Superposed epoch analysis of physiological fluctuations: possible space weather connections.

There is a strong connection between space weather and fluctuations in technological systems. Some studies also suggest a statistical connection between space weather and subsequent fluctuations in the physiology of living creatures. This connection, however, has remained controversial and difficult to demonstrate. Here we present support for a response of human physiology to forcing from the explosive onset of the largest of space weather events-space storms. We consider a case study with over 16 years of high temporal resolution measurements of human blood pressure (systolic, diastolic) and heart rate variability to search for associations with space weather. We find no statistically significant change in human blood pressure but a statistically significant drop in heart rate during the main phase of space storms. Our empirical findings shed light on how human physiology may respond to exogenous space weather forcing.

Effects of Interfraction Dose Variations of Target and Organs at Risk on Clinical Outcomes in High Dose Rate Brachytherapy for Cervical Cancer.

Meeting dose prescription is critical to control tumors in radiation therapy. Interfraction dose variations (IDVs) from the prescribed dose in high dose rate brachytherapy (HDR) would cause the target dose to deviate from the prescription but their clinical effect has not been widely discussed in the literature. Our previous study found that IDVs followed a left-skewed distribution. The clinical effect of the IDVs in 100 cervical cancer HDR patients will be addressed in this paper. An in-house Monte Carlo (MC) program was used to simulate clinical outcomes by convolving published tumor dose response curves with IDV distributions. The optimal dose and probability of risk-free local control (RFLC) were calculated using the utility model. The IDVs were well-fitted by the left-skewed Beta distribution, which caused a 3.99% decrease in local control probability and a 1.80% increase in treatment failure. Utility with respect to IDV uncertainty increased the RFLC probability by 6.70% and predicted an optimal dose range of 83 Gy-91 Gy EQD2. It was also found that a 10 Gy dose escalation would not affect toxicity. In conclusion, HRCTV IDV uncertainty reduced LC probabilities and increased treatment failure rates. A dose escalation may help mitigate such effects.

Patient-specific dose correction for prostate postimplant evaluation with flexible timing of postimplant imaging.

PURPOSE: The dosimetric effect of edema on prostate implants have long been realized, but large uncertainties still exist in the estimation of dose actually received by the prostate. This study attempted to develop a new method to accurately estimate dose delivered to the prostate accounting for the variation of prostate volume and seed distribution, edema half-lives, and times for postimplant evaluation. METHODS AND MATERIALS: A series of prostate seed implants for Cs-131, Pd-103, and I-125 with various prostate volumes were simulated in a water phantom using the TG-43 algorithm on the Varian Eclipse treatment planning system. Dose analysis was performed to derive a quantitative relationship between the prostate peripheral dose and the prostate radius with the variation of prostate volume and seed distribution. Using this relationship to calculate dynamically, the total dose accumulated in the prostate (DT ) accounting for the variation of prostate volume and seed distribution and edema half-lives. Moreover, the total dose can be estimated statically based on the prostate volume that can be determined in a computerized tomography (CT) image taken at a time after implantation. The statically estimated total dose (DCT ) was compared with DT to determine optimal imaging times as well as dose correction factors for other imaging times. RESULTS: An inverse power law was established between the prostate peripheral dose and prostate radius. The value of the power was 1.3 for Cs-131 and I-125, and 1.5 for Pd-103, respectively. DT was derived dynamically using the inverse power law. Given the edema half-lives, TE , of 4, 9.3, and 25 days and the volume expansion of 1.1 and 2.0 times of the prostate without edema, the optimal times for postimplant imaging were: 7, 9, and 16 days for TE  = 4 days; 10, 14, and 28 days for TE  = 9.3 days; and 12, 19, 45 days TE  = 25 days, for Cs-131, Pd-103, and I-125, respectively. DCT calculated using the prostate volume determined on the optimal days agreed with DT to 0.0%-1.8% and within 0.3% for most cases. For various prostate volumes, edema half-lives, and nonoptimal times, DCT was able to achieve a 1% accuracy. CONCLUSION: The postimplant dose calculation based on the proposed inverse power law for prostate seed implants with edema has improved the accuracy of postimplant dosimetry with accurate and patient-specific dose corrections accounting for prostate size, edema half-life, and postimplant imaging times. Optimal times for postimplant imaging have been accurately determined, and the high accuracy of postimplant dose calculation can be achieved for both optimal imaging times and nonoptimal imaging times.

Statistical Analysis of Interfraction Dose Variations of High-Risk Clinical Target Volume and Organs at Risk for Cervical Cancer High-Dose-Rate Brachytherapy.

Purpose: High-dose-rate (HDR) brachytherapy for cervical cancer treatment includes significant uncertainties. The aim of this study was to quantify the interfraction dosimetric variation (IDV) of the high-risk clinical target volume (HRCTV) from the prescribed dose and the corresponding effect on organ-at-risk (OAR) dose based on a comprehensive statistical analysis. Methods and Materials: Fifty patients with cervical cancer treated with high-dose-rate intracavity brachytherapy from October 2019 to December 2020 were retrospectively analyzed. The OARs of interest were the rectum, bladder, sigmoid, and bowel. The dosimetric parameters evaluated for all patients was the dose absorbed by 90% of the HRCTV ( D 90 ) and the dose absorbed by 0.1 ( D 0.1 c c ) and 2 cm3 ( D 2 c c ) of each respective OAR. The HRCTV variations were from the prescribed dose and the OAR variations were from the corresponding tolerance dose. Distribution fitting of the HRCTV variations was determined to quantify the IDV. Comparative statistics of the HRCTV variations with the OAR variations were conducted to determine correlations. Results: The mean HRCTV variation from the prescribed dose was -2.53% ± 8.74%. The HRCTV variations and OAR variations showed moderate to weak linear correlations despite the variations being relative to each other, with the bladder D 2 c c having the strongest correlation. There was a 30.0% (±2.62%, 95% confidence interval) probability of underdosing the HRCTV (-5% variation from prescription) and a 23.3% (±2.62%, 95% confidence interval) probability of overdosing the HRCTV (+5% variation from prescription). This tendency to underdose the HRCTV was a consequence of HRCTV IDV not being normally distributed. Conclusions: HRCTV dosimetric variations and OAR variations were complexly correlated with the bladder D 2 c c having the strongest correlation. HRCTV IDV was best described as a left-skewed distribution that indicates a tendency of underdosing the HRCTV. The clinical significance of such dose variations is expected and will be further investigated.