margins. These are affected by respiration-induced organ motion. This

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tomical levels were established for the 3 esophageal divisions: cervical ESO (E1) from ... but 3 of them showed new lesions elsewhere with a median of 15 months ... percentage of residual errors within ± 3 mm action level tolerance (current ...
Proceedings of the 49th Annual ASTRO Meeting margins. These are affected by respiration-induced organ motion. This study evaluates the intra-fractional esophageal motion induced by respiration and determines the population-based approach for esophageal margins. Materials/Methods: Eleven 4D-CT scans acquired for radiation treatment planning were used for this analysis. The ESO was contoured by a single clinician using contrast-enhanced CTs. In all patients, the outer esophageal wall was identified and manually contoured cranio-caudally from the post-cricoid level to the gastro-esophageal junction (GEJ) on the axial CT slices. Three anatomical levels were established for the 3 esophageal divisions: cervical ESO (E1) from esophageal inlet to T1-T2 level (sternal notch), thoracic ESO (E2) from T1-T2 level to T5-T6 (carina), and lower thoracic/abdominal (E3) from T5-T6 to GEJ. Esophagus were contoured for all phases of the respiratory cycle and divided according to the above landmarks. The DICOM-RT files were extracted from the Eclipse workstation and analyzed. Each structure was modeled by line composed of the centroids of each esophageal contour at all CT slices. Cubic splines with the same number of knots were used with the T2-T3 landmark as a homologous point to normalize all structures. The mean location of the ESO and the standard deviation (sigma) of its displacement were determined for each and for all patients. The margins were computed using 1.65*sigma which corresponds to 95% coverage. Results: Population-based maximal margins for described esophageal segments for the medial-lateral (ML) direction ranged as follows 2.2 mm; for E1, 7.4 mm for E2, and 16.0 mm for E3. For the Anterio-Posterior (AP) direction, the margins were 4.0 mm for E1, 7.8 mm for E2 and for E3 it was 12.0 mm (Fig. 1). For individual patients in both directions the margins for E3 were the largest. The AP margins for E1 and E2 segments were similar. The ML margins increased following the subsequent esophageal segments in the caudal direction. Conclusions: The largest motion was seen for the lower part of the esophagus. The esophageal margins that reflect the structure’s mobility differ for each section and direction. Knowledge of the motion of each segment may be of value in determining extent of margin necessary for radiation treatment planning, especially in cases treated with IMRT. A much larger cohort of patients is currently being evaluated.

Fig. 1. Esophagus mobility. Author Disclosure: D. Michalski, None; R.S. de Andrade, None; D.E. Heron, None; M.S. Huq, None.

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Is Post-Treatment FDG-PET/CT Useful in Differentiating Tumor From Fibrosis After Curative Radiotherapy (RT) Alone for Lung Cancer?

S. Faria1, R. Lisbona2, J. Stern3, W. Sheshtawy1, L. Souhami1, S. Devic4, C. R. Freeman1 1 McGill University, Radiation Oncology, Montreal, PQ, Canada, 2McGill University, Nuclear Medicine, Montreal, PQ, Canada, 3Jewish General Hospital, Nuclear Medicine, Montreal, PQ, Canada, 4McGill University, Medical Physics, Montreal, PQ, Canada Purpose/Objective(s): Curative RT in non-small cell lung cancer (NSCLC) often causes radiological abnormalities that can mimic local recurrence. FDG-PET/CT is an attractive functional imaging method that may be useful in differentiating local recurrence versus radiation induced fibrosis in this group of patients. We report our experience assessing the value of PET/CT in differentiating tumor from fibrosis after curative RT for NSCLC. Material/Methods: Fifteen inoperable NSCLC patients with localized disease, treated with RT alone to a dose of 52.5 Gy/15 fractions are the subjects of this analysis. All had PET/CT performed before and after RT. Follow-up was every 3–6 months and always included physical examination and chest x-ray (CXR). Post-treatment PET/CT was performed 7–8 months after RT in a routine basis. For this study, the treated primary lung tumor had the post-treatment PET/CT metabolic response scored as ‘‘negative’’ when there was a complete or almost complete response, or ‘‘positive’’ if there was partial, stable or increased hypermetabolic disease when compared to the pre-treatment PET/CT. Evaluation of tumor control/progression was also done by physical examination and imaging studies during follow-up. Results: Median follow-up time after RT was 22 months. Median follow-up time after the post-treatment PET was 13 months. Median = 76 years. Stages: T1 = 5, T2 = 8, T3 = 1, T4 = 1 patient. Median PTV = 142 cc. All patients were alive when this analysis was performed. Post-treatment PET/CT was considered ‘‘positive’’ in 4 and ‘‘negative’’ in 11 patients concerning local control. Of the latter, all still had local control at the last follow-up, but 3 of them showed new lesions elsewhere with a median of 15 months after the post-PET/CT. Of the 4 cases with ‘‘positive’’ PET/CT, 2 had confirmed local relapse and new lesions during further follow-up, while the remaining 2 cases had non-evidence of disease in subsequent follow-up 13 and 16 months after post-PET/CT. Figure shows an example of T3N0 right NSCLC. Pre (above) and post (below) treatment PET and CT.

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Volume 69, Number 3, Supplement, 2007

Conclusions: Our preliminary results show that post-treatment PET/CT may be useful in differentiating tumor from fibrosis or inactive tumor after RT for NSCLC. This information may be valuable when assessing local control after curative RT and when counseling patients on second line treatment.

Author Disclosure: S. Faria, None; R. Lisbona, None; J. Stern, None; W. Sheshtawy, None; L. Souhami, None; S. Devic, None; C.R. Freeman, None.

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Feasibility and Reproducibility of Cone-Beam CT Guided Lung Radiotherapy Using Registration to Bone, Carina, and Tumor

J. Higgins1,2, A. Bezjak1,2, K. Franks1, D. Payne1,2, J. Cho1,2, L. Le1, J. Bissonnette1,2 1 Princess Margaret Hospital, Toronto, ON, Canada, 2University of Toronto, Toronto, ON, Canada Purpose/Objective(s): For locally advanced lung cancer, stable bony landmarks have been used traditionally in portal imaging as target surrogates for patient alignment and field verification. In comparison to portal imaging, cone-beam CT (CBCT) permits direct visualization of the tumor along with other structures such as the carina. Alternative image guidance methods may yield more accurate patient positioning, thereby allowing smaller planning margins, dose escalation, reduction in chance of geometric miss and decreased normal tissue toxicity for the patient. The aim of this study was to assess the feasibility and reproducibility of automatic and manual CBCT image matching using bone (spine), carina and tumor as registration landmarks. Materials/Methods: Day 1 verification CBCT images were independently assessed for 30 locally advanced lung and mediastinal cancer patients on a research ethics-approved retrospective study. Six image registration methods were evaluated; automatic and manual matching of datasets using bone, carina and tumor. Four radiation therapists (RTTs) defined the volume of interest ‘‘clipbox’’ and carried out all automatic matching. Each RTTs also performed manual matching for bone and carina. Due to complexity in delineating lung and mediastinal tumors, 4 radiation oncologists performed manual tumor matching. The residual errors (resultant table shifts after image matching) were recorded and analyzed to determine the feasibility and reproducibility of each registration method. Intra-class correlation (ICC) was used to determine the reproducibility of image registration methods. Results: Six verification techniques, performed by four observers on 30 CBCTs resulted in 720 observations. The image-guided process took an average of 1 minute for all techniques, with the exception of manual tumor matching which took 4 minutes. The percentage of residual errors within ± 3 mm action level tolerance (current clinical standard) in the left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions respectively was 86.7%, 83.3%, 100% for automatic bone; 76.7%, 63.3%, 100% for automatic carina and 80%, 60%, 100% for automatic tumor matching. For manual matching, the percentage of residual errors was 83.3%, 70%, 90% for bone; 73.3%, 40.3%, 73.3% for carina and 80%, 73.3%, 76.7% for tumor. The ICCs for manual bone matching were 0.75, 0.92, 0.61 in the LR, SI and AP directions respectively; 0.93, 0.90, 0.94 for manual carina and 0.43, 0.41, 0.10 for manual tumor. Conclusions: Cone-Beam CT using bone and carina as target surrogates for image registration is feasible and reliable for patients with locally advanced lung cancer. Manual registration using the tumor, however, is impeded by time and poor correlation (ICC) given the ambiguous delineation of the target on CBCT data sets. Additional enhancements in soft tissue CBCT imaging will help to release the full potential of direct tumor-tumor matching in the future. Percentage residual errors illustrate the disparity amongst the six registration methods explored in this study, thus highlighting the need for an optimal method for cone-beam CT guided lung radiotherapy. Additional studies are currently exploring tumor coverage using the six registration methods. Author Disclosure: J. Higgins, Elekta Inc., B. Research Grant; A. Bezjak, Elekta Inc., B. Research Grant; K. Franks, Elekta Inc., B. Research Grant; CIHR, B. Research Grant; D. Payne, None; J. Cho, None; L. Le, None; J. Bissonnette, None.

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Quantification of Progression of Non-small Cell Lung Cancer in the Interval Between Diagnostic and Radiotherapy Treatment Planning PET Scans

D. V. Eastham1, D. Weerasuriya1, H. Wakelee2, A. Quon3, P. Maxim1, Q. Le1, E. E. Graves1, B. W. Loo1 1 Dept. of Radiation Oncology, 2Dept of Medical Oncology, 3Dept of Radiology-Nuclear Medicine, Stanford Medical Center, Stanford, CA

Purpose/Objective(s): It has been observed that non-small cell lung cancer (NSCLC) frequently progresses in the interval between diagnosis and the initiation of radiation therapy. Our purpose was to quantify NSCLC progression as measured by positron