Adaptive Dose Painting by Numbers for Head-and-Neck Cancer

Purpose: To investigate the feasibility of adaptive intensity-modulated radiation therapy (IMRT) using dose painting by numbers (DPBN) for head-and-neck cancer. Methods and Materials: Each patient's treatment used three separate treatment plans: fractions 1-10 used a DPBN ([18-F]fluoro-2-deoxy-D-glucose positron emission tomography [18F-FDG-PET]) voxel intensity-based IMRT plan based on a pretreatment 18F-FDG-PET/computed tomography (CT) scan; fractions 11-20 used a DPBN plan based on a 18F-FDG-PET/CT scan acquired after the eighth fraction; and fractions 21-32 used a conventional (uniform dose) IMRT plan. In a Phase I trial, two dose prescription levels were tested: a median dose of 80.9 Gy to the high-dose clinical target volume (CTVhighdose) (dose level I) and a median dose of 85.9 Gy to the gross tumor volume (GTV) (dose level II). Between February 2007 and August 2009, 7 patients at dose level I and 14 patients at dose level II were enrolled. Results: All patients finished treatment without a break, and no Grade 4 acute toxicity was observed. Treatment adaptation (i.e., plans based on the second 18F-FDG-PET/CT scan) reduced the volumes for the GTV (41%, p = 0.01), CTVhighdose (18%, p = 0.01), high-dose planning target volume (14%, p = 0.02), and parotids (9-12%, p < 0.05). Because the GTV was much smaller than the CTVhighdose and target adaptation, further dose escalation at dose level II resulted in less severe toxicity than that observed at dose level I. Conclusion: To our knowledge, this represents the first clinical study that combines adaptive treatments with dose painting by numbers. Treatment as described above is feasible.