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

H. Everaert, A. Hoorens, C Vanhove, A. Sermeus, G Ceulemans, B Engels, Marieke Vermeersch, Dirk Verellen, D. Urbain, Guy Storme, Mark De Ridder

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

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(max), SUV(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(max) 12.9 +/- 6.0). When patients were classified as histologic responders and nonresponders, significant differences in %DeltaSUV(max) (55.8% vs. 37.4%, p = 0.023) and %DeltaSUV(mean) (40.1% vs. 21.0%, p = 0.001) were observed between the two groups. For %DeltaMV and %DeltatGV, decreases were more prominent in responders but were not significantly different from those in nonresponders. As demonstrated by receiver operating characteristic analysis, %DeltaSUV(mean) was a more powerful discriminator than was %DeltaSUV(max). The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for optimal threshold of %DeltaSUV(mean) (24.5%) were 80%, 72%, 76%, 70%, and 82% respectively.

CONCLUSION: Sequential 18FDG-PET allows assessment of the response to preoperative RT. Both %DeltaSUV(mean) and %DeltaSUV(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(mean) and Delta%SUV(max) are, however, too low to justify modification of the standard treatment protocol of an individual patient.
Original languageEnglish
Pages (from-to)91-96
JournalInt J Radiat Oncol Biol Phys
Volume80
Issue number1
Publication statusPublished - 2011

Keywords

  • radiotherapy
  • rectal cancer
  • neoadjuvant radiotherapy

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