Tumor volume definitions in head and neck squamous cell carcinoma – Comparing PET/MRI and histopathology
Emmanouil Terzidis, Jeppe Friborg, Ivan R. Vogelius, Giedrius Lelkaitis, Christian von Buchwald, Anders B. Olin, Helle Hjorth Johannesen, Barbara Malene Fischer, Irene Wessel, Jacob H. Rasmussen
Abstract
Background and purpose: In cancer treatment precise definition of the tumor volume is essential, but despite development in imaging modalities, this remains a challenge. Here, pathological tumor volumes from the surgical specimens were obtained and compared to tumor volumes defined from modern PET/ MRI hybrid imaging. The purpose is to evaluate mismatch between the volumes defined from imaging and pathology was estimated and potential clinical impact. Methods and Materials: Twenty-five patients with head and neck squamous cell carcinoma were scanned on an integrated PET/MRI system prior to surgery. Three gross tumor volumes (GTVs) from the primary tumor site were delineated defined from MRI (GTV MRI ), PET (GTV PET ) and one by utilizing both anatomical images and clinical information (GTV ONCO ). Twenty-five primary tumor specimens were extracted en bloc, scanned with PET/MRI and co-registered to the patient images. Each specimen was sectioned in blocks, sliced and stained with haematoxylin and eosin. All slices were digitalized and tumor delineated by a head and neck pathologist. The pathological tumor areas in all slices were interpolated yielding a pathological 3D tumor volume (GTV PATO ). GTV PATO was compared with the imaging GTV's and potential mismatch was estimated. Results: Thirteen patients were included. The mean volume of GTV ONCO was larger than the GTV's defined from PET or MRI. The mean mismatch of the GTV PATO compared to the GTV PET , GTV MRI and GTV ONCO was 31.9 %, 54.5 % and 27.9 % respectively, and the entire GTV PATO was only fully encompassed in GTV ONCO in 1 of 13 patients. However, after the addition of a clinical 5 mm margin the GTV PATO was fully encompassed in GTV ONCO in 11 out of 13 patients. Conclusions: Despite modern hybrid imaging modalities, a mismatch between imaging and pathological defined tumor volumes was observed in all patients. A 5 mm clinical margin was sufficient to ensure inclusion of the entire pathological volume in 11 out of 13 patients.