A pilot study investigating the role of F-FDG-PET in the early identification of chemoradiotherapy response in anal cancer.

Introduction: Anal cancer (AC) is F-FDG-PET avid and has been used to evaluate treatment response several months after chemoradiotherapy. This pilot study aimed to assess the utility of semi-automated contouring methods and quantitative measures of treatment response using F-FDG-PET imaging at the early time point of 1-month post-chemoradiotherapy.

Methods: Eleven patients with AC referred for chemoradiotherapy were prospectively enrolled into this study, with 10 meeting eligibility requirements. F-FDG-PET imaging was obtained pre-chemoradiotherapy (TP1), and then 1-month (TP2), 3-6 months (TP3) and 9-12 months (TP4) post-chemoradiotherapy. Manual and semi-automated (Threshold) contouring methods were used to define the primary tumour on all F-FDG-PET images. Resultant contours from each method were interrogated using quantitative measures, including volume, response index (RI), total lesion glycolysis (TLG), SUV , SUV and SUV . Response was assessed quantitatively as reductions in these measures and also qualitatively against established criteria.

Results: Nine patients were qualitatively classified as complete metabolic responders at TP2 and all 10 at TP3. All quantitative measures demonstrated significant (P < 0.05) reductions at TP2 for both Manual and Threshold methods. All reduced further at TP3 and again at TP4 for Threshold methods. TLG showed the highest reduction at all post-chemoradiotherapy time points and classified the most responders for each method at each time point. All patients are recurrence-free at minimum 4-year follow-up.

Conclusion: Based on our small sample size, semi-automated methods of disease definition using F-FDG-PET imaging are feasible and appear to facilitate quantitative response classification of AC as early as 1-month post-chemoradiotherapy. Early identification of treatment response may potentially improve disease management.