title: Comparison of tumor volume between PET and MRI in cervical cancer with hybrid PET/MR.
abstract: OBJECTIVE
  This study aimed to compare the tumor volume between magnetic resonance imaging-defined gross tumor volume (MR-GTV) and positron emission tomography-defined GTV (PET-GTV) in cervical cancer with hybrid PET/MR.
  
  
  METHODS
  Twenty-seven patients with cervical cancer underwent PET/MR pelvic examination before radiotherapy. The MR-GTV was manually outlined on T2-weighted MR images. The PET-GTV was autocontoured on PET images using a 40% maximum standardized uptake value threshold. Results were analyzed by Pearson analysis, Bland-Altman plot, and 1-way analysis of variance.
  
  
  RESULTS
  Magnetic resonance imaging-GTV significantly correlated with PET-GTV (r(2) = 0.797, P < 0.001). The Bland-Altman plot showed a bad agreement between MR-GTV and PET-GTV. The PET-GTV underestimated the MR-GTV in 23 of 27 tumors. Patients were divided into the following 3 groups according to MR-GTV: less than 14 mL (n = 6), 14 to 62 mL (n = 12), and 62 mL or more (n = 9). The mean (SD) MR-GTV, PET-GTV, ratio, and overlap between MR-GTV and PET-GTV for the less than 14 mL cohort were 9.6 (2.6) mL, 16.7 (10.1) mL, 0.77 (0.40), and 0.47 (0.20), respectively. The PET-GTV overestimated MR-GTV in 4 of the 6 lesions by a mean (SD) of 11.1 (9.4) mL. Among the 14 to 62 mL cohort, the mean (SD) MR-GTV, PET-GTV, ratio, and overlap were 38.6 (14.5) mL, 24.9 (8.6 mL), 1.54 (0.25), and 0.87 (0.08), respectively. The PET-GTV underestimated MR-GTV for 12 tumors by a mean (SD) of 13.7 (8.4) mL. In the 62 mL or more cohort, the mean (SD) MR-GTV, PET-GTV, ratio, and overlap were 85.9 (25.8) mL, 54.3 (14.1) mL, 1.61 (0.35), and 0.87 (0.09), respectively. The PET-GTV underestimated MR-GTV 9 tumors by a mean (SD) of 31.6 (19.5) mL. The ratio and overlap differences were statistically significant among groups (F = 14.619, P < 0.001; F = 25.134, P < 0.001).
  
  
  CONCLUSIONS
  Tumor volume discrepancies were observed between MR-GTV and PET-GTV for cervical cancer. With an increasing tumor volume, there was an increase in the difference between MR-GTV and PET-GTV. In addition, larger tumors had a higher degree of overlap compared with small tumors.
authors.affiliation: Departments of *Radiology, †Nuclear Medicine, and ‡Oncology, Shengjing Hospital of China Medical University, Shenyang, China.
authors.forename: Shaomin
authors.initials: S
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Xin
authors.forename: Qiyong
authors.initials: Q
authors.lastname: Guo
authors.forename: Jietao
authors.initials: J
authors.lastname: Ma
authors.forename: Quanmei
authors.initials: Q
authors.lastname: Ma
authors.forename: Hongzan
authors.initials: H
authors.lastname: Sun
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals; D047368:Tumor Burden; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18