Bone Dose Calculations In Radiotherapy Based On The Updated VCH Adult Male Phantom

Ionizing radiation is widely used in the areas of medical science, scientific researchand industy, and the damage of human body caused by radiation become more serious，especially for bone marrow. Red bone marrow (RBM) is an important dose-limiting tissuewhich is associated with high radiosensitivity but difficult to be identified from usualclinical medical images, such as CT and MRI. In radiotherapy applications, RBM isassumed to be a homogeneous mixture with the other parts of skeleton which may resultinsignificant deviation. We investigated in detail the dose distribution in bone especiallyRBM in case of radiotherapy by use of the voxel-based visible Chinese human（VCH）adult male phantom.The skeleton at167different bone sites of this voxel-based phantom was identified asfour suborgans: cortical bone (CB), trabecular bone (TB), RBM, and yellow bone marrow(YBM. Using the commercial linear acceleration treatment head, dose distribution in thephantom of each beam angle and the plan using six equi-spaced beam angles weresimulated by the Monte Carlo system of BEAMnrc and DOSXYZnrc.The main research results are as follows:(1) The percentage of the different bone sites mass to the total bone mass is2%lessthan that of CAM reference value, and1%less than the ICRP89reference values (errorrange）. In general, the volume fraction and calculated cellularity of VCH phantom are ingood agreement with the reference values.(2) The simulation results of dose distributions agree with the measured results, theerror between each other is less than4%, which is lower than the dose calculation errorstandard (less than5%） provided by reference. Therefore, the virtual source modelobtained from simulation based on Monte Carlo method for dose calculation ofradiotherapy could be using.(3) In the case of prostate cancer radiotherapy, difference in absorbed dose betweenRBM, CB and TB is up to20%, while it is much smaller, namely≤3.1%, between RBMand YBM. And RBM dose is positive correlate to the PTV size. However, when beam angle is close to the lateral sides, the dose volume of RBM with different PTVs staysapproximately the same.Using the dose to homogeneous mixture of bone marrow as an estimate of the dose toRBM is valid, especially when the RBM is not available in the computational phantom. Asthe RBM playing an important role in radiation therapy planning and radiation riskassessing, the human skeletal system developed in this study can be used to as a referenceof the RBM dose in considering the selection of beam angles, the weight of each beam andthe ranges of PTV in radiotherapy plans.