We compared visualization of patient anatomy on images acquired on a ... therapy for cancer in the abdomen (n Z 3), head/neck (n Z 3), thorax (n. Z 2), and ...
Oral Scientific Sessions S133
Volume 84 Number 3S Supplement 2012 Results: Measured XRF spectrum showed a sharp peak characteristic of Pt with the narrow full-width at half-maximum (FWHM) (FWHMK1 Z 1.138 keV, FWHMK2 Z 1.052 keV). The distribution of Pt drug in the water phantom was clearly identifiable on the reconstructed XRF images. Our results showed a linear relationship between the XRF intensity of Pt and its concentrations (R2 Z 0.9949), suggesting that XFCT is capable of quantitative imaging. Finally, a transmission CT image was obtained to show the potential of the approach for providing attenuation correction and morphological information. Conclusions: This study reveals the high sensitivity and specificity of XFCT for monitoring the spatial distribution of Pt drugs. This novel approach, with exquisite spatial resolution arising from CT, would offer treatment insight impossible with the current design. It may be useful in tailoring tumor treatment regimens which combine radiation and chemotherapy in the future. Author Disclosure: Y. Kuang: None. G. Pratx: None. J. Qian: None. B. Meng: None. M. Bazalova: None. L. Xing: E. Research Grant; NIH/NCI R01CA133474, NIH/NCI R21CA153587, NSF 0854492, the Friends for an Earlier Breast Cancer Test Foundation.
329 Comparison of Onboard Low-field MRI Versus CBCT/MVCT for Anatomy Identification in Radiation Therapy P.J. Parikh, C.E. Noel, C. Spencer, O. Green, Y. Hu, S. Mutic, and J.R. Olsen; Washington University in St. Louis School of Medicine, St. Louis, MO Purpose/Objective(s): Multiple groups are investigating MR-XRT devices, but are using different field strength MR. Moreover, a comparison of MR versus available onboard imaging (CBCT/MVCT) has not been performed. We compared visualization of patient anatomy on images acquired on a 0.35T MR-Co-60 system to those acquired with CBCT/ MVCT. Materials/Methods: Fourteen patients undergoing image guided radiation therapy for cancer in the abdomen (n Z 3), head/neck (n Z 3), thorax (n Z 2), and pelvis (n Z 6) were enrolled on an IRB approved protocol and imaged with a 0.35T onboard MRI. Sequences varied depending on the site. CBCT/MVCT image sets used for routine treatment localization were collected for each patient within 2 weeks of MRI imaging. For each of the 14 patients, the volumetric MRI and CBCT/MVCT image sets were displayed side-by-side on clinical image viewing software and independently reviewed by three radiation oncologists (PJP, JRO, and CRS). Each physician was asked to evaluate which image set (if either) offered better visualization of the target and individual organs at risk (OAR), as derived from a standardized list of site-specific critical structures (Santanam, IJROBP, 2012). Results: Fifteen to 24 OARs were evaluated per anatomical site (n Z 15 for the abdomen, n Z 24 for the head/neck, thorax, and pelvis). In total, 234 OARs and 10 unique target structures were compared for visualization on MRI and CBCT/MVCT image sets by each physician. At least 2/3 physicians evaluated MRI as offering better visualization for 71% of structures, CBCT offering better visualization in 9% of structures, and both offering equivalent visualization in 19% of structures. Physicians agreed unanimously in consensus for 74% and in majority for 99% of structures evaluated, respectively. For 1% of structures, no consensus was reached. For structures that were better visualized on MRI, 100% of the time included the anal canal, bladder, blood vessels, brachial plexus, lobes of the brain, brain stem, cerebellum, colon, cranial nerves, duodenum, esophagus, most structures of the heart, hippocampus, kidneys, liver, optic chiasm, optic nerve, parotids, penile bulb, pituitary gland, prostate, rectum, seminal vesicles, small bowel, spleen, stomach, submandibular glands, spinal cord, uterus, and vagina. Targets were better visualized on MRI in 4/10 cases, and were never better visualized on CBCT/MVCT images. Conclusions: Low field MR provides better anatomic verification of many radiation therapy targets and most organs at risk as
compared to CBCT/MVCT. Further work is needed to quantify improvements for specific tasks, such as repositioning and adaptive planning. Author Disclosure: P.J. Parikh: E. Research Grant; Calypso, Varian, Philips, Viewray. F. Honoraria; AAMD. G. Consultant; Innovative Pulmonary Solutions, Oraya. J. Funding Other; Medical Litigation. K. Stock; Innovative Pulmonary Solutions. C.E. Noel: None. C. Spencer: None. O. Green: None. Y. Hu: None. S. Mutic: E. Research Grant; Varian. K. Stock; Radiologica, Viewray. J.R. Olsen: None.
330 Noninvasive Real-time Prostate Tracking Using a Transperineal Ultrasound Approach M.C. Abramowitz,1 E. Bossart,1 R. Flook,1 X. Wu,1 R. Brooks,2 M. Lachaine,2 F. Lathuiliere,2 X. Wu,1 and A. Pollack1; 1University of Miami, Miami, FL, 2Elekta, Montreal, QC, Canada Purpose/Objective(s): Interfraction image guidance in the management of prostate cancer reduces uncertainty and has become standard of care. More recently, real-time fiducial/transponder tracking to further reduce uncertainty from intrafraction target motion has become available. Currently available techniques for prostate tracking require the placement of markers. We describe a new transperineal ultrasound system that offers a noninvasive means of correcting for interfraction and intrafraction motion. This system uses a rigid registration algorithm to calculate changes between a current image and the reference image allowing the calculation of translations and rotations every 0.5 sec. Traditional trans-abdominal ultrasound-based techniques are used for interfraction adjustments; this approach is affected by user variability (pressure and approach), anatomy, bowel gas, and bladder filling impacting image quality and accuracy. In addition, transabdominal ultrasound is not amenable to real-time tracking. The transperineal ultrasound imaging approach significantly reduces these issues. Materials/Methods: A programmable 3D motion phantom consisted of a tank filled with a water/Zerdine mixture, and motorized control of a target along thee translational axes in the liquid. As the submerged target could only be tracked by the Clarity 4D system, Calypso beacons as well as optical markers were affixed to an external stem which moved in tandem with the target within approximately 1 mm. A 3D sine wave as well as 6 motion profiles taken from published studies were programmed and transferred to the phantom. A large unidirectional excursion was performed prior to each sequence to synchronize the data sets. Data from all 4 sources (Calypso transponders, optical imaging, 4D-US and the programmed motion) were compared in 3 directions (ant/post, Sup/Inf, L/R). Mean, Standard deviation, 25%, 50% and 75% percentiles of the directional differences as well as the min, mean, 50%, 90%, 95% percentiles and max value for the absolute directional differences were calculated for each profile. Results: Phantom motion tracked via the optical and the Calypso systems showed the 95% bond of the maximum distance variation to be less than 0.6 mm. There was no consistent directional error. For the Clarity system, 95% of the maximum distance variation was within 1.3 mm of programmed motion, the majority were less than 1 mm. No directional preference was identified. Part of this variation may be attributed to the 1 mm uncertainty between the internal target and the external stem. Conclusions: Phantom studies show that a novel 4D transperineal ultrasound system accurately and reproducibly tracks prostate phantom motion. Transperineal ultrasound tracking of the prostate offers a noninvasive alternative to currently marker-based systems. Author Disclosure: M.C. Abramowitz: None. E. Bossart: None. R. Flook: None. X. Wu: None. R. Brooks: A. Employee; Elekta. M. Lachaine: A. Employee; Elekta. F. Lathuiliere: A. Employee; Elekta. X. Wu: None. A. Pollack: None.
