221 poster What percent of seeds need to be detected for effective intraoperative dosimetry during permanent prostate brachytherapy?

Posters

Materials and Methods: We performed a Medline search and reviewed all recently published articles to determine success rates and side effects for radical prostatectomy and prostate brachytherapy. The following endpoints were chosen: biochemical disease-free survival, preservation of potency, rectal complications, and urinary symptoms. There was insufficient data regarding the incidence of bowel perforation or fistula and venous thrombosis to be included. The graphical representation uses the methods of Paling ~ to produce a visual analog of treatment results, in which an endpoint is shown as a pictogram with a display of 100 human figures. In contrast to the previously described methodology, in which the figures are hand-colored to represent outcomes, our design has been adapted for a hypertext-based module by having the designated percentage turn green to indicate a positive effect, while complications are shown by the figures turning red (Figure 1). This is incorporated in a web design that allows the patient to review the treatment techniques and outcome data without supervision. Results: The completed web is available at and will be provided without charge for ESTRO and ABS members, and a user-modifiable version will be available on CD-ROM for interested parties who wish to incorporate additional information. Data on patient satisfaction and recall will be presented. Conclusions: Patient education materials using web-based visual representation of data may help men decide on their course of treatment for early-stage prostate cancer by providing more concrete representation of the issues of survival and complications. Figure 1 :

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function of the percent of seeds detected. These data are relevant in evaluating different imaging strategies to facilitate intraoperative dosimetry and immediate correction of suboptimal implants.

Materials and Methods: Post-PPB computed tomography data on 9 patients (pts) who underwent 1-125 PPB at our institution in 2002 are used in this study. Pts had mean prostate volume of 37cc (range: 8-60cc), mean seed number implanted of 102.3 (range: 49-134), mean seed activity of 0.35mCi (range: 0.260.43mCi), and median prescribed dose of 145Gy. Percent seed detection rates (PSDR) of 30,50,60,70,80,85,90,95,96,97,98 and 99 were simulated with prostate D90s and V100s computed using accepted practice. All seeds were assumed to have the same activity in a given computation, but seed activity was weighted in such a manner that for each PSDR computation the total implant activity remained constant and equal to the actual activity implanted. For all pts, 100 simulations were performed for each PSDR for a total of 10,800 computations. Results: Statistical analysis demonstrated convergence of the mean of D90s for 100 simulations to less than 0.2%. The mean Dg0 decreases and the variance increases as the PSDR decreases in spite of maintaining constant total seed activity in mCi. For PSDRs of 99, 95, 90, 80 and 50% the mean and 95% confidence interval (CI) simulated D90s are 99.8 (97.9;101.7), 99.2 (95.5;102.9), 98.2 (92.7;103.7), 96.4 (88.3;104.4), and 88.1 (73.9;102.2). The maximum errors in Gy for the 95% CI in any one case for these same PSDRs are 5.7 Gy (99% PSDR), 7.5 Gy (95% PSDR), 13.1 Gy (90% PSDR), 20.1 Gy (80% PSDR), and 38.3 Gy (50% PSDR), whereas the average maximum error for all patients are 2.5 Gy (99% PSDR), 5.5 Gy (95% PSDR), 8.8 Gy (90% PSDR), 14.2 Gy (80% PSDR), and 32.2 Gy (50% PSDR). Conclusions: The results of this study suggest that identification of 95% or more of seeds at the time of PPB is satisfactory to estimate the prostate D90 as compared to other sources of variability in PID parameters. These data are useful in evaluating and implementing intraoperative PPB seed imaging modalities which may identify a majority, but not all, of seeds implanted. 222 poster Combined ultrasound-radiographic approach intraoperative detection of seeds in brachytherapy: a feasibility study

to the prostate

G.N. Cohen, V.A. Dumane, M. Zaider, M.F. Worman Memorial Sloan Kettering Cancer Ctr, Medical Physics, New York, U.S.A. Purpose: Intraoperative treatment planning for permanent

1. Paling J. Strategies to help patients understand risks. BMJ 327, 745-748, 2003. 221 poster What percent of seeds need to be detected for effective intraoperative dosimetry during permanent prostate brachytherapy? Y. SuE, B. Davis ~, M. Herman ~, R. Robb2 ~Mayo Clinic and Foundation, Radiation Oncology, Rochester, U.S.A. 2Mayo Clinic and Foundation, Biomedical Imaging Resource, Rochester, U.S.A. Purpose: To examine the accuracy of post-implant dosimetry (PID) following permanent prostate brachytherapy (PPB) as a

prostate implants has been shown to result in superior target coverage and improved urethral sparing, and is recommended by the ABS. However, the ability to deliver the planned dose continues to be hindered by unavoidable random fluctuations in the positioning of seeds in the gland. Intraeperative dynamic dose optimization (IDDO) attempts to minimize this difference by accounting for seed misplacements and modifying the treatment plan accordingly. For IDDO to work, accurate and reliable seed localization is a crucial step. Since treatment plans are based on transrectal ultrasound (US), it is preferable to localize the seeds in the US images themselves. However, due to the inherent noisy nature of US images, development of ultrasonic features/parameters that can achieve 100% detection with no false positives, a prerequisite for making any dosimetric judgments, remains a challenging task. When the insertion of seeds is performed under fluoroscopic guidance (where seeds are more clearly visible compared to ultrasound) it may be possible to combine information from the two imaging