Live implant dosimetry may be an effective replacement for postimplant computed tomography in localized prostate cancer patients receiving low dose rate brachytherapy

PURPOSE

To determine if Live Implant Dosimetry (LIDO) utilizing intraoperative transrectal ultrasound (TRUS) is equivalent to postimplant CT dosimetry (either day 0 or day 30) in patients with localized prostate cancer (PC) treated with low dose rate (LDR) prostate seed brachytherapy.

METHODS AND MATERIALS

The treated population consisted of 628 men with localized (T1-T2) PC. All d'Amico risk categories (low, intermediate, and high) were included, and 437 patients were treated with monotherapy (160 Gy) [low and low tier intermediate], and the remainder (191) [high tier intermediate and high risk] with an implant boost (106 Gy) post external beam radiation, to a volume including the prostate and seminal vesicles (46 Gy). LIDO with intraoperative TRUS, postimplant CT (day 0 and day 30) were performed in all cases. Prostate volumes (V), V₁₀₀ (prostate) and dose (D) D₉₀ (prostate), D₃₀ (urethra), and Rectum D_2cc, were recorded. No urinary catheter was used on Day 30 CT.

RESULTS

More than 91.33% of monotherapy patients reached the target D₉₀ according to LIDO while only 82.99% of Day 0 CT and 92.82% of Day 30 CT achieved target D₉₀. When considering V₁₀₀, monotherapy patients recorded target dosimetry in 90.93%, 82.31%, and 92.02% of cases assessed by LIDO, Day 0 CT and Day 30 CT, respectively. Strong correlations are observed in D₉₀, Rectum D_2cc and Urethra D₃₀ across imaging modalities but V₁₀₀ and V₁₅₀ were poorly correlated due to the relative quantification of this parameter and high degree of error in measurement. Of all monotherapy patients with satisfactory dosimetry on LIDO, 94.82% reached target D₉₀ at day 30 CT and 94.19% reached target V₁₀₀.

CONCLUSIONS

LIDO and CT are both effective tools for assessing postimplant dosimetry. Patients with satisfactory LIDO dosimetry are highly likely to have equivalent dosimetry on CT at follow-up, indicating that postimplant CT may be eliminated in PC a patients implanted with this technique.

Prostate-specific antigen spikes with ¹³¹Cs brachytherapy. Is there a difference with other radioisotopes?

PURPOSE

There is a suggestion that a dose-rate effect exists for the prostate-specific antigen (PSA) spike after brachytherapy. ¹³¹Cs is a newer radioisotope with a half-life of 9.7 days that is being used for prostate brachytherapy. There is no published data on the PSA spike with this radioisotope and the goal of this study was to quantify PSA spikes with ¹³¹Cs and compare it with published data for other isotopes.

METHODS AND MATERIALS

We have been maintaining a prospective database for all patients treated with ¹³¹Cs prostate brachytherapy at our institution. We selected patients for whom followup PSA was available for at least 24 months. The PSA spike was defined as an increase of 0.2 ng/mL, followed by a decline to prespike level.

RESULTS

One hundred twenty-three patients had monotherapy, whereas 32 had external beam radiation therapy followed by a brachytherapy boost. Median followup was 36 months and mean numbers of PSAs obtained were 7. Forty-six (29.7%) patients had a PSA spike. The mean time and duration for the PSA spike were 12.5 and 8.8 months, respectively. The mean magnitude of increase and mean PSA value at increase were 0.63 and 1.56 ng/mL, respectively.

CONCLUSIONS

The incidence of a PSA spike in our series is consistent with reported numbers for other radioisotopes. The occurrence of the spike at 12.5 months appears to be at the early end of the spectrum reported for (125)I, but the duration and magnitude are similar to other radioisotopes.