The Study of Field Equivalence Determined by the Modeled Percentage Depth Dose in Electron Beam Radiation Therapy.

INTRODUCTION: This study presents an empirical method to model the curve of electron beam percent depth dose (PDD) by using the primary-tail function in electron beam radiation therapy. The modeling parameters N and n can be used to predict the minimal side length when the field size is reduced below that required for lateral scatter equilibrium (LSE) in electron radiation therapy. METHODS AND MATERIALS: The electrons' PDD curves were modeled by the primary-tail function in this study. The primary function included the exponential function and the main parameters of N and µ, while the tail function was composed of a sigmoid function with the main parameter of n. The PDD of five electron energies was modeled by the primary and tail function by adjusting the parameters of N, µ, and n. The R 50 and R p can be derived from the modeled straight line of 80% to 20% region of PDD. The same electron energy with different cone sizes was also modeled by the primary-tail function. The stopping power of different electron energies in different depths can also be derived from the parameters N, µ, and n. RESULTS: The main parameters N and n increase but µ decreases in the primary-tail function for characterizing the electron beam PDD when the electron energy increased. The relationship of parameter n, N, and ln(-µ) with electron energy are n = 31.667E 0 - 88, N = 0.9975E 0 - 2.8535, and ln(-µ) = -0.1355E 0 - 6.0986, respectively. Percent depth dose was derived from the percent reading curve by multiplying the stopping power relevant to the depth in water at a certain electron energy. The stopping power of different electron energies can be derived from n and N with the following equation: stopping power = (-0.042ln(N E 0 ) + 1.072)e (-nE0 · 5 · 10-5 + 0.0381)·x , where x is the depth in water. The lateral scatter equivalence (LSE) of the clinical electron beam can be described by the parameters E 0, n, and N in the equation of Seq = (n E 0 - N E 0 )0.288/(E 0/n E 0 )0.0195. The LSE was compared with the root mean square scatter angular distribution method and shows the agreement of depth dose distributions within ±2%. CONCLUSIONS: The PDD of the electron beam at different energies and cone sizes can be modeled with an empirical model to deal with what is the minimal field size without changing the percent depth dose when approximate LSE is given in centimeters of water.

Anesthetic management of precise radiotherapy under apnea-like condition.

OBJECTIVE: To study the safety and feasibility of implementation of precise radiotherapy with inducement of an apnea-like condition. METHODS: Two patients with lung tumors underwent precise radiotherapy under an apnea-like condition. The apnea-like condition was induced 11 times between the two patients for tumor localization and treatment. The changes in the blood oxygen saturation, blood pressure, heart rate, and end-tidal carbon dioxide during the apnea-like periods were observed, and the incidence of adverse reactions was recorded. RESULTS: The average apnea-like time was 6.2 minutes (range, 3-9 minutes), and the average radiotherapy time was 4.6 minutes (range, 1-7 minutes). The lowest blood oxygen saturation level was 97%, with a change of <1%. The heart rate and average arterial blood pressure increased during the apnea-like periods. Contact sores appeared on the patients' posterior pharyngeal wall after the first apnea-like period; no other adverse events occurred. CONCLUSION: Precise radiotherapy under an apnea-like condition is safe and feasible for patients with lung tumors.

Comparison between the effects of elective nodal irradiation and involved-field irradiation on long-term survival in thoracic esophageal squamous cell carcinoma patients: A prospective, multicenter, randomized, controlled study in China.

BACKGROUND: This study's initial results revealed significant decreases in treatment-related esophagitis and pneumonitis cases in patients with thoracic esophageal squamous cell carcinoma (ESCC) treated with involved-field irradiation (IFI), compared to elective nodal irradiation (ENI). This report outlines the long-term trial results, specifically; overall survival (OS), progression-free survival (PFS), metastasis-free survival (MFS), and locoregional progression-free survival (LRFS). MATERIALS AND METHODS: Stage II-III thoracic ESCC patients were assigned randomly, in a 1:1 ratio, into either the ENI or IFI arm. Radiation therapy was delivered once a day in 1.8-2.0 Gy fractions to a total dose of 60.0-66.0 Gy to the gross tumor volume and 50.0-54.0 Gy to the clinical target volume. The primary endpoints were acute treatment-related esophagitis and pneumonitis. The results for the primary endpoints were previously published in 2018. In this article, we analyzed the secondary endpoints including PFS, LRFS, MFS, and OS. RESULTS: Between April 2012 and October 2016, 228 patients from nine participating centers in China were enrolled into this study and randomly assigned to two treatment groups. For ENI and IFI groups, respectively, the results showed similarity and were as follows: median PFS (20.3 months vs 21.4 months), OS (32.5 months vs 34.9 months), MFS (28.2 months vs 26.0 months), and LRFS (25.0 months vs 26.6 months). In particular, respective OS rates in the ENI and IFI groups were 84.6% and 82.5% after 1 year, 45.1% and 48.7% after 3 years, and 29.8% and 30.7% at 5 years. PFS rates after 1, 3, and 5 years were 58.9%, 34.2%, and 26.9%, respectively, in the ENI arm compared to 64.4%, 30.8%, and 27.7%, respectively, in the IFI arm. Multivariate analysis identified clinical stage and tumor responses as independent predictors of OS. Meanwhile, tumor location, cStage, and tumor response were identified as independent factors influencing PFS. CONCLUSION: IFI was associated with similar survival as ENI in patients with thoracic ESCC, suggesting that IFI is an acceptable treatment method for thoracic ESCC.