Myths and fallacies in permanent prostate brachytherapy

Effect of planning margin on dosimetric quality in 131Cs permanent prostate brachytherapy

PURPOSE

To investigate the dosimetric effect of planning margin in (131)Cs prostate seed implants.

METHODS AND MATERIALS

The transrectal ultrasonography images are obtained intraoperatively in 5-mm steps from base to apex. The prostate is contoured as clinical target volume (CTV). The CTV is enlarged with 3mm expansion except the posterior. The CTV and planning target volume (PTV) are then used as planning target for treatment planning, respectively. Dose calculations are performed using VariSeed treatment planning system using AAPM TG-43 formalism. The total activity implanted, target coverage (the percent of the prostate volume covered by the prescription dose, V(100); the dose that covers 90% of the prostate volume, D(90)) for CTV and PTV, dose inhomogeneity (the percentage volume of the prostate receiving 150% of the prescription dose [V(150)]), and the critical organ dose (the dose that covers 10% of the urethra volume [UD(10)] for urethra and the dose that covers 50% of the rectum volume [RD(50)] for rectum) are compared.

RESULTS

When CTV is used as target for planning, compared with PTV as planning target, the total activity implanted is decreased by 5.6%. Integral dose is thus lower by 5.6%. Coverage for CTV (CTV(100)) is increased by 0.3%. Coverage for PTV (PTV(100)) is lower by 2.1%. CTV(150) is increased by 13.6%. PTV(150) is higher by 2.5% with a standard deviation of 10.2%. Rectum dose (RD(50)) is lower by 4.5%. Urethra dose (UD(10)) is higher by 10.0%.

CONCLUSION

It is shown that the planning margin has minimal effect on dosimetric quality because of (131)Cs's gradual dose fall-off. Thus, it is possible to reduce or even eliminate planning margin using (131)Cs. The modest benefits in reducing the planning margin, such as lower total activity (lower integral dose), dose reduction to surrounding healthy tissues and reduced likelihood of seeds migration, can be achieved while adequate coverage is maintained.

Interstitial implant alone or in combination with external beam radiation therapy for intermediate-risk prostate cancer: A survey of practice patterns in the United States

PURPOSE

This study is aimed at understanding and defining the current patterns of care with respect to prostate brachytherapy for patients with intermediate-risk localized disease in the combined academic and community setting.

METHODS AND MATERIALS

A nomogram-based survey was developed at the Seattle Prostate Institute defining the accepted criteria for intermediate-risk prostate cancer. Patients were defined as having intermediate-risk prostate cancer if they met one of the following criteria: prostate-specific antigen (PSA) >10 ng/dL, Gleason score (GS) > or = 7, or cT2b or cT2c disease. Additional potential predictive factors including perineural invasion (PNI), GS 3+4 vs. 4+3, and high-volume disease were included.

RESULTS

In the absence of PNI, all of those surveyed would perform monotherapy for intermediate-risk patients, GS 7 (3+4) or PSA 10-20, with cT1c and <30% cores +. Up to 80% would perform monotherapy for patients with cT1c, GS 7 (4+3), and <30% cores +. Eighty to 90% of physicians would perform an implant alone with cT2a and either a PSA of 10-20 or GS of 7 (3+4) and <30% cores +. Fifty to 60% of those surveyed stated that they would treat a patient with cT2b disease, GS 7 (3+4), or PSA 11-20, with less than two-thirds of the biopsy cores positive in the absence of PNI.

CONCLUSIONS

This Patterns of Care (POC) study reveals that certain subsets of intermediate-risk localized prostate cancer patients are considered appropriate candidates for an interstitial implant alone.

Improved biochemical relapse-free survival for patients with large/wide glands treated with prostate seed implantation for localized adenocarcinoma of prostate

OBJECTIVES

To analyze whether prostate size affects biochemical relapse-free survival (bRFS).

METHODS

The bRFS outcomes for 390 patients with a minimum of 2 years of follow-up were determined from a review of a prospectively maintained database. All patients were treated with iodine-125 alone as the radiotherapeutic modality and had a minimum of four posttreatment prostate-specific antigen values. None were treated with androgen deprivation. The factors examined in the univariate and multivariate analyses predicting for bRFS included gland volume, patient age, initial prostate-specific antigen value, biopsy Gleason score, clinical stage, and postimplant dosimetric variables.

RESULTS

Most patients had low-risk disease, and the median follow-up was 45 months (range 24 to 102). Using the American Society for Therapeutic Radiology Oncology definition of biochemical failure, the overall 5-year bRFS rate was 89.3%. On separate multivariate analyses, only the pretreatment prostate width and volume significantly influenced bRFS favorably (P = 0.0069 and P = 0.0255, respectively). No association was found between gland size/width and postimplant dosimetry.

CONCLUSIONS

The results of our study have shown that implantation of large/wide prostates independently confers better bRFS.

Reducing the toxicity associated with the use of radiotherapy in men with localized prostate cancer

The risk for serious complications associated with modern radiotherapy is relatively low. Compared with conventional radiotherapy, 3DCRT and IMRT allow higher doses to be given more safely. The use of IMRT increases the time and effort required by physicians and physicists. Although there is a clear move toward IMRT, 3DCRT is considered standard. The quality assurance procedures for and fundamental questions regarding IMRT are evolving, including the radiobiologic consequences of altered time-dose fractionation and the greater dose heterogeneity in the target. Defining an accurate target volume and routinely correcting for set-up error and organ movement before each treatment promise to reduce the complications associated with EBRT in the next 5 years. Complications following prostate brachytherapy are better understood now than 10 years ago. Dosimetric or patient selection factors that correlate with a higher risk for complications, such as acute retention, strictures, severe prolonged urinary symptoms, fistulas, proctitis, and impotence, often can be accounted for or avoided. Finally, the role of radiation protectors is beginning to be addressed. It is hoped that these advances will eliminate toxicity associated with radiotherapy and increase cure rates.