A novel immobilization device dedicated to precise intracranial radiation treatments: clinical application and accuracy assessment
Authors: Ong Chin Lin , Levra Niccolò Giaj , Nicosia Luca , Figlia Vanessa , Tomasini Davide , Franken Eric M. , Alongi Filippo 
Published: May 2020

Abstract
Background: Immobilization devices are crucial to minimize patient positioning uncertainties in radiotherapy (RT) treatments. Recently, a new immobilization device has been developed specifically for the radiation treatment of intracranial malignancies (Solstice ™ SRS Immobilization System, CIVCO Radiotherapy). To date, no data are available on the use of this device in daily clinical practice. The aim of this study is to investigate the intra and interfraction variations, patient comfort and radiographer confidence of the Solstice system from two distinct institutions. This report includes data from HagaZiekenhuis, Den Haag, Netherlands and IRCCS Ospedale Sacro Cuore Don Calaria, Negrar, Italy. From both institutions, the inclusion criteria were: a) age > 18 years, (b) diagnosis of oncological brain disease eligible to RT, (c) informed consent. Exclusion criteria were: (a) patients not eligible to RT, (b) claustrophobic patients. Focusing on dose prescription, IRCCS Ospedale Sacro Cuore Don Calabria included patients eligible to standard fractionation or moderate hypofractionated, while HagaZiekenhuis enrolled only stereotactic radiation treatments. In all patients, the immobilization device was assembled during CT simulation. A short interview to the patient regarding the comfort of the device was conducted at the end of the simulation procedure. Additionally, simulation setup time and radiographers (RTT) procedures (i.e. mask preparation) were evaluated. Prior to the radiation treatment at least one pre-RT cone beam CT (CBCT) was performed to verify the position of the patients. Additional CBCT was acquired after the treatment in order to verify any possible variation in patient position during the treatment. Results: A total number of 126 CBCT were analyzed from the match data of 16 patients treated in IRCCS Ospedale Sacro Cuore Don Calaria (10 diagnosed with brain metastases and 6 with primary central nervous systemic tumor) and 17 patients (all diagnosed with brain metastases tumor) treated in HagaZiekenhuis . The median target volume was 436 cc (range 3.2-1628 cc) and 4.58cc (range 0.4-27.19cc) for IRCCS and Haga, respectively. For patients treated in IRCCS Sacro Cuore Don Calabria, the median dose prescription was 30 Gy (range 27-60 Gy) and median number of fractions 10 (range 3-30). In Haga the median dose prescription was 21 Gy (range 8-21 Gy) and the median number of fraction was 1 (range 1-3). All patients responded positive to the comfort of the mask. Median time request to RTT to perform with Solstice ™ SRS Immobilization System was 9 minutes (range 6-12 minutes). In terms of comfort, all patients reported a good-to high level of satisfaction. Results of positioning uncertainties were comparable between the two institutes. The mean interfraction motion for all translational and rotational directions were <1mm (SD <4mm) and <0.5°(SD < 1.5°), respectively, while the mean intrafraction motions were <0.2mm (SD < 0.6mm) and 0.5° (SD < 0.6°).Conclusions: This study demonstrates the efficacy and feasibility of the Solstice ™ SRS Immobilization System, CIVCO Radiotherapy immobilization device in the intracranial radiation treatment. Both patient comfort and preparation time by radiographers are considered adequate. In combination with online daily imaging procedure, this device can achieve submillimeter accuracy required for stereotactic intracranial treatments.