Adaptive radiotherapy using helical tomotherapy for head and neck cancer in definitive and postoperative settings: initial results.

AIMS To assess whether routine mid-treatment replanning in head and neck squamous cell carcinoma patients results in meaningful improvements in target or normal tissue dosimetry and to assess which patients derive the greatest benefit. MATERIALS AND METHODS Twenty patients treated with either postoperative chemoradiotherapy or definitive chemoradiotherapy with primary or nodal disease ≥3cm in size were included in this prospective pilot study. Seven patients received adjuvant chemoradiotherapy and 13 received definitive chemoradiotherapy. Patients were planned and treated on a helical tomotherapy system. All patients had a second computed tomography scan after 15 fractions and a new plan based on this was initiated from fraction 20. RESULTS Relative volume changes between computed tomography scans were: GTV 29%; CTV60 (adjuvant patients) 4%; parotid volume 17.5%; median reduction in neck separation 6-7 mm; weight loss 3%. For the group overall and for the definitively treated patient cohort, respectively, adapted plans resulted in reductions in PTV66 D(1) (0.3Gy, P=0.01 and 0.5Gy, P=0.01); PTV54 D(1) (0.6Gy, P<0.0001 and 0.9Gy, P=0.0002); spinal cord maximum (0.5Gy, P=0.004 and 0.6Gy, P=0.04) and volume of skin receiving ≥50Gy (16 cm(2), P=0.01 and 19 cm(2), P=0.001). Definitively treated patients also had a reduction in mean parotid dose (0.6Gy, P=0.046) and volume of normal tissue receiving ≥50Gy (67 cm(3), P=0.02). Patients with nasopharyngeal carcinoma received the greatest benefits with treatment adaptation with reduction in spinal cord maximum 1.2Gy, mean parotid dose 1.2Gy and parotid V(26) 6.3%. There was no significant benefit for adjuvant patients. Other factors associated with greater benefits were greater weight loss and greater reduction in neck separation and higher T stage. CONCLUSIONS There is minimal benefit to routine adaptive replanning in unselected patients, and no benefit in adjuvantly treated patients. Patients with nasopharyngeal carcinoma or with greater weight loss or reduction in neck separation did have clinically significant benefits. These patients should be targeted for adaptive strategies.