Author: Siju C. George, Alonso N. Gutierrez, Vivek Mishra, Ranjini P. Tolakanahalli 👨🔬
Affiliation: Miami Cancer Institute, Baptist Health South Florida, Miami Cancer Institute 🌍
Purpose: This presentation focuses on optimizing dosimetry in RPT clinics by tackling initial setup challenges and ensuring the accuracy of SPECT/CT imaging for dosimetry. It will address the qualification of SPECT/CT images specifically for dosimetry rather than for diagnostics. Additionally, the presentation will help physicists navigate the QA requirements of SPECT/CT systems, enabling them to produce image sets that accurately quantify the delivered dose.
Methods: Our phantom experiment was developed to permit the quantitative evaluation of the necessary treatment protocol parameters while representing a clinical protocol. Quality control tests, including volumetric and image alignment assessments, were conducted to ensure accurate dose calculations. An end-to-end (E2E) test was performed to validate the workflow and quantitative dose accuracy.
Results: Image alignment tests on the SPECT/CT showed discrepancies exceeding the maximum tolerance of 2.2 mm, which were corrected to achieve an accuracy of <1 mm in all directions. These adjustments ensured precise dose delivery and improved image quality for dosimetry.
A thorough analysis of the reconstruction required for accurate dosimetry was conducted for an available Dosimetry software. This approach yields more accurate absorbed doses, and our study demonstrated that scatter corrections did not plateau until a particular number of iterations are used. We found that the precision between MLEM and OSEM mean doses was within 1.1% Coefficient of Variation, with 95% of SPECT/CT reconstructions falling within 2% of the mean dose estimate. Consequently, 24 subsets and 20 iterations were identified as the optimal balance of accuracy and speed.
Conclusion: Rigorous quality control measures significantly enhanced the accuracy and reliability of dosimetry in RPT clinics. By addressing initial setup challenges and ensuring precise image alignment, the work demonstrates a successful integration of patient-specific dosimetry into an established RPT program, ultimately improving quality of the dosimetry calculation outputs.