2892

Author Disclosure: M.J. Mitchell, None; C.R. Ramsey, TomoTherapy, Inc., D. Speakers Bureau/Honoraria; TomoTherapy, Inc., F. Consultant/Advisory Board. 2892 Interim Report of A Randomized Trial Comparing Two Forms of Immobilization of the Head for Fractionated Stereotactic Radiotherapy G. Bednarz 1 , M. Machtay 1 , M. Werner-Wasik 1 , B. Downes 2 , J. Bogner 3 , W. Curran 1 , A. Dicker 1 , R. Valicenti 1 , J. Evans 2 , D. Andrews 2 1 Department of Radiation Oncology, Kimmel Cancer Center of the Jefferson Medical College, Philadelphia, PA, 2 Department of Neurosurgery, Thomas Jefferson University, Philadelphia, PA, 3 Department of Radiotherapy and Radiobiology, Medical University of Vienna, Vienna, Austria Purpose/Objective(s): Fractionated stereotactic radiotherapy (SRT) requires extremely precise and reproducible immobilization of the patient’s head. This study compared the efficacy of two commonly used forms of immobilization used for SRT. Materials/Methods: Two routinely used methods of immobilization, which differ in their approach to reproduce head position from day-to-day are the Gill-Thomas-Cosman (GTC) frame and the BrainLab thermoplastic mask. The GTC frame fixates on the patient upper dentition and thus is in direct mechanical contact with the cranium. The BrainLab mask is a two-part masking system custom fitted to the front and back of patient’s head. After patients signed an IRB-approved informed consent form, eligible patients were randomized to either GTC frame or mask for their course of SRT. Patients were treated as per standard procedure; however, prior to each treatment a set of orthogonal digital kV images (ExacTrac, BrainLabAB, Germany) was taken. These images were fused with reference digitally reconstructed radiographs obtained from treatment planning CT to yield lateral, longitudinal and vertical deviations of isocenter and head rotations about respective axes. The primary endpoint of the study was to compare the two systems with respect to mean and standard deviations (SDs) using the distance to isocenter measure. Results: A total of 68 pts have been enrolled; positioning data for 37 patients (19 frame patients and 18 mask patients) are currently analyzable. The means, the distance measures and their SDs (in mm) for both immobilization systems are shown in Table 1. Table 1. The mean lateral (lat), longitudinal (long) and vertical (vert) shifts and distances [mm], and rotations [deg] with their respective SDs for frame and mask. Positive mean shifts indicate shifts to the patient left, superior and anterior. A mixed-effects linear regression and two-tiled t-test were used to compare the distance measure for both the systems. There was a statistically significant (p0.004) difference between mean distances for these systems, suggesting that the GTC frame was more accurate. Conclusions: Both immobilization techniques were highly effective, but the GTC frame was a more accurate immobilization system as determined by analyzing distance measurements obtained using ExacTrac system, particularly in the longitudinal dimension. To optimize the accuracy of SRT, daily kV image guidance is recommended with either immobilization system. Author Disclosure: G. Bednarz, None; M. Machtay, None; M. Werner-Wasik, None; B. Downes, None; J. Bogner, None; W. Curran, None; A. Dicker, None; R. Valicenti, None; J. Evans, None; D. Andrews, None. Lat Long Vert Distance Lat Angle Long Angle Vert Angle GTC Frame Mean 0.34 0.55 0.45 1.93 0.26 0.27 0.01 SD 1.08 1.28 1.12 0.98 0.74 0.99 0.69 BrainLab Mask Mean 0.02 0.41 0.00 3.19 0.24 0.07 0.18 SD 1.16 3.32 1.37 2.06 2.37 1.26 1.57 S715 Proceedings of the 48th Annual ASTRO Meeting

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Author Disclosure: M.J. Mitchell, None; C.R. Ramsey, TomoTherapy, Inc., D. Speakers Bureau/Honoraria; TomoTherapy, Inc.,F. Consultant/Advisory Board.

2892 Interim Report of A Randomized Trial Comparing Two Forms of Immobilization of the Head forFractionated Stereotactic Radiotherapy

G. Bednarz1, M. Machtay1, M. Werner-Wasik1, B. Downes2, J. Bogner3, W. Curran1, A. Dicker1, R. Valicenti1, J. Evans2,D. Andrews2

1Department of Radiation Oncology, Kimmel Cancer Center of the Jefferson Medical College, Philadelphia, PA,2Department of Neurosurgery, Thomas Jefferson University, Philadelphia, PA, 3Department of Radiotherapy andRadiobiology, Medical University of Vienna, Vienna, Austria

Purpose/Objective(s): Fractionated stereotactic radiotherapy (SRT) requires extremely precise and reproducible immobiliza-tion of the patient’s head. This study compared the efficacy of two commonly used forms of immobilization used for SRT.

Materials/Methods: Two routinely used methods of immobilization, which differ in their approach to reproduce head positionfrom day-to-day are the Gill-Thomas-Cosman (GTC) frame and the BrainLab thermoplastic mask. The GTC frame fixates onthe patient upper dentition and thus is in direct mechanical contact with the cranium. The BrainLab mask is a two-part maskingsystem custom fitted to the front and back of patient’s head. After patients signed an IRB-approved informed consent form,eligible patients were randomized to either GTC frame or mask for their course of SRT. Patients were treated as per standardprocedure; however, prior to each treatment a set of orthogonal digital kV images (ExacTrac, BrainLabAB, Germany) wastaken. These images were fused with reference digitally reconstructed radiographs obtained from treatment planning CT to yieldlateral, longitudinal and vertical deviations of isocenter and head rotations about respective axes. The primary endpoint of thestudy was to compare the two systems with respect to mean and standard deviations (SDs) using the distance to isocentermeasure.

Results: A total of 68 pts have been enrolled; positioning data for 37 patients (19 frame patients and 18 mask patients) arecurrently analyzable. The means, the distance measures and their SDs (in mm) for both immobilization systems are shown inTable 1.

Table 1. The mean lateral (lat), longitudinal (long) and vertical (vert) shifts and distances [mm], and rotations [deg] with theirrespective SDs for frame and mask. Positive mean shifts indicate shifts to the patient left, superior and anterior.

A mixed-effects linear regression and two-tiled t-test were used to compare the distance measure for both the systems. Therewas a statistically significant (p�0.004) difference between mean distances for these systems, suggesting that the GTC framewas more accurate.

Conclusions: Both immobilization techniques were highly effective, but the GTC frame was a more accurate immobilizationsystem as determined by analyzing distance measurements obtained using ExacTrac system, particularly in the longitudinaldimension. To optimize the accuracy of SRT, daily kV image guidance is recommended with either immobilization system.

Author Disclosure: G. Bednarz, None; M. Machtay, None; M. Werner-Wasik, None; B. Downes, None; J. Bogner, None; W.Curran, None; A. Dicker, None; R. Valicenti, None; J. Evans, None; D. Andrews, None.

Lat Long Vert DistanceLat

AngleLongAngle

VertAngle

GTC Frame Mean 0.34 0.55 0.45 1.93 0.26 0.27 0.01SD 1.08 1.28 1.12 0.98 0.74 0.99 0.69

BrainLab Mask Mean 0.02 0.41 0.00 3.19 0.24 0.07 0.18SD 1.16 3.32 1.37 2.06 2.37 1.26 1.57

S715Proceedings of the 48th Annual ASTRO Meeting