Abstract
The aim of this study is to evaluate the patient positioning uncertainty in noncoplanar stereotactic radiosurgery or stereotactic radiotherapy (SRS/SRT) for intracranial lesions with the frameless 6D ExacTrac system. In all, 28 patients treated with SRS/SRT of 70 treatment plans at our institution were evaluated in this study. Two X‐ray images with the frameless 6D ExacTrac system were first acquired to correct (XC) and verify (XV) the patient position at a couch angle of 0º. Subsequently, the XC and XV images were also acquired at each planned couch angle for using noncoplanar beams to detect position errors caused by rotating a couch. The translational XC and XV shift values at each couch angle were calculated for each plan. The percentages of the translational XC shift values within 1.0 mm for each planned couch angle for using noncoplanar beams were 77.86%, 72.26%, and 98.47% for the lateral, longitudinal, and vertical directions, respectively. Those within 2.0 mm were 98.22%, 97.96%, and 99.75% for the lateral, longitudinal, and vertical directions, respectively. The maximum absolute values of the translational XC shifts among all planned couch angles for using noncoplanar beams were 2.69, 2.45, and 2.17 mm for the lateral, longitudinal, and vertical directions, respectively. The overall absolute values of the translational XV shifts were less than 1.0 mm for all directions except for one case in the longitudinal direction. The patient position errors were detected after couch rotation for using noncoplanar beams, and they exceeded a planning target volume (PTV) margin of 1.0–2.0 mm used commonly in SRS/SRT treatment. These errors need to be corrected at each planned couch angle, or the PTV margin should be enlarged.
Highlights
Stereotactic radiosurgery or stereotactic radiotherapy (SRS/SRT) for intracranial benign and malignant lesions has been a well‐established technique and a standard modality for many years.[1]
Some reports showed the high detection of patient position errors and positioning accuracy using the frameless 6D ExacTrac system,[17,18] no study were precisely dealing with the uncertainties in case of rotating a couch with noncoplanar beams
If the calculated position error values (XC shifts) exceeded our institutional criteria, which are within 1.0 mm in a vector quantity and 1.0° for the translational and rotational shift values, respectively, the couch position was corrected using the IR guidance system by monitoring IR reflective markers attached to the cranial positioning array (BrainLAB A.G., Heimstetten, Germany)
Summary
Stereotactic radiosurgery or stereotactic radiotherapy (SRS/SRT) for intracranial benign and malignant lesions has been a well‐established technique and a standard modality for many years.[1]. Using invasive fixation devices to the patient's skull, such as metal frames or rings were essential for patient immobilization and target localization in SRS/SRT treatment of intracranial lesions.[6] noninvasive (frameless) SRS/SRT treatment has become a standard procedure owing to the development of image‐ guided radiotherapy (IGRT) systems in recent years.[7,8,9,10] Chang et al reported that the accuracy of the patient setup with cone‐beam computed tomography (CBCT) image guidance was comparable to that with frame‐based radiosurgery systems.[7] The frameless 6D ExacTrac system (BrainLAB A.G., Heimstetten, Germany), which is mainly an integration of an infrared (IR)‐based optical positioning system and a radiographic kV X‐ray imaging system, is one of the advanced IGRT system.[11,12,13] Keeling et al evaluated the patient setup accuracy of SRS/SRT with this system of 35 patients with cranial lesions using the positioning shift values in this system They reported that the residual setup errors at a couch angle of 0° after positioning correction were less than 0.3 mm and 0.3° in the translational and rotational directions, respectively.[13] the 6D ExacTrac system can be used even when a couch is rotated using noncoplanar beams. Some reports showed the high detection of patient position errors and positioning accuracy using the frameless 6D ExacTrac system,[17,18] no study were precisely dealing with the uncertainties in case of rotating a couch with noncoplanar beams
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