Impact of Combined PET/CT on Radiotherapy Treatment Planning and Outcomes in Esophageal Cancer.

e15519 Background: To date, there is no universally accepted method to accurately delineate the gross tumor volume (GTV) of primary esophageal cancer in patients undergoing radiotherapy (RT). This prospective study aims to determine the impact of PET/CT on RT planning and outcomes in patients with localized esophageal cancer. Methods: 57 eligible patients with localized esophageal cancer were recruited between June 2003 and May 2008. All underwent PET/CT scanning in the RT treatment position and received treatment planned using the PET/CT dataset. Of these, 13 (23%) had metastatic disease detected on PET and 3 patients had no radical RT, while another 3 patients had missing planning PET/CT data (excluded from planning component analysis). GTV was defined separately on PET/CT (GTV-PET) and CT (GTV-CT) data sets. A corresponding planning target volume (PTV) was generated for each patient. Volumetric and spatial analysis quantified the proportion of FDG-avid disease not included in CT-based volumes. Clinical data was collected for 38 patients treated radically to determine locoregional control and overall survival rates. Results: Mean age was 67 years (range: 32 - 88). Median follow up was 4 years (range: 2.7 – 6.8). FDG-avid disease would have been excluded from GTV-CT in 29 patients (76%; median volume = 17%, range: 1-100%). In 5 patients, FDG-avid disease would have been completely excluded from the PTV-CT (Grade 1 geographic miss; median volume = 6%, range: 2-92%). For 8 patients, less than 95% of PTV-PET would have received at least 95% of prescription dose based on the CT-based plan (Grade 2 geographic miss). GTV-CT underestimated the cranial and caudal extent of FDG-avid tumor in 14 (37%) and 10 (26%) patients respectively. There were no significant differences in radiation doses to the lungs and liver. 5-year overall survival and locoregional failure free survival were 24% and 42% respectively. Conclusions: PET/CT prevented futile RT for 1 in 4 patients and avoided geographic misses without significant impact on dose-limiting tissues in apparently localized esophageal cancer. However, survival remains suboptimal and indicates the need for further improvement in planning and therapeutic paradigms.