International Journal of Radiation Oncology*Biology*Physics
Clinical investigationLungInsertion and fixation of fiducial markers for setup and tracking of lung tumors in radiotherapy
Introduction
Interest in four-dimensional (4D) planning (1, 2) and the 4D delivery of radiotherapy (RT) (3, 4, 5) to improve the temporal accuracy of beam delivery for tumors in motion, such as lung tumors, has been great. We previously reported the existence of intrafractional and interfractional changes in tumor position due, not only to the normal respiratory cycle, but also to unpredictable baseline shifts and variable amplitude and respiration rates (6, 7). To track the changes in tumor position, fiducial markers near the lung tumor are useful for daily setup and real-time tumor tracking of the tumor position (8). Insertion of the marker through the skin surface was not recommended in a recent study because of the high frequency of pneumothorax after the procedure (9). The pneumothorax that resulted made treatment planning difficult, and sometimes adversely affected the general condition of patients with poor respiratory function. The endoscopists at our institution have developed equipment to insert markers through a bronchial fiberscope in conjunction with a virtual bronchoscopic navigation system (10). Reports have been published describing the feasibility of this equipment, and showing that marker insertion into the lungs is as safe as it is for other organs (11, 12). The fixation of the marker relative to the isocenter of the target volume was shown to be reliable for various organs, including the prostate, liver, and paraspinal region (12, 13, 14).
The real-time tumor-tracking RT (RTRT) system consists of four sets of diagnostic X-ray television systems (two of which offer an unobstructed view of the patient at any time), an image processor unit, a gating control unit, and an image display unit (8, 12). The position of the patient can be corrected by adjusting the actual marker position to the planned marker position, which has been transferred from the three-dimensional treatment planning system and superimposed on the fluoroscopic image on the display unit of the RTRT system. The system recognizes the position of a 2.0-mm gold marker in the human body 30 times/s using two X-ray television systems. The position of the markers can be visualized during RT and after treatment delivery to verify the accuracy of the localization. Setup of the target volume in solid organs has been shown to be improved with the use of three markers and the RTRT system (8, 12, 14, 15, 16). However, the accuracy of the setup in lung tissue with three markers has not been reported.
In the present study, we investigated the fixation rate of markers placed using the bronchial insertion technique, the reliability of the setup using markers around the target volume, and the dislocation of the markers after RTRT during the follow-up period. The long-term toxicity of the inserted markers in patients with lung cancer was also investigated.
Section snippets
Methods and materials
Details on the technique for inserting gold markers with a diameter of 1.5 mm into the lung have been previously reported (11, 12). In brief, special equipment for the insertion of gold markers through bronchoscopy was developed and used to insert the markers into small bronchi with a diameter of ≤1.5 mm (Olympus, Tokyo, Japan). Insertion of the markers during the fiberscopic examination took 20–30 min for each patient. This technique was used for peripheral lung tumors <6 cm in diameter in
Results
Table 1 shows the performance of the fixation technique of the gold markers. Of the 154 markers, 122 (79%) were detected at CT planning, which was performed 0–5 days after insertion (median, 2 days). Of 122 markers seen on CT, 117 (96%) were ready to be used at the start of RTRT (or 76% of the 154 inserted markers). Of the 117 markers, 115 (98%) were detected throughout the treatment period (median 10 days, range, 6–15 days). The marker was detected at the last follow-up date (range, 16–181
Discussion
Markers dropped within the first week after insertion at a high rate (38 markers, 76% of total dropped markers) and at a much lower rate 1 week after insertion (12 markers, 24%; p <0.001, Mann-Whitney U test).
The diameter of the bronchial lumina is most likely grossly related to the DMC, because the diameter of the bronchial lumina is large at the central part of the lung, where the DMC is long, and is small at the periphery of the lung, where the DMC is short. The statistical correlation
Conclusion
The relationship between fiducial markers and gross tumor volume can change during RT owing to changes in the volume and location of the tumor mass, as well as possible migration of the marker. Nevertheless, in combination with CT measurement for recalculation between the marker and tumor volume in <10% of the setups, implantation of three markers using our technique was useful for setup, with an accuracy of ±2 mm. For RT lasting >2 weeks, three gold markers and the RTRT system would play an
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2023, Physics and Imaging in Radiation OncologyCitation Excerpt :In addition, widening the gating window may increase unplanned irradiation and dose differences between the planned and actual doses. Because of residual errors, such as marker position movement and setup errors during actual treatment [18], we believe that the amplitude difference between the lung tumor and fiducial marker should be minimized within the gating window. A limitation of this study is the statistical uncertainty due to the small sample size.