Comparing step-and-shoot IMRT with dynamic helical tomotherapy IMRT plans for head-and-neck cancer
van Vulpen M, Field C, Raaijmakers CPJ, Parliament MB, Terhaard CHJ, MacKenzie MA, Scrimger R, Lagendijk JJW, Fallone BG
International Journal of Radiation Oncology*Biology*Physics 01 August 2005 (Vol. 62, Issue 5, Pages 1535-1539)

Comparison of dose distribution between tomotherapy plan and step-and-shoot plan for same patient. Same computed tomography slice shown for both plans. Note, steeper dose gradient for tomotherapy plan compared with step-and-shoot plan

Purpose: 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 and Materials: 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 6090 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%).

Conclusion: 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.