Prostate Brachytherapy Quality Assurance Research Articles

Ultrasound–CT fusion compared with MR–CT fusion for postimplant dosimetry in permanent prostate brachytherapy

Postplan evaluation is essential for quality assurance in prostate brachytherapy. MRI has demonstrated greater interobserver consistency in prostate contouring compared with CT. Although a valuable tool in postimplant assessment, MRI is costly and not always available. Our purpose is to compare dosimetry obtained using fusion of postimplant CT with preimplant transrectal ultrasound (TRUS) vs. CT-MR fusion. Twenty patients receiving permanent (125)I seed prostate brachytherapy underwent preimplant TRUS with urethrography, 1-month CT with a Foley catheter, and 1-month MRI. No patient received androgen deprivation therapy or external beam radiotherapy. The prescription dose of (125)I implant monotherapy was 144Gy. The preimplant TRUS and postimplant CT images were fused based on urethral position, and the CT-TRUS images were subsequently fused to the MRI using a seed-to-seed match. Dosimetric parameters for the ultrasound- and MR-derived prostate were compared. The mean absolute difference between dosimetry from MRI or CT-TRUS fusion for D(90) was 3.2% and in V(100) was 1.2%. Only 1 patient had a difference in MR- and ultrasound-derived D(90) of more than 10% (11.4%) and only 1 had a difference in V(100) of more than 5%. Fusion of preimplant TRUS with 1-month postimplant CT appears to lead to acceptable agreement with MR-based dosimetric parameters in postplan evaluation. TRUS-based volumes may be a reasonable alternative to MRI in settings where MRI is not available.

Defining a magnetic resonance scan sequence for permanent seed prostate brachytherapy postimplant assessment

We describe a magnetic resonance (MR) scan sequence for prostate brachytherapy postimplant assessment. One brachytherapy team at the British Columbia Cancer Agency has incorporated MR-CT fusion into their permanent seed prostate brachytherapy quality assurance procedure. Several attempts were required to ensure that the diagnostic MR scanner at the adjoining general hospital performed the desired sequence, providing many examples of suboptimal scans and underlining the pitfalls for a center trying to incorporate the use of MR scanning into their brachytherapy program. The recommended sequence (Fast Spin Echo T2-weighted, repetition time [TR]/echo time [TE] 4500/90, echo train length [ETL] 10, 20×20 field of view [FOV], 80 bandwidth [BW]) is associated with superior edge detection when compared with those images in which a typical diagnostic sequence was used. The use of a low bandwidth sequence does not compromise edge detection or seed identification when compared with a higher bandwidth. We have defined a magnetic resonance imaging sequence, which appears to optimize both prostate delineation and identification of seeds, lending itself to straightforward fusion with CT images and allowing for less uncertainty in permanent seed prostate brachytherapy quality assurance.

Improving Prostate Brachytherapy Quality Assurance with MRI-based Sector Analysis in a Phase II Prospective Trial

Purpose/Objectives: Sector analysis is a clinical tool that can be used in the post-implant quality assurance process for prostate brachytherapy by calculating the dose delivered to different sectors within the prostate. Each sector can be correlated to biopsy results for individual patients. However, sector analysis has not been translated to clinical practice, in part due to poor anatomic visualization of the prostate base and apex on post-implant CT scans. The purpose of this study is to evaluate MRI-based sector analysis as a method to improve the post-implant quality assurance process of brachytherapy.

TH-A-BRB-01: Low Dose Rate Prostate Brachytherapy Quality Assurance and Treatment Evaluation

Most medical events in prostate seed brachytherapy may be attributed to physician or physicist error, but human failures resulting in patient harm often can be attributed to inadequate mechanisms to prevent failures from propagating to the patient. Quality assurance (QA) of permanent seed brachytherapy is particularly important because this modality, unique to radiotherapy, leaves a permanent record of the implant quality within the patient. This symposium aims to review the properties of permanent LDR brachytherapy that have made it so successful and the challenges that have prevented the full realization of its theoretical advantages. The temporal interplay between radioactive decay, resolution rate of procedure‐induced edema, and cellular processes will be discussed along with their effect on the design and evaluation of LDR prostate brachytherapy. Recent recommendations of AAPM TG‐137 on prostate brachytherapytreatment planning and dose reporting will be reviewed. An analysis of actual medical events and typical errors, for example seed strength in the plan versus the strength ordered versus the strength implanted, will help focus on critical components of the process map. A methodology to score failure modes and effects via the product of Likelihood × Severity × Undetectability will allow users to score procedural steps dynamically. Quality control steps such as second checks or calibrations will be seen as vital in keeping the scores below a level of concern. Finally, the physicist has a responsibility to offer suggestions to improve dosimetry when systematic trends are evident and to identify and report errors. Learning objectives: 1. Discuss recent developments and insights in LDR prostate brachytherapy 2. Identify critical physics components and their impact on QA and treatment evaluation 3. Highlight factors that require special attention in the planning and execution of implants 4. Demonstrate implementation of QA practices in an LDR prostate brachytherapy program

Postimplant rectal dosimetry is not dependent on 103Pd or 125I seed activity

Purpose In this study, the effect of prostate brachytherapy seed activity on postimplant rectal dosimetry was evaluated in Pro-Qura (Prostate Brachytherapy Quality Assurance; Seattle, WA) proctored, community-based programs. Methods and Materials Twenty-three hundred patients (1563 iodine-125 [ 125I] and 737 palladium-103 [ 103Pd]) from 78 brachytherapists with postimplant rectal dosimetry were identified. Seed activity was stratified into three tertiles for each isotope (≤0.300, 0.301–0.326, and >0.326 mCi/seed for 125I and ≤1.330, 1.331–1.547, and >1.547 mCi/seed for 103Pd). Postimplant dosimetry was performed in a standardized fashion. The rectum was contoured by outlining the outer rectal wall. The volume of the rectum receiving 100% of the prescription dose ( R 100) was calculated in cubic centimeters. The prostate V 100 and D 90 volumes were also calculated. Results The mean prostate volume was 35.8 and 32.3 cm 3 for 125I and 103Pd. The median time to postimplant CT was 30 days. For 125I, the V 100 increased from 91.0% to 93.7% ( p = 0.012) and the D 90 increased from 105.9% to 108.7% ( p < 0.001) for the lowest to the highest 125I seed activities. In contrast, no significant changes in V 100 ( p = 0.751) or D 90 ( p = 0.200) were discerned when stratified by seed activity. For both isotopes, there was no correlation between seed activity and R 100, and R 100 was highest for the intermediate seed activities. Overall, the R 100 was lower for 103Pd vs. 125I (0.63 vs. 0.82 cm 3, p < 0.001). Conclusions Within the confines of seed activities used in this study, higher activity seeds did not result in a deleterious effect on rectal dose. Higher activity seeds were associated with improved prostate dosimetry for 125I, whereas 103Pd dosimetry was not dependent on seed activity.

Matching and reconstruction of brachytherapy seeds using the Hungarian algorithm (MARSHAL)

Intraoperative dosimetric quality assurance in prostate brachytherapy critically depends on discerning the three-dimensional (3D) locations of implanted seeds. The ability to reconstruct the implanted seeds intraoperatively will allow us to make immediate provisions for dosimetric deviations from the optimal implant plan. A method for seed reconstruction from segmented C-arm fluoroscopy images is proposed. The 3D coordinates of the implanted seeds can be calculated upon resolving the correspondence of seeds in multiple x-ray images. We formalize seed-matching as a combinatorial optimization problem, which has salient features: (a) extensively studied solutions by the computer science community; (b) proof for the nonexistence of any polynomial time exact algorithm; and (c) a practical pseudo-polynomial algorithm that mostly runs in O(N3) time using any number of images. We prove that two images are insufficient to correctly match the seeds, while a third image renders the matching problem to be of nonpolynomial complexity. We utilize the special structure of the problem and propose a pseudopolynomial time algorithm. Using three presegmented images, matching and reconstruction of brachytherapy seeds using the Hungarian algorithm achieved complete matching in simulation experiments; and 98.5% in phantom experiments. 3D reconstruction error for correctly matched seeds has a mean of 0.63 mm, and 0.9 mm for incorrectly matched seeds. The maximum seed reconstruction error in each implant was typically around 1.32 mm. Both on synthetic data and in phantom experiments, matching rate and reconstruction error achieved using presegmented images was found to be sufficient for prostate brachytherapy. The algorithm is extendable to deal with arbitrary number of images without any loss in speed or accuracy. The algorithm is sufficiently generic to provide a practical solution to any correspondence problem, across different imaging modalities and features.

Genitourinary Cancer Committee

The Genitourinary (GU) Cancer Committee focuses on prostate cancer and bladder cancer. The highlights of the current grant period include 1.Activated and completed two large Phase III prostate cancer trials (RTOG 94-08 and 94-13) with monthly accrual of 49 patients. RTOG 94-08 has enrolled nearly 2000 patients and is the largest cooperative group trial for the treatment of localized prostate cancer.2.RTOG 92-02 (1, 2) results demonstrated significantly improved overall and disease-free survival rates for men with high-grade prostate cancer who received long-term androgen ablation and radiotherapy (RT).3.Demonstrated that 4 months of total androgen suppression along with external beam RT (EBRT) resulted in a decrease in cause-specific mortality (3).4.Completed the first cooperative group prostate cancer brachytherapy trial (RTOG 98-05).5.Created a Prostate Brachytherapy Quality Assurance Center.6.Demonstrated that short-term androgen ablation does not confer relative androgen independence for patients who fail after receiving neoadjuvant androgen ablation (RTOG 86-10) (4).7.Demonstrated good overall and pelvic recurrence-free survival rates for invasive bladder cancer patients, but no benefit from neoadjuvant chemotherapy (RTOG 89-03) (5).8.Completed a large, Phase I–II conformal therapy trial (RTOG 94-06).9.Completed two Phase I–II invasive bladder studies (RTOG 95-06 and 97-06) with good accrual (6).10.Demonstrated that prostate cancer clinical trials results are dependent on central pathologic review of prostate biopsy specimens to assign Gleason score (7).11.Obtained approval of the National Cancer Instititute’s Prostate Cancer Concept Evaluation Panel of two of the first protocols approved by this new, peer-reviewed mechanism.12.Completed a study, in collaboration with the Outcomes Committee, testing the RTOG Modified Sexual Adjustment Questionnaire in a prostate cancer population.13.Determined, with the RTOG three-dimensional (3D) Quality Assurance Center and the Outcomes Committee, that the dose of RT to the bulb of the penis may correlate with risk of impotence after 3D RT (RTOG 94-06) (8).14.In cooperation with the Outcomes Committee, observed differences in prostate-specific antigen (PSA) between black and white men with prostate cancer (RTOG 94-12) (9).