A Statistical Analysis of Correlations Between HRCTV Dose and OAR Doses for Cervix HDR
B Washington*, M Randall, D Fabian, D Cheek, C Wang, W Luo, University of Kentucky, Lexington, KY
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PO-GePV-T-35 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To evaluate the effect of interfractional dosimetric variations (IDV) of the high-risk clinical target volume (HRCTV) from the prescribed dose on organs at risk (OAR) in high dose rate (HDR) tandem and ovoid (T&O) brachytherapy.
Methods: Fifty patients diagnosed with cancers of the uterine cervix and treated with HDR T&O brachytherapy were retrospectively analyzed. The OARs of interest were the rectum, bladder, sigmoid, and bowel. The dosimetric parameters evaluated for all patients was the dose absorbed by 90% of the HRCTV (D_90) and the dose absorbed by 0.1 (D_0.1cc) and 2 cc (D_2cc) of each respective OAR. The HRCTV variations were from the prescribed dose and the OAR variations were from the corresponding tolerance dose (80% of the prescribed dose). Each patient’s average variation throughout their course of brachytherapy represented one data point for each structure. This provided a single value to quantify a patient’s IDV. Spearman’s rank correlation test was conducted for each OAR dosimetric parameter variation against the HRCTV D_90 variations. Correlation coefficients (ρ) that surpassed a value of ±0.700 and or p-values < 0.05 determined statistical significance.
Results: Some OAR variations only showed moderate correlations with the HRCTV variations despite the variations being relative to each other. The bladder D_2cc had the strongest correlation (ρ =-0.508, p-value < 0.001) with the HRCTV variations. The rectum D_2cc and bladder D_0.1cc also had statistically significant correlations with the HRCTV variations. The mean HRCTV D_90 variation from the prescribed dose was -2.53% ± 8.74%.
Conclusion: HRCTV IDVs from the prescribed dose are correlated to bladder dosimetric parameters and the rectum D_2cc. These correlations were only moderate despite the variations being relative to each other. The rectum D_0.1cc, sigmoid, and bowel dosimetric parameters were not correlated to HRCTV IDVs from the prescribed dose.
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