MRI-Readable 3D Radiation Dosimetry and Sensing

Radiation therapy is a common treatment for cancer using high-energy X-rays (~5 MeV) or proton beams (70 to 230 MeV) to kill cancer cells. Gel dosimeters measure the amount of radiation applied and its distribution to ensure a lethal dose is applied to the cancerous tissue while sparing surrounding healthy tissue. We are developing MRI-readable gel dosimeters that can image X-ray and proton beam doses in 3D biomimetic phantoms and validate computational models. Fricke and polymer gels were tested. In Fricke gel dosimeters, ferrous ions transform into ferric ions when irradiated. In polymer gel dosimeters, monomers polymerize when exposed to radiation. The dosimeters were exposed to X-rays from a microCT. Quantitative MRI was used to image changes in spin relaxation times T1, T2, and water diffusion constant D. Large changes to relaxation times were observed with resolution better than 1 mm. Methacrylic and ascorbic acid in gelatin initiated by copper (MAGIC) gels were the most sensitive. Monte Carlo simulations of the radiation were used to model the attenuation throughout the tissue mimic. In addition to correlating changes in T1, T2, and D to X-ray dose, these measurements give information on how materials are changing in response to radiation. Measuring radiation effects will be important to fully understand and personalize radiation treatment. Measuring toxicity effects of sublethal doses is critical since, as more people survive cancer, long term quality of life after treatment is a primary concern.