Article

Detection of treatment setup errors between two CT scans for patients with head and neck cancer

Department of Radiation Oncology, University of California San Francisco, San Francisco, California 94143-1708, USA.
Medical Physics (Impact Factor: 2.64). 09/2007; 34(8):3233-42. DOI: 10.1118/1.2751074
Source: PubMed

ABSTRACT

Accuracy of treatment setup for head and neck patients undergoing intensity-modulated radiation therapy is of paramount importance. The conventional method using orthogonal portal images can only detect translational setup errors while the most frequent setup errors for head and neck patients could be rotational errors. With the rapid development of image-guided radiotherapy, three-dimensional images are readily acquired and can be used to detect both translational and rotational setup errors. The purpose of this study is to determine the significance of rotational variations between two planning CT scans acquired for each of eight head and neck patients, who experienced substantial weight loss or tumor shrinkage. To this end, using a rigid body assumption, we developed an in-house computer program that utilizes matrix transformations to align point bony landmarks with an incremental best-fit routine. The program returns the quantified translational and rotational shifts needed to align the scans of each patient. The program was tested using a phantom for a set of known translational and rotational shifts. For comparison, a commercial treatment planning system was used to register the two CT scans and estimate the translational errors for these patients. For the eight patients, we found that the average magnitudes and standard deviations of the rotational shifts about the transverse, anterior-posterior, and longitudinal axes were 1.7 +/- 2.3 degrees, 0.8 +/- 0.7 degrees, and 1.8 +/- 1.1 degrees, respectively. The average magnitudes and standard deviations of the translational shifts were 2.5 +/- 2.6 mm, 2.9 +/- 2.8 mm, 2.7 +/- 1.7 mm while the differences detected between our program and the CT-CT fusion method were 1.8 +/- 1.3 mm, 3.3 +/- 5.4 mm, and 3.0 +/- 3.4 mm in the left-right, anterior-posterior, and superior-inferior directions, respectively. A trend of larger rotational errors resulting in larger translational differences between the two methods was observed. In conclusion, conventional methods used for verifying patient positioning may misinterpret rotational shifts as translational shifts, and our study demonstrated that rotational errors may be significant in the treatment of head and neck cancer.

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    • "Second, they can only visualize bony structures, so changes in soft tissue are not detected using this method. Third, 2D-radiographs are not adequate for detecting rotational movement of the head [49] [59] [60]. As such, recent advances in three-dimensional (3D) (or volumetric) in-room imaging have offered new solutions to the limitations of conventional patient positioning. "
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    ABSTRACT: Radiotherapy has a well-established role in the management of head and neck cancers. Over the past decade, a variety of new imaging modalities have been incorporated into the radiotherapy planning and delivery process. These technologies are collectively referred to as image-guided radiotherapy and may lead to significant gains in tumor control and radiation side effect profiles. In the following review, these techniques as they are applied to head and neck cancer patients are described, and clinical studies analyzing their use in target delineation, patient positioning, and adaptive radiotherapy are highlighted. Finally, we conclude with a brief discussion of potential areas of further radiotherapy advancement.
    Full-text · Article · Feb 2009 · Journal of Oncology
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    • "In clinical radiotherapy, there exists a considerable body of literature on the accuracy of patient positioning and repositioning (Ezzell et al 2007, Allison et al 2006, Murray et al 2007, Lovelock et al 2005). Based on these methodologies, we have developed a special cradle for animal positioning and atraumatic immobilization which includes a stereotactic template with fiduciary markers to facilitate registration. "
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    ABSTRACT: Dedicated small-animal imaging devices, e.g. positron emission tomography (PET), computed tomography (CT) and magnetic resonance imaging (MRI) scanners, are being increasingly used for translational molecular imaging studies. The objective of this work was to determine the positional accuracy and precision with which tumors in situ can be reliably and reproducibly imaged on dedicated small-animal imaging equipment. We designed, fabricated and tested a custom rodent cradle with a stereotactic template to facilitate registration among image sets. To quantify tumor motion during our small-animal imaging protocols, 'gold standard' multi-modality point markers were inserted into tumor masses on the hind limbs of rats. Three types of imaging examination were then performed with the animals continuously anesthetized and immobilized: (i) consecutive microPET and MR images of tumor xenografts in which the animals remained in the same scanner for 2 h duration, (ii) multi-modality imaging studies in which the animals were transported between distant imaging devices and (iii) serial microPET scans in which the animals were repositioned in the same scanner for subsequent images. Our results showed that the animal tumor moved by less than 0.2-0.3 mm over a continuous 2 h microPET or MR imaging session. The process of transporting the animal between instruments introduced additional errors of approximately 0.2 mm. In serial animal imaging studies, the positioning reproducibility within approximately 0.8 mm could be obtained.
    Preview · Article · Nov 2008 · Physics in Medicine and Biology
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    ABSTRACT: During helical tomotherapy, gantry angle accuracy is one of the vital geometric factors that assure accurate dose delivery to the target and organs at risk adjacent to it. The purpose of this study is to investigate the dosimetric impact of gantry angle misalignment on the target volume and critical organs during helical tomotherapy treatment. Five prostate cases were chosen to calculate the effects of gantry angle deviations on both patient-specific delivery quality assurance (DQA) and helical tomotherapy treatment plans. For DQA plans, the cheese phantom was rotated for up to +/-5 degrees from the preset position to simulate the gantry angle deviations during tomotherapy. Point doses at 5 mm below the isocenter and the dose distribution for each gantry angle were measured and reconstructed, respectively. For helical tomotherapy treatment plans, the same gantry misalignment effect was simulated by adjusting the automatic roll correction for up to +/-5 degrees using Planned Adaptive software. Variations of dose volume histograms (DVHs) and isodose lines were evaluated for both target and critical organs. There was no significant difference found, however, among the point dose measurements for gantry rotation up to +/-5 degrees in DQA plans. Shifts of isodose lines could be observed for gantry rotations larger than +/-27 degrees. Dosimetric discrepancies (less than 2%) were also found among DVHs of the PTV in the cases when gantry angle misalignment was larger than +/-2 degrees. However, for DVHs of either bladder or rectum under different gantry rotations, no significant differences were detected when gantry angle errors were up to +/-5 degrees. In summary, point dose measurements alone cannot reveal the dosimetric deviation due to gantry angle misalignment in DQA plans. For a 5 degrees gantry deviation, the dose to PTV increased by 0.5% comparing to the planned dose. The influence on organs at risk, i.e., rectum and bladder, is also negligible. Further studies are needed on the dosimetric impacts of gantry angle deviations for other treatment sites.
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