Description
Purpose: Recent advances in radiation therapy physics have enabled sophisticated treatment plans that conform accurately to the target volume while sparing normal tissue. The complex 3D treatment planning requires dose verification techniques that can validate high spatial resolution 3D dose distribution with accuracy and precision. Traditional dosimetry techniques include ionization chambers, which map accurately but are restricted to 2D film based techniques. Polymer gel dosimetry integrates a 3D dosimeter with high spatial resolution, precision, and accuracy for the verification of a large range of treatment plans. In addition, polymer gel dosimetry uses human tissue equivalent phantoms and a wide range of dose algorithms to increase dose measurement accuracy. However, polymer gel dosimetry has not been widely evaluated for its extensive range of statistical regression methods in advanced radiation therapy units, such as Stereotactic Radiotherapy (SRT) and Stereotactic Radiosurgery (SRS). In addition, the construction of polymer gel dosimeters is a toxic process, and sunlight and oxygen environments degrades the gel. Described is a method in which a deformable phantom is introduced that is non-toxic and safe to handle. In addition, the phantom decreases oxygen sensitivity and increases its ease of use towards translational use in the Radiation Oncology clinical environment. Methods: Radiation dose treatment plans were evaluated with the gel dosimeter. In addition, T2 fitting methods were evaluated to determine the best fitting technique. Statistical regression algorithms for T2 fitting included: Maximum Likelihood Estimation (MLE), MLE with Rician, Least Squares No Constant Term, and Weighted Least Squares. Since the dose calibration curves did not yield accurate absolute values of dose, several methods for scaling were evaluated. Results: Evaluation of statistical regression algorithms yielded a range of signal-tonoise ratios, and internal scaling schemes provided accurate absolute values. While being characterized as a phantom that is non-toxic and protected from oxygen contamination, the deformable gel phantom expressed reduced oxygen sensitivity. Conclusion: Deformable polymer gel dosimetry provides dose verification of complex radiotherapy treatment plans. Future work includes internal dose calibration methods to increase the accuracy of absolute dose quantification.
