A method for confirming a third-party assay of I-125 seeds used for prostate implants.

The purpose of this work is to describe a method and apparatus that can be used to confirm the source strength of a large number of I-125 seeds while maintaining sterility, accuracy, reproducibility, and time efficiency. Source strengths ranging from 0.395 to 0.504 U/seed were available for this study. Three different seed configurations were measured: loose, linked, and loaded needles. A third-party 10% assay (NIST traceable) was provided. A custom stand was built out of aluminum to hold an exposure meter [Inovision (Fluke) 451P pressurized ion chamber] at 25 cm above the I-125 sources to measure the exposure rate. The measurements were made in an operating room, and a sterile sheet was placed under the nonsterile aluminum stand on a sterile loading table. Seeds and needles were placed in a sterile tray for these measurements. Two hundred and six loose seeds in six batches (0.395, 0.395, 0.409, 0.444, 0.444, and 0.444 U/seed) and 1434 seeds in 10 batches containing various strands (0.444, 0.444, 0.444, 0.444, .0444, 0.466, 0.466, 0.504, and 0.504 U/seed) were measured. For the loose and stranded seeds, the average exposure rate per unit activity was measured to be 0.589 mR/h·U with a standard deviation of 0.017. Loaded needles were measured with an average exposure rate per unit activity to be 0.269 mR/h·U with a standard deviation of 0.014. We conclude that the method described here is capable of confirming a third-party assay when performed on a large number of loose or stranded seeds in bulk. It is less reliable for preloaded needles.

Method for verifying the air kerma strength of I-125 plaques for the treatment of ocular melanoma.

The purpose of this work was to develop a method for easily verifying that the activity or air kerma strength of pre-assembled eye plaques, used in the treatment of ocular melanomas, agrees with the activity or air kerma strength called for in the treatment plan. A Capintec CRC-7 Dose Calibrator with its standard vial/syringe sample holder was used to measure the activity of pre-assembled COMS and Eye Physics EP917 eye plaques using IsoAid Advantage I-125 seeds. Plaque activity measurements were made by placing the plaque face up in the center of a 5 cm tall Styrofoam insert in the source holder. Activity measurements were made with the source holder rotated to four angles (0°, 90°, 180°, and 270°). The average of these four values was converted to air kerma strength and divided by the assay air kerma strength, from the NIST traceable source calibration, and decayed to the plaque measurement date, to determine a plaque calibration factor. The average of the calibration factors for each plaque type was used to establish a calibration factor for each plaque type. Several partially loaded plaque configurations were included in this study and different methods were used to determine the effects of partial loading. This verification method is easy to implement with commonly available equipment and is effective in identifying possible errors. During this two-year study, the air kerma strength of 115 eye plaques was checked and 11 possible errors were identified.

Influence of zonal dosimetry on prostate brachytherapy outcomes.

PURPOSE: To examine the influence of zone-specific dosimetry on outcomes during permanent prostate implantation (PI), where the peripheral zone (PZ) and transitional zone (TZ) may receive varying radiation doses. MATERIAL AND METHODS: Four hundred and sixteen patients treated with I-125 PI (target dose: 144 Gy) between 1996 and 2003 were included in this Institutional Review Board (IRB) approved, retrospective analysis. Whole prostate (WP), TZ, and PZ were contoured, and zone-specific D90 and V100 were computed. Their influence on biochemical failure (BF) was evaluated using Cox proportional hazards analysis. RESULTS: The median age and initial prostate-specific antigen (PSA) was 68 years and 6.1 ng/ml, respectively, and the median follow-up time was 8.8 years. There were 329 subjects with Gleason score (GS) 6 disease (79.1%), and 82 subjects had GS 7 disease (19.7%). Androgen deprivation therapy (ADT) was used in 20.4% of patients. Median D90 and V100% in the WP, PZ, and TZ were 141.2 Gy, 156.1 Gy, and 134.5 Gy; and 88.8%, 93.3%, and 84.2%, respectively. Ten-year rates for biochemical recurrence-free survival, distant metastasis-free survival, and prostate cancer-specific mortality were 82.4%, 92.4%, and 0.97% respectively. Only initial PSA, GS7+ disease, ADT, and PSA frequency were significant on multivariate analysis. Ten-year rates of grade 3 or higher GU and GI toxicity was 10.9% and 1.8%, respectively. TZ V200 and TZ V300 were significantly associated with late genitourinary toxicity. CONCLUSIONS: The TZ received significantly lower doses of radiation compared to the PZ. On multivariate analysis, no dosimetric parameter was associated with efficacy. Higher TZ doses may be associated with higher late GU toxicity without improving efficacy.

Long-Term Efficacy and Toxicity of Low-Dose-Rate ¹²5I Prostate Brachytherapy as Monotherapy in Low-, Intermediate-, and High-Risk Prostate Cancer.

PURPOSE/OBJECTIVES: To report long-term efficacy and toxicity for a single-institution cohort of patients treated with low-dose-rate prostate brachytherapy permanent implant (PI) monotherapy. METHODS AND MATERIALS: From 1996 to 2007, 1989 patients with low-risk (61.3%), intermediate-risk (29.8%), high-intermediate-risk (4.5%), and high-risk prostate cancer (4.4%) were treated with PI and followed up prospectively in a registry. All patients were treated with (125)I monotherapy to 144 Gy. Late toxicity was coded retrospectively according to a modified Common Terminology Criteria for Adverse Events 4.0 scale. The rates of biochemical relapse-free survival (bRFS), distant metastasis-free survival (DMFS), overall survival (OS), and prostate cancer-specific mortality (PCSM) were calculated. We identified factors associated with late grade ≥3 genitourinary (GU) and gastrointestinal (GI) toxicity, bRFS, DMFS, OS, PCSM, and incontinence. RESULTS: The median age of the patients was 67 years, and the median overall and prostate-specific antigen follow-up times were 6.8 years and 5.8 years, respectively. The overall 5-year rates for bRFS, DMFS, OS, and PCSM were 91.9%, 97.8%, 93.7%, and 0.71%, respectively. The 10-year rates were 81.5%, 91.5%, 76.1%, and 2.5%, respectively. The overall rates of late grade ≥3 GU and GI toxicity were 7.6% and 0.8%, respectively. On multivariable analysis, age and prostate length were significantly associated with increased risk of late grade ≥3 GU toxicity. The risk of incontinence was highly correlated with both pre-PI and post-PI transurethral resection of the prostate. CONCLUSIONS: Prostate brachytherapy as monotherapy is an effective treatment for low-risk and low-intermediate-risk prostate cancer and appears promising as a treatment for high-intermediate-risk and high-risk prostate cancer. Significant long-term toxicities are rare when brachytherapy is performed as monotherapy.

Failure modes and effects analysis applied to high-dose-rate brachytherapy treatment planning.

PURPOSE: To apply failure modes and effects analysis to high-dose-rate treatment planning to identify the most likely and significant sources of error in the process. METHODS: We have made a list of 25 failure modes grouped into six categories (imaging, catheter reconstruction, dwell position activity, dose points/normalization, optimization/dose, and evaluation). Each mode was rated on a one to five scale for severity, likelihood of occurrence, and probability of escaping detection. An overall ranking was formed from the product of the three scores. The authors assigned scores independently and the resulting rankings were averaged. We also analyzed 44 reported medical events related to high-dose-rate treatment planning listed on the Nuclear Regulatory Commission Web site and compared them with our own rankings. RESULTS: Failure modes associated with image sets, catheter reconstruction, indexer length, and incorrect dose points had the highest ranking in our analysis (scores higher than 20). The most often cited failure modes in the Nuclear Regulatory Commission reports examined were indexer length (20/44) and incorrect dose points (6/44). Several of our high-ranking modes are not associated with reported events. CONCLUSION: It is a useful exercise to identify failure modes locally and analyze the efficacy of the local quality assurance program. Comparison with nationally reported failures can help direct the local analysis, but the absence or small number of reports for failure modes with a high score may be owing to low detectability. Such modes obviously cannot be ignored.

PSA bounce predicts early success in patients with permanent iodine-125 prostate implant.

OBJECTIVES: To determine the clinical and dosimetric factors that predict prostate-specific antigen (PSA) bounce after iodine-125 prostate brachytherapy and to determine the predictive value of PSA bounce relative to biochemical relapse-free survival (bRFS). METHODS: A multivariate analysis of factors thought to predict for PSA bounce was performed in 295 consecutive patients with T1-T2 prostate cancer treated by prostate brachytherapy as the sole radiotherapeutic modality and a minimum follow-up of 2 years. The variables examined included age, initial PSA level, biopsy Gleason score, use of androgen deprivation, occurrence of PSA bounce, dose received by 90% of the prostate gland, and volume of gland receiving 100% of the prescribed dose. A PSA bounce was defined as a rise of at least 0.2 ng/mL greater than a previous PSA level with a subsequent decline equal to, or less than, the initial nadir. A second analysis investigating the same factors and adding PSA bounce as a predictor of bRFS was also performed. RESULTS: The median follow-up was 38 months. A PSA bounce was noted in 82 (28%) of 295 patients. On multivariate analysis, only younger age (younger than 65 years) significantly predicted for a PSA bounce. Patients who experienced a PSA bounce were less likely to have biochemical failure (P = 0.037). Overall, the bRFS rate at 5 years in those experiencing a PSA bounce was 100% versus 92% in those with no bounce. CONCLUSIONS: Immediate salvage therapy in patients with a rising PSA level after permanent prostate brachytherapy should not be initiated provided the PSA increase does not exceed the pretreatment PSA value. A PSA bounce may be associated with improved bRFS but was not associated with any of the pretreatment clinical and dosimetric factors examined.

Effect of anatomic, procedural, and dosimetric variables on urinary retention after permanent iodine-125 prostate brachytherapy.

OBJECTIVES: To correlate anatomic, procedural, and dosimetric parameters with the rate of intermittent self-catheterization (ISC). METHODS: The records of 402 patients with a median age of 69 years treated with 125I prostate seed implantation from 1996 to 2001 were reviewed for the use of ISC. The records were examined for the preimplant factors: prostate volume, use of androgen deprivation, and prostate length. The intraprocedural factor reviewed was the number of needles used. The following postimplant information was also collected: preimplant transrectal ultrasound-generated prostate volume/postimplant computed tomography-generated prostate volume ratio, V100, V150, V200, V300, V400, D90, and D100. Correlation was assessed using logistic regression analysis. RESULTS: Forty-four patients had to use ISC (10.9%). The mean and median duration of ISC was 11.9 and 6 weeks, respectively. From univariate analysis, prostate length and prostate volume were found to be statistically significant predictors of ISC after 125I prostate seed implantation with a P value of 0.0002 and 0.0042, respectively. With multivariate analysis, only prostate length was a statistically significant predictor of ISC use after 125I prostate seed implantation (P = 0.0095). CONCLUSIONS: Prostate length is an important predictor of ISC after 125I prostate seed implantation.