Multiparametric MRI and post implant CT-based dosimetry after prostate brachytherapy with iodine seeds: The higher the dose to the dominant index lesion, the lower the PSA bounce.

PURPOSE

To determine whether post-implant MRI-based dosimetry of the Dominant Intra-prostatic Lesion (DIL) could best predict the occurrence of PSA bounce after prostate brachytherapy.

METHODS AND MATERIALS

We selected 66 patients with a low risk prostate cancer treated with (125)I prostate brachytherapy as monotherapy. Post-implant dosimetry based on day 30 CT-scan and multiparametric MRI co-registration was generated: planned D90, D95, V100, V150 values were calculated for each DIL. Bounce was defined as a PSA elevation ⩾ 0.2 ng/mL from the previous baseline value followed by a decrease to or below the prior nadir with no additional treatment.

RESULTS

After a median follow-up of 35.5 months (range 13.2-72.5), a PSA bounce occurred in 24 (36.4%) patients. The mean planned D90 of the DIL was significantly lower in bouncers: 196 ± 61 Gy vs. 234 ± 62 Gy, p = 0.018. The mean planned V150 of the DIL was 56 ± 32% for bouncers while it was 75 ± 30% for non-bouncers, p = 0.026.

CONCLUSION

A lower planned D90 or V150 in the DIL were predictive of PSA bounce after prostate brachytherapy. PSA bounce could be caused by delayed cell death related to sublethal damage accumulation in the tumor.