Abstract
PurposeTo investigate the set‐up error and consequent dosimetric change in HexaPOD evo RT 6D couch under image‐guided intensity‐modulated radiotherapy (IG‐IMRT) for primary malignant tumor of the cervical spine.MethodsTen cases with primary malignant tumor of the cervical spine were treated with intensity‐modulated radiotherapy (IMRT) in our hospital from August 2013 to November 2014. The X‐ray volumetric images (XVI) were scanned and obtained by cone‐beam CT (CBCT). The six directions (6D) of set‐up errors of translation and rotation were obtained by planned CT image registration. HexaPOD evo RT 6D couch made online correction of the set‐up error, and then the CBCT was conducted to obtain the residual error.ResultsWe performed set‐up error and dosimetric analysis. First, for the set‐up error analysis, the average error in three translation directions of 6D set‐up error of the primary tumor of the cervical spine was <2 mm, whereas the single maximum error (absolute value) is 7.0 mm. Among average errors of rotation direction, Rotation X (RX) direction 0.67° ± 0.04°, Rotation Y (RY) direction 1.06° ± 0.06°, Rotation Z (RZ) direction 0.78° ± 0.05°; and the single maximum error in three rotation directions were 2.8°, 3.8°, and 2.9°, respectively. On three directions (X, Y, Z axis), the extended distance from clinical target volume (CTV) to planning target volume (PTV) was 3.45, 3.17, and 3.90 mm by calculating, respectively. Then, for the dosimetric analysis, the parameters, including plan sum PTV D98 and D95, planning gross tumor volume D98 and D95, V100% of the plan sum were significantly lower than the treatment plan. Moreover, Dmax of the spinal cord was significantly higher than the treatment plan.Conclusion6D set‐up error correction system should be used for accurate position calibration of precise radiotherapy for patients with malignant tumor of the cervical spine.
Highlights
The radiotherapy for the tumor of spine demands high techniques and equipment
Linear accelerators equipped with image‐guided radiotherapy (IGRT) function have been applied in radiotherapy
The D98 and D95 of the dosimetry parameter planning target volume (PTV), as well as the D98 and D95 of Planning gross tumor volume (PGTV) was significantly lower than the original treatment plan (Tables 4 and 5).There were differences in patient’s plan sum the treatment plan dose–volume histograms (DVH) (Fig. 7).The set‐up error will result in an average reduction in 2.71 and 2.98 Gy of PTV D98 and D95, respectively, and a missing volume of average PTV 8.46%
Summary
The radiotherapy for the tumor of spine demands high techniques and equipment. Due to the physiological and anatomical characteristics of the spine which is close to the spinal cord, a strict‐dose‐limiting organ, high doses irradiation must have strict position verification, etc., to ensure the accuracy and safety of treatment. There are many reports on the study of set‐up error, and different image verification techniques, different parts, different ways of position fixing and even set‐up errors in different unit are not the same. After correction of translation 3D position, the radiotherapy residual error which still remained more than 5 mm in different parts including chest, abdomen, and head and neck accounted for 18%, 27%, and 10%, respectively. The successful development and application of HexaPOD evo RT 6D treatment couch and CBCT image‐guided system in clinical tumor radiotherapy is to improve the accuracy of radiotherapy by improving image‐guided technology. This paper analyzes the set‐up error by image‐guided of cervical spine patients, as well as the dosimetric changes caused by set‐up errors
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