Pelvic shape and prostate motion: implications for target volume design and analysis of acute toxicity.
ABSTRACT To study the impact of pelvic shape on prostate motion and the implications for radiotherapy target design and treatment outcomes.
A total of 3741 measurements (daily shift moves in the 3 principal directions) on 29 consecutive prostate cancer patients were reviewed. All patients had 3 prostatic fiducials placed and were tracked using kilovoltage on-board imaging. Pelvic shape was categorized into android (n = 21; 2580 measurements) and gynecoid (n = 8; 1161 measurements) (defined geometrically by postoutlet to preoutlet ratio). Multivariate analyses of means/standard deviations in each principal direction were performed using major demographic, disease, anatomic, and treatment factors as covariates. Toxicity rates were compared using Fisher exact test.
On simple t test comparisons, no mean/standard deviation reached significance, although there was a nonsignificant (0.38 vs. 0.31 cm, P = 0.083) larger mean antero-posterior (AP) movement in the gynecoid group. On multivariate analyses, gynecoid shape (P = 0.032) significantly predicted for mean AP movement, and gynecoid shape (P = 0.045) significantly predicted for standard deviation of AP movement. Pelvic AP and RL dimensions also correlated with mean and standard movement along the respective axes. There were no differences between rates of acute (GI or GU) toxicity (P = 0.456) between the android and gynecoid groups.
Treatment strategies that do not employ daily motion tracking may require wider planning target volume margins in gynecoid patients. Tracking the prostate daily, as done in our case using fiducials/on-board imaging, can counter differences in pelvic shape to produce similar treatment outcomes.
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ABSTRACT: Intensity modulated radiation therapy (IMRT) has allowed accurate delivery of prostate radiotherapy; Volumetric modulated arc therapy (VMAT) offers an advancement of this technique with possible dosimetric advantages and delivery in a shorter time than standard IMRT. We hypothesize that treatment duration is a controllable factor associated with intrafraction target motion. Included patients were treated for localized prostate cancer using IMRT or VMAT (RapidArc, Varian Medical Systems, Palo Alto, CA). Continuous motion data were monitored simultaneously using electromagnetic transponders (Calypso 4D Localization System, Calypso Medical Technologies, Inc, Seattle, WA). Displacements were recorded in the RL (right-left), SI (superior-inferior), and AP (anterior-posterior) directions at 10/second (Hz). Daily motion was reported as the mean (R̄̄) and 95th percentile (R95) displacement value for the entire session. Time effect was assessed by measuring daily displacement variables (R̄̄, R95) after each successive minute of treatment. Thirty-seven patients were included, accounting for 1332 treatment sessions. Mean session time was 7.4 minutes (range, 0.5-37.2; interquartile range, 4.8-9.2). R̄̄ (0.06, 0.08, 0.11, 0.18) and R95 (0.14, 0.18, 0.23, 0.36) values (RL, SI, AP, 3-dimensional [3D], respectively) were evaluated for the entire cohort. Regression analysis showed treatment time to be the strongest predictor of observed displacements (P < .001 AP, SI, 3D; P < 0.05 RL). Ninety-five displacements increased continuously from 0.05 cm, 0.09 cm, 0.12 cm, and 0.16 cm after 1 minute to 0.21 cm, 0.20 cm, 0.29 cm, and 0.47 after 10 minutes (RL, SI, AP, and 3D). Mean session time for VMAT was 4.6 minutes compared to 8.4 minutes for IMRT (difference = 3.8 min, P < .0001); VMAT was associated with reduced motion for both (difference = 0.02, 0.03, 0.05, 0.07 cm) and (0.03, 0.04, 0.11, 0.12 cm) displacements. Our study is unique in exploring the role of session duration on intrafraction motion in the setting of electromagnetic transponders as well as VMAT. Our main results demonstrate that observed intrafraction prostate motion during radiotherapy is greater with increasing session time. Additionally, VMAT, due to shorter treatment sessions, resulted in significant reduction (30%-40%) in intrafraction displacements.Practical radiation oncology. 10/2011; 1(4):243-50.
Conference Paper: Fast simulation of VLSI interconnects[Show abstract] [Hide abstract]
ABSTRACT: This work introduces an efficient and accurate interconnect simulation technique. A new formulation for typical VLSI interconnect structures is proposed which, in addition to providing a compact set of modeling equations, also offers a potential for exploiting sparsity at the simulation level. Simulations show that our approach can achieve 50 × improvement in computation time and memory over INDUCTWISE (which in turn has been shown to be 400 × faster than SPICE) while preserving simulation accuracy.Computer Aided Design, 2004. ICCAD-2004. IEEE/ACM International Conference on; 12/2004