Po-Thur Eve General-03: The Use of Megavoltage Computed Tomography (MVCT) in Treatment Planning

In modern radiotherapytreatment planning, the information in diagnostic CTimages is used for two purposes: to delineate tumour and surrounding critical structures and to provide an electron density map of the patient that is used to calculate the dose distribution resulting from exposure to a certain beam arrangement. In pelvic cancer patients with hip prostheses, the metal implants produce artifacts in the diagnostic CTimages such that both the location of the tumour and accurate electron densities are either difficult or impossible to obtain. We have used megavoltage CT (MVCT) images for treatment planning in an attempt to quantify the impact of metal artifacts and overcome the problems they introduce. This has been done in three different sets of experiments. The first was a calibration of the megavoltage CT number‐to‐electron density curve using a CIRS phantom. This also allowed for measurements of the impact of metal artifacts on apparent relative electron density in both kVCT and MVCT images. The second was the comparison of treatment plans generated for patients with metal implants using both diagnostic and megavoltage CT studies. This allowed for quantitative measurements of the calculated dosimetric effect of metal artifacts. The final set of experiments compared MVCT and kVCT treatment plans of a water tank containing a stainless steel 316L rod. Dose measurements were taken at various points and compared to the doses calculated using both MVCT and kVCT studies.