# Kinetics of prostate volume reduction under hormonal treatment: Timing and impact on external beam radiotherapy – A PRISMA-Compliant systematic review

## TL;DR

Hormonal treatment causes prostate shrinkage, which affects radiotherapy planning, with the most significant reduction happening in the first three months.

## Contribution

This study systematically characterizes prostate volume reduction kinetics under hormonal therapy and their implications for radiotherapy planning.

## Key findings

- Prostate volume reduction follows a logarithmic decay pattern during hormonal treatment.
- The most significant shrinkage occurs within the first three months, reaching up to 35%.
- Radiotherapy planning must consider prostate downsizing to optimize treatment delivery.

## Abstract

•Prostate volume reduction follows a predictable logarithmic decay under hormonal treatment.•Up to 35% shrinkage occurs within the first three months of hormonal therapy.•Radiotherapy planning must account for hormonal treatment-induced prostate downsizing.

Prostate volume reduction follows a predictable logarithmic decay under hormonal treatment.

Up to 35% shrinkage occurs within the first three months of hormonal therapy.

Radiotherapy planning must account for hormonal treatment-induced prostate downsizing.

Understanding how hormonal treatment affects prostate volume is essential for optimizing external beam radiotherapy (EBRT) planning in localized prostate cancer. The study aimed to characterize the kinetics of prostate volume reduction during hormonal therapy and assess its implications for EBRT delivery and planning strategies.

A systematic review following PRISMA guidelines was conducted. Clinical studies assessing prostate volume changes under hormonal therapy in non-metastatic prostate cancer patients were included. Imaging modalities (MRI, CT, TRUS) were used to track prostate volume over treatment durations of up to 25 months. The review excluded preclinical studies and salvage therapy cases. Data were synthesized descriptively due to heterogeneity in regimens and methodologies.

Across 35 studies, prostate volume followed a logarithmic decay under hormonal treatment, with the most significant reductions occurring in the first three months (up to 35%). The extent of volume reduction during EBRT varied by EBRT initiation timing and fractionation scheme, with greater changes observed in normofractionated regimens. A weak correlation was found between initial prostate volume and reduction rate. Limitations included heterogeneity in imaging protocols and lack of formal bias assessment.

Prostate volume reduction is most pronounced early in hormonal treatment, emphasizing the need to synchronize imaging and EBRT planning. For high-precision techniques (e.g., SBRT or DIL boosting), accounting for volume kinetics is critical. Clinical practice should evolve toward integrating prostate volume reduction timelines into EBRT workflows.