2723 Changes in the Distance Between an Internal Fiducial Marker and a Motion Tumor on FluoroscopicReal-Time Tumor-Tracking System Evaluated With an In-Room CT System

K. Taguchi, K. Ebe, A. Hiyama, K. Tsukamoto, H. Sasai, Y. Nakashima, S. Yamatogi, R. Kanzaki, T. Matsumoto,N. Matsunaga

Department of Radiology, Ube, Japan

Purpose/Objective(s): Fluoroscopic real-time tumor-tracking radiotherapy (RTRT) system with the aid of an internal fiducialmarker for tracking has been shown to be useful for the precise irradiation for tumors in motion. However, there has been fearfor the migration of the marker and change in the distance between the marker and target volume. We examined spatialrelationship between a marker and a tumor withan in-room CT system before every RTRT. Reliability of an embedded markerfor tracking is reported.

Materials/Methods: Twenty four patients with pulmonary cancer (30 treatment sites, 77 markers) underwent CT examinations(n�182). Treatment periods ranged from 3 to 22 days. Four patients with hepatic carcinoma (5 treatment sites, 10 markers)underwent CT examinations (n�40). Treatment periods ranged from 12 to 18 days. Gold markers of 1.5 mm and 2.0 mm indiameter as an internal fiducial marker were embedded in adjacent area to pulmonary tumors and to hepatic tumors,respectively. An in-room CT scans were performed before every RTRT. CT helical imaging parameters were as follows: pitch,1.5; FOV, 400 mm; slice thickness, 3 mm. CT data sets were transferred to TPS (Pinnacle-3, Hitachi Medico, Tokyo). Thethree-dimensional (3D) distance between each center of a marker and a tumor was measured after delineating each contour(n�471 in the lung, n�80 in the liver).

Results: Mean discrepancy plus minus standard deviation(SD) was -0.40 plus minus 1.98 mm in the lung (n�471), 0.35 plusminus 1.70 mm in the liver (n�80).

Conclusions: We evaluated changes in the distance between an internal fiducial marker and a motion tumor quantitatively withan in-room CT system. A value of SD was around 2 mm. An embedded marker either in the lung or the liver seemed to bereliable.

Author Disclosure: K. Taguchi, None; K. Ebe, None; A. Hiyama, None; K. Tsukamoto, None; H. Sasai, None; Y. Nakashima,None; S. Yamatogi, None; R. Kanzaki, None; T. Matsumoto, None; N. Matsunaga, None.

2724 Verification of Average Tumor Position for Phase-Gated Lung Cancer Patients Using Integrated EPIDs

J. Cuijpers, J. van Sorensen de Koste, B. Slotman, S. Senan

VU University Medical Centre, Amsterdam, The Netherlands

Purpose/Objective(s): The toxicity of concurrent chemo-radiotherapy for stage III lung cancer can be reduced if smallermargins can be used to account for respiration-induced mobility. One such example is the use of respiration-gated treatment,but the use of smaller margins implies that accurate patient setup becomes of major importance. Current off-line setupcorrection protocols like the SAL or NAL protocols use bony anatomy matching to reduce systematic setup errors. The tumormotion relative to the bony anatomy during gated treatment delivery can be derived from a 4D CT-scan. However, variationsin breathing amplitude and residual tidal volume during gated delivery may cause a significant baseline shift in tumor position.We explored the use of integrated EPIDs for imaging of the tumor and carina-complex during treatment in order to assesssystematic displacements.

Materials/Methods: An Integrated EPID (IE) consists of the sum of all EPID frames that are acquired during the entire durationof a treatment beam. The technique of generating an IE using phase gating was tested using a moving phantom. An IE of oneof the treatment fields was acquired during every treatment fraction in 7 patients with stage III lung cancer who were treatedusing audio coached phase-gating at the expiratory phase of the breathing cycle. A match of the bony anatomy between IE andDRR’s derived from the selected phases of a 4DCT used for gating was performed to assess the setup errors in the patientpositioning. The impact of using a two-stage NAL protocol, with EPID imaging at the start and halfway during treatment, wasinvestigated. In a recent analysis of 4DCT datasets (J. van Sornsen de Koste, unpublished data), we found a correlation betweenthe carina position in superior-inferior axis and the position of the tumor. A method of adapting field borders using 4DCTinformation and the average position of the carina will be presented and applied to the clinical data sets.

Results: The moving phantom test showed that the average position of an object, with a residual motion typical for anexpiration phase gated treatment, can adequately be assessed within 1 mm accuracy using an IE. The standard deviation � forsystematic setup errors measured using bony anatomy was 3.9 and 4.1 mm in the lateral and longitudinal directions,respectively. This is larger than the respective standard deviations for random setup errors of 2.7 mm (lateral) and 3.3 mm(longitudinal). A significant time trend was observed in 4 patients, but use of a two-stage NAL protocol could compensate forthe time trends and � could be reduced to 1.9 mm and 1.3 mm, respectively. The standard deviation for systematic errors inaverage carina position at expiration phase was on average 0.2 mm (sd 1.2 mm), and the corresponding value for random errorswas approximately 1.6 mm.

Conclusions: Imaging of bony anatomy and carina complex using Integrated EPIDs provides an efficient manner for assessingboth patient setup and average tumor position.

Author Disclosure: J. Cuijpers, None; J. van Sorensen de Koste, None; B. Slotman, None; S. Senan, None.

2725 On Accounting for Patient-Specific Tumor Motion in Target Definition for Lung Cancer TreatmentPlanning: Comparison of a Multi-Phase CT Simulation Approach and MRI CINE Study

L. Wang, S. Feigenberg, L. Chen, K. Paskalev, L. Jin, C. C. M. Ma

Fox Chase Cancer Center, Philadelphia, PA

Purpose/Objective(s): In order to determine patient-specific tumor motion, a multi-phase CT scanning and MRI cine imagingapproaches were used. In this work, we compared tumor motion measured by the two approaches as well as the tumor coverage

S612 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006