A Phase II Comparative Study of Gross Tumor Volume Definition with or without PET/CT Fusion in Dosimetric Planning for Non–small-cell Lung Cancer (NSCLC): Primary Analysis of Radiation Therapy Oncology Group (RTOG) 0515

Article Outline

• Purpose/Objective(s)
• Materials/Methods
• Results
• Conclusions
• Copyright

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Purpose/Objective(s) 

The RTOG 0515 is a prospective Phase II trial designed to quantify the impact of PET/CT compared to CT alone on radiation treatment plans and to determine the rate of elective nodal failure for PET/CT-derived volumes.

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Materials/Methods 

Each enrolled patient underwent definitive radiation therapy for NSCLC (≥60 Gy) and had two radiation treatment plan (RTP) datasets generated for CT alone and qualitatively assessed PET/CT-derived gross tumor volume (GTV) contours, respectively. Each participating institution assigned two radiation oncologists who alternated tumor delineation and treatment plan construction responsibilities for CT alone and PET/CT datasets. Patients received treatment using the PET/CT-derived plan directed to the GTV+margin. Elective nodal stations were not included. The primary endpoint and the impact of PET/CT fusion on treatment plans was measured by differences of the following variables from each patient: absolute GTV, number of involved nodes, involvement by nodal station, mean lung dose (MLD), the volume of normal lung exceeding 20 Gy (V20), and mean esophageal dose (MED). The rate of regional failure within elective nodal stations was a secondary endpoint. The nonparametric Wilcoxon Matched-Pairs Signed-Ranks test was used with Bonferroni method to keep an overall significance level of 0.05.

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Results 

The RTOG 0515 accrued 52 patients. Forty-seven patients were eligible after 5 patients were excluded; 2 patients were ineligible and 3 were invaluable due to either progressive distant disease or data corruption. The follow-up time for all patients is 12.9 months (2.7–22.2); for surviving patients it was 13.6 months (5.9–22.2). The median age was 64 years (range, 46–84). Tumor staging was as follows: II = 6%; IIIA = 40%; and IIIB = 53%. The GTV was statistically significantly smaller for PET/CT volumes (mean 98.7 vs. 86.2 cc; p < 0.0001). The MLDs for PET/CT plans were slightly lower (19 vs. 17.8 Gy; p = 0.06). There was no statistical difference for the number of involved nodes (mean 2.1 vs. 2.4), V20 (mean 32% vs. 30.8%), or MED (mean 28.7 vs. 27.1 Gy). Nodal contours (scored by nodal station) were altered by PET/CT for 51% of the patients. One patient (2%) has developed an elective nodal failure.

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Conclusions 

The PET/CT-derived tumor volumes were smaller than those derived by CT alone. The resultant MLD was slightly lower. The PET/CT changed nodal GTV contours in 51% of patients. The elective nodal failure rate for GTVs derived by PET/CT is quite low, supporting the RTOG standard of limiting the target volume to the primary tumor and involved nodes.