Dose Calculation Accuracy of Individualized Bulk Electron Density Assignment Approaches for Simulated MRI-only Planning of Thoracic Tumors

Objective This study aimed to investigate the dose calculation accuracy of individualized bulk electron density(IBED)assignment approaches for simulated magnetic resonance imaging(MRI)-only planning of thoracic tumors via the use of a 3 DVH system.Methods 8 patients with thoracic cancer were included in this study.Based on standard planning CT,single-arc dynamic conformal therapy(DCT)and double-arc volumetric modulated arc therapy(VMAT)plans with a6 MV photon beam were generated as a baseline plan(Plan-CT)for each patient.The simulated MRI-only planning(Plan-IBED)was implemented by copying the Plan-CT and forcing the electron density of each region of interest to its average value and recalculating the dose distribution.A 3 DVH system was used to visualize and compare the dosimetric differences between Plan-CT and Plan-IBED,and the criteria of the 3 D-Gamma pass rate were set to 1.0%/1.0 mm.Results The maximum percentage relative deviation(MPRD)of the dosimetric parameters D2,D95,D98,and Dmean of planning tumor volumes(PTVs)between Plan-CT and Plan-IBED was less than 1.3%.The MPRD of the average dose for organs at risk(OARs)was less than 1.5%.The MPRDs of the lung V5,V20,and V30 were 1.29%,3.26%,and 2.78%,respectively.Gamma analysis revealed an averaged pass rate of>95.0%for the body,as well as between 91.9%and 98.2%for OARs.Conclusion The proposed IBED assignment in simulated MRI-only treatment planning allows for dose calculation with comparable accuracy to the baseline plan and is appropriate for thoracic tumors.

A Novel Unsupervised MRI Synthetic CT Image Generation Framework with Registration Network

In recent years,radiotherapy based only on Magnetic Resonance(MR)images has become a hot spot for radiotherapy planning research in the current medical field.However,functional computed tomography(CT)is still needed for dose calculation in the clinic.Recent deep-learning approaches to synthesized CT images from MR images have raised much research interest,making radiotherapy based only on MR images possible.In this paper,we proposed a novel unsupervised image synthesis framework with registration networks.This paper aims to enforce the constraints between the reconstructed image and the input image by registering the reconstructed image with the input image and registering the cycle-consistent image with the input image.Furthermore,this paper added ConvNeXt blocks to the network and used large kernel convolutional layers to improve the network’s ability to extract features.This research used the collected head and neck data of 180 patients with nasopharyngeal carcinoma to experiment and evaluate the training model with four evaluation metrics.At the same time,this research made a quantitative comparison of several commonly used model frameworks.We evaluate the model performance in four evaluation metrics which achieve Mean Absolute Error(MAE),Root Mean Square Error(RMSE),Peak Signal-to-Noise Ratio(PSNR),and Structural Similarity(SSIM)are 18.55±1.44,86.91±4.31,33.45±0.74 and 0.960±0.005,respectively.Compared with other methods,MAE decreased by 2.17,RMSE decreased by 7.82,PSNR increased by 0.76,and SSIM increased by 0.011.The results show that the model proposed in this paper outperforms other methods in the quality of image synthesis.The work in this paper is of guiding significance to the study of MR-only radiotherapy planning.