Application of Medical Imaging for Dosimetry and Evaluation of the Required Irradiation Time in X-Ray Radiotherapy for Liver Cancer to Prevent Radiation Overdose

To prevent any tissue from absorbing the excess dose during radiotherapy, dosimetry and irradiation time calculation must be carried out as accurately as possible. Water phantoms and the medical internal radiation dose (MIRD) methods are appropriate for dosimetry. At present, measurement of the required irradiation time in clinical settings is done only based on estimation.

Our primary objective was to determine the accurate dosimetry of liver tissue for the course of X-ray radiotherapy and the secondary objective was to calculate the required irradiation time for this course.

First, the Hounsfield unit (HU) of every existing tissue in the abdominal region was defined. Then, their constituent materials were determined and fed into MATLAB and MCNPX codes, in sequence. The abdominal region was completely filled up with the related components to obtain its own radiodensity. Afterward, the liver tissue was contoured and separated in the middle of the abdominal region. The exact information of the separated liver tissue was extracted as data, and these data were converted to MCNPX nuclear code. The accurate irradiation time was then obtained by keeping up a proper proportion between absorbed dose and X-ray activity.

The accurate duration of X-ray treatment was calculated via a highly developed software application (Delphi 7 programming language) by making an equivalence between the absorbed dose and X-ray activity. This calculation was performed based on the energy of X-ray photons and interpolating the value of the required treatment dose according to the values of absorbed doses obtained by the software package.

This technique can be used for every patient based on his/her own digital imaging and communications in medicine (DICOM) images. The required time for irradiation of liver tissues is determined to reach the desired absorbed dose during X-ray therapy for analogous liver tissues. This method might also be applicable to other types of radiation therapy including proton therapy and neutron therapy and for various soft tissues with different shapes and sizes.