Joshua L. Reed

Electromagnetic Tracking of Intrafraction Prostate Displacement in Patients Externally Immobilized in the Prone Position

PURPOSE To evaluate intrafraction prostate displacement among patients immobilized in the prone position using real-time monitoring of implanted radiofrequency transponders. METHODS AND MATERIALS The Calypso localization system was used to track prostate motion in patients receiving external beam radiation therapy (XRT) for prostate cancer. All patients were treated in the prone position and immobilized with a thermoplastic immobilization device. Real-time measurement of prostate displacement was recorded for each treatment fraction. These measurements were used to determine the duration and magnitude of displacement along the three directional axes. RESULTS The calculated centroid of the implanted transponders was offset from the treatment isocenter by >or=2 mm, >or=3 mm, and >or=4 mm for 38.0%, 13.9%, and 4.5% of the time. In the lateral dimension, the centroid was offset from the treatment isocenter by >or=2 mm, >or=3 mm, and >or=4 mm for 2.7%, 0.4%, and 0.06% of the time. In the superior-inferior dimension, the centroid was offset from the treatment isocenter by >or=2 mm, >or=3 mm, and >or=4 mm for 16.1%, 4.7%, and 1.5% of the time, respectively. In the anterior-posterior dimension, the centroid was offset from the treatment isocenter by >or=2 mm, >or=3 mm, and >or=4 mm for 13.4%, 3.0%, and 0.5% of the time. CONCLUSIONS Intrafraction prostate displacement in the prone position is comparable to that in the supine position. For patients with large girth, in whom the supine position may preclude accurate detection of implanted radiofrequency transponders, treatment in the prone position is a suitable alternative.

High-Risk Prostate Cancer With Gleason Score 8–10 and PSA Level ≤15 ng/ mL Treated With Permanent Interstitial Brachytherapy

PURPOSE With widespread prostate-specific antigen (PSA) screening, there has been an increase in men diagnosed with high-risk prostate cancer defined by a Gleason score (GS) ≥8 coupled with a relatively low PSA level. The optimal management of these patients has not been defined. Cause-specific survival (CSS), biochemical progression-free survival (bPFS), and overall survival (OS) were evaluated in brachytherapy patients with a GS ≥8 and a PSA level ≤15 ng/mL with or without androgen-deprivation therapy (ADT). METHODS AND MATERIALS From April 1995 to October 2005, 174 patients with GS ≥8 and a PSA level ≤15 ng/mL underwent permanent interstitial brachytherapy. Of the patients, 159 (91%) received supplemental external beam radiation, and 113 (64.9%) received ADT. The median follow-up was 6.6 years. The median postimplant Day 0 minimum percentage of the dose covering 90% of the target volume was 121.1% of prescription dose. Biochemical control was defined as a PSA level ≤0.40 ng/mL after nadir. Multiple parameters were evaluated for impact on survival. RESULTS Ten-year outcomes for patients without and with ADT were 95.2% and 92.5%, respectively, for CSS (p = 0.562); 86.5% and 92.6%, respectively, for bPFS (p = 0.204); and 75.2% and 66.0%, respectively, for OS (p = 0.179). The median post-treatment PSA level for biochemically controlled patients was <0.02 ng/mL. Multivariate analysis failed to identify any predictors for CSS, whereas bPFS and OS were most closely related to patient age. CONCLUSIONS Patients with GS ≥8 and PSA level ≤15 ng/mL have excellent bPFS and CSS after brachytherapy with supplemental external beam radiotherapy. The use of ADT did not significantly impact bPFS, CSS, or OS.

Electromagnetic transponders indicate prostate size increase followed by decrease during the course of external beam radiation therapy.

PURPOSE Real-time image guidance enables more accurate radiation therapy by tracking target movement. This study used transponder positions to monitor changes in prostate volume that may be a source of dosimetric and target inaccuracy. METHODS AND MATERIALS Twenty-four men with biopsy-proven T1c-T3a prostate cancer each had three electromagnetic transponders implanted transperineally. Their coordinates were recorded by the Calypso system, and the perimeter of the triangle formed by the transponders was used to calculate prostate volumes at sequential time points throughout the course of radiation therapy to a dose of 81 Gy in 1.8-Gy fractions. RESULTS There was a significant decrease in mean prostate volume of 10.9% from the first to the final day of radiation therapy. The volume loss did not occur monotonically but increased in most patients (75%) during the first several weeks to a median maximum on Day 7. The volume increased by a mean of 6.1% before decreasing by a mean maximum difference of 18.4% to nadir (p < 0.001 for both increase and decrease). Glandular shrinkage was asymmetric, with the apex to right base dimension varying more than twice that of the lateral dimension. For all dimensions, the mean change was <0.5 cm. CONCLUSION Real-time transponder positions indicated a volume increase during the initial days of radiation therapy and then significant and asymmetric shrinkage by the final day. Understanding and tracking volume fluctuations of the prostate during radiation therapy can help real-time imaging technology perform to its fullest potential.

Intrafraction displacement of prone versus supine prostate positioning monitored by real‐time electromagnetic tracking

Implanted radiofrequency transponders were used for real‐time monitoring of the intrafraction prostate displacement between patients in the prone position and the same patients in the supine position. Thirteen patients had three transponders implanted transperineally and were treated prone with a custom‐fitted thermoplastic immobilization device. After collecting data from the last fraction, patients were realigned in the supine position and the displacements of the transponders were monitored for 5–7 minutes. Fourier transforms were applied to the data from each patient to determine periodicity and its amplitude. To remove auto correlation from the stream of displacement data, the distribution of short‐term and long‐term velocity components were calculated from Poincaré plots of paired sequential vector displacements. The mean absolute displacement was significantly greater prone than supine in the superior–inferior (SI) plane (1.2±0.6mm vs. 0.6±0.4mm, p=0.015), but not for the lateral or anterior–posterior (AP) planes. Displacements were least in the lateral direction. Fourier analyses showed the amplitude of respiratory oscillations was much greater for the SI and AP planes in the prone versus the supine position. Analysis of Poincaré plots confirmed greater short‐term variance in the prone position, but no difference in the long‐term variance. The centroid of the implanted transponders was offset from the treatment isocenter by > 5 mm for 1.9% of the time versus 0.8% of the time for supine. These results confirmed significantly greater net intrafraction prostate displacement of patients in the prone position than in the supine position, but most of the difference was due to respiration‐induced motion that was most pronounced in the SI and AP directions. Because the respiratory motion remained within the action threshold and also within our 5 mm treatment planning margins, there is no compelling reason to choose one treatment position over the other. PACS number: 87.50.st

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 [(125)I] and 737 palladium-103 [(103)Pd]) 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 (125)I and ≤1.330, 1.331-1.547, and >1.547 mCi/seed for (103)Pd). 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 (125)I and (103)Pd. The median time to postimplant CT was 30 days. For (125)I, 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 (125)I 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 (103)Pd vs. (125)I (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 (125)I, whereas (103)Pd dosimetry was not dependent on seed activity.