Reirradiation of nasopharyngeal carcinoma focusing on volumetric modulated arcs with flattening filter-free beams.

OBJECTIVE

The goal of this study was to assess the role of flattening filter-free (FFF) beams in volumetric modulated arc radiotherapy for patients with recurrent nasopharyngeal carcinoma (rNPC).

METHODS

13 patients with rNPC were replanned for FFF RapidArc(®) (RA-FFF) and conventional RapidArc (RA) (Varian Medical Systems, Palo Alto, CA). Quantitative evaluation was performed for the planning target volume (PTV) and organs at risk (OARs). Phantom dose verifications, treatment delivery time and monitor units (MUs) were also assessed.

RESULTS

Each technique delivered similar doses to the PTV. RA-FFF had a better sparing effect on the brain stem and normal tissue when compared with RA, whereas RA provided lower mean doses to the skin. No significant difference between the two techniques could be established for other OAR parameters. Both techniques showed equally good gamma scores in dosimetric verification. RA-FFF required more MUs than RA, whereas the delivery time for RA-FFF was slightly shorter than for RA.

CONCLUSION

Both treatment plans met the planning objectives. Dose measurements also showed good agreement with computed doses. In addition to slightly faster delivery times, RA-FFF produced better sparing of brain stem and normal tissue with uncompromised target coverage compared with RA.

ADVANCES IN KNOWLEDGE: FFF beams have recently been assembled for clinical use. Our findings show RA-FFF is useful in the salvage treatment of rNPC owing to better brain stem and normal tissue sparing with uncompromised target coverage compared with RA. This may be beneficial in the case of tumour invasion close to the brain stem.