Compositional functional regression and isotemporal substitution analysis: Methods and application in time-use epidemiology.

The distribution of time that people spend in physical activity of various intensities has important health implications. Physical activity (commonly categorised by the intensity into light, moderate and vigorous physical activity), sedentary behaviour and sleep, should not be analysed separately, because they are parts of a time-use composition with a natural constraint of 24 h/day. To find out how are relative reallocations of time between physical activity of various intensities associated with health, herewith we describe compositional scalar-on-function regression and a newly developed compositional functional isotemporal substitution analysis. Physical activity intensity data can be considered as probability density functions, which better reflects the continuous character of their measurement using accelerometers. These probability density functions are characterised by specific properties, such as scale invariance and relative scale, and they are geometrically represented using Bayes spaces with the Hilbert space structure. This makes possible to process them using standard methods of functional data analysis in the L2 space, via centred logratio (clr) transformation. The scalar-on-function regression with clr transformation of the explanatory probability density functions and compositional functional isotemporal substitution analysis were applied to a dataset from a cross-sectional study on adiposity conducted among school-aged children in the Czech Republic. Theoretical reallocations of time to physical activity of higher intensities were found to be associated with larger and more progressive expected decreases in adiposity. We obtained a detailed insight into the dose-response relationship between physical activity intensity and adiposity, which was enabled by using the compositional functional approach.

Development and performance assessment of an advanced Lucas-Kanade algorithm for dose mapping of cervical cancer external radiotherapy and brachytherapy plans.

PURPOSE: The aim of this study was to verify the possibility of summing the dose distributions of combined radiotherapeutic treatment of cervical cancer using the extended Lucas-Kanade algorithm for deformable image registration. MATERIALS AND METHODS: First, a deformable registration of planning computed tomography images for the external radiotherapy and brachytherapy treatment of 10 patients with different parameter settings of the Lucas-Kanade algorithm was performed. By evaluating the registered data using landmarks distance, root mean square error of Hounsfield units and 2D gamma analysis, the optimal parameter values were found. Next, with another group of 10 patients, the accuracy of the dose mapping of the optimized Lucas-Kanade algorithm was assessed and compared with Horn-Schunck and modified Demons algorithms using dose differences at landmarks. RESULTS: The best results of the Lucas-Kanade deformable registration were achieved for two pyramid levels in combination with a window size of 3 voxels. With this registration setting, the average landmarks distance was 2.35 mm, the RMSE was the smallest and the average gamma score reached a value of 86.7%. The mean dose difference at the landmarks after mapping the external radiotherapy and brachytherapy dose distributions was 1.33 Gy. A statistically significant difference was observed on comparing the Lucas-Kanade method with the Horn-Schunck and Demons algorithms, where after the deformable registration, the average difference in dose was 1.60 Gy (P-value: 0.0055) and 1.69 Gy (P-value: 0.0012), respectively. CONCLUSION: Lucas-Kanade deformable registration can lead to a more accurate model of dose accumulation and provide a more realistic idea of the dose distribution.

Prolonged treatment planning can increase real rectal dose in 3D brachytherapy for cervical cancer.

PURPOSE: The purpose of this study was to evaluate the influence of 3D brachytherapy planning time on the real dose distribution. MATERIAL AND METHODS: 10 patients with cervical cancer were evaluated using 2 computed tomography (CT) scans brachytherapy. The first scan was performed after the insertion of UVAG applicators, and the second was done after creating the treatment plan, just before the irradiation of first and third fraction. Both plans were compared in terms of changes of volumes and differences in the dose for high-risk organs using GEC-ESTRO Working Group parameters. RESULTS: The median planning time was 54 minutes (36-64 minutes). The absolute median change of volume for bladder, rectum, and sigmoid was 32.1 cm3 (1.6-108.6 cm3), 5.6 cm3 (0.4-61.8 cm3), and 8.4 cm3 (0.2-74.1 cm3), respectively. This difference led to an increased dose for bladder and sigmoid for D0.1cc by 46.7 cGy and 25.7 cGy, for D1cc by 59.2 cGy and 11.8 cGy, and for D2cc by 44.7 cGy and 10 cGy, respectively, per each fraction. Measured volume change in case of rectum led to a decreased dose per each fraction for D0.1cc with 7.1 cGy, for D1cc with 3.5 cGy, and for D2cc with 4.8 cGy. We observed that statistically significant dependency between the planning time and the dose was proved for rectum. The longer time for planning, the higher dose for rectum. The correlation coefficient for D0.1cc was 0.6715 (p = 0.0061), for D1cc was 0.6404 (p = 0.011), and for D2cc was 0.5891 (p = 0.0197). CONCLUSIONS: Extended treatment planning time for brachytherapy due to the changes in topography of small pelvis can lead to different dose in high-risk organs than previously planned. It seems that the most significant changes are related to rectum.