Validation of a detector-response correction model for in vivo dosimetry in high-dose-rate prostate brachytherapy.

BACKGROUND

High-dose-rate brachytherapy (HDRBT) is an established treatment for localized prostate cancer. Despite its efficacy, HDRBT can exhibit dosimetric discrepancies between planned and delivered doses. In vivo dosimetry (IVD) using metal-oxide-semiconductor field-effect transistors (MOSFETs) enables real-time monitoring of administered doses, though factors such as temperature, source-to-detector distance, and detector orientation can affect accuracy. Appropriate correction models may reduce these uncertainties.

PURPOSE: To evaluate a mathematical correction model for microMOSFET response dependencies under in vivo conditions during HDRBT with 192Ir in prostate cancer patients.

METHODS

The model, correcting for temperature, source-detector distance, and angular dependence, was applied to IVD data obtained during 29 HDRBT implant procedures. Corrected and uncorrected detector-measured doses were compared with treatment planning system (TPS) calculations at the neurovascular bundle and periurethral zone.

RESULTS

The full correction reduced the mean dose difference between measured and TPS doses from -5.9% to 0.7%. Omitting angular correction yielded a -2.1% discrepancy. For patients with two detectors in distinct regions, the average difference was 0.2% (SD 5.2%). Monte Carlo simulations confirmed that combining measurements from multiple positions improves dosimetric precision and provides quantitative support for a ±10% investigation level for detecting treatment delivery errors.

CONCLUSIONS

Applying the correction model to microMOSFET-based IVD in prostate HDRBT significantly improved agreement with TPS-calculated doses, particularly when two measurement points were used. Angular dependence was a primary source of residual error. Dual-point Monte Carlo simulations further supported the robustness of the proposed approach.