Is intraoperative real-time dosimetry in prostate seed brachytherapy predictive of biochemical outcome?

Dosimetric outcomes of preoperative treatment planning with intraoperative optimization using stranded seeds in prostate brachytherapy

This study aimed to evaluate the quality of low-dose-rate (LDR) prostate brachytherapy (BT) based on treatment-related dosimetric outcomes. Data of 100 patients treated using LDR BT with stranded seeds from November 2012 to November 2017 were collected. The prescription dose for the prostate was 145 Gy. The dose constraints for the preoperative plan were: V100% ≥ 95%, V150% ≤ 60%, V200% ≤ 20% for the prostate; V100% for rectum, ≤ 1 cc; and V200 Gy for urethra, 0.0 cc. Intraoperative real-time dose calculation and postoperative dose distribution analysis on days 0 and 30 were performed. Median dosimetric outcomes on days 0 and 30 respective were: V100% 92.28% and 92.23%, V200% 18.63% and 25.02%, and D90% 150.88 Gy and 151.46 Gy for the prostate; V100% for the rectum, 0.11 cc and 0.22 cc; and V200 Gy for the urethra, 0.00 cc and 0.00 cc, respectively. Twenty patients underwent additional seed implantation to compensate for insufficient dose coverage of the prostate. No loss or substantial migration of seeds or severe toxicity was reported. With stranded seed implantation and intraoperative optimization, appropriate dose delivery to the prostate without excessive dose to the organs at risk could be achieved.

Superior Postimplant Dosimetry Achieved Using Dynamic Intraoperative Dosimetry for Permanent Prostate Brachytherapy

PURPOSE

Low-dose-rate brachytherapy is a highly effective treatment modality for prostate carcinoma, but postimplant dosimetry quality is essential and correlated with likelihood of treatment success. Registered ultrasound and fluoroscopy (iRUF) can facilitate real-time intraoperative monitoring and plan adaptation, with the aim of attaining superior dosimetric outcomes. The purpose of this research was to compare clinical postimplant dosimetric results of iRUF-guided brachytherapy against brachytherapy using standard ultrasound-guided intraoperative dosimetry methods.

METHODS AND MATERIALS

We analyzed postimplant dosimetry in 292 patients treated with Pd-103 between January 2007 and December 2018. All patients had postimplant dosimetry measured on day 0 to 1 using fused magnetic resonance/computed tomography assessment. Fifty-two patients were treated in 2 prospective clinical trials using iRUF intraoperative dosimetry, including 6 patients in a pilot study and 46 treated in a phase 2 study. Postimplant dosimetry in iRUF-treated patients was compared with dosimetry from 240 patients treated using standard (real-time ultrasound) intraoperative seed tracking.

RESULTS

For every parameter measuring dose coverage to the prostate, iRUF patients had significantly higher values, irrespective of adjustment for year of treatment. In adjusted analyses, parameters of dose to urethra and rectum were not significantly higher among iRUF-treated patients.

CONCLUSIONS

Use of iRUF intraoperative dosimetry was associated with improved postimplant dose coverage in prostate, without associated increases in doses to urethra or rectum.

Evaluation of transrectal ultrasound-based dosimetry for brachytherapy of prostate cancer: a single-center experience

Purpose

To explore the possibility of intraoperative transrectal ultrasound (TRUS)-based dose verification in transperineal brachytherapy (BT) with iodine-125 (¹²⁵I) seeds for prostate cancer.

Material and methods

Fifteen patients with prostate cancer were treated using BT with ¹²⁵I seeds. Post-implant TRUS and computed tomography (CT) images were imported into treatment planning system (TPS) for dosimetry. Dosimetry parameters, including minimum dose received by 90% of the volume (D₉₀), percentage of the volume receiving 100% of prescribed dose (V₁₀₀), and percentage of the volume receiving 200% of prescribed dose (V₂₀₀) were calculated based on TRUS and CT images, separately. The D₉₀ value of TRUS-based dosimetry was transformed to its expected value. Comparisons of the dosimetric parameters between post-operative verification and preoperative plans were made by paired t-test. One-way ANOVA model was used to assess the differences in preoperative plans. Agreements were evaluated between the preoperative planning and post-operative actual dose parameters using Bland-Altman analysis.

Results

In total, 825 of ¹²⁵I seeds were implanted successfully in 15 patients. In TRUS-based dosimetry, 674 seeds (81%) were identified clearly in TRUS-based images, and the expected value of D₉₀ parameter showed no significant differences compared with the preoperative planning and CT post-operation results (p > 0.05). In CT-based dosimetry, 810 seeds (98%) were identified clearly in CT-based images, and there was good consistency of D₉₀, V₁₀₀, and V₂₀₀ values (p > 0.05). Post-implant CT-based dosimetry indicated that ¹²⁵I seed implantation had fulfilled the expected plan.

Conclusions

Intraoperative TRUS can be used for dosimetric verification of BT for prostate cancer.

Acute and late toxicities in localized prostate cancer patients treated with low-dose 125I brachytherapy (110 Gy) in combination with external beam radiation therapy versus brachytherapy alone (160 Gy)

Purpose

The aim of this analysis was to compare acute and late toxicities between low-dose-rate brachytherapy (LDR-BT) (110 Gy) in combination with 45 Gy in 25 fractions external beam radiation therapy (EBRT) and LDR-BT (160 Gy) alone for localized prostate cancer.

Material and methods

One hundred five consecutive patients with localized prostate cancer treated from May 2014 to May 2017 were included in this retrospective analysis. Sixty patients received combination therapy and 45 patients received BT monotherapy. The LDR-BT procedure was performed using ¹²⁵I seeds.

Results

The median follow-up time was 28 months in both groups. Three-year effect rates were overall survival: 100% in both groups. The biochemical failure rate was 2.3% in the combination group and 0% in the monotherapy group (p = 0.373). No patients died during the study period. In both groups, almost all the patients experienced acute urethritis. There was a significant difference between the combination therapy group (8.3%) and BT monotherapy group (11.1%) in late genitourinary (GU) toxicities ≥ grade 2 (p = 0.035). Only 2 patients (3.3%) in the combination therapy group developed late ≥ grade 2 rectal hemorrhage. There were no significant differences between two groups in hematuria ≥ grade 2 (p = 0.068) or rectal hemorrhage ≥ grade 2 (p = 0.206).

Conclusions

To our knowledge, this is the first report to compare the GU and gastrointestinal toxicities between the combination therapy and BT monotherapy (160 Gy) for localized prostate cancer. Unexpectedly, there were more late GU toxicities (except for hematuria) in the BT monotherapy group.

Plan reproducibility of intraoperatively custom-built linked seeds compared to loose seeds for prostate brachytherapy

Purpose

Few studies have compared the implant quality of linked and loose seeds for prostate brachytherapy. This study aimed to evaluate and compare plan reproducibility of intraoperatively built custom linked seeds and loose seeds for prostate brachytherapy.

Material and methods

Between December 2010 and March 2014, 76 localized prostate cancer patients received Iodine-125 brachytherapy with external beam radiotherapy. Linked and loose seeds were implanted in 39 and 37 patients, respectively. The primary endpoint was the mean (± standard deviation) of the absolute change in the minimum dose received by 90% of the prostate volume between intraoperative and post-operative planning (ΔD₉₀) to confirm plan reproducibility. Comparisons between the groups were evaluated using 2-sample t tests.

Results

The ΔD₉₀ values were 6.95 ± 11.6% and –0.41 ± 8.5% for the loose and linked seed groups, respectively (p < 0.01). The linked seed group showed decreased post-operative D₉₀ (118.8% vs. 127.2%), V₁₅₀ (51.7% vs. 66.7%), and RV₁₀₀ (0.44 ml vs. 0.61 ml) compared to the loose seed group (p < 0.01), whereas lung migration tended to be reduced (0% vs. 8%).

Conclusions

The plan reproducibility of the linked seed group was better than that of the loose seed group. Moreover, the linked seed group showed less migration and lower rectal dose.

Phase II study of intraoperative dosimetry for prostate brachytherapy using registered ultrasound and fluoroscopy

PURPOSE

To assess the performance of a system of intraoperative dosimetry and obtain estimates of dosimetry outcomes achieved when utilizing the system in a Phase II clinical trial.

METHODS AND MATERIALS

Forty-five patients undergoing permanent Pd-103 seed implantation for prostate cancer were prospectively enrolled. Seed implantation was performed and dose was tracked intraoperatively using intraoperative registered ultrasound and fluoroscopy (iRUF). Three-dimensional seed locations were computed from X-rays and registered to ultrasound for intraoperative dosimetry, followed by adaptive plan modification to achieve prostate V100 ≥95% and ≥95% D90. Time required for iRUF was recorded. Postoperative CT/MRI scans were performed 1 day after the implantation and used as reference for dosimetric analysis. Dosimetric parameters for the prostate and urethra were compared between standard ultrasound-based dosimetry (USD), iRUF, and postoperative CT/MRI.

RESULTS

Mean total time for iRUF was <30 min. A mean of four seeds (0-12) were added per implant to correct cold spots discovered by iRUF. Day 1 CT/MRI prostate V100 was ≥95% for 44/45 patients; 1 patient had Day 1 V100 93%. No patient had rectal V100 exceeding 1 cc. Compared to CT/MRI, iRUF dosimetry had significantly smaller mean differences and higher correlations for all prostate and urethral dosimetric parameters examined than USD. Both USD and iRUF tended to overestimate dose, but with less bias in iRUF than USD.

CONCLUSIONS

Intraoperative dosimetry utilizing iRUF was associated with acceptable increase in procedure time and enabled very high rates of achieving excellent prostate dose coverage. iRUF intraoperative dosimetry approximated postoperative CT/MRI dosimetry to a greater degree than USD for the prostate and urethra.

Correlations of post-implant regional dosimetric parameters at 24 hours and one month, with clinical results of low-dose-rate brachytherapy for localized prostate cancer

Purpose

To evaluate the correlations of post-implant regional dosimetrics at 24 hours (24 h) and 1 month after implant procedures, with clinical outcomes of low-dose-rate (LDR) brachytherapy for localized prostate cancer.

Material and methods

Between January 2008 and December 2014, 130 consecutive patients treated for localized prostate cancer, receiving definitive iodine-125 (¹²⁵I) brachytherapy treatment were retrospectively analyzed. All patients underwent post-implant CT imaging for dosimetric analysis at 24 h and 1 month after implantation procedure. Prostate contours were divided into quadrants: anterior-superior (ASQ), posterior-superior (PSQ), anterior-inferior (AIQ), and posterior-inferior (PIQ). Predictive factors and cut-off values of biochemical failure-free survival (BFFS) and toxicities of LDR brachytherapy were analyzed.

Results

The median follow-up time was 69.5 months. Seven patients (5.4%) had biochemical failure. The 3-year and 5-year BFFS rates were 96.7% and 93.1%, respectively. On multivariate analysis, prostate-specific antigen and Gleason score were significant prognostic factors for biochemical failure. D₉₀ (the minimal dose received by 90% of the volume) of PSQ and PIQ at 24 h, and D₉₀ of PSQ at 1 month were also significant factors. The cut-off values of PSQ D₉₀ were 145 Gy at 24 h and 160 Gy at 1 month. D₉₀ of the whole prostate was not significant at 24 h and at 1 month. D₉₀ of PSQ at 1 month was a significant factor for rectal hemorrhage.

Conclusions

Post-implant D₉₀ of PSQ is significantly associated with BFFS for localized prostate cancer not only at 1 month, but also at 24 hours. D₉₀ of PSQ at 1 month is also a significant factor for rectal hemorrhage.