Abstract
2 plans. One plan was computed by incorporating the contrast enhancement in the IMRT planning optimization and calculation. In the second step, the first plan was recalculated on a modified CT. The CT was modified to remove the effect of contrast by reassigning the tissue density in predominant regions of contrast uptake (i.e., bladder and small bowel) to the average tissue density without contrast. Paired t tests were used to assess if there were any statistically significant differences in the mean doses given with and without contrast to the following structures: planning treatment volume (PTV) lymph nodes (LN), PTV vagina, internal target volume (ITV), bladder, small bowel, rectum, nontarget tissue, and femoral heads. Results: The mean dose to the different targets turned out to be slightly higher when the contrast was removed with the difference in the mean dose reaching a statistically significant level. These results suggest that if oral contrast is used for the pelvic planning CT and an IMRT treatment plan is generated with contrast in the bowel, the target volumes will on a daily basis receive a dose which is higher than the prescribed dose. Conclusions: Caution should be used when utilizing contrast in density corrected planning. If a patient is given oral contrast one should correct for it when planning by assigning standard tissue values. Acknowledgment: This project was supported by NCI grants: U10 CA21661, U10 CA37422, ATC U24 CA37422, and the 2009 Pennsylvania Department of Health Formula Grant 4100050889. Author Disclosure: R. Hashem: None. K. Winter: None. R. Ruo: None. L. Portelance: None. A. Jhingran: None. W. Demas: None. G.M. Jacobson: None. D. Gaffney: None.
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