Prediction of Response to Neoadjuvant Radiotherapy in Patients With Locally Advanced Rectal Cancer by Means of Sequential 18FDG-PET

Journal Article · Sun May 01 04:00:00 EDT 2011 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/j.ijrobp.2010.01.021· OSTI ID:21491711

Everaert, Hendrik ^[1]; Hoorens, Anne ^[2]; Vanhove, Christian ^[1]; Sermeus, Alexandra ^[3]; Ceulemans, Gaetane ^[1]; Engels, Benedikt; Vermeersch, Marieke; Verellen, Dirk ^[4]; Urbain, Daniel ^[3]; Storme, Guy ^[4]

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1. Department of Nuclear Medicine, UZ Brussel, Vrije Universiteit Brussel, Brussels (Belgium)
2. Department of Pathology, UZ Brussel, Vrije Universiteit Brussel, Brussels (Belgium)
3. Department of Gastroenterology, UZ Brussel, Vrije Universiteit Brussel, Brussels (Belgium)
4. Department of Radiation Oncology, UZ Brussel, Vrije Universiteit Brussel, Brussels (Belgium)

Purpose: Morphologic imaging techniques perform poorly in assessing the response to preoperative radiotherapy (RT), mainly because of desmoplastic reactions. The aim of this study was to investigate the potential of sequential 18-fluoro-2-deoxy-D-glucose (18FDG-PET) in assessing the response of rectal cancer to neoadjuvant RT and to determine which parameters can be used as surrogate markers for histopathologic response. Methods and Materials: 18FDG-PET scans were acquired before and during the 5th week after the end of RT. Tracer uptake was assessed semiquantitatively using standardized uptake values (SUV). The percentage differences (%{Delta}) between pre- and post-RT scans in SUV{sub max}, SUV{sub mean}, metabolic volume (MV), and total glycolytic volume (tGV) were calculated. Results: Forty-five consecutive patients with histologically confirmed rectal adenocarcinoma were enrolled. After neoadjuvant RT, 20 of the 45 patients were classified as histopathologic responders and 25 as non-responders. Intense 18F-FDG uptake was seen in all tumors before neoadjuvant RT (average SUV{sub max} 12.9 {+-} 6.0). When patients were classified as histologic responders and nonresponders, significant differences in %{Delta}SUV{sub max} (55.8% vs. 37.4%, p = 0.023) and %{Delta}SUV{sub mean} (40.1% vs. 21.0%, p = 0.001) were observed between the two groups. For %{Delta}MV and %{Delta}tGV, decreases were more prominent in responders but were not significantly different from those in nonresponders. As demonstrated by receiver operating characteristic analysis, %{Delta}SUV{sub mean} was a more powerful discriminator than was %{Delta}SUV{sub max}. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for optimal threshold of %{Delta}SUV{sub mean} (24.5%) were 80%, 72%, 76%, 70%, and 82% respectively. Conclusion: Sequential 18FDG-PET allows assessment of the response to preoperative RT. Both %{Delta}SUV{sub mean} and %{Delta}SUV{sub max} correlate with histopathologic response and can be used to evaluate and compare the effectiveness of different neoadjuvant treatment strategies. The maximum accuracy figures and the positive predictive value figures for both {Delta}%SUV{sub mean} and {Delta}%SUV{sub max} are, however, too low to justify modification of the standard treatment protocol of an individual patient.

• OSTI ID: 21491711
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 1 Vol. 80; ISSN IOBPD3; ISSN 0360-3016
• Country of Publication: United States
• Language: English

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