CT-Based Quantification of Prostate Volume Change After LHRH-Agonist Androgen Deprivation: A Prospective, Three-Reader Study for Radiotherapy Planning.

introductionADT is routinely combined with radiotherapy (RT) for intermediate- and high-risk prostate cancer. While prostate shrinkage may facilitate planning, prospective CT-based, patient-level estimates over short, workflow-relevant intervals are scarce.

methodsWe conducted a prospective study of 47 patients starting luteinizing hormone-releasing hormone agonist (LHRHa) therapy (leuprolide, 6-month depot). Prostate volumes were independently contoured by three blinded radiation oncologists on paired CT scans at baseline and ~8 weeks post-injection. The primary outcomes were the mean relative volume change and the proportion achieving a clinically relevant reduction (≥15%). PSA and testosterone were recorded at both time points; correlations and exploratory univariable logistic regression for ≥15% reduction were performed at the patient level.

resultsMean relative volume reduction ranged from -18.5% to -21.3% across observers; ≥60% of patients met the ≥15% threshold (RT-A 61.7%, RT-B 66.0%, RT-C 74.5%). PSA and testosterone decreased substantially (e.g., median PSA from 9.64 to 1.84 nmol/L) and were moderately correlated (Spearman ρ = 0.43,

conclusionsShort-course LHRHa induced consistent CT-measured cytoreduction, with more than half of cases achieving ≥15% shrinkage within 8 weeks. Prostate downsizing was reproducible across readers and accompanied by marked PSA and testosterone declines, although biochemical responses did not predict volumetric change. These findings support incorporating a short neoadjuvant "window" before RT simulation and highlight the need for larger studies to refine predictors and compare agonist vs. antagonist trajectories.