Intra‐fractional motion error during HyperArc stereotactic radiosurgery on patients with brain metastases: Comparison of open and full‐face clamshell‐style immobilization devices

Abstract

Purpose To compare the intrafractional motion error (IME) during stereotactic irradiation (STI) in patients with brain metastases immobilized using open‐ (Encompass) and full‐face (DSPS) clamshell‐style immobilization devices. Methods Encompass (38 patients) and DSPS (38 patients) were used for patient immobilization, and HyperArc plans with three to four non‐coplanar beams were generated to deliver 25 to 35 Gy in three to five fractions. Cone‐beam computed tomography (CBCT) was performed on patients before and after the treatment. Moreover, the difference in patient position between the two CBCT images was considered as the IME. The margins to compensate for IME were calculated using the van Herk margin formula. Results For Encompass, the mean values of IME in the translational setup were 0.1, 0.2, and 0.0 mm in the anterior–posterior, superior–inferior, and left–right directions, respectively, and the mean values of IME about rotational axes were −0.1, 0.0, and 0.0° for the Pitch, Roll, and Yaw rotations, respectively. For DSPS, the mean values of IME in the translational setup were 0.2, 0.2, and 0.0 mm in the anterior–posterior, superior–inferior, and left–right directions, respectively, and the mean values of IME about rotational axes were −0.1, −0.1, and 0.0° for the Pitch, Roll, and Yaw rotations, respectively. No statistically significant difference was observed between the IME of the two immobilization systems except in the anterior–posterior direction (p = 0.02). Moreover, no statistically significant correlation was observed between three‐dimensional IME and treatment time. The margin compensation for IME was less than 1 mm for both immobilization devices. Conclusions The IME during STI using open‐ and full‐face clamshell‐style immobilization devices is approximately equal considering the adequate accuracy in patient positioning.

Dosimetric comparison of HyperArc and InCise MLC‐based CyberKnife plans in treating single and multiple brain metastases

“…In SRS, setup error, particularly rotational errors in single iso-center non-coplanar plans, is critical. 32 Ohira's comparison of intra-fractional motion errors (IME) using open and full-face masks suggested adding a 1 mm margin to compensate for errors in both groups. However, the American Association of Physicists in Medicine (AAPM) Task Group 135 report recommends a tolerance of less than 0.95 mm for end-to-end examinations in monthly quality assurance of robotic radiosurgery systems.…”

A prospective randomized study comparing two frameless immobilization systems for cranial stereotactic radiotherapy

“…This clamshell style Fibreplast thermoplastic mask consists of an anterior and a posterior shell, connected through pushpins [16] . Intrafractional motion smaller than 0.5 mm and 0.5° have been reported, leading to a stereotactically compliant of patient movements during therapy [17] , [18] , [19] . Besides the DS-Encompass, CQ Medical provides an alternative option in which the rear shell is replaced with a supportive AccuForm-Moldcare® (M) neck cushion.…”

Geometric and dosimetric consequences of intra-fractional movement in single isocenter non-coplanar stereotactic radiosurgery

“…However, how such movement translates into individual tumor shifts remains uncertain, particularly for targets that are distant from the isocenter in SIMT SRS treatments. Some studies [ 10 , 13 , 14 ], proposed that tumor shifts due to intra-fractional rotation could increase with the target-to-isocenter distance. This would be true if the origin of the head rotation is located at the isocenter, yet it is unclear how the two could be related physically.…”

“…Some studies [ 10 , 13 , 14 ], proposed that tumor shifts due to intra-fractional rotation could increase with the target-to-isocenter distance. This would be true if the origin of the head rotation is located at the isocenter, yet it is unclear how the two could be related physically.…”

“…(1) Most intra-fractional movements studies [8][9][10][11][12] investigated the overall head movement in terms of translation and rotation about the isocenter. However, how such movement translates into individual tumor shifts remains uncertain, particularly for targets that are distant from the isocenter in SIMT SRS treatments.…”