Comparing step-and-shoot IMRT with dynamic helical tomotherapy IMRT plans for head-and-neck cancer.
OBJECTIVE
The goal of this planning study was to compare step-and-shoot intensity-modulated radiotherapy (IMRT) plans with helical dynamic IMRT plans for oropharynx patients on the basis of dose distribution.


METHODS
Five patients with oropharynx cancer had been previously treated by step-and-shoot IMRT at the University Medical Centre Utrecht, The Netherlands, applying five fields and approximately 60-90 segments. Inverse planning was carried out using Plato, version 2.6.2. For each patient, an inverse IMRT plan was also made using Tomotherapy Hi-Art System, version 2.0, and using the same targets and optimization goals. Statistical analysis was performed by a paired t test.


RESULTS
All tomotherapy plans compared favorably with the step-and-shoot plans regarding sparing of the organs at risk and keeping an equivalent target dose homogeneity. Tomotherapy plans in particular realized sharper dose gradients compared with the step-and-shoot plans. The mean dose to all parotid glands (n = 10) decreased on average 6.5 Gy (range, -4 to 14; p = 0.002). The theoretical reduction in normal tissue complication probabilities in favor of the tomotherapy plans depended on the parotid normal tissue complication probability model used (range, -3% to 32%).


CONCLUSIONS
Helical tomotherapy IMRT plans realized sharper dose gradients compared with the clinically applied step-and shoot plans. They are expected to be able to reduce the parotid normal tissue complication probability further, keeping a similar target dose homogeneity.
van Vulpen
Marco
M
Department of Radiation Oncology, University Medical Centre Utrecht, Utrecht, The Netherlands.
Field
Colin
C
Raaijmakers
Cornelis P J
CP
Parliament
Matthew B
MB
Terhaard
Chris H J
CH
MacKenzie
Marc A
MA
Scrimger
Rufus
R
Lagendijk
Jan J W
JJ
Fallone
B Gino
BG
D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D006801:Humans; D010306:Parotid Gland / Q000000981:diagnostic imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D036542:Tomography, Spiral Computed