Original Article

European Journal of Nuclear Medicine and Molecular Imaging

, Volume 34, Issue 10, pp 1583-1593

First online:

Sequential FDG-PET/CT reliably predicts response of locally advanced rectal cancer to neo-adjuvant chemo-radiation therapy

  • Carlo CapirciAffiliated withDivision of Radiotherapy, “S. Maria della Misericordia” Hospital
  • , Lucia RampinAffiliated withNuclear Medicine and PET Service, “S. Maria della Misericordia” Hospital
  • , Paola A. ErbaAffiliated withRegional Center of Nuclear Medicine, University of Pisa Medical School
  • , Fabrizio GaleottiAffiliated withDivision of Surgery, “S. Maria della Misericordia” Hospital
  • , Giorgio CrepaldiAffiliated withDivision of Oncology, “S. Maria della Misericordia” Hospital
  • , Elena BantiAffiliated withNuclear Medicine and PET Service, “S. Maria della Misericordia” Hospital
  • , Marcello GavaAffiliated withMedical Physics Service, “S. Maria della Misericordia” Hospital
  • , Stefano FantiAffiliated withDepartment of Nuclear Medicine, PET Unit, ‘Policlinico S. Orsola-Malpighi’
  • , Giuliano MarianiAffiliated withRegional Center of Nuclear Medicine, University of Pisa Medical School
    • , Pier Carlo MuzzioAffiliated withDepartment of Radiology, Istituto Oncologico Veneto (IOV)-IRCCS
    • , Domenico RubelloAffiliated withNuclear Medicine Service, PET Unit, “S. Maria della Misericordia” Rovigo Hospital, Istituto Oncologico Veneto (IOV)-IRCCS Email author 

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Abstract

Purpose

Prediction of rectal cancer response to preoperative, neo-adjuvant chemo-radiation therapy (CRT) provides the opportunity to identify patients in whom a major response is expected and who may therefore benefit from alternative surgical approaches. Traditional morphological imaging techniques are effective in defining tumour extension in the initial diagnostic and staging work-up, but perform poorly in distinguishing residual neoplastic tissue from scarring post CRT, when restaging the patient before surgery. Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) is a promising tool for monitoring the effect of anti-tumour therapy. The aim of this study was to prospectively assess the value of sequential FDG-PET scans in predicting the response of locally advanced rectal cancer to neo-adjuvant CRT.

Methods

Forty-four consecutive patients with locally advanced (cT3–4) primary rectal cancer and four patients with pelvic recurrence of rectal cancer were enrolled in this prospective study. Treatment consisted of external beam intensified radiotherapy (50 Gy to the posterior pelvis, 56 Gy to the tumour), chemotherapy (in most cases PVI 5-FU at 300 mg/m2 per day) and, 8–10 weeks later, surgery with curative intent. All patients underwent FDG-PET/CT both before CRT and 5–6 weeks after completing CRT. One patient died before surgery because of acute myocardial infarction, and was therefore excluded from further analysis. Semi-quantitative measurements of FDG uptake (SUVmax), absolute difference (ΔSUVmax) and percent SUVmax difference (Response Index, RI) between pre- and post-CRT PET scans were considered. Results were correlated with pathological response, assessed both by histopathological staging of the surgical specimens (pTNM) and by the tumour regression grade (TRG) according to Mandard’s criteria (patients with TRG1–2 being defined as responders and patients with TRG3–5 as non-responders).

Results

Following neo-adjuvant CRT, of the 45 patients submitted to surgery, 23 (51.1%) were classified as responders according to Mandard’s criteria (8 TRG1 and 15 TRG2), while the remaining 22 (48.9%) were non-responders (9 TRG3 and 13 TRG4–5). Considering all patients, the mean pre-CRT SUVmax was 15.6, significantly higher than the mean value of 5.4 post CRT (p < 0.001). Nevertheless, when stratifying patients according to response to CRT (using Mandard’s criteria), the mean RI was significantly higher in responders than in non-responders (75.9% versus 46.9%,p = 0.0015). Using a 66.2% SUVmax decrease as the cut-off value (identified by ROC analysis) for defining response to therapy, the following parameters were obtained: 79.2% specificity, 81.2% sensitivity, 77% positive predictive value, 89% negative predictive value and 80% overall accuracy.

Conclusion

The results suggest the potential utility of FDG-PET as a complementary diagnostic and prognostic procedure in the assessment of neo-adjuvant CRT response of locally advanced rectal cancer. ΔSUVmax and RI seem the best predictors of CRT response.

Keywords

Rectal cancer Chemo-radiation PET/CT Pathological response