IMRT

Invasive frame-based: immobilization l Image-guidance g Quantification of intrafraction motion g Frame-based system SBRT set up A clinical comparison of patient setup and intra-fraction motion using frame-based radiosurgery versus a frameless image-guided radiosurgery system for intracranial lesions Naren Ramakrishna * , Florin Rosca, Scott Friesen, Evrim Tezcanli, Piotr Zygmanszki, Fred Hacker Department of Radiation Oncology, Brigham and Women’s Hospital and Dana Farber Cancer Institute, Boston, MA, USA Contents lists available at ScienceDirect Radiotherapy and Oncology journal homepage: www.thegreenjournal.c m Frame-based radiosurgery depends critically on maintenance of the spatial relationship of the frame to the skull. Any slippage or deformation of the fra e between planning and treatment will re- sult in a displacement of the stereotactic space relative to the tar- get and is important to exclude carefully at the time of treatment [8] . A depth helmet has been routinely employed to monitor for frame slippage between treatment planning and treatment [2] . The depth-helmet technique relies on potentially imprecise skin markings and depth measurements which are particularly difficult in patients with certain hair types or loose skin. The passive use of X-ray IG allowed us an offline method to accurately detect frame slippage in one patient in our series for whom the X-ray IG system determined a predicted shift of 4.81 mm in the vertical direction ( Fig. 4 ). Based on this, we propose routinely combining X-ray IG with frame-based radiosurgery as a replacement for depth-helmet verification. This combination would also provide a useful offline method to verify patient setup. Another major concern regarding frameless radiosurgery treat- ment is of intra-fraction motion. As an accurate assessment of real- time motion was not possible using our system, we utilized intra- fraction displacement as a proxy to estimate intra-fract on motion and to compare immobilization properties of the BRW head frame age-guided radiosurgery differs from fra e-based radiosurgery and non X-ray image-guided frameless radiosurgery in that the relationship between the immobilization device and the skull anat- omy need not be preserved from treatment planning to actual treatment. Instead, imaging at the time of treatment is used to di- rectly de ermine the position of the patient in st reotactic space. While en -t -end phantom testing supports the tech ical capabil- ity of the e system to accura ely localiz and deliver dose to he treatment isocenter under idealized conditions [19,21] , clinical application presents a mor compl x challe ge to the use of these systems. We have utilized hidden-target testing in a cranial phantom to evaluate the e d-to-end overall system accuracy of the Novalis Body Exac-Trac system and have demonstrated a total error mag- nitude of 0.7 mm (±0.3 mm standard deviation). This compares favorably with other published IG systems such as Cyberknife [19] and with traditional frame-based radiosurgery using a linac [2,22] . Our results are consistent with other published studies of overall system accuracy of the Novalis Body Exac-Trac system using anthropomorphic phantom testing for intracranial targets [23,24] . Radiotherapy and Oncology 95 (2010) 109–115 as were the predicted shifts. These results emphasize the impor- tance of careful overview of the image-fusion step of the image- guidance process and suggest that systematic exclusion from im- age fusion of regions of skull prone to such imaging artifacts may be prudent.

11 atomy and their interaction with the guidance systems may in theory reduce to idealized phantom testing results. ong concordance between frame-based ing. The clinical positioning coordinates ance for our group of 69 patients and 1.0 mm (SD = 0.5) of the frame-based ance is similar to that observed by Sol- . [23,24] . A systematic anterior–poster- = 0.3 mm) between frame-based and bserved by Lamba et al. among their anterior–posterior direction shift was diosurgery has been the de facto gold eatment. It provides reliable immobili- efficacy is well established. However, d frame is associated with substantial tient comfort, safety, clinical and tech- risk of errors related to frame slippage of relocatable stereotactic immobiliza- ill-Thomas Cosman frame were devel- facilitating fractionated stereotactic radiosurgery [17] The potential weak- at the patient may shift relative to the during relocation of the device or be- ment [5] . y of image-guided frameless radiosur- veloped for clinical use which rely on ce [13,18] , X-ray image guidance [19] , r patient localization [14,20] . X-ray im- iffers from frame-based radiosurgery ed frameless radiosurgery in that the mobilization device and the skull anat- ed from treatment planning to actual at the time of treatment is used to di- on of the patient in stereotactic space. testing supports the technical capabil- urately localize and deliver dose to the idealized conditions [19,21] , clinical e complex challenge to the use of these -target testing in a cranial phantom to verall system accuracy of the Novalis have demonstrated a total error mag- m standard deviation). This compares ished IG systems such as Cyberknife rame-based radiosurgery using a linac sistent with other published studies of f the Novalis Body Exac-Trac system antom testing for intracranial targets

determined a predicted shift of 4.81 mm in the vertical direction ( Fig. 4 ). Based on this, we propose routinely combining X-ray IG with frame-based radiosurgery as a replacement for depth-helmet verification. This combination would also provide a useful offline method to verify patient setup. Another major concern regarding frameless radiosurgery treat- ment is of intra-fraction motion. As an accurate assessment of real- time motion was not possible using our system, we utilized intra- fraction displacement as a proxy to estimate intra-fraction motion and to compare immobilization properties of the BRW head frame

a r t i c l e i n f o Variations in patient anatomy and their interaction with the immobilization and image-guidance systems may in theory reduce overall accuracy compared to idealized phantom testing results. Our results demonstrate strong concordance between frame-based and image-guided positioning. The clinical positioning coordinates determined by image-guidance for our group of 69 patients and 102 isocenters were within 1.0 mm (SD = 0.5) of the frame-based patient setup. This concordance is similar to that observed by Sol- berg et al., and Lamba et al. [23,24] . A systematic terior–poster- ior shift of 0.5 mm (SD = 0.3 mm) between frame-based and im ge-guided setup was observed by Lamba et al. among their group of 19 patients. The anterior–posterior direction shift was also largest in the report by Solberg et al. for their group of 35 pa- ti nts [23,24] . This difference was not observed in our study with the mean shift distributed essentially equally among the three axes. Our radiosurgery setup procedure utilizes a Radionics localiz- er which, in contrast to the BrainLAB localizer te plate box used by Lamba et al., does not cause flex of the ring and frame mount resulting in a systematic deviation in the anterior–posterior direction. We found that for certain patient setups, the kV X-ray images did not initially fuse accurately to the planning DRR resulting in aberrant predicted shifts ( Fig. 3 ). In each of these cases, the kV X-ray images demonstrated a graded density through the skull at the vertex distinct from the CT-DRR images, resulting in aber- Article history: Received 12 June 2009 Received in revised form 8 December 2009 Accepted 29 December 2009 Available online 28 January 2010 Keywords: Frameless Radiosurgery Image-guided Stereotactic Radiosurgery has an important role in the treatment of primary brain tumors, metastases, and functional disorders. Effective radi-

a b s t r a c t 4.5 mm frame slippage detected in one patient

Background and purpose: A comparison of patient positioning and intra-fraction motion using invasive frame-based radiosurgery with a frameless X-ray image-guided system utilizing a thermoplastic mask for immobilization. Materials and methods: Overall system accuracy was determined using 57 hidden-target tests. Positioning agreement between invasive frame-based setup and image-guided (IG) setup, and intra-fraction displace- ment, was evaluated for 102 frame-based SRS treatments. Pre and post-treatment imaging was also acquired for 7 patients (110 treatments) immobilized with an aquaplast mask receiving fractionated IG treatment. Results: The hidden-target tests demonstrated a mean error magnitude of 0.7 mm (SD = 0.3 mm). For SRS treatments, mean deviation between frame-based and image-guided initial positioning was 1.0 mm (SD = 0.5 mm). Fusion failures were observed among 3 patients resulting in aberrant predicted shifts. The image-guidance system detected frame slippage in one case. The mean intra-fraction shift magnitude observed for the BRW frame was 0.4 mm (SD = 0.3 mm) compared to 0.7 mm (SD = 0.5 mm) for the frac- tionated patients with the mask system. Conclusions: The overall system accuracy is similar to that reported for invasive frame-based SRS. The intra-fraction motion was larger with mask-immobilization, but remains within a range appropriate for stereotactic treatment. These results support clinical implementation of frameless radiosurgery using the Novalis Body Exac-Trac system. ! 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 95 (2010) 109–115

Fig. 4. CT confirmation of fr me slipp g detected by X- ay image-guidance: X-ray image guidance suggested a 4.81 mm VRT shift in isocenter position relative to frame-bas d positioning. The p tient was re-imaged by CT. The CT was relocalized revealing that the stereotactic space had shifted by approximately 4.5 mm relative to the target isocenter, confirming frame slippage.

Radiotherapy and Oncology 2010;95:109–115

infection, and requires pre-medication. Furthermore, the care of patients wearing head frames creates a clinical resource burden