Evaluation of eGFR's Relation to Intra-Fractional Bladder Filling and the Dosimetric Impact during Online Adaptive Radiotherapy for Pelvic Lymph Node Cases
Abstract
Purpose
To quantify the relationship between estimated glomerular filtration rate (eGFR) and intra-fractional bladder filling during online adaptive radiotherapy (oART) and to evaluate the dosimetric effect on surrounding organs at risk (OARs).
Methods
A retrospective study was conducted on 53 patients with adaptive prostate cancer. For each fraction, the initial CBCT images acquired were compared with verification CBCTs to assess intra-fractional bladder filling. Bladder volumes were delineated, and bladder inflow rates (mL/min) were calculated. Inflow rates were compared with patients’ eGFR values. Additionally, 9 patients with pelvic lymph node (LN) disease were used to validate the previous findings and analyze the dosimetric impact of bladder filling on targets and OARs.
Results
The mean interval between scans was 15.5 min ± 4.3 min. The cohort’s average eGFR was 79.8 ± 20.1 mL/min/1.73m², with an overall inflow rate of 2.9 ± 2.1 mL/min. Patients with an eGFR above the cohort average had a higher bladder inflow rate than those with an eGFR below the cohort average. In pelvic lymph node patients, we observed increases of 12.5% and 66.3% in the mean and maximum bladder doses, respectively, while the mean doses to the large bowel and small bowel decreased by 17.1% and 27.1%, respectively. The absolute percent difference in the mean dose increased with time, reaching 3% for the PTV and 2% for the GTV after 20 minutes.
Conclusion
Results suggest a positive correlation between eGFR and intra-fractional bladder filling rate. Patients with eGFR above the cohort average exhibit higher bladder inflow rates, resulting in greater volume changes and intra-fractional uncertainty. Limiting the time interval between CBCTs might help reduce potential dosimetric effects on the PTV and GTV.