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Study On the Effect of Different CT Value Division On the Dose Distribution of Radiotherapy Plan for Nasopharyngeal Carcinoma

x YAO1,2*, G Gong1 , g zuo2 , Y Yin1 , (1) Radiation Physics Department of Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong (2) University of South China, Hengyang, Hunan


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To divide CT values into different ranges and investigate the influence of CT value division on dose calculation of radiotherapy plan for nasopharyngeal carcinoma (NPC)

Methods: The treatment plans of intensity-modulated radiotherapy were selected from 32 patients with NPC. The average CT values of bone, cavity and soft tissue such as brain, eyeball, optic nerve, lens, parotid gland, masseter and skin were calculated. Four different segmentation methods were used in simulated CT (method 1, segmentation of bone/cavity/organs at risk/other tissues. Method 2, segmentation of bone/cavity/soft tissue. method 3, segmentation of cavity/other tissues. method 4, all tissues as a whole).By assigning the segmented region corresponding to the previous region to the CT value of the previous statistic,the CT value assigned to the remaining region was 0 Hu, and four pseudo-CT images were generated. Then the original plan was transplanted to each pseudo-CT respectively. Recalculate the dose calculation and compare the dosimetric parameters with the original plan

Results: In the same treatment plan, there were small differences in dosimetric parameters between the original CT and new CT after re-assignment of CT value by method 1. The D99, D95 and Dmean of PTV and GTV, the Dmax and D5 of brainstem, the Dmean and D50 of parotid gland and the Dmax of spinal cord, eyeball and lens were all below 1%. Maximum point dose, V30 of parotid gland and Dmax of optic nerve were below 2%. The difference of dosimetric parameters between new plan by method 4 and original plan was the greatest. The Dmax of optic nerve and V30 of parotid gland were up to 5%

Conclusion: Re-assignment of CT value after fine division of each tissue structure have an acceptable impact on the dose calculation results of treatment plan for NPC, so it can be used in combination with MRI


Dosimetry, Treatment Planning, Tissue Density


IM/TH- MRI in Radiation Therapy: MRI for treatment planning

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