A comparison of radiation treatment plans using IMRT with helical tomotherapy and 3D conformal radiotherapy for nasal natural killer/T-cell lymphoma.

The purpose of this study was to compare radiation treatment plans (RTPs) that used intensity-modulated radiation therapy (IMRT) with helical tomotherapy (HT) or three-dimensional conformal radiation therapy (3D-CRT) for nasal natural killer/T-cell lymphoma (NNKTL). We created RTPs that used IMRT with HT or 3D-CRT for eight NNKTL patients previously treated at our institution and conducted a pilot comparison between the two modalities using the parameters of the target coverage and homogeneity for the planning target volume (PTV) and the maximum and mean doses for organs at risk (OARs). The clinical target volume (CTV) included the gross tumour volume with an additional margin of 1.5 cm and the nasopharynx, palates and nasal cavity; the PTV with the CTV plus a 2 mm margin received a total dose of 50 Gy. IMRT achieved significantly better PTV coverage, with more than 99% of the PTV receiving 90% and 95% of the prescribed dose, whereas 3D-CRT could not provide adequate coverage of the PTV, with 89.1+/-2.6% and 84.5+/-2.7% of the PTV receiving 90% and 95% of the prescribed dose, respectively (both p <0.0001). The homogeneity index was 0.29+/-0.06 for IMRT and 0.046+/-0.022 for 3D-CRT, which was statistically significant (p <0.0001). IMRT tended to provide equivalent or slightly better OAR avoidance than 3D-CRT. In conclusion, 3D-CRT could not provide adequate coverage of the PTV because the PTV was close to many OARs. IMRT should be used for NNKTL because a lack of optimal RTPs could cause local failure.