SU-E-J-149: Is Rotational IMRT More Susceptible to Tumor Motion than Dynamic IMRT?
PURPOSE
To investigate whether rotational IMRT is more susceptible to organ motion than IMRT that uses fixed fields.


METHODS
RapidArc and sliding window IMRT treatment plans were each created for five lung and five pancreas cases. Dosimetric effects due to tumor motion were simulatedby incorporating sinusoidal couch motion into plans using in-house Monte Carlo dose verification software. Motion was emulated longitudinally (10 mm) for all cases with additional lateral and vertical motion (5 mm) for pancreatic tumors. Dose distributions of original and modified plans were compared using Gamma analysis and dose profiles.


RESULTS
Preliminary results show that for one lung case, a 95% Gamma pass rate can be achieved using 6%-6-mm criterion for RapidArc versus 8%-8-mm for sliding window. Findings are supported by expanding on a well-known model that demonstrates the effects of intra-fraction motion on the delivery of dynamic intensity modulation.


CONCLUSIONS
Rotational IMRT deliveries are believed to be no more susceptible to organ motion than sliding window IMRT, and results thus far support this conclusion.