International Journal of Radiation Oncology*Biology*Physics
Clinical investigation: lungPrecise and real-time measurement of 3D tumor motion in lung due to breathing and heartbeat, measured during radiotherapy
Introduction
Recent developments in radiotherapy such as intensity-modulated radiotherapy, noncoplanar conformal radiotherapy 1, 2, 3, 4, 5, and active breathing controlled-gated treatments (6) are all aimed at increasing the tumor dose and reducing the dose to normal tissue. Discrepancies in tumor position between treatment and a planning computed tomography (CT) scan can be caused by setup errors and organ motion 7, 8, 9. To account for these errors, a safety margin is added to the clinical target volume to obtain the planning target volume. Reducing setup error and understanding organ motion are essential in designing the tightest possible safety margin without compromising the tumor coverage. To examine the motion of lung tumors during respiration, Ekberg et al. (10) used fluoroscopy at the time of simulation. They demonstrated an average movement of 3.9 mm (range: 0–12 mm) in the cranial-caudal direction, 2.4 mm (range: 0–5 mm) in the mediolateral direction, and 2.4 mm (range: 0–5 mm) in the dorsoventral direction. Breath-hold 6, 11 or gated 12, 13 radiotherapy is designed to reduce tumor motion due to breathing. A novel method of accurate dose delivery to moving tumors with small margins is the real-time tumor tracking radiotherapy (RTRT) system 14, 15, 16.
Three-dimensional (3D) treatment planning is often performed on a CT scan made while the patient breathes freely, under the assumption that the CT image represents the average position of the tumor. However, breathing motion can cause misdetection of the tumor during CT scanning, especially for small tumors, resulting in a smaller planning volume or a distorted tumor shape (17). To obtain an accurate tumor image, a breath-hold CT is preferable. The ideal breathing phase in which the breath-hold CT is taken must correspond to the average tumor position. When the breathing motion of the tumor is not symmetric, the average tumor location is no longer midway between the inhale and exhale tumor position.
In this study, precise 3D recordings of tumor position were made during RTRT treatment, both beam-on and beam-off periods, at a high sampling rate to determine and model tumor motion due to breathing, heartbeat, and patient motion.
Section snippets
Patients and methods
Twenty patients with tumors at different sites in the lung (One patient had two tumors) were included in the analysis (Table 1). Seventeen patients had non-small-cell primary lung cancer, and three had metastatic lung tumors. A typical treatment schedule consisted of 4 × 10 Gy with a four-field noncoplanar conformal technique using multiple static beams (4 MV) shaped with a multileaf collimator.
A 2.0-mm gold marker was implanted into or near the tumor mass using bronchial endoscopy or, when
Amplitude
For each patient, the average amplitude of the tumor motion was assessed in all three directions (Table 2). In the cranial-caudal (y) direction, tumors situated in the lower lobes and not attached to rigid structures, such as the chest wall or vertebrae, move more than upper-lobe tumors or tumors attached to rigid structures: 12 ± 6 and 2 ± 2 mm (SD), respectively, (p = 0.005, two-tailed, unequal variances). For tumors attached to rigid structures and for the LR and AP directions, there was no
Discussion
The RTRT system is unique in recording the tumor position in all three directions simultaneously at a high sampling rate. This enabled us to detect tumor motion due to the heartbeat, as well as hysteresis. The system measures the position of a gold marker implanted in or near the tumor. In some studies 11, 12, 19, 20, 21, the position of the chest wall or diaphragm is used to monitor breath-holding or to trigger the linear accelerator. However, the position of the tumor can be different from
Conclusion
In conclusion, the RTRT system has been used to measure tumor position in all three orthogonal directions simultaneously, at a high sampling rate that enabled the detection of tumor motion due to heartbeat, as well as hysteresis. Tumor motion and hysteresis could be modeled with an asymmetric trigonometric function. Tumor motion due to breathing was greatest in the cranial-caudal direction for lower-lobe unfixed tumors.
References (25)
- et al.
Promising survival with three-dimensional conformal radiation therapy for non-small cell lung cancer
Radiother Oncol
(1997) - et al.
Dose escalation in NSCLC using three dimensional conformal radiotherapy (3DCRT)
Lung Cancer
(2000) - et al.
A new approach to dose escalation in non-small cell lung cancer
Int J Radiat Oncol Biol Phys
(2001) - et al.
Dose escalation for non-small cell lung cancer using conformal radiation therapy
Int J Radiat Oncol Biol Phys
(1997) - et al.
The use of active breathing control (ABC) to reduce margin for breathing motion
Int J Radiat Oncol Biol Phys
(1999) - et al.
Transfer errors of planning CT to simulatorA possible source of setup inaccuracies?
Radiother Oncol
(1994) - et al.
Analysis and reduction of 3D systematic and random setup errors during the simulation and treatment of lung cancer patients with CT-based external beam radiotherapy dose planning
Int J Radiat Oncol Biol Phys
(2001) - et al.
Uncertainties in CT-based radiation therapy treatment planning associated with patient breathing
Int J Radiat Oncol Biol Phys
(1996) - et al.
What margins should be added to the clinical target volume in radiotherapy treatment planning for lung cancer?
Radiother Oncol
(1998) - et al.
Deep inspiration breath-hold technique for lung tumorsThe potential value of target immobilization and reduced lung density in dose escalation
Int J Radiat Oncol Biol Phys
(1999)
Real-time tumour-tracking radiotherapy
Lancet
Physical aspects of a real-time tumor-tracking system for gated radiotherapy
Int J Radiat Oncol Biol Phys
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