To frame or not to frame? Cone-beam CT-based analysis of head immobilization devices specific to linac-based stereotactic radiosurgery and radiotherapy.

Steven Babic,May Tsao,Fiona Lochray,Hany Soliman,Arjun Sahgal,Alex Lightstone,Nic Phan,Mark Ruschin,Todd Mainprize,Young Lee,Eshetu Atenafu

doi:10.1002/acm2.12251

Abstract

PurposeNoninvasive frameless systems are increasingly being utilized for head immobilization in stereotactic radiosurgery (SRS). Knowing the head positioning reproducibility of frameless systems and their respective ability to limit intrafractional head motion is important in order to safely perform SRS. The purpose of this study was to evaluate and compare the intrafractional head motion of an invasive frame and a series of frameless systems for single fraction SRS and fractionated/hypofractionated stereotactic radiotherapy (FSRT/HF‐SRT).MethodsThe noninvasive PinPoint system was used on 15 HF‐SRT and 21 SRS patients. Intrafractional motion for these patients was compared to 15 SRS patients immobilized with Cosman‐Roberts‐Wells (CRW) frame, and a FSRT population that respectively included 23, 32, and 15 patients immobilized using Gill‐Thomas‐Cosman (GTC) frame, Uniframe, and Orfit. All HF‐SRT and FSRT patients were treated using intensity‐modulated radiation therapy on a linear accelerator equipped with cone‐beam CT (CBCT) and a robotic couch. SRS patients were treated using gantry‐mounted stereotactic cones. The CBCT image‐guidance protocol included initial setup, pretreatment and post‐treatment verification images. The residual error determined from the post‐treatment CBCT was used as a surrogate for intrafractional head motion during treatment.ResultsThe mean intrafractional motion over all fractions with PinPoint was 0.62 ± 0.33 mm and 0.45 ± 0.33 mm, respectively, for the HF‐SRT and SRS cohort of patients (P‐value = 0.266). For CRW, GTC, Orfit, and Uniframe, the mean intrafractional motions were 0.30 ± 0.21 mm, 0.54 ± 0.76 mm, 0.73 ± 0.49 mm, and 0.76 ± 0.51 mm, respectively. For CRW, PinPoint, GTC, Orfit, and Uniframe, intrafractional motion exceeded 1.5 mm in 0%, 0%, 5%, 6%, and 8% of all fractions treated, respectively.ConclusionsThe noninvasive PinPoint system and the invasive CRW frame stringently limit cranial intrafractional motion, while the latter provides superior immobilization. Based on the results of this study, our clinical practice for malignant tumors has evolved to apply an invasive CRW frame only for metastases in eloquent locations to minimize normal tissue exposure.

Highlights

Accurate treatment positioning and patient immobilization is of the upmost importance for cranial stereotactic radiosurgery (SRS).[1]
All hypofractionated stereotactic radiotherapy (HF-SRT) and fractionated stereotactic radiotherapy (FSRT) patients were treated using intensity-modulated radiation therapy on a linear accelerator equipped with conebeam CT (CBCT) and a robotic couch
Noninvasive immobilization systems such as thermoplastic masks have been shown to offer patient immobilization inferior to what is required for SRS, but sufficient for fully fractionated stereotactic radiotherapy (FSRT).[7–12]

Summary

Introduction

Accurate treatment positioning and patient immobilization is of the upmost importance for cranial stereotactic radiosurgery (SRS).[1]. With noninvasive head immobilization devices, common practice has been to apply a small planning target volume (PTV) margin to account for uncertainties. Noninvasive immobilization systems such as thermoplastic masks have been shown to offer patient immobilization inferior to what is required for SRS, but sufficient for fully fractionated stereotactic radiotherapy (FSRT).[7–12]. These immobilization systems have been increasingly used in hypofractionated stereotactic radiotherapy (HF-SRT), stereotactic radiation delivered in 2 to 5 fractions, but the performance has not been well studied.[13] Noninvasive immobilization systems such as thermoplastic masks have been shown to offer patient immobilization inferior to what is required for SRS, but sufficient for fully fractionated stereotactic radiotherapy (FSRT).[7–12] These immobilization systems have been increasingly used in hypofractionated stereotactic radiotherapy (HF-SRT), stereotactic radiation delivered in 2 to 5 fractions, but the performance has not been well studied.[13]

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