SU‐GG‐J‐100: A Comparison of the Effect of Intra‐Fraction Motion on Tomotherapy and IMRT Delivery Systems

Abstract

Purpose: To illustrate the variation in dose distribution caused by a moving target volume that can be expected from a Tomotherapy treatment plan and a conventional step and shoot intensity modulated radiation therapy (IMRT) plan. Method and Materials: A two‐dimensional Motionsim platform was used with Mapcheck2 to obtain the measurements. Tumor motion with a superior‐inferior amplitude of 1cm and lateral amplitude of 0.2cm was used. Similar IMRT treatment plans were created for a volume vertically centered on the diode array using Tomotherapy and CMS Xio, respectively. A planned dose of 2Gy per fraction was delivered onto both a stationary Mapcheck2 diode array, as well as on the array when the tumor motion was simulated. The process was then repeated using a 9 beam step and shoot IMRT plan on a conventional Linac. Results: When compared to the plan with a stationary target, the motion file introduced single fraction dose variation at the superior and inferior borders of the field of up to 20%. This was the case for both the helical Tomotherapy and co‐planar IMRT scenarios. Detectors inferior of the target volume received more dose than planned, while superior detectors received up to 20% less dose than planned. The penumbra for these resulting hot/cold spots for the Tomotherapy plan was larger than for the IMRT plan. Conclusion: The results reiterate the need for tumor motion management when IMRT is used during treatment. Motion effects may even be more pronounced for helical tomotherapy treatments than for conventional IMRT.