Effect of the discrepancy of the dose calculation results of different algorithms on CyberKnife lung tumor treatment plan / 中华放射肿瘤学杂志

Objective To evaluate the effect of the discrepancy of the dose calculation results of different algorithms upon the CyberKnife lung tumor treatment plan,and assess the impact of tumor volume and location on the dose calculation results. Methods Thirty-two cases of lung tumors were treated with MultiPlan 5.2.1 planning system of CyberKnife VSI.Ray Tracing and Monte Carlo algorithms were adopted to calculate the dose distribution, and then the calculation results were statistically compared between two algorithms. Results For the enrolled cases,the calculation results of these two algorithms demonstrated that the deviation range of prescription dose coverage of planning target volume (PTV),conformal index,new conformal index and uniformity index were 0.93%~68. 80%, 0.87%~17. 21%,-212.38%~8. 27% and 0%~15. 17%, respectively. Conclusions In the CyberKnife treatment of lung tumors, the volume and location of tumors exert significant impact on the discrepancies of the dose calculation results of different algorithms. The smaller tumor volume and longer beam heterogeneity path are likely to generate a greater discrepancy. It is recommended to adopt or refer to the calculation results of Monte Carlo algorithm to deliver corresponding treatment.

The correlation study between the difference of equal IOL pre-and post Lasik and the degree of my-opia / 中国医师杂志

Objective The difference of the equivalent IOL powers before and after LASIK was calculated by using the Haigis-L formula and Sirius ray-tracing respectively.And study the correlation be-tween the intraocular lens power and the myopic before laser in situ keratomileusis.Methods Ninety-one patients undergoing myopic laser in situ keratomileusis were enrolled, they were divided into 3 groups ac-cording to myopic diopter, group I (-1.00D~-3.00D) 13cases, group II( -3.25D and -6.00D)60 cases, group III(-6.25D~-10.0D)18 cases.The equivalent IOL power before and after LASIK will be calculated using Haigis-L formula and Sirius ray-tracing.The data were analyzed using SPSS20.0.Results 80.2%of the cases calculated using Haigis-L formula were within ±0.50D of the predicted refraction , 94.5%were within ±1.00D, and 100%within ±1.50D.also, within ±0.50D of the predicted refrac-tion 13cases(100%),51cases(85%),9cases(50%) in group I, II, III respectively.74.7% of the eyes calculated using Sirius ray-tracing were within ±0.50D of the predicted refraction , 89.0%were within ± 1.00D, and 100%within ±1.50D.within ±0.50D of the predicted refraction 12cases(92.3%),48cases (80%),8cases(44.4%) in group I, II, III respectively.Conclusions Sirius ray-tracing and Haigis-L formula can calculate IOL power accurately in eyes with prior myopic LASIK, with no need for preoperative data.and there is positive correlation between the intraocular lens power aberration and the myopic diopter before LASIK.

Evaluation of Optical Quality Parameters and Ocular Aberrations in Multifocal Intraocular Lens Implanted Eyes

PURPOSE: We investigated the correlations between optical quality parameters obtained from the double-pass system and ocular aberrations obtained from the ray-tracing aberrometer in multifocal intraocular lens (IOL) implanted eyes. MATERIALS AND METHODS: Twenty eyes from 20 patients were enrolled in this study. Modulation transfer function cutoff frequency, The Strehl ratio, objective scatter index, and objective pseudo-accommodation obtained from the double-pass system were compared with root mean square (RMS) total aberration, RMS higher-order aberration, and spherical aberration obtained from the ray-tracing aberrometer. Additionally, parameters of the double-pass system and ray-tracing aberrometer were compared with manifested refraction values and subjective visual acuity, respectively. RESULTS: There was no statistically significant correlation between optical quality parameters obtained from the double-pass system and ocular aberrations, except between the Strehl ratio and RMS total aberration (r=-0.566, p=0.018). No significant correlations were found between the parameters of both devices, and manifested refraction values or subjective visual acuity. CONCLUSION: Optical quality parameters, especially the Strehl ratio, in multifocal IOL implanted eyes were affected by RMS total aberration. Further studies based on accurate measurements of ocular aberrations and additional optical quality parameters are needed to delineate relationships between optical quality parameters and ocular aberrations in multifocal IOL implanted eyes.

Clinical Comparison of Laser Ray Tracing Aberrometer and Shack-Hartmann Aberrometer

PURPOSE: To compare ocular aberrations measured with a laser ray tracing aberrometer (iTrace(R), Tracey technology) or a Shack-Hartmann aberrometer (Zywave(TM), Bausch & Lomb). METHODS: A total of 68 eyes were included in this study. After manifest refraction (MR) and pupil dilation, aberrations and phoroptor predicted refraction (PPR) were measured with the Zywave(TM) and iTrace(R) devices. The study group was subdivided into a more myopic group (-4.33 D). The root mean square (RMS) errors of the total high order, spherical, coma and 3rd~5th order aberrations were compared. RESULTS: The mean and SE of MR was -4.33+/-2.03 diopter (D), and that of the PPR was -4.20+/-2.13 D in iTrace(R) and -4.42+/-2.23 D in Zywave(TM). A paired-t test of the PPR and MR indicated that they were not statistically different. Zernike coefficients were expressed in the opposite sign in the 2nd and 4th order. The coma and spherical aberrations were larger in Zywave(TM). In a scattergram of each Zernike coefficient, the coefficient of determination (R2) was very low with higher order aberrations, with an exception for coma and spherical aberrations. The correlation of RMS error was greater in the less myopic group. CONCLUSIONS: Taking PPR values as a good reference of MR was a reliable method. For the HOA, only coma and spherical aberrations showed good correlations between Zywave(TM) and iTrace(R), and the correlations for HOA were decreased for the high myopic eyes.

Development of Regularized Expectation Maximization Algorithms for Fan-Beam SPECT Data / 대한핵의학회잡지

PURPOSE: SPECT using a fan-beam collimator improves spatial resolution and sensitivity. For the reconstruction from fan-beam projections, it is necessary to implement direct fan-beam reconstruction methods without transforming the data into the parallel geometry. In this study, various fan-beam reconstruction algorithms were implemented and their performances were compared. MATERIALS AND METHODS: The projector for fan-beam SPECT was implemented using a ray-tracing method. The direct reconstruction algorithms implemented for fan-beam projection data were FBP (filtered backprojection), EM (expectation maximization), OS-EM (ordered subsets EM) and MAP-EM OSL (maximum a posteriori EM using the one-step late method) with membrane and thin-plate models as priors. For comparison, the fan-beam projection data were also rebinned into the parallel data using various interpolation methods, such as the nearest neighbor, bilinear and bicubic interpolations, and reconstructed using the conventional EM algorithm for parallel data. Noiseless and noisy projection data from the digital Hoffman brain and Shepp/Logan phantoms were reconstructed using the above algorithms. The reconstructed images were compared in terms of a percent error metric. RESULTS: For the fan-beam data with Poisson noise, the MAP-EM OSL algorithm with the thin-plate prior showed the best result in both percent error and stability. Bilinear interpolation was the most effective method for rebinning from the fan-beam to parallel geometry when the accuracy and computation load were considered. Direct fan-beam EM reconstructions were more accurate than the standard EM reconstructions obtained from rebinned parallel data. CONCLUSION: Direct fan-beam reconstruction algorithms were implemented, which provided significantly improved reconstructions.

A Novel Method of Normal Estimation for Visualization of Medical Images / 航天医学与医学工程

Objective Normal estimation is the key step for volume visualization. Commonly used methods for normal estimation are based on interpolation and derivative. A novel normal estimation algorithm based on approximation for visualization of medical images was presented in this paper. Method It approximated the density function in local neighborhood with a second-degree polynomial function. The coefficients of the polynomial function were solved by minimizing the error of the approximation and the gradient vector at arbitrary point was obtained directly from the analytical derivative of the density function without interpolation. Because of symmetry, the solution of this equation was simplified.This method was tested in several volume data sets. The results and the generation time by different methods were obtained and compared. Result The results showed that this algorithm produced satisfactory quality images while the computational complexity was not increased. Conclusion This approach is preferable for most applications, especially for medical images reconstruction.