Endoscopic ultrasound is a unique tool to acquire in vivo data on alimentary tract wall thicknesses of sufficient resolution needed in radiation dosimetry studies. Through their different echo texture and intensity, five layers of differing echo patterns for superficial mucosa, deep mucosa, submucosa, muscularis externa and serosa/adventitia exist within the walls of organs composing the alimentary tract. In this study, retrospective image analyses of patient video data were made for ten examinations of the stomach and eight examinations of the rectum covering a range of patient ages. Thicknesses for stomach mucosa ranged from 1030 +/- 130 microm to 1640 +/- 80 microm (total stomach wall thicknesses from 2.80 +/- 0.12 to 4.23 +/- 0.03 mm). Measurements made for the rectal images revealed rectal mucosal thicknesses from 660 +/- 50 microm to 1130 +/- 250 microm (total rectal wall thicknesses from 2.28 +/- 0.05 to 3.55 +/- 0.43 mm). The mucosa accounted for approximately 32 +/- 7% and approximately 32 +/- 8% of the total thickness of the stomach and rectal wall, respectively. These values can thus be utilized to investigate uncertainties in alimentary tract dosimetry that are based upon fixed reference individual definitions of organ wall structure.

Risk assessment associated with the inhalation of radioactive aerosols requires as an initial step the determination of particle deposition within the various anatomic regions of the respiratory tract. The model outlined in ICRP Publication 66 represents to date one of the most complete overall descriptions of not only particle deposition, but of particle clearance and local radiation dosimetry of lung tissues. In this study, a systematic review of the deposition component within the ICRP 66 respiratory tract model was conducted in which probability density functions were assigned to all input parameters. These distributions were subsequently incorporated within a computer code LUDUC (LUng Dose Uncertainty Code) in which Latin hypercube sampling techniques are used to generate multiple (e.g., 1,000) sets of input vectors (i.e., trials) for all of the model parameters needed to assess particle deposition within the extrathoracic (anterior and posterior), bronchial, bronchiolar, and alveolar-interstitial regions of the ICRP 66 respiratory tract model. Particle deposition values for the various trial simulations were shown to be well described by lognormal probability distributions. Geometric mean deposition fractions from LUDUC were found to be within approximately +/- 10% of the single-value estimates from the LUDEP computer code for each anatomic region and for particle diameters ranging from 0.001 to 50 microm. In all regions of the respiratory tract, LUDUC simulations for an adult male at light exertion show that uncertainties in particle deposition fractions are distributed only over a range of about a factor of approximately 2-4 for particle sizes between 0.005 to 0.2 microm. Below 0.005 microm, uncertainties increase only for deposition within the alveolar region. At particle sizes exceeding 1 microm, uncertainties in the deposition fraction within the extrathoracic regions are relatively small, but approach a factor of 20 for deposition in the bronchial region. Deposition fractions for particles above 1 microm become very uncertain within the deeper regions of the lungs (bronchiolar and alveolar-interstitial).

Pseudo-single domain superparamagnetic nanoparticles demonstrate highly efficient magnetic hyperthermia performance at the biologically safe and physiologically tolerable range of AC magnetic field (fappl < 120 kHz and Happl < 190 Oe).

Stereotactic radiotherapy (SRT) methods have become common for the treatment of small tumors in various parts of the body. Small field dosimetry has a unique set of challenges when it comes to the pre‐treatment validation of a radiotherapy plan that involves film dosimetry or high‐resolution detectors. Comparison of commercial quality assurance (QA) devices to the film dosimetry method for pre‐treatment evaluation of stereotactic radiosurgery (SRS), fractionated SRT, and stereotactic body radiation therapy treatment plans have been evaluated in this study. Forty stereotactic QA plans were measured using EBT‐XD film, IBA Matrixx Resolution, SNC ArcCHECK, Varian aS1200 EPID, SNC SRS MapCHECK, and IBA myQA SRS. The results of the commercial devices are compared to the EBT‐XD film dosimetry results for each gamma criteria. Treatment plan characteristics such as modulation factor and target volume were investigated for correlation with the passing rates. It was found that all detectors have greater than 95% passing rates at 3%/3 mm. Passing rates decrease rapidly for ArcCHECK and the Matrixx as criteria became more strict. In contrast, EBT‐XD film, SNC SRS MapCHECK, and IBA myQA SRS passing rates do not decline as rapidly when compared to Matrix Resolution, ArcCHECK, and the EPID. EBT‐XD film, SNC SRS MapCHECK, and IBA myQA SRS maintain greater than 90% passing rate at 2%/1 mm and greater than 80% at 1%/1 mm. Additionally, the ability of these devices to detect changes in dose distribution due to MLC positioning errors was investigated. Ten VMAT SBRT/SRS treatment plans were created with 6 MV FFF or 10 MV FFF beam energies using Eclipse 15.6. A MATLAB script was used to create two MLC positioning error scenarios from the original treatment plan. It was found that errors in MLC positioning were most reliably detected at 2%/1 mm for high‐resolution detectors and that lower‐resolution detectors did not consistently detect MLC positioning errors.

The computer code LUDUC (Lung Dose Uncertainty Code), developed at the University of Florida, was originally used to investigate the range of potential doses from the inhalation of either plutonium or uranium oxides. The code employs the ICRP Publication 66 Human Respiratory Tract model; however, rather than using simple point estimates for each of the model parameters associated with particle deposition, clearance, and lung-tissue dosimetry, probability density functions are ascribed to these parameters based upon detailed literature review. These distributions are subsequently sampled within LUDUC using Latin hypercube sampling techniques to generate multiple (e.g., approximately 1,000) sets of input vectors (i.e., trials), each yielding a unique estimate of lung dose. In the present study, the dosimetry component of the ICRP-66 model within LUDUC has been extended to explicitly consider variations in the beta particle absorbed fraction due to corresponding uncertainties and biological variabilities in both source and target tissue depths and thicknesses within the bronchi and bronchioles of the thoracic airways. Example dose distributions are given for the inhalation of absorption Type S compounds of 90Sr (Tmax = 546 keV) and 90Y (Tmax = 2,284 keV) as a function of particle size. Over the particle size range of 0.001 to 1 microm, estimates of total lung dose vary by a factor of 10 for 90Sr particles and by a factor of 4 to 10 for 90Y particles. As the particle size increases to 10 microm, dose uncertainties reach a factor of 100 for both radionuclides. In comparisons to identical exposures scenarios run by the LUDEP 2.0 code, Reference Man doses for inhaled beta-emitters were shown to provide slightly conservative estimates of lung dose compared to those in this study where uncertainties in lung airway histology are considered.