Design of a semi-spherical applicator for intraoperative radiotherapy with a linear accelerator and assessment of its dosemetric characteristics based on Monte Carlo simulation / 中华放射医学与防护杂志

Objective:To design a semi-spherical applicator for delivery of semi-spherical dose distributions and assess its dosemetric characteristics.Methods:The applicator was designed in the following way. First, the scattering angle and dose rate of the electron beam having passed through a series of scattering foils of different thicknesses were calculated to determine the thickness of the scattering foil. And then, a series of location model was designed, and the variances of the mean electron energy on the surface of these models were calculated to determine the foil location. Finally, the relationship between the geometric characteristics of the layer and the surface dose on the applicator was established to design the modulator. Monte Carlo (MC) codes EGSnrc/BEAMnrc and EGS4/DOSXYZ were employed to model the head of the Mobetron, the location model, the layer, the semi-spherical applicator, and to calculate the dose distributions.Results:A semi-spherical applicator was designed for electron beam of energy 12 MeV, which consisted of a 2.5 cm diametre cylindrical collimator with 0.5 cm thick wall made of 0.3 cm thick steel and 0.2 cm thick water equivalent material (WEM), a 0.14 cm-thick foil made of tansgen, and a 2.5 cm diametre hollow semi-sphere containing a crescent modulator made of WEM. The dose rate was about 160 cGy/min, and the depth of the 50% isodose curve was 0.85 cm.Conclutions:We designed and performed a MC simulation of a semi-spherical applicator to deliver a semi-spherical dose distribution from a high energy electron beam.

3D-printing non-coplanar template assisted 125I seed implantation for pelvic tumor: individual template design method / 中华放射医学与防护杂志

Objective To compare the dosimetric data between preoperative plans and postoperative verification in computed tomography (CT)-guided and 3D-printing non-coplanar templateassisted 125I seed implantation for pelvic tumor,and to explore the feasibility and accuracy of the personalized template designmethod.Methods A total of 51 patients registered from Dec 2015 to Dec 2016 who were applied with 3D-printing guided template assisted radioactive seed implantations in the hospital were included in this study.A prescribed dose of 110-160 Gy was adopted.3D-printing templates were designed and produced for 51 cases.The dosimetric parameters:Dg0,minimum peripheral dose (mPD),V100,V150,V200,conformal index (CI),external index (EI),and homogeneity index (HI) were compared between pre-and post-plans.Results 51 cases' templates were in place well during the operations.Compared with the preoperative planning,the postoperative D90,V100,V150,V200,CI,EI and HI differences had no statistical difference (P ＞ 0.05);mPD is larger than before (t =-2.96,P ＜ 0.05).Conclusions The main dosimetric parameters of postoperative verification were consistent well with the preoperative planning and have good accuracy,which could meet the clinical requirements.

Initial clinic verification of internal target volume generated with four-dimensional CT and deformable registration / 中华放射肿瘤学杂志

Objective To study preliminary the accuracy of clinical target volume (CTV) and internal target volume (ITV) automatically generated by an in-house deformable registration software on fourdimensional CT (4DCT),and evaluate its feasibility of clinical application.Methods Clinic treated one lung cancer patient and one liver cancer patient were selected for the study.CTV was delineated by radiation oncologist according to a single respiratory phase image of 4DCT scanning,and then deformed to the other phases and generated the CTVdefm on each phase image.Differences between the CTVdefm and CTVmanu were then compared.A composite ITVcopm was created by overlapping all the CTVdefm of 10 phases and compared with the ITVMIP which was contoured on the maximum intensity projection (MIP) CT images,including the shape,volume and geometric center position of the ITV contour.Results For the tested lung case,average volume difference between the CTVdefm and CTV was (-2.59 ± 5.02)％ for the all 10 phases,and the vector departure of the two ITV centers was (1.04 ± 0.89) mm.The ITVcomp almost completely matched the ITVMIP on the tested liver case with a volume difference smaller the 1％ and only 1.4 mm vector departure between their geometric centers.Conclusion The validity of the CTVdefm and ITVcomp gained from automatic deformation of manual delineation reference based on 4DCT images were preliminary evaluated and proved to be good enough for clinic planning.

A GPU-based fast volume CT reconstructive algorithm method / 生物医学工程学杂志

In order to solve the time-consuming problem in volume CT image reconstruction field, we brought forward a fast reconstructive algorithm method to fit the clinic medicine. First, using the great parallel and Floating-Point power of graphic processing unit (GPU), we proposed a volume CT GPU- based reconstruction method. Second, in order to reduce the repetitive operation, we separated the geometry computation and pixel computation. As a result, the computation efficiency was further improved. At last, based on the background of medical engineering, the parallel of volume CT scan and reconstruction was implemented. The results demonstrated that the volume CT reconstruction time could reduce up to 70 times compared to the previous one in common PC by the fast reconstructive algorithm method.

Breathing motion analysis based on cone beam CT images / 生物医学工程学杂志

Breathing motion is a rule-based motion. The traditional breathing motion is described by mathematical model which can not reflect the different properties of different patients or the different breathing periods of the same patient. So, it can not satisfy the needs of the real-time and accurate analysis. Accordingly, in this paper is proposed a method to establish the breathing model through tracking the cone beam CT images which are gained when the patient is breathing freely. The model obtained by the proposed method is similar to the traditional model, which verifies the feasibility and effectiveness of the proposed method. Simultaneously, the proposed method has "real-time" and "accurate" properties, which make it valuable in clinical application.

Multi-spectral MR image segmentation of brain / 生物医学工程学杂志

A novel multi-spectral MR image segmentation method based on multi-modality image fusion is presented in this paper. The basic idea of the method is that every single image is clustered using the FCM clustering method first, and then the final clustering results can be obtained by data fusion. The experimental results show that the presented method separates the white matter, gray matter and cerebro-spinal fluid (CSF) more accurately than does any single image segmentation method.