Author Disclosure: S.A. Dini, None; S.B. Awan, None; K. Dou, None; R. Mokhberiosgouei, None; A.S. Meigooni, None.

2869 CT Protocol for Artifact-free Imaging of a Novel Intracavitary Brachytherapy Cervical Applicator

M. Price, F. Mourtada, K. Gifford, J. Horton, P. Eifel

University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): To develop a computational tomography (CT) scanning protocol for the artifact-free imaging of a novel,intracavitary brachytherapy (ICBT) cervical applicator, in vivo. This protocol will exploit the rotating / translatable colpostatshield that is the characteristic feature of the prototype, high-dose-rate (HDR) ICBT applicator.

Materials/Methods: A prototype cervical ICBT applicator was designed and constructed to feature a tungsten shield thatrotates as well as translates along the long axis of the colpostat. The prototype was designed so that (a) its external dimensionsare nearly equivalent to the clinical Fletcher-Williamson HDR ICBT applicator and (b) compatible with current Ir-192 remoteafter-loading technology. These features will facilitate an easier transition into a clinical setting. To acquire images, a“step-and-shoot” methodology was implemented. After inserting the prototype applicator into a plastic-water phantom andpositioning the shield in its most proximal orientation, scout images were acquired with a GE Lightspeed CT scanner utilizedfor therapy simulations. From the scout images, one can determine the midpoint of the colpostat after insertion into patient.Utilizing a technique of 120keV and 200mA (derived from metallic implant CT protocols), an axial scan is taken inferiorly tothe midpoint of the colpostat at which time the scanner is paused and the shield is translated remotely to its most distal position.The remaining slices are then taken as the scan is completed. This protocol was tested with the colpostat’s long-axis parallelto the couch as a “proof of principle” exercise as well as its long-axis oriented so that it made a 50 degree angle w.r.t. the couch;a clinically-applicable position. For the clinically-applicable orientation, the tilt of the scanner bore was utilized to minimizethe relative angle between the applicator shield and primary direction of the imaging radiation.

Results: Utilizing this “step-and-shoot” method, CT image sets of the prototype applicator were acquired that did not containthe anatomy-blurring artifacts that are common to equivalent imaging of current LDR/HDR technologies. The results were truefor both applicator shield orientations examined.

Conclusions: A protocol has been developed for use in conjunction with a prototype ICBT cervical applicator, which featuresa remotely adjustable tungsten shield, which allows for the acquisition of CT images that are free from anatomy-blurringartifacts that are common to currently utilized HDR ICBT applicators.

Author Disclosure: M. Price, None; F. Mourtada, None; K. Gifford, None; J. Horton, None; P. Eifel, None.

2870 In Vivo Measurement of Surgical Needle Intervention Parameters During Prostate Brachytherapy

T. Podder, J. R. Sherman, D. J. Fuller, E. M. Messing, D. J. Rubens, J. G. Strang, R. A. Brasacchio, Y. Yu

University of Rochester Medical Center, Rochester, NY

Purpose/Objective(s): Numerous medical procedures require accurate placement of surgical needle. But precise interstitialintervention is quite challenging. Robot-assisted needle intervention can significantly improve accuracy and consistency ofvarious procedures. However, to design and control any robotic system, we must know the forces and the motion trajectoriesfor the system. To the best of our knowledge, there is no in-vivo measurement data available in the literature. We present forcesand motion trajectories measured during transperineal needle insertion in actual brachytherapy for implanting seeds in theprostate glands of 25 patients.

Materials/Methods: In vivo force and velocity data were collected using a hand-held adapter equipped with a 6 DOF forcesensor (Nano17) and a 6 DOF electromagnetic-based position sensor (miniBIRD). The miniBIRD was attached to the hand-heldadapter to measure 3D position of the needle and the corresponding time stamps are recorded for calculating the needle insertionvelocity. The needle progression into the patient’s body was recorded using transrectal ultrasound imaging technique. Therewere thirty-six 17G needle insertions in 12 patients and thirty-six 18G needle insertions in another 13 patients. The time,position, and force data during needle insertion were recorded at a frequency of 100Hz.

Results: Average (Avg.) and standard error (SE) of the in-vivo data collected from all 25 patients (total 72 insertions) arepresented in Table 1. Highest force on 17G needle was about 17N. We noticed a significant reduction of insertion force (20.5%)when the needle was in the prostate. This reduction in force was mainly due to softer tissue. For 17G needle this reduction wasabout 33%. It indicates that the force difference for 17G needle was more prominent compared to 18G needle. Overall max.perineum force on an 18G needle was 43.5% less and the prostate force was 32.6% less as compared to that on a 17G needle,suggesting a relatively less prominent effect of needle size in softer tissue. The avg. velocity of 17G needle (1.44m/s) was higherthan that of 18G needle (1.15m/s). This was due to the fact the surgeon anticipated larger force on 17G needle and he tried tothrust the needle faster to compensate it.

S701Proceedings of the 48th Annual ASTRO Meeting