Dosimetric guidance on using brachytherapy (low-dose-rate or high-dose-rate) to offset a flawed permanent prostate implant

Abstract 

Purpose

To provide practical dosimetric advice on mending suboptimal permanent implants using low-dose-rate (LDR) or high-dose-rate (HDR) brachytherapy. The problem is to make the combination of the two radiation treatments (the initial, flawed one and the compensatory boost) clinically isoeffective with the planned dose.

Methods and Materials

The device of isoeffective dose is the appropriate tool for this purpose as it accounts for the physical (temporal distribution of dose) and biologic (radiosensitivity, repair kinetics, proliferation rate) treatment settings.

Results

I give, as a function of separation time from the initial, flawed treatment, and stratified by risk group representative values for the additional dose (low-dose-rate or high-dose-rate) needed to make the combined treatment isoeffective with a prescription of 144Gy of permanently implanted ¹²⁵I seeds.

Conclusions

Although the isoeffective dose concept, within the constraints stated in the text, is rigorously valid, its practical implementation depends importantly on the relevant radiobiologic parameters, and in this respect the reader is urged to use his own critical judgment.

Keywords: Prostate cancer, Brachytherapy, Permanent implants, High-dose-rate brachytherapy, Salvage brachytherapy