Abstract
Achieving accurate optical CT 3D dosimetry without the use of viscous refractive index (RI) matching fluids would greatly increase convenience. Software has been developed to simulate optical CT 3D dosimetry for a range of scanning configurations including parallel-beam, point and converging light sources. For each configuration the efficacy of 3 refractive media were investigated: air, water, and a fluid closely matched to Presage (RI = 1.00, 1.33 and 1.49 respectively). The results revealed that the useable radius of the dosimeter (i.e. where data was within 2% of truth) reduced to 68% for water-matching, and 31% for dry-scanning in air. Point source incident ray geometry produced slightly more favourable results, although variation between the three geometries was relatively small. The required detector size however, increased by a factor six for dry-scanning, introducing cost penalties. For applications where dose information is not required in the periphery, some dry and low-viscous matching configurations may be feasible.
Highlights
Immersion of dosimeters in a refractively matched fluid is a ubiquitous technique to minimize refraction artifacts in optical-CT 3D dosimetry [1,2,3,4,5]
A total of 20 combinations of geometry and refractive index (RI) were simulated and the usable fraction ru/r0 and required detector size Δθ are given in table 1
Reconstructed images corresponding to each scanning configuration are shown, together with line profiles comparing measured and true dose
Summary
Immersion of dosimeters in a refractively matched fluid is a ubiquitous technique to minimize refraction artifacts in optical-CT 3D dosimetry [1,2,3,4,5]. Radiochromic dosimeters [6] like PRESAGE® [7] have high refractive index (RI) of ~1.51. Transparent solutions with this magnitude RI tend to be viscous, and require regular cleaning as they accumulate dust and particles from dosimeters. Work reported the feasibility of dryscanning for small volumes with a laser microbeam CT [5, 9]. Several works have begun to explore the feasibility of dry-scanning for larger volumes [10,11,12]. The present work builds on these efforts, and presents simulations of various optical-CT configurations and refractive matching scenarios
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