Is 9-field IMRT superior to 7-field IMRT in the treatment of nasopharyngeal carcinoma?

Abstract

To evaluate the pros and cons of 9-field intensity modulated radiotherapy (IMRT) compared to 7-field IMRT in the treatment of nasopharyngeal carcinoma (NPC). Ten NPC patients were treated with 7F-IMRT and 9F-IMRT. A dose prescription of 70 Gy was delivered in 35 fractions to gross planning target volume (PTV1). Plan verification was performed via 2D-array and film dosimetry. Dose-Volume Histogram (DVH) parameters were used to evaluate the quality of IMRT plans. Dose data for the investigated planning techniques obeyed the Radiation Therapy Oncology Group (RTOG) protocol no. 0615. The dose delivered to PTV1 and organs-at-risk (OARs) for 9F-IMRT was significantly better than 7F-IMRT, except for OARs which were at a distance from PTV1, such as eyes, optical nerves, and chiasma. Ninety five percent of PTV1 was covered by more than 95% of the prescribed dose (67.75 ± 1.1 Gy and 68.57 ± 1.2 Gy for 7F-IMRT and 9F-IMRT, respectively). The maximum dose to 1% of brainstem was 50.06 ± 2.7 Gy and 47.75 ± 2.6 Gy for 7F-IMRT and 9F-IMRT, respectively. Dose verification showed good agreement with treatment planning system with a maximum deviation for 2D-array of 2.16% ± 0.86 and 1.73% ± 0.33 for 7F-IMRT and 9F-IMRT, respectively. Similarly, radiochromic film reported maximum dose deviations of 3.38% ± 1.68 and 2.77% ± 1.3, respectively. 9F-IMRT provides better homogenous dose to PTV1 and more sparing of OARs over 7F-IMRT for NPC patients, except for OARs which are are a distance from PTV1.