Combined structural and functional imaging has been shown to improve tumour localization and help assess the extent of nodal and metastatic spread, leading to more accurate staging and appropriate changes in radiation therapy planning. But while previous reports suggest that both the sensitivity and specificity of PET/CT are superior to either CT or PET alone, there is little information available regarding clinical outcomes.
Now, researchers at the Medical College of Wisconsin (Milwaukee, WI) have evaluated the clinical outcomes of head-and-neck-cancer patients receiving PET/CT-guided radiation therapy. The study results demonstrated that the use of PET/CT for treatment planning in head-and-neck carcinoma patients provided excellent local and regional disease control when compared with CT-based planning (Int. J. Radiat. Oncol. Biol. Phys. 70 678).
"PET/CT provides a higher level of confidence that we are not missing tumours as we attempt to lessen treatment side effects by delivering radiation therapy that tightly conforms in three dimensions to a given tumour volume," said Christopher Schultz, professor of radiation oncology at the Medical College of Wisconsin. "Most importantly, the PET/CT-guided conformal radiotherapy was clearly no worse and based on our early results, may in fact lead to superior clinical outcomes as compared to CT only planned radiotherapy."
Between December 2002 and August 2006, the Wisconsin team examined 42 patients with head-and-neck squamous-cell carcinoma. All patients underwent PET/CT for staging and as part of their radiotherapy treatment planning and were observed for at least six months following their treatment, with a mean follow-up time of 32 months. Seven subjects were treated using 3D conformal radiotherapy while the remaining 35 received intensity-modulated radiation therapy (IMRT).
The overall survival of the 42 study patients was 82.8% at two years and 74.1% at three years. The disease-free survival was 71% and 66.9% at two and three years, respectively. Survival times for the conformal radiotherapy and IMRT groups were similar. Seven treatment failures were observed, with a mean time to recurrence of 9.4 months. The cumulative risk of recurrence was 18.7%.
The survival rates of the patients in this study were superior to those found in the Radiation Therapy Oncology Group 9003 trial (the largest randomized radiotherapy trial for locally advanced head-and-neck cancer), in which patients received standard fractionation or accelerated fractionation with concomitant boost. The survival outcomes for the 42 patients were comparable to published results of several smaller studies of head-and-neck-cancer patients receiving IMRT.
The Wisconsin study also examined the correlation between the maximum standard uptake value (SUV) obtained on the PET scan and tumour recurrence. All patients had abnormal FDG uptake on the planning PET scans. However, the researchers noted that that the maximum SUV was not predictive of recurrence, with mean values of 12.0 for treatment failures versus 11.7 for all patients. As such, they concluded that dose escalation based on SUV is unlikely to be a successful treatment strategy.