MARGIN EVALUATION IN THE PRESENCE OF DEFORMATION, ROTATION, AND TRANSLATION IN PROSTATE AND ENTIRE SEMINAL VESICLE IRRADIATION WITH DAILY MARKER-BASED SETUP CORRECTIONS

Purpose: To develop a method for margin evaluation accounting for all measured displacements during treatment of prostate cancer. Methods and Materials: For 21 patients treated with stereographic targeting marker-based online translation corrections, dose distributions with varying margins and gradients were created. Sets of possible cumulative delivered dose distributions were simulated by moving voxels and accumulating dose per voxel. Voxel motion was simulated consistent with measured distributions of systematic and random displacements due to stereographic targeting inaccuracies, deformation, rotation, and intrafraction motion. The method of simulation maintained measured correlation of voxel motions due to organ deformation. Results: For the clinical target volume including prostate and seminal vesicles (SV), the probability that some part receives <95% of the prescribed dose, the changes in minimum dose, and volume receiving 95% of prescription dose compared with planning were 80.5% +/- 19.2%, 9.0 +/- 6.8 Gy, and 3.0% +/- 3.7%, respectively, for the smallest studied margins (3 mm prostate, 5 mm SV) and steepest dose gradients. Corresponding values for largest margins (5 mm prostate, 8 mm SV) with a clinical intensity-modulated radiotherapy dose distribution were 46.5% +/- 34.7%, 6.7 +/- 5.8 Gy, and 1.6% +/- 2.3%. For prostate-only clinical target volume, the values were 51.8% +/- 17.7%, 3.3 +/- 1.6 Gy, and 0.6% +/- 0.5% with the smallest margins and 5.2% +/- 7.4%, 1.8 +/- 0.9 Gy, and 0.1% +/- 0.1% for the largest margins. Addition of three-dimensional rotation corrections only improved these values slightly. All rectal planning constraints were met in the actual reconstructed doses for all studied margins. Conclusion: We developed a system for margin validation in the presence of deformations. In our population, a 5-mm margin provided sufficient dosimetric coverage for the prostate. In contrast, an 8-mm SV margin was still insufficient owing to deformations. Addition of three-dimensional rotation corrections was of minor influence. (C) 2011 Elsevier Inc

Day-to-Day Reproducibility of Prostate Intrafraction Motion Assessed by Multiple kV and MV Imaging of Implanted Markers During Treatment

Purpose: When one is performing online setup correction for prostate positioning displacements prior to daily dose delivery, intrafraction motion can become a limiting factor to prostate targeting accuracy. The aim of this study was to quantify and characterize prostate intrafraction motion assessed by multiple kilovoltage (kV) and megavoltage (MV) imaging of implanted markers during treatment in a large patient group. Methods and Materials: Intrafraction motion in the sagittal plane was studied by retrospective analysis of displacements of implanted gold markers on (nearly) lateral kV and MV images obtained at various time points during the treatment fractions (mean, 27 per patient) in 108 consecutive patients. The effective prostate motion in a fraction was defined as the time-weighted mean displacement. Results: Prostate displacements in the sagittal plane increased during the fraction (mean, 0.2 +/- 0.2 mm/min). Forty percent of patients had a systematic (i.e., appearing in all fractions) effective displacement in the sagittal plane greater than 2 mm. Observed effective population mean-of-means (mu eff) vertical bar/ systematic (Sigma eff) intrafraction motion (mu(eff) +/- Sigma(eff)) was 0.9 +/- 1.1 mm and 0.6 +/- 1.0 mm for the anterior-posterior and superior inferior directions, respectivel Conclusion: For a large subgroup of patients, the systematic component of intrafraction prostate motion was substantial. Intrafraction motion correction prior to each beam delivery or offline corrections could likely be beneficial for the subgroup of patients with significant motion. The systematic component is well predicted by measurements in the initial fractions. (C) 2012 Elsevier Inc

Software-controlled, highly automated intrafraction prostate motion correction with intrafraction stereographic targeting: System description and clinical results

Purpose: A new system for software-controlled, highly automated correction of intrafraction prostate motion," intrafraction stereographic targeting" (iSGT), is described and evaluated. Methods: At our institute, daily prostate positioning is routinely performed at the start of treatment beam using stereographic targeting (SGT). iSGT was implemented by extension of the SGT software to facilitate fast and accurate intrafraction motion corrections with minimal user interaction. iSGT entails megavoltage (MV) image acquisitions with the first segment of selected IMRT beams, automatic registration of implanted markers, followed by remote couch repositioning to correct for intrafract Results: SDs of systematic (Sigma) and random (sigma) displacements relative to the planning CT measured directly after initial SGT setup correction were < 0.5 and < 0.8 mm, respectively. Without iSGT corrections, effective Sigma and sigma for the 11-min treatments would increase to Sigma(eff) < 1.1 mm and sigma(eff) < 1.2 mm. With the iSGT procedure with an action level of 4 mm, effective positioning errors were reduced to Sigma(eff) < 0.8 mm and sigma(eff) < 1.0 mm, with 23.1% of all fractions Conclusions: Without increasing imaging dose, iSGT successfully reduces intrafraction prostate motion with minimal workload and increase in fraction time. An action level of 2 mm is recommended. (C) 2012 American Association of Physicists in Medicine. [DOI: 10.1118/1.3684953