for measuring dose distributions for objects with complex shapes.

Features of 2Day.QA® as a 2D radiation dosimeter

PURPOSE

A new commercial 2D ionising radiation dosimeter (2Day.QA®) was developed. This work aims to introduce the basic functions of 2Day.QA®.

METHODS

The dosimeter is made mainly of a linear polysaccharide consisting of β(1 → 4) linked d-glucose units and radiation active substances, which make it environmentally friendly. For 2Day.QA® irradiation, radiotherapy ionising radiation sources were used. The analysis of 2Day.QA® was performed using three scanners: Vidar® Red LED Dosimetry Pro Advantage™, Vidar® VXR 12-plus™ and HP Scanjet G3010 flatbed scanner. The stability of 2Day.QA® was tested. Exemplary applications of 2DayQA® for QA studies of accelerator light and radiation field coincidence and brachytherapy source position were carried out.

RESULTS

The dosimeter responded to the lowest applied dose of 0.95 Gy and saturated at over 94.9 Gy. The quasi-linear dose response is below 20 Gy. Vidar® Red LED Dosimetry Pro Advantage™ has proven to be superior to other scanners at determining dose effects in 2Day.QA®. The stability of the non-irradiated 2Day.QA® is at least 18 months. After 18 months of storage, the dosimeter reacted to irradiation. In the case of the irradiated samples, a slight color drift related to the absorbed dose was observed. Tests of the use of 2Day.QA® to control the quality of the accelerator light and radiation field coincidence and brachytherapy source position have shown that it can be used for such applications.

CONCLUSIONS

The study reveals the potential of 2Day.QA® for 2D radiation dosimetry and concludes with recommendations for the use of the dosimeter for radiotherapy QA tests.

Fast Isocenter Determination Using 3D Polymer Gel Dosimetry with Kilovoltage Cone-Beam CT Reading and the PolyGeVero-CT Software Package for Linac Quality Assurance in Radiotherapy

This work presents an approach to the fast determination of a medical accelerator irradiation isocenter as a quality assurance (QA) procedure in radiotherapy. The isocenter determination tool is the tissue equivalent high-resolution 3D polymer gel dosimeter (PABIG^nx) in a dedicated container combined with kilovoltage imaging systems and the polyGeVero-CT software package (v. 1.2, GeVero Co., Poland). Two accelerators were employed: Halcyon and TrueBeam (Varian, USA), both equipped with cone beam computed tomography (CBCT) and iterative reconstruction CBCT (iCBCT) algorithms. The scope of this work includes: (i) the examination of factors influencing image quality (reconstruction algorithms and modes), radiation field parameters (dose and multi-leaf collimator (MLC) gaps), fiducial markers, signal averaging for reconstruction algorithms and the scanning time interval between consecutive scans, (ii) the examination of factors influencing the isocenter determination, image processing (signal averaging, background subtraction, image filtering) and (iii) an isocenter determination report using a 2D and 3D approach. An optimized protocol and isocenter determination conditions were found. The time and effort required to determine the isocenter are discussed.