Small-Field Measurements of 3D Polymer Gel Dosimeters through Optical Computed Tomography

Abstract

With advances in therapeutic instruments and techniques, three-dimensional dose delivery has been widely used in radiotherapy. The verification of dose distribution in a small field becomes critical because of the obvious dose gradient within the field. The study investigates the dose distributions of various field sizes by using NIPAM polymer gel dosimeter. The dosimeter consists of 5% gelatin, 5% monomers, 3% cross linkers, and 5 mM THPC. After irradiation, a 24 to 96 hour delay was applied, and the gel dosimeters were read by a cone beam optical computed tomography (optical CT) scanner. The dose distributions measured by the NIPAM gel dosimeter were compared to the outputs of the treatment planning system using gamma evaluation. For the criteria of 3%/3 mm, the pass rates for 5 × 5, 3 × 3, 2 × 2, 1 × 1, and 0.5 × 0.5 cm2 were as high as 91.7%, 90.7%, 88.2%, 74.8%, and 37.3%, respectively. For the criteria of 5%/5 mm, the gamma pass rates of the 5 × 5, 3 × 3, and 2 × 2 cm2 fields were over 99%. The NIPAM gel dosimeter provides high chemical stability. With cone-beam optical CT readouts, the NIPAM polymer gel dosimeter has potential for clinical dose verification of small-field irradiation.

Technical Note: Evaluation of an iterative reconstruction algorithm for optical CT radiation dosimetry

“…The final dataset (Phantom C) was the result of a small‐field radiation dosimetry experiment. Small‐field dosimetry via optical CT has previously been reported using radiochromic and polymer gels, as well as radiochromic plastics (references and citations therein). In this experiment, we used a leuco crystal violet (LCV) gel dosimeter which uses sodium dodecyl sulfate (SDS) as a surfactant to prevent diffusion .…”

Different dosimeters/detectors used in small-field dosimetry: Pros and cons

“…[ 84 ] Although these dosimeters cannot be introduced as a standard dosimeter due to issues concerning repeatability and their requirement for advanced data processing techniques, some reports suggest that they are suitable for measuring the relative output factor, beam profile, and dose distributions in small fields because of their high spatial resolution and lack of issues concerning positioning. [ 10 29 85 86 87 ] Radiochromic gel dosimeters are insensitive to oxygen, have desirable diffusion rates, and can readout by optical methods. [ 6 88 89 ] These dosimeters are new compared to other gel dosimetry systems and need to perform further research.…”

Three-dimensional radiation dosimetry using polymer gel and solid radiochromic polymer: From basics to clinical applications

“…There are a few publications on applications of PGD/FGD/SPD[25-30], and more studies on this topic are needed.…”