Is there a role for an FDG derived biological boost in squamous cell anal cancer?

Journal article

Aim We aim to investigate the potential role for a biological boost in anal cancer by assessing whether subvolumes of high FDG avidity, identified at outset, are spatially consistent during a course of chemoradiotherapy (CRT).

Methods FDG-PET scans from 21 patients enrolled into the ART study (NCT02145416) were retrospectively analysed. A total of twenty-nine volumes including both primary tumours and involved nodes >2 cm were identified. FDG-PET scans were performed prior to treatment and day 8 or 9 of CRT. FDG subvolumes were created using a percentage of maximum FDG avidity at thresholds of 34%, 40%, 50%, on the pre-treatment scans, and 70% and 80% on the subsequent scans. Both FDG-PET scans were deformably registered to the planning CT scan. The overlap fraction (OF) and vector distance (VD) were calculated to assess spatial consistency. FDG subvolumes for further investigation had OF >0.7, as this has been defined in previous publications as a “good” correlation.

Results The median OF between the diagnostic FDG-PET subvolumes 34%, 40% and 50% of max SUV and subsequent FDG-PET subvolumes of 70% of max SUV were 0.97, 0.92 and 0.81. The median OF between the diagnostic FDG-PET subvolumes 34%, 40% and 50% and subsequent FDG-PET subvolumes of 80% were 1.00, 1.00 and 0.92. The median (range) VD values between diagnostic FDG-PET subvolumes 34%, 40% and 50% and subsequent FDG-PET subvolumes of 80% were 0.74mm (0.19-2.94) 0.74mm (0.19-3.39) and 0.71 (0.2-3.29) respectively. Twenty out of 29 volumes (69.0%) achieved a threshold of >0.7 between the FDG 50% subvolume on the diagnostic scan and the FDG 80% subvolume on the subsequent scan.

Conclusion FDG avid subvolumes identified at baseline were spatially consistent during a course of CRT treatment. The subvolume of 50% of SUVmax on the pre-treatment scan could be considered as a potential target for dose escalation.

Authors: Sabbagh, A; Jacobs, C; Cooke, R; Chu, K; Ng, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Clinical Oncology
• Volume: 31
• Issue: 2
• Pages: 72-80
• Publication date: 2018-12-21
• Acceptance date: 2018-11-08
• DOI: 10.1016/j.clon.2018.11.034
• ISSN: 0938-7714
• Keywords: radiotherapy; anal cancer; biological boost; FDG PET scan