Frame-based radiosurgery: Is it relevant in the era of IGRT?

Purpose: To assess the setup errors and intrafraction motion in patients treated with frame-based and frameless stereotactic radiosurgery (SRS).

Materials And Methods: Ten patients treated with frame-based and six patients treated with frameless radiosurgery were prospectively enrolled in the study. Leksell frame was used for frame-based and a customized uniframe orfit cast for frameless techniques. Cone beam computed tomography (CBCT) scans were taken immediately before and after each treatment to evaluate the positional accuracy and corrections applied with the use of hexapod couch for both groups.

Results: The mean translational shifts with frame-based SRS were 1.00 ± 0.30 mm in the lateral direction (X), 0.20 ± 1.20 mm in craniocaudal direction (Y) and -0.10 ± 0.31 mm in the anteroposterior direction (Z). The rotational shifts for frame-based treatments were as follows: roll 0.32 ± 0.70, pitch 0.44 ± 0.66 and yaw 0.20 ± 0.4. For frameless SRS, translational shifts were -0.40 ± 0.90, 1.10 ± 1.10, and 0.50 ± 1.30 mm in X, Y, and Z directions, respectively, and rotational shifts were -0.11 ± 0.78, 0.20 ± 0.44, and 0.29 ± 0.35 in roll, pitch, and yaw, respectively. Intrafraction shifts with frame-based SRS were: X = 0.60 ± 1.80 mm, Y = 0.20 ± 0.60 mm, and Z = 0.00 ± 0.05 mm; and rotational shifts were: roll 0.01 ± 0.27, pitch 0.06 ± 0.15, and yaw 0.01 ± 0.09. For frameless SRS, these were: X = 0.11 ± 0.20 mm, Y = 0.20 ± 0.40 mm, and Z = 0.20 ± 0.20 mm and rotational shifts were: roll 0.09 ± 0.23, pitch 0.00 ± 0.12, and yaw 0.00 ± 0.09.

Conclusions: In our experience, set up accuracy of frameless SRS is as good as frame-based SRS. With availability of verification methods such as CBCT and hexapod couch, an accurate and precise treatment delivery is feasible with frameless techniques.