Is there a "mucosa-sparing" benefit of IMRT for head-and-neck cancer?

Purpose: To investigate whether intensity-modulated radiation therapy (IMRT) allows more mucosal sparing than standard three-field technique (3FT) radiotherapy for early oropharyngeal cancer. Methods and Materials: Whole-field IMRT plans were generated for 5 patients with early-stage oropharyngeal cancer according to Radiation Therapy Oncology Group 0022 (66 Gy/30 fractions/6 weeks) guidelines with and without a dose objective on the portion of mucosa not overlapping any PTV. 3FT plans were also generated for the same 5 patients with two fractionation schedules: conventional fractionation (CF) to 70 Gy/35 fractions/7 weeks and concomitant boost (CB) to 72 Gy/40 fractions/6 weeks. Cumulative dose volume histograms (DVHs) of the overall mucosal volume (as per in-house definition) from all trials were compared after transformation into the linear quadratic equivalent dose at 2 Gy per fraction with a time factor correction. Results: Compared with IMRT without dose objective on the mucosa, a 30-Gy maximum dose objective on the mucosa allows ∼20% and ∼12% mean absolute reduction in the percentage of mucosa volume exposed to a dose equivalent to 30 Gy (p < 0.01) and 70 Gy (p < 0.01) at 2 Gy in 3 and 7 weeks, respectively, without detrimental effect on the coverage of other regions of interest. Without mucosal dose objective, IMRT is associated with a larger amount of mucosa exposed to clinically relevant doses compared with both concomitant boost and conventional fractionation; however, if a dose objective is placed, the reverse is true, with up to ∼30% reduction in the volume of the mucosa in the high-dose region compared with both concomitant boost and conventional fractionation (p < 0.01). Conclusions: Intensity-modulated radiation therapy can be potentially provide more mucosal sparing than traditional approaches.