Clinical assessment of a method for comparative analysis of planned vs. delivered isodoses in radiation therapy

The effectiveness of external beam photon radiotherapy relies on precise planning and execution, involving patient-specific quality assurance to ensure clinical goals are met. This involves verifying the therapy plan against constraints set by the oncology team and confirming its correct implementation. Standard QA methods include gamma analysis and dose-volume histograms (DVH), each with limitations. Gamma analysis highlights delivery errors without distinguishing between over- and under-dosage, while DVH can show coinciding planned and delivered doses despite spatial distribution differences. In this work, a novel method, quantitative isodose analysis, is evaluated on treatment plans with the purpose of determining whether it can address these limitations, and assessing their clinical significance.

Quantitative isodose analysis works by comparing planned and delivered isodoses for each structure, identifying volumes of under- and over-dosage. This method was validated using anonymized patient data involving 75 treatment plans for different cancer locations.

In a prostate cancer case, significant rectal overdosage was detected, leading to a treatment plan revision. Another rectal cancer case showed underdosage but met clinical implementation criteria.

Results showed that quantitative isodose analysis could detect clinically significant dose delivery errors that standard QA might miss. The findings suggest that while standard QA methods are essential, quantitative isodose analysis provides an additional layer of scrutiny, enhancing the detection of dose discrepancies. The study highlights the potential of quantitative isodose analysis in improving radiotherapy QA, despite limitations such as reliance on reconstructed 3D dose distributions and the need for broader patient cohort studies.