Using an onboard kilovoltage imager to measure setup deviation in intensity‐modulated radiation therapy for head‐and‐neck patients

Abstract

The purpose of the present study was to use a kilovoltage imaging device to measure interfractional and intrafractional setup deviations in patients with head‐and‐neck or brain cancers receiving intensity‐modulated radiotherapy (IMRT) treatment.Before and after IMRT treatment, approximately 3 times weekly, 7 patients were imaged using the Varian On‐Board Imager (OBI: Varian Medical Systems, Palo Alto, CA), a kilovoltage imaging device permanently mounted on the gantry of a Varian 21EX LINAC (Varian Medical Systems). Because of commissioning of the remote couch correction of the OBI during the study, online setup corrections were performed on 2 patients. For the other 5 patients, weekly corrections were made based on a sliding average of the measured data. From these data, we determined the interfractional setup deviation (defined as the shift from the original setup position suggested by the daily image), the residual error associated with the weekly correction protocol, and the intrafractional setup deviation, defined as the difference between the post‐treatment and pretreatment images. We also used our own image registration software to determine interfractional and intrafractional rotational deviations from the images based on the template‐matching method. In addition, we evaluated the influence of inter‐observer variation on our results, and whether the use of various registration techniques introduced differences. Finally, translational data were compared with rotational data to search for correlations.Translational setup errors from all data were 0.0±0.2 cm, −0.1±0.3 cm, and −0.2±0.3 cm in the right–left (RL), anterior–posterior (AP), and superior–inferior (SI) directions respectively. Residual error for the 5 patients with a weekly correction protocol was −0.1±0.2 cm (RL), 0.0±0.3 cm (AP), and 0.0±0.2 cm (SI). Intrafractional translation errors were small, amounting to 0.0±0.1 cm, −0.1±0.2 cm, and 0.0±0.1 cm in the RL, AP, and SI directions respectively. In the sagittal and coronal views respectively, interfractional rotational errors were −1.1±1.7 degrees and −0.5±0.9 degrees, and intrafractional rotational errors were 0.3±0.6 degrees and 0.2±0.5 degrees. No significant correlation was seen between translational and rotational data.The OBI image data were used to study setup error in the head‐and‐neck patients. Nonzero systematic errors were seen in the interfractional translational and rotational data, but not in the intrafractional data, indicating that the mask is better at maintaining head position than at reproducing it.PACS numbers:87.53.Kn, 87.53.Oq

An assessment of the magnitude of intra-fraction movement of head-and-neck IMRT cases and its implication on the action-level of the imaging protocol

“…The results of the sub-millimetre magnitude of intra-fraction movement measured in this study were found to be in accordance with those findings from previous studies [7,8,15]. The overall magnitude of the intra-fraction movement of 0.3 mm in our study was similar to the intra-fraction movement of 0.2 mm reported by Suzuki et al [7].…”

Method comparison of automated matching software-assisted cone-beam CT and stereoscopic kilovoltage x-ray positional verification image-guided radiation therapy for head and neck cancer: a prospective analysis

“…A rectangular region of interest was set by the physician in the AP and lateral views on the initial day of setup and was replicated for matching purposes throughout treatment (Djodjevic 2007, Fox et al 2006). The kV x-ray OBI/automatching hardware/software system has been presented previously (Kim et al 2008, Mechalakos et al 2007, Sorcini and Tilikidis 2006), in phantom verification tests, and is reported to have demonstrated ‘overall uncertainty in the positioning of known offsets [of] approximately 1.4 mm for most clinical cases’ (Fox et al 2006). Automatic KVX to DRR (2D–2D) registration was also accomplished using the same manufacturer-supplied software package (Varian OBI 1.3/Varian Vision, Varian Medical Systems, Palo Alto, CA).…”

Comparative Analysis of Dose Variations in Tumor Volumes and Organs at Risk in IMRT Plans for Head-And–Neck, Pelvis and Brain Cancers with Varying Dose Calculation Grid Sizes

“…Rigid errors, such as setup, have been extensively studied. Mechalakos et al [6]. for instance evaluated the interfraction and interfraction errors in treatments of HNC and compared their results with previous studies from others authors.…”