IMRT

Frameless: targeting Setup error for ExacTrac ! X-Ray 6D and CBCT in SRT Statistical analysis The root-mean-square (RMS) and standard deviation (SD) of the residual setup errors measured with ExacTrac ! X-ray 6D and CBCT, as well as the setup differences between them were calculated. The paired Student’s t -test was used to test the setup differences, and to evaluate the changes in setup differences caused by retrospec- tive analysis of CBCT data wi h offline 6D fusion in Eclipse. Statis- tical significance was considered at p < 0.05.

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18 nalyses of CBCT scans using offline 6D fusion se in the RMS of residual errors for transla- as well as a slight decrease in the RMS of , in comparison with online 3D CBCT setup however, were statistically not significant .642 for translations in LR, SI and AP direc- 0.629 for yaw). are (RMS) and standard deviation (SD) of the easured with ExacTrac ! X-ray 6D and CBCT, ferences between them were calculated. The was used to test the setup differences, and es in setup differences caused by retrospec- ata with offline 6D fusion in Eclipse. Statis- considered at p < 0.05. r phantom he residual setup errors for translation in ther with the rotation(s) for the phantom residual setup errors measured with Exac- und 0.30 mm for translations and 0.30 de- respectively. The residual errors for with online 3D CBCT were within +/ ! less than 0.50 mm. The RMS of the residual ed with CBCT was <0.20 degree. lly, no shifts were applied in between CBCT images to ensure comparability of positions. re then determined by registering each pair the corresponding DRRs using online Exac- re, or planning CT using online CBCT 3D fu- tively. All registrations were done using hm. If the offsets measured by CBCT were determined by the treating physician, shifts re treatment, as CBCT is favored for the rea- lity and image contrast exceeds that of p a- parison, registration of CBCT images with of offline 6D fusion in Eclipse (version 8.5) ll to evaluate the impact of the rotations in ns (i.e., SI and LR) which are not available of Varian online review software (version

Cranial stereotactic radiotherapy ExacTrac X-ray 6 degree-of-freedom image-guidance for intracranial non-invasive stereotactic radiotherapy: Comparison with kilo-voltage cone-beam CT Jinli Ma a,b, * , Zheng Chang b , Zhiheng Wang b , Q. Jackie Wu b , John P. Kirkpatrick b , Fang-Fang Yin b a Department of Radiation Oncology, Fudan University Cancer Hospital, Shanghai, China; b Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA in Fig. 2 . The RMS and SD of residual setup errors were calculated for all patients ( Table 3 ). As can be seen from Table 3 , the residual setup errors measured with online CBCT were generally larger than that determined by the ExacTrac system. In general, the RMS of residual setup errors measured with 3D CBCT was <1.50 mm for translations, and <1.00 degre for rotation; whereas the RMS of residual setup errors measured with ExacTrac system was no more than 1.00 mm for translations, and 0.50 degree for rotations, respectively. Results Setup measurements for phantom Tabl 2 pre nts the esidual s tup errors for translation i three directions, togethe with the rotation(s) for the phantom study. The RMS of the residual setup errors measured with Exac- Trac X-ray 6D was around 0.30 mm for translations and 0.30 de- gree for rotations, respectively. The residual errors for translations measured with online 3D CBCT were within +/ ! 1.00 mm, with RMS of less than 0.50 mm. The RMS of the residual errors for yaw measured with CBCT was <0.20 degree.

a r t i c l e i n f o Article history: Received 23 May 2009 Received in revised form 25 August 2009 Accepted 27 September 2009 Available online 19 October 2009 Keywords: Intracranial non-invasive stereotactic radiotherapy IGRT ExacTrac X-ray 6D Cone-beam CT The retrospective analyses of CBCT scans using offline 6D fusion showed a slight increase in the RMS of residual errors for transla- tions in all directions, as well as a slight decrease in the RMS of residual errors for yaw, in comparison with online 3D CBCT setup data. These changes, however, were statistically not significant ( p = 0.463, 0.637 and 0.642 for translations in LR, SI and AP direc- tions, respectively; p = 0.629 for yaw). The residual setup difference between ExacTrac ! X-ray 6D and 3D CBCT was plotted f r each phantom measurement ( Fig. 1 ). The RMS of the residual setup difference between each pair of mea- urements with ExacTrac system and CBCT is also presented in Ta- ble 2 . For the 3D CBCT data, none of the differences in residual errors were statistically significant. The difference for translations and yaw was generally within 0.50 mm and 0.20 degree, respec- tively. By comparison, the retrospective analysis using offline 6D fusion showed an increased difference. However, none of these dif- ferences reached statistical significance (see p -values in Table 2 ). In general, the RMS difference between ExacTra ! X-ray 6D and off- line 6D CBCT was <0.40 mm for translations, and <0.3 degree for rotations. Setup measurements for patients A total of 50 pairs of X-ray and CBCT scans w re collected, with 9 patient having >one pa r of sc ns. A represe t ive example of a p tient’s planning CT ( r DRRs), CBCT, and orthogonal X-ray images, as seen during one se sion of image registration, is shown a b s t r a c t Recent advances in non-invasive immobilization and image- guided localization have aroused increased interest in the use of fractionated stereotactic radiotherapy (SRT) as an alternative to sin- gle fraction stereotactic radiosurgery (SRS) [1] . The potential benefit of utilizing SRT is that normal tissues undergo repair between treat- ments, while tumor cell kill may be increased by delivering a higher total dose, thereby improving the therapeutic ratio [2,3] . Key to the high accuracy of SRS is the use of invasive immobilization devices to accurately localize the tumor. Non-invasive masks used for SRT can

Background and purpose: To compare the residual setup errors measured with ExacTrac X-ray 6 degree- of-freedom (6D) and cone-beam computed tomography (CBCT) for a head phantom and patients receiv- ing intracranial non-invasive fractionated stereotactic radiotherapy (SRT). Materials and methods: Setup data were collected on a Novalis Tx treatment unit for an anthropomorphic head phantom and 18 patients with intracranial tumors. Initial corrections were determined and cor- rected with the ExacTrac system only, and then the residual setup error was determined by means of three different procedures. These procedures included registrations of ExacTrac X-ray images with the corresponding digitally reconstructed radiographs (DRRs) using the ExacTrac 6D fusion, and registrations of CBCT images with the planning CT using both online 3D fusion and offline 6D fusion. The difference in residual setup errors between ExacTrac system and CBCT was computed. The impact of rotations on the difference was evaluated. Results: A modest difference in residual setup errors was found between ExacTrac system and CBCT. The root-mean-square (RMS) of the differences observed for translations was typically <0.5 mm for phantom, and <1.5 mm for patients, respectively. The RMS of the differences for rotation(s) was however <0.2 degree for phantom, and <1.0 degree for patients, respectively. The impact of rotation on the setup dif- ference was minor but not negligible. Conclusions: This study indicates that there is a general agreement between ExacTrac system and CBCT. ! 2009 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 93 (2009) 602–608

has been developed in a novel dedicated platform for non-invasive SRS and conventional RT (Novalis Tx, Varian, CA, USA and BrainLAB, Heimstetten, Germany). The implementation of kV-CBCT is partic- ularly favorable because anatomical structures and soft tissues are often better visualized on transaxial images than planar images [10,12] . In contrast, ExacTrac " X-ray 6D offers several advantages, including faster setup, motion tracking, 3D quantitative rotational errors, real-time imaging during treatment, and less radiation to the patient [13] . However, it is important to determine if localiza- Fig. 1. A plot of the residual setup discrepancy between ExacTrac ! X-ray 6D and 3D CBCT for each phantom measurement for (a) tr nslation in the le t– ight (LR), (b) translation in the superior–inferior (SI), (c) translation in the anterior–posterior (AP) directions, and (d) rotation around the AP direction (yaw). The X-ray images were registered with the corresponding digitally reconstructed radiographs (DRRs) sing the ExacTrac 6D fusion software, while the CBCT was r gistered with planning CT using online CBCT 3D fusion software. Modest difference in localiz t on accura y f r ph n om and patient measurements between 2D and 3D Radiotherapy and Oncology 2009;93:602–608