Clinical comparison of positional accuracy and stability between dedicated versus conventional masks for immobilization in cranial stereotactic radiotherapy using 6-degree-of-freedom image guidance system-integrated platform

Ohtakara, Kazuhiro; Hayashi, Shinya; Tanaka, Hidekazu; Hoshi, Hiroaki; Kitahara, Masashi; Matsuyama, Katsuya; Okada, Hitoshi

doi:10.1016/j.radonc.2011.10.012

« Previous Next »Radiotherapy & Oncology
Volume 102, Issue 2 , Pages 198-205, February 2012

Clinical comparison of positional accuracy and stability between dedicated versus conventional masks for immobilization in cranial stereotactic radiotherapy using 6-degree-of-freedom image guidance system-integrated platform

Kazuhiro Ohtakara
- Department of Radiology, Gifu University Graduate School of Medicine, Japan
- Division of Radiation Oncology, Gifu University Hospital, Japan
- Corresponding author. Address: Department of Radiology, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu 501-1194, Japan.
Shinya Hayashi
- Department of Radiology, Gifu University Graduate School of Medicine, Japan
- Division of Radiation Oncology, Gifu University Hospital, Japan
Hidekazu Tanaka
- Division of Radiation Oncology, Gifu University Hospital, Japan
Hiroaki Hoshi
- Department of Radiology, Gifu University Graduate School of Medicine, Japan
Masashi Kitahara
- Division of Radiation Oncology, Gifu University Hospital, Japan
Katsuya Matsuyama
- Division of Radiation Oncology, Gifu University Hospital, Japan
Hitoshi Okada
- Division of Radiation Oncology, Gifu University Hospital, Japan

Received 1 June 2011; received in revised form 17 October 2011; accepted 20 October 2011. published online 21 November 2011.

Abstract

Purpose

To compare the positioning accuracy and stability of two distinct noninvasive immobilization devices, a dedicated (D-) and conventional (C-) mask, and to evaluate the applicability of a 6-degrees-of-freedom (6D) correction, especially to the C-mask, based on our initial experience with cranial stereotactic radiotherapy (SRT) using ExacTrac (ET)/Robotics integrated into the Novalis Tx platform.

Materials and methods

The D- and C-masks were the BrainLAB frameless mask system and a general thermoplastic mask used for conventional radiotherapy such as whole brain irradiation, respectively. A total of 148 fractions in 71 patients and 125 fractions in 20 patients were analyzed for the D- and C-masks, respectively. For the C-mask, 3D correction was applied to the initial 10 patients, and thereafter, 6D correction was adopted. The 6D residual errors (REs) in the initial setup, after correction (pre-treatment), and during post-treatment were measured and compared.

Results

The D-mask provided no significant benefit for initial setup. The post-treatment median 3D vector displacements (interquatile range) were 0.38mm (0.22, 0.60) and 0.74mm (0.49, 1.04) for the D- and C-masks, respectively (p<0.001). The post-treatment maximal translational REs were within 1mm and 2mm for the D- and C-masks, respectively, and notably within 1.5mm for the C-mask with 6D correction. The pre-treatment 3D vector displacements were significantly correlated with those for post-treatment in both masks.

Conclusions

The D-mask confers positional stability acceptable for SRT. For the C-mask, 6D correction is also recommended, and an additional setup margin of 0.5mm to that for the D-mask would be sufficient. The tolerance levels for the pre-treatment REs should similarly be set as small as possible for both systems.

Keywords: ExacTrac/Robotics, Frameless, Image-guided, Intrafractional movement, Novalis Tx, Stereotactic radiotherapy