Purpose: To investigate and characterize a novel 3D dosimetry system consisting of ClearView radiochromic gel dosimeters and telecentric optical CT imaging.
Methods: ClearView radiochromic dosimeters (Modus Medical Devices) are gellan gum based radiochromic dosimeters containing a water-soluble tetrazolium salt which reduces into an insoluble formazan dye (with associated color change) under ionizing radiation. Initial spectrophotometric studies investigated linearity of dose response on small volumes of ClearView in optical cuvettes. Simple single beam benchmark radiation therapy treatments were then delivered to 10 and 15-cm diameter ClearView dosimeters. The treatments were modeled with a commissioned Eclipse treatment planning system. Dosimeters were scanned submerged in a refractive index (RI) matching fluid (ca. 10% propylene glycol) by optical CT both pre- and post-irradiation (within 24h) and 3D reconstructions of the change in linear-optical-attenuation was determined using in-house software. Percent depth-dose, cross plane and in-plane profiles, and 3D gamma analysis were performed and compared to the commissioned Eclipse dose, which served as ground truth.
Results: Linearity of dose response was confirmed in the cuvette study with excellent agreement (R² ≥ 0.9986) at two wavelengths (520-and 632 nm) at 3 post-irradiation time points: 21 hours, 6 and 10 days. Dosimeter reconstructions were performed at 1mm³ resolution in full 3D. Relative dose profiles in both 15-and 10 cm dosimeters show good agreement in comparison to Eclipse dose calculations, with root mean square errors (RMSE) 0.00107-0.006649, and R² ≥ 0.9808. Relative 3D gamma analysis performed at 3%3mm range from 82.91% - 99.99% agreement. Regions of known artifacts were excluded from analysis (jar walls and neck), but some remain unaccounted for (e.g., ring and cupping artifacts).
Conclusion: This work presents the first use of a telecentric optical-CT scanner with ClearView. The system shows substantive promise for a new comprehensive 3D dosimetry system.
Funding Support, Disclosures, and Conflict of Interest: None. ClearView dosimeters provided by Modus Medical Devices.