Dose verification of a clinical intensity-modulated radiation therapy eye case by the magnetic resonance imaging of N-isopropylacrylamide gel dosimeters

Investigation of the beam quality and dose rate dependence of PAKAG polymer gel dosimeter in optical readout technique

This study aims to evaluate the optical response dependence of the PAKAG polymer gel dosimeter on photon energy and dose rate. The produced gel dosimeters were irradiated using a Varian CL 21EX medical linear accelerator with delivered doses of 0, 2, 4, 6, 8, and 10 Gy. To examine the response dependence on the delivered dose rate, dose rates of 50, 100, 200, and 350 cGy min-1were investigated. Additionally, two incident beam qualities of 6 and 18 MV were examined to study the response dependence on the incident beam energy. The irradiated polymer gel dosimeters were readout using a UV-vis spectrophotometer in the 300 to 800 nm scan range. The results reveal that a wide variation in dose rate (50-350 cGy.min-1) influences the absorbance-dose response and the sensitivity of PAKAG gel. However, smaller variations did not show a significant effect on the response. Furthermore, the response changed insignificantly with beam quality for investigated energies. It was concluded that the optical reading response of the PAKAG polymer gel dosimeter is satisfactorily independent of external parameters, including dose rate and incident beam quality.

In vitro and in vivo biocompatibility study of polyacrylate TiO2@Ag coated nanoparticles for the radiation dose enhancement

To enhance the efficacy of radiation therapy, functionalised core-shell nanoparticles (CS NPs) are used as a radiosensitizer. These NPs can act as a therapeutic agent and carrier for other therapeutic agents. In this study, the first poly-acrylic acid modified silver-coated titanium dioxide NPs were fabricated to evaluate the radiation dose enhancement within the human tissue equivalent polymer gel after investigating the biocompatibility. Macrophage cell line and rats model were used for in vitro and in vivo study respectively. Two different beam qualities were applied to quantify the radiation dose enhancement with different concentrations of NPs in the polymer gel. The dose enhancement factors (DEFs) indicated that these biocompatible CS NPs are more effective for the radiation dose enhancement at low energy x-rays (80 kV) as compared to the high energy gamma (1.25 MeV Co60). These results suggested that functionalised core-shell silver-coated titanium dioxide NPs have great potential as a radiosensitizer in radiation therapy.

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

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.

A Comprehensive Evaluation of NIPAM Polymer Gel Dosimeters on Three Orthogonal Planes and Temporal Stability Analysis

Polymer gel dosimeters have been proven useful for dose evaluation in radiotherapy treatments. Previous studies have demonstrated that using a polymer gel dosimeter requires a 24 h reaction time to stabilize and further evaluate the measured dose distribution in two-dimensional dosimetry. In this study, the short-term stability within 24 h and feasibility of N-isopropylacrylamide (NIPAM) polymer gel dosimeters for use in three-dimensional dosimetry were evaluated using magnetic resonance imaging (MRI). NIPAM gels were used to measure the dose volume in a clinical case of intensity-modulated radiation therapy (IMRT). For dose readouts, MR images of irradiated NIPAM gel phantoms were acquired at 2, 5, 12, and 24 h after dose delivery. The mean standard errors of dose conversion from using dose calibration curves (DRC) were calculated. The measured dose volumes at the four time points were compared with those calculated using a treatment planning system (TPS). The mean standard errors of the dose conversion from using the DRCs were lower than 1 Gy. Mean pass rates of 2, 5, 12, and 24 h axial dose maps calculated using gamma evaluation with 3% dose difference and 3 mm distance-to-agreement criteria were 83.5% ± 0.9%, 85.9% ± 0.6%, 98.7% ± 0.3%, and 98.5% ± 0.9%, respectively. Compared with the dose volume histogram of the TPS, the absolute mean relative volume differences of the 2, 5, 12, and 24 h measured dose volumes were lower than 1% for the irradiated region with an absorbed dose higher than 2.8 Gy. It was concluded that a 12 h reaction time was sufficient to acquire accurate dose volume using the NIPAM gels with MR readouts.

Polymer gel dosimeter based on itaconic acid

A new polymeric dosimeter based on itaconic acid and N, N'-methylenebisacrylamide was studied. The preparation method, compositions of monomer and crosslinking agent and the presence of oxygen in the dosimetric system were analyzed. The resulting materials were irradiated with an X-ray tube at 158cGy/min, 226cGymin and 298cGy/min with doses up to 1000Gy. The dosimeters presented a linear response in the dose range 75-1000Gy, sensitivities of 0.037 1/Gyat 298cGy/min and an increase in the sensitivity with lower dose rates. One of the most relevant outcomes in this study was obtaining different monomer to crosslinker inclusion in the formed gel for the dosimeters where oxygen was purged during the preparation method. This effect has not been reported in other typical dosimeters and could be attributed to the large differences in the reactivity among these species.

Incorporating multislice imaging into x-ray CT polymer gel dosimetry

PURPOSE

To evaluate multislice computed tomography (CT) scanning for fast and reliable readout of radiation therapy (RT) dose distributions using CT polymer gel dosimetry (PGD) and to establish a baseline assessment of image noise and uniformity in an unirradiated gel dosimeter.

METHODS

A 16-slice CT scanner was used to acquire images through a 1 L cylinder filled with water. Additional images were collected using a single slice machine. The variability in CT number (NCT) associated with the anode heel effect was evaluated and used to define a new slice-by-slice background subtraction artifact removal technique for CT PGD. Image quality was assessed for the multislice system by evaluating image noise and uniformity. The agreement in NCT for slices acquired simultaneously using the multislice detector array was also examined. Further study was performed to assess the effects of increasing x-ray tube load on the constancy of measured NCT and overall scan time. In all cases, results were compared to the single slice machine. Finally, images were collected throughout the volume of an unirradiated gel dosimeter to quantify image noise and uniformity before radiation is delivered.

RESULTS

Slice-by-slice background subtraction effectively removes the variability in NCT observed across images acquired simultaneously using the multislice scanner and is the recommended background subtraction method when using a multislice CT system. Image noise was higher for the multislice system compared to the single slice scanner, but overall image quality was comparable between the two systems. Further study showed NCT was consistent across image slices acquired simultaneously using the multislice detector array for each detector configuration of the slice thicknesses examined. In addition, the multislice system was found to eliminate variations in NCT due to increasing x-ray tube load and reduce scanning time by a factor of 4 when compared to imaging a large volume using a single slice scanner. Images acquired through an unirradiated, active gel revealed NCT varies between the top and bottom of the 1 L cylinder as well as across the diameter of the cylinder by up to 7 HU.

CONCLUSIONS

Multislice CT imaging has been evaluated for CT PGD and found to be the superior technique compared to single slice imaging in terms of the time required to complete a scan and the tube load characteristics associated with each scanning method. The implementation of multislice scanning is straightforward and expected to facilitate routine gel dosimetry measurements for complex dose distributions in modern RT centers.