International Journal of Hematology and Oncology 2021, Vol 31, Num 4 Page(s): 067-074
FDG-PET/CT Imaging-Based Target Volume Delineation for Preoperative Conformal Radiotherapy of Rectal Carcinoma

Melek N. YAVUZ1, Erkan TOPKAN1, A. Aydin YAVUZ1, Mehmet AYDIN2, Cem ONAL1, Mehmet REYHAN2, Ayse KOTEK1, Berrin PEHLIVAN1, A. Fuat YAPAR2

1Baskent University Faculty of Medicine, Department of Radiation Oncology, Adana Medical and Research Center Adana, TURKEY
2Baskent University Faculty of Medicine, Department of Nuclear Medicine, Adana Medical and Research Center, Adana, TURKEY

Keywords: Rectal cancer, Positron emission tomography, Radiation therapy, Gross target volume, Treatment planning
Positron emission tomography (PET) has the potential to improve staging and radiation treatment-planning (RTP) for tumors in various sites. We compared computed tomography (CT) with co-registered 18F-fluorodeoxyglucose (FDG)-PET-CT) as the basis for delineating gross tumor volume (GTV) in patients with rectal carcinoma undergoing preoperative three-dimensional conformal radiotherapy (3D-CRT).

Twenty-three patients diagnosed with localized rectal carcinoma who were candidates for preoperative chemoradiation were evaluated using both CT and PET imaging. For each patient, two 3D-CRT plans were created using the CT and PET-CT fusion data sets. GTV was contoured on both CT (GTVCT) and co-registered PET-CT (GTVPET-CT) images. The resulting GTVCT and GTVPET-CT images were analyzed comparatively.

The median GTVPET-CT (40 cm3) was significantly greater than the median GTVCT (25.7 cm3) (p= 0.0001). The median difference between GTVPET-CT and GTVCT was 65%. The intersected tumor volume determined by the two methods was median 19.7 cm3, and tumor volumes remaining outside CT was median 15.2 cm3. The median volume identified by PET but not by CT (PEToutCT) was 35% of GTVPET-CT, indicating the possibility of a geographic miss in GTV.

Co-registration of PET and CT information in localized rectal cancer may improve the delineation of GTV and theoretically reduce the likelihood of geographic misses, thus potentially having a positive impact on treatment planning.