Influence of CT value division on dose calculation in treatment planning / 中华放射肿瘤学杂志

ABSTRACT

Objective To divide computed tomography (CT) values into different ranges and investigate the influence of CT value division on dose calculation, and to propose a method to combine magnetic resonance imaging (MRI) with assigned CT values.Methods Ten CT images each were collected from patients with head and neck, chest, and pelvic tumors.Random sampling was performed for the CT values of main tissues or organs at the three parts, and then the mean CT value of each tissue or organ was calculated to divide the CT values into different ranges.A virtual phantom was built in the Varian Eclipse treatment planning system, and for the prescribed dose of 100 cGy, the machine output was recorded at different CT values.The influence of different CT value ranges on dose calculation was analyzed.The treatment plans of intensity-modulated radiotherapy were selected from 5 cervical cancer patients, and new CT values were assigned to the planning target volume (PTV) and organs at risk to obtain new CT images.The plans were transferred to the new CT images and compared with the results on the original CT images in terms of dosimetric parameters.Results After dividing the CT values into different ranges and verifying the results in dose calculation, the CT values corresponding to different human tissues or organs were-100 to 100 HU.The influence of CT value variation on dose calculation was within 3%.In the same treatment plan, there were small differences in dosimetric parameters between new CT images and original CT images.Dmax, Dmean, D98%, D95%, D5%, and D2% of PTV were all below 3%, and Dmax and Dmean of the bladder, rectum, small intestine, femoral head, and bone marrow were below 2%.Conclusions The influence of CT value division on dose calculation in the treatment planning for pelvic tumors is acceptable, so it can be used in combination with MRI.