Clinical investigation
Lung
Insertion and fixation of fiducial markers for setup and tracking of lung tumors in radiotherapy

https://doi.org/10.1016/j.ijrobp.2005.04.024Get rights and content

Purpose: Internal 1.5-mm fiducial markers were used in real-time tumor-tracking radiotherapy (RT) for lung cancer. The fixation rate of the markers using the bronchial insertion technique, reliability of the setup using markers around the target volume, dislocation of the markers after real-time tumor-tracking RT, and long-term toxicity of marker insertion were investigated.

Methods and Materials: Between July 2000 and April 2004, 154 gold markers were inserted into 57 patients with peripheral lung cancer. The distances between the implanted markers in 198 measurements in 71 setups in 11 patients were measured using two sets of orthogonal diagnostic X-ray images of the real-time tumor-tracking RT system. The distance between the markers and the chest wall was also measured in a transaxial CT image on 186 occasions in 48 patients during treatment planning and during follow-up. The median treatment time was 6 days (range, 4–14 days).

Results: In 115 (75%) of the 154 inserted markers, the gold marker was detected throughout the treatment period. In 122 markers detected at CT planning, 115 (94%) were detected until the end of treatment. The variation in the distances between the implanted markers was within ±2 mm in 95% and ±1 mm in 80% during treatment. The variation in the distances between the implanted markers was >2 mm in at least one direction in 9% of the setups for which reexamination with a CT scan was indicated. The fixation rate in the left upper lobe was lower than in the other lobes. A statistically significant relationship was found between a shorter distance between the markers and the chest wall and the fixation rate, suggesting that the markers in the smaller bronchial lumens fixed better than those in the larger lumens. A learning curve among the endoscopists was suggested in the fixation rate. The distance between the markers and the chest wall changed significantly within a median of 44 days (range, 16–181 days) after treatment.

Conclusion: The fixation of markers into the bronchial tree was useful for the setup for peripheral lung cancer and had an accuracy of ±2 mm during the 1–2-week treatment period. The relationship between the markers and tumor can change significantly after 2 weeks, suggesting that adaptive four-dimensional RT is required.

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

References (20)

There are more references available in the full text version of this article.

Cited by (156)

  • Patient-specific respiratory motion management using lung tumors vs fiducial markers for real-time tumor-tracking stereotactic body radiotherapy

    2023, Physics and Imaging in Radiation Oncology
    Citation 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.

View all citing articles on Scopus
View full text