Abstract:

Objective To compare dosing levels and exposure of organs at risk（OARs） after treating patients with nasopharyngeal carcinoma using helical tomotherapy （HT） or rapid arc therapy （RA）. Methods Eleven patients were subjected to HT and RA using simultaneously integrated boost，and examined by computed tomography. The two techniques were compared in terms of dose volume histograms（DVH），isodose distribution，dosing of OARs，monitor units （MU），treatment time and Gamma value. Results Both HT and RA showed good target coverage and acceptable OAR sparing. HT was superior to RA for dosing the HI and for sparing certain OARs；for example，HT was associated with lower maximum doses to the cord and lens and parotids. RA was superior to HT for protecting the chiasm and optic nerves and eyes，and it was associated with 60% shorter treatment time and 85% lower MU. Both techniques were associated with a similar Gamma result. Conclusion Both HT and RA are clinically useful for treating nasopharyngeal carcinoma，but RA may be more efficient.

Key words: Nasopharyngeal neoplasms, Helical tomotherapy, Rapid Arc, Radiotherapy, Dosimetry