Difference of the MU Calculation from RTP System Using the Contrast-enhanced CT

Keimyung Medical Journal 2010;29(2):120-128.

Contrast-enhanced CT를 이용한 방사선치료계획에서의 MU 계산 변화

오영기; 최태진; 김진희; 김옥배

Abstract

To use contrast-enhanced CT is more effective in the calculation of radiation dose from RTP(radiation therapy planning) if the results of dose calculation is not significantly different with non-enhanced CT. In this study; we investigated the usefulness of contrast-enhanced CT to calculate the radiation dose in the RTP from quantitative comparison with the calculation results of the non-enhanced CT. The calculation of radiation dose and MU (monitor unit) was carried out for selected 3-5 patients treated by 3D CRT (3-dimensional conformal radiation therapy) from separated subparts of brain; head and neck; breast; lung; liver; and pelvis; respectively. The method and algorithm for calculation of radiation dose and MU were SAD (source-to-axis distance) technique and convolution-superposition method. The isodose curves of radiation dose were normalized to 100% at the isocenter and MU for prescription dose was calculated at the same point. The difference from the isodose lines could not be distinguished quantitatively for most of all patients of each subpart. The result of MU calculation based contrast-enhanced CT in the brain case were slightly increased to about 0.3% from results of non-enhanced CT. It was calculated to about 0.8%-increase in the liver; and about 0.6% in the pelvis. But it was decreased to about 0.8% in the head and neck; about 1.0% in the lung; and about 0.8% in the breast. Especially; in one breast patient the result was greatly decreased to 2.4%. These results were shown that the difference of MU by the use of contrast medium is not significant; but the change of SSD (sourceto- surface distance) from the patient motion or respiration effect have affect on the MU calculation.

Key Words: Contrast medium, CT, Monitor unit, Radiation treatment planning