The current practice for patient-specific quality assurance (QA) uses ion chambers or diode arrays primarily because of their ease of use and reliability. A standard routine compares the dose distribution measured in a phantom with the dose distribution calculated by the treatment planning system for the same experimental conditions. For the particular problems encountered in the treatment planning of complex radiotherapy techniques, such as small fields/segments and dynamic delivery systems, additional tests are required to verify the accuracy of dose calculations. The dose distribution verification should be throughout the total 3D dose distribution for a high dose gradient in a small, irradiated volume, instead of the standard practice of one to several planes with 2D radiochromic (GAFChromic) film. To address this issue, we have developed a 3D radiochromic dosimeter that improves the rigor of current QA techniques by providing high-resolution, complete 3D verification for a wide range of clinical applications. The dosimeter is composed of polyurethane, a radical initiator, and a leuco dye, which is radiolytically oxidized to a dye absorbing at 633 nm. Since this chemical dosimeter is single-use, it represents a significant expense. The purpose of this research is to develop a cost-effective reusable dosimeter formulation. Based on prior reusability studies, three promising dosimeter formulations were studied using small volume optical cuvettes and irradiated to known clinically relevant doses of 0.5–10 Gy. After irradiation, the change in optical density was measured in a spectrophotometer. All three formulations retained linearity of optical density response to radiation upon re-irradiations. However, only one formulation retained dose sensitivity upon at least five re-irradiations, making it ideal for further evaluation as a 3D dosimeter.

New and improved developments in the field of radiotherapy have created extremely effective and efficient procedures for the treatment of tumors. Such developments require complex radiotherapy systems and plans which have ultimately improved the successfulness of treatments and improved the options available to patients. However, these advanced treatments present challenges for current dosimetric verification techniques which struggle to keep up. We will be examining radiochromic plastics as a way of addressing this conflict. Radiochromic plastics are synthetic materials whose optical properties change upon absorption of dose. The color darkens when the dose is absorbed, and the change in optical density is proportional to the dose absorbed. We examine a formulation which is designed to clear its response slowly after irradiation to determine if the formulation is reusable after it clears. If upon reirradiation the dose response remains linear, then reusability is an option. Our results show that the response remains linear over a range of five irradiations and a timespan of two years, but their sensitivity drops around 20% after the first reirradiation and less than that upon further irradiation. The plastics clear at an exponential rate, but the time it took to clear increased after each reirradiation. These results suggest that a long term reusable dosimeter is possible. Data on a faster clearing formulation will also be presented.