However, obtaining accurate tumor position is the key to successful implementation of any of these motion compensated radiotherapy techniques. Motion compensated radiotherapy that uses motion management techniques, such as respiratory gating, 2, 3 dynamic multileaf collimators (MLCs), 3 and the use of dynamic couch, 4, 5 have been developed to restrict radiation doses accurately to tumors by incorporating the time-resolved positional information. 1 However, the required high conformity of dose distribution to the tumor poses a challenge especially for thoracic and abdominal tumors due to respiratory and cardiac motions.
Intensity modulated radiation therapy (IMRT) has the ability to deliver escalated radiotherapeutic doses to tumors while sparing the surrounding healthy tissues.
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Accuracy of template matching makes it a suitable candidate to replace the labor intensive manual tumor localization for obtaining the ground truth when testing other motion management techniques. This study serves as preliminary investigations towards developing online motion tracking techniques for hybrid MRI-Linac systems. Also, a strong correlation was observed between tracking error and interoperator variability ( y = 0.26 + 1.25 x, R = 0.84, p < 0.001) with the latter larger.Ĭonclusions: Results from this study indicate that the performance of template matching is comparable with or better than that of manual tumor localization. The median tracking error was positively correlated with the tumor motion magnitude in both the AP ( R = 0.55, p = 0.06) and SI ( R = 0.67, p = 0.02) directions. Furthermore, the median tracking error for seven patients in the AP direction and nine patients in the SI direction was less than half a pixel (= 0.975 mm). Results: The median tracking error for ten out of the 12 patients studied in both the AP and SI directions was less than 1 pixel (= 1.95 mm). Additionally, the tracking error of template matching, defined as the difference in the tumor positions determined with template matching and the ground truth, was investigated and compared to the interoperator variability for all patients in the anterior-posterior (AP) and superior-inferior (SI) directions, respectively. Performance of the automated template matching was compared against the ground truth established by the radiation oncologist. Tumor positions were determined both automatically with template matching and manually by a radiation oncologist and two additional reviewers trained by the radiation oncologist. Methods: Cine-MR images of 12 lung cancer patients were analyzed. This study tested the performance of an automated template matching algorithm in tracking the tumor position on cine-MR images by examining the tracking error and further comparing the tracking error to the interoperator variability of three human reviewers. Purpose: Accurate determination of tumor position is crucial for successful application of motion compensated radiotherapy in lung cancer patients.
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