Development, Construction, and Evaluation of an Alternative Dosimetry Phantom for Computed Tomography

Standard phantoms for computed tomography dose index (CTDI) measurements rely on polymethyl methacrylate (PMMA), a material with known radiological properties. However, PMMA may not fully replicate the behavior of human tissue in all CT imaging scenarios. Prior research has shown that PMMA-based phantoms are widely used but may introduce minor discrepancies in dose measurements. No prior work had resolved whether alternative materials could match PMMA's radiological characteristics while offering comparable or improved dosimetric accuracy. This gap motivated the exploration of new phantom materials. The need for a phantom that more closely mimics human tissue in CT imaging remains unmet. Alternative materials may offer better performance in dose evaluation. Researchers have proposed using epoxy resin mixed with iodine to achieve this. This approach may provide a more accurate representation of human tissue in CT imaging. The goal is to improve dosimetric consistency across different imaging conditions.

This study aimed to develop, construct, and evaluate an alternative phantom for measuring CT dose indices. The researchers sought to create a phantom material that closely resembles PMMA in radiological properties but may offer improved accuracy in dose measurements. The specific problem addressed is the potential mismatch between PMMA and human tissue in CT imaging scenarios. The motivation stems from the need for a phantom that better simulates human tissue behavior under CT exposure. The researchers proposed that an epoxy-iodine mixture could serve as a viable alternative to PMMA. This material was selected for its ability to approximate PMMA's electron density and effective atomic number. The study also aimed to compare the new phantom's performance against the standard PMMA phantom. The goal was to determine whether the alternative phantom could yield comparable or improved dose measurements.

The researchers prepared 12 variations of epoxy resin mixed with iodine-based contrast agents. Each mixture was tested using CT imaging at 80 and 120 kVp to determine relative electron density (ρ) and effective atomic number (Z). The selected mixture was one that produced ρ and Z values closest to those of PMMA. The alternative phantom was constructed using this optimized mixture. Dose measurements were then taken at various tube voltages (80, 100, 120, and 135 kVp) using both the new and standard phantoms. The results were compared to assess the accuracy of the alternative phantom. A Student’s t-test was used to evaluate statistical differences between the two phantom types. The evaluation focused on dose discrepancies and statistical significance to determine comparability.

The alternative phantom was constructed using an epoxy-iodine mixture with a concentration of 0.46%. At this concentration, the material’s ρ and Z values deviated from PMMA by 0.12% and 1.58%, respectively. Dose measurements showed an average discrepancy of 5% for the head phantom and 1% for the body phantom across tested voltages. The differences between the alternative and standard phantoms were statistically significant (P < 0.05). These results suggest the alternative phantom is comparable to PMMA in dose measurement accuracy. The smallest deviations occurred at the highest tube voltages tested. The material’s radiological properties closely matched those of PMMA. The statistical analysis confirmed the reliability of the alternative phantom’s performance.

The study demonstrated that an epoxy-iodine mixture can serve as a viable alternative to PMMA in CT dose index phantoms. The material’s radiological properties closely matched those of PMMA, with minimal deviations in electron density and effective atomic number. Dose measurements using the alternative phantom showed acceptable accuracy compared to the standard phantom. The statistical analysis confirmed the comparability of the two phantom types. The results suggest the alternative phantom could be used in place of PMMA for CT dosimetry. The study did not propose that the new phantom is superior to PMMA but that it is functionally equivalent. The findings support the potential use of the alternative phantom in clinical and research settings. The researchers did not suggest further development of the material beyond its current formulation.