Abstract
Purpose: To evaluate the usefulness of a 6-degrees-of freedom (6D) correction using ExacTrac Robotics system in patients with head-and-neck (HN) cancer receiving radiation therapy. Methods: Local setup accuracy was analyzed for 12 patients undergoing intensity-modulated radiation therapy (IMRT). Patient position was imaged daily upon two different protocols, cone-beam computed tomography (CBCT) and ExacTrac (ET) images correction. Setup data from either approach were compared in terms of both residual errors after correction and punctual displacement of selected regions of interest (Mandible, C2 and C6 vertebral bodies). Results: On average, both protocols achieved reasonably low residual errors after initial correction. The observed differences in shift vectors between the two protocols showed that CBCT tends to weight more C2 and C6 at the expense of the mandible, while ET tends to average more differences among the different ROIs. Conclusions: CBCT, even without 6D correction capabilities, seems preferable to ET for better consistent alignment and the capability to see soft tissues. Therefore, in our experience, CBTC represents a benchmark for positioning head and neck cancer patients.
Highlights
Proper daily patient alignment is one fundamental pre-requisite for patients with head and neck (HN) cancer undergoing intensity modulated radiotherapy (IMRT) due to the high conformality of the dose distribution.Set-up uncertainties and anatomic variations represent critical points for HN cancer because of the complexity of the HN anatomy, proximity of cancer to several normal structures, different relative motion among HN structures
To our knowledge, ExacTrac has not been directly compared to cone-beam computed tomography (CBCT) for set up of patients with head and neck cancers
The present study aims at comparing the performance of both methods, in terms of 6-degrees-of freedom (6D) residual setup errors
Summary
Set-up uncertainties and anatomic variations represent critical points for HN cancer because of the complexity of the HN anatomy, proximity of cancer to several normal structures, different relative motion among HN structures (i.e. mandible, upper neck region, lower neck region). Patient position accuracy has been assessed with megavolt (MV) X-rays, a two-dimensional (2D) radiographs projection technique after traditional immobilization with standard thermoplastic face masks, bite blocks or vacuum bags [4,5]. Determination of setup errors have been performed off-line using anatomic bony landmarks due to poor visualization of soft tissues in the planar projection X-ray images [6]. While off-line correction ameliorates the systematic component of set-up errors, it is less effective than on-line correction to minimize both systematic and random setup errors [7]
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