Preliminary analysis of the sequential simultaneous integrated boost technique for intensity-modulated radiotherapy for head and neck cancers

The aim of this study was to compare three strategies for intensity-modulated radiotherapy (IMRT) for 20 head-and-neck cancer patients. For simultaneous integrated boost (SIB), doses were 66 and 54 Gy in 30 fractions for PTVboost and PTVelective, respectively. Two-phase IMRT delivered 50 Gy in 25 fractions to PTVelective in the First Plan, and 20 Gy in 10 fractions to PTVboost in the Second Plan. Sequential SIB (SEQ-SIB) delivered 55 Gy and 50 Gy in 25 fractions, respectively, to PTVboost and PTVelective using SIB in the First Plan and 11 Gy in 5 fractions to PTVboost in the Second Plan. Conformity indexes (CIs) (mean +/- SD) for PTVboost and PTVelective were 1.09 +/- 0.05 and 1.34 +/- 0.12 for SIB, 1.39 +/- 0.14 and 1.80 +/- 0.28 for two-phase IMRT, and 1.14 +/- 0.07 and 1.60 +/- 0.18 for SEQ-SIB, respectively. CI was significantly highest for two-phase IMRT. Maximum doses (Dmax) to the spinal cord were 42.1 +/- 1.5 Gy for SIB, 43.9 +/- 1.0 Gy for two-phase IMRT and 40.3 +/- 1.8 Gy for SEQ-SIB. Brainstem Dmax were 50.1 +/- 2.2 Gy for SIB, 50.5 +/- 4.6 Gy for two-phase IMRT and 47.4 +/- 3.6 Gy for SEQ-SIB. Spinal cord Dmax for the three techniques was significantly different, and brainstem Dmax was significantly lower for SEQ-SIB. The compromised conformity of two-phase IMRT can result in higher doses to organs at risk (OARs). Lower OAR doses in SEQ-SIB made SEQ-SIB an alternative to SIB, which applies unconventional doses per fraction.