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      Investigation of the location effect of external markers in respiratory‐gated radiotherapy

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          Abstract

          In 7 lung and breast cancer patients, we investigated the location effect of external markers on the correlation between the motions of external markers and of an internal target under various breathing patterns.

          Our department developed a tumor tracking system consisting of two infrared cameras and a medical simulator. Using the system, we monitored the simultaneous motions of tumor and external markers placed at various locations on a patient's skin and saved the results for offline analysis. We then used a cross‐covariance approach to analyze the correlation between the motions of individual markers and of the tumor. Based on the additive model, we evaluated the predictability of tumor motion from the motions of the external markers.

          The effect of marker location on the correlation between the motions of the tumor and of the external markers varied widely from patient to patient. At no specific marker location did the surrogate signal consistently present superior correlation with tumor motion in 3 breathing sessions with 7 patients. When the composite external signal generated from multiple external motion signals was correlated with tumor motion, the quality of the correlation improved significantly. In most cases, the composite signal provided the best surrogate signal for correlating with tumor motion.

          Correlation between the motions of external markers and of a tumor may be affected by several factors, including patient characteristics, marker locations, and breathing pattern. A single external marker cannot provide sufficient and reliable tracking information for tumor motion. A composite signal generated from the motions of multiple external makers provides an excellent surrogate signal, which in this study demonstrated superior correlation with tumor motion as compared with the signal provided by an individual marker. A composite signal would be a more reliable way to track tumor motion during respiratory‐gated radiotherapy.

          PACS numbers: 87.53.Jw

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          The use of active breathing control (ABC) to reduce margin for breathing motion.

          J Wong, M B Sharpe, D A Jaffray … (1999)
          For tumors in the thorax and abdomen, reducing the treatment margin for organ motion due to breathing reduces the volume of normal tissues that will be irradiated. A higher dose can be delivered to the target, provided that the risk of marginal misses is not increased. To ensure safe margin reduction, we investigated the feasibility of using active breathing control (ABC) to temporarily immobilize the patient's breathing. Treatment planning and delivery can then be performed at identical ABC conditions with minimal margin for breathing motion. An ABC apparatus is constructed consisting of 2 pairs of flow monitor and scissor valve, 1 each to control the inspiration and expiration paths to the patient. The patient breathes through a mouth-piece connected to the ABC apparatus. The respiratory signal is processed continuously, using a personal computer that displays the changing lung volume in real-time. After the patient's breathing pattern becomes stable, the operator activates ABC at a preselected phase in the breathing cycle. Both valves are then closed to immobilize breathing motion. Breathing motion of 12 patients were held with ABC to examine their acceptance of the procedure. The feasibility of applying ABC for treatment was tested in 5 patients by acquiring volumetric scans with a spiral computed tomography (CT) scanner during active breath-hold. Two patients had Hodgkin's disease, 2 had metastatic liver cancer, and 1 had lung cancer. Two intrafraction ABC scans were acquired at the same respiratory phase near the end of normal or deep inspiration. An additional ABC scan near the end of normal expiration was acquired for 2 patients. The ABC scans were also repeated 1 week later for a Hodgkin's patient. In 1 liver patient, ABC scans were acquired at 7 different phases of the breathing cycle to facilitate examination of the liver motion associated with ventilation. Contours of the lungs and livers were outlined when applicable. The variation of the organ positions and volumes for the different scans were quantified and compared. The ABC procedure was well tolerated in the 12 patients. When ABC was applied near the end of normal expiration, the minimal duration of active breath-hold was 15 s for 1 patient with lung cancer, and 20 s or more for all other patients. The duration was greater than 40 s for 2 patients with Hodgkin's disease when ABC was applied during deep inspiration. Scan artifacts associated with normal breathing motion were not observed in the ABC scans. The analysis of the small set of intrafraction scan data indicated that with ABC, the liver volumes were reproducible at about 1%, and lung volumes to within 6 %. The excursions of a "center of target" parameter for the livers were less than 1 mm at the same respiratory phase, but were larger than 4 mm at the extremes of the breathing cycle. The inter-fraction scan study indicated that daily setup variation contributed to the uncertainty in assessing the reproducibility of organ immobilization with ABC between treatment fractions. The results were encouraging; ABC provides a simple means to minimize breathing motion. When applied for CT scanning and treatment, the ABC procedure requires no more than standard operation of the CT scanner or the medical accelerator. The ABC scans are void of motion artifacts commonly seen on fast spiral CT scans. When acquired at different points in the breathing cycle, these ABC scans show organ motion in three-dimension (3D) that can be used to enhance treatment planning. Reproducibility of organ immobilization with ABC throughout the course of treatment must be quantified before the procedure can be applied to reduce margin for conformal treatment.
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            Physical aspects of a real-time tumor-tracking system for gated radiotherapy.

            T. Nishioka, C Peer, S Hashimoto … (2000)
            To reduce uncertainty due to setup error and organ motion during radiotherapy of tumors in or near the lung, by means of real-time tumor tracking and gating of a linear accelerator. The real-time tumor-tracking 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. The system recognizes the position of a 2.0-mm gold marker in the human body 30 times per second using two X-ray television systems. The marker is inserted in or near the tumor using image guided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within a given tolerance from its planned coordinates relative to the isocenter. The accuracy of the system and the additional dose due to the diagnostic X-ray were examined in a phantom, and the geometric performance of the system was evaluated in 4 patients. The phantom experiment demonstrated that the geometric accuracy of the tumor-tracking system is better than 1.5 mm for moving targets up to a speed of 40 mm/s. The dose due to the diagnostic X-ray monitoring ranged from 0.01% to 1% of the target dose for a 2.0-Gy irradiation of a chest phantom. In 4 patients with lung cancer, the range of the coordinates of the tumor marker during irradiation was 2.5-5.3 mm, which would have been 9.6-38.4 mm without tracking. We successfully implemented and applied a tumor-tracking and gating system. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic X-ray exposure.
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              Irradiation synchronized with respiration gate.

              M J Calaguas, T Inada, Amani T Mori … (1989)
              A respiratory gating technique was developed for radiotherapy of tumors unable to remain stable due to respiration. Irradiation was started and stopped with a microwave oscillator of a linear accelerator controlled by gating signals at specific points in the respiratory cycle. This technique was tested in a phantom specially designed to simulate a patient with lung cancer and in clinical therapy for lung tumors of seven patients. A mask was used to check ventilation in the phantom and airbags were used to measure thoracoabdominal pressure in patients and in the phantom; this enabled us to detect the excursion of the tumors. Low sensitivity film for verification demonstrated the efficacy of this technique. The gated irradiation was proved to ensure more precise radiotherapy for tumors located close to the diaphragm.
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                Author and article information

                Contributors
                Hui Yan: hui.yan@duke.edu
                Journal
                Journal ID (nlm-ta): J Appl Clin Med Phys
                Journal ID (iso-abbrev): J Appl Clin Med Phys
                Journal ID (doi): 10.1002/(ISSN)1526-9914
                Journal ID (publisher-id): ACM2
                Title: Journal of Applied Clinical Medical Physics
                Publisher: John Wiley and Sons Inc. (Hoboken )
                ISSN (Electronic): 1526-9914
                Publication date (Electronic): 16 April 2008
                Publication date Collection: Spring 2008
                Volume: 9
                Issue: 2 ( doiID: 10.1002/acm2.2008.9.issue-2 )
                Pages: 57-68
                Affiliations
                [ 1 ] Department of Radiation Oncology Duke University Medical Center Durham North Carolina U.S.A.
                [ 2 ] Department of Radiation Oncology Henry Ford Hospital Detroit Michigan U.S.A.
                [ 3 ] Department of Radiation Oncology Cancer Hospital of Fudan University Shanghai China
                [ 4 ] Department of Biostatistics Henry Ford Hospital Detroit Michigan U.S.A.
                Author notes
                [*] [* ]Corresponding author: Hui Yan, Department of Radiation Oncology, Duke University Medical Center, Durham, NC, U.S.A.; phone: 919‐681‐9618; fax: 919‐681‐7183; email: hui.yan@ 123456duke.edu
                Article
                Publisher ID: ACM20057
                DOI: 10.1120/jacmp.v9i2.2758
                PMC ID: 5721714
                PubMed ID: 18714280
                SO-VID: a011937f-b01c-4105-b5fd-1c92fde29738
                Copyright © © 2008 The Authors.
                License:

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 30 August 2007
                Date accepted : 13 December 2007
                Page count
                Figures: 3, Tables: 5, References: 33, Pages: 12, Words: 5958
                Categories
                Subject: Radiation Oncology Physics
                Subject: Radiation Oncology Physics
                Custom metadata
                source-schema-version-number 2.0
                component-id acm20057
                cover-date Spring 2008
                details-of-publishers-convertor Converter:WILEY_ML3GV2_TO_NLMPMC version:5.2.5 mode:remove_FC converted:16.11.2017

                Keywords: external marker,tumor tracking,respiratory‐gated radiotherapy
                Data availability:
                Keywords: external marker, tumor tracking, respiratory‐gated radiotherapy

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