Design and characterization of an aperture system and spot configuration for ocular treatments with a gantry-based spot scanning proton beam.

BACKGROUND AND PURPOSE: Proton therapy is a key modality used in the treatment of ocular melanoma. Traditionally ocular sites are treated using a dedicated eyeline with a passively scattered proton beam and a brass aperture. This work aims to design and characterize a beam-collimating aperture to treat ocular targets with a gantry-based spot scanning proton beam. METHODS: A plastic aperture system that slides into the gantry nozzle of a spot scanning proton beam was designed and constructed. It consists of an intermediate scraper layer to attenuate stray protons and a 3D-printed patient-specific aperture positioned 5.7 cm from the surface of the eye. The aperture system was modeled in TOPAS and Monte Carlo simulations were validated with film measurements. Two different spot configurations were investigated for treatment planning and characterized based on lateral penumbra, central axis (CAX) dose and relative efficiency. Alignment and leakage were investigated through experimental film measurements. Range was verified using a multi-layer ionization chamber. Reference dose measurements were made with a PinPoint 3D ion chamber. Neutron dose was evaluated through Monte Carlo simulations. RESULTS: Aperture alignment with radiation isocenter was determined to be within 0.31 mm at a gantry angle of 0°. A single-spot configuration with a 10 mm diameter aperture yielded film-measured lateral penumbras of 1 mm to 1.25 mm, depending on depth in the spread-out Bragg peak. TOPAS simulations found that a single spot configuration results in a flat dose distribution for a 10 mm diameter aperture and provides a CAX dose of less than 106% for apertures less than 14 mm in diameter. For larger targets, adding four corner spots to fill in the dose distribution is beneficial. Trade-offs between lateral penumbra, CAX dose and relative efficiency were characterized for different spot configurations and can be used for future clinical decision-making. The aperture was experimentally determined to not affect proton beam range, and no concerning leakage radiation or neutron dose was identified. Reference dose measurements with a PinPoint ion chamber were within 2.1% of Monte Carlo calculated doses. CONCLUSION: The aperture system developed in this work provides a method of treating ocular sites on a gantry-based spot scanning proton system. Additional work to develop compatible gaze tracking and gating infrastructure is ongoing.

A new method for assessing anal distensibility with a barostat and magnetic resonance imaging in healthy and constipated women.

OBJECTIVES: Defecation requires relaxation of the internal and external anal sphincters. High anal resting pressure is associated with painful constipation, defecatory disorders, and increased healthcare utilization in constipated patients; the mechanisms are unclear. Perhaps patients with a high anal resting pressure have a less distensible canal, which impedes defecation. METHODS: In 50 of 64 participants (33 healthy and 17 constipated women), anal pressures and distensibility were measured, respectively, with manometry and balloon distention combined with magnetic resonance imaging; rectal balloon expulsion time (BET) was also studied. RESULTS: The BET (P = .006) was longer, and the mean (SD) rectoanal pressure gradient (-58[40] vs -34[26] mm Hg, P = .03) was more negative in constipated than healthy women; anal resting pressure was not different. During anal distention, the balloon expanded rapidly at an opening pressure of 49 (18) mm Hg, which was lower (P < .0001) than resting pressure (90 [25] mm Hg). The resting pressure was correlated with the opening pressure (r = 0.57, P < .0001) and inversely (r = -0.38, P = .007) with maximum volume but not with anal distensibility (volume-pressure slope). In healthy women, the difference (opening-resting pressure) was correlated with anal relaxation during evacuation (r = 0.35, P = .04). Anal distensibility and sensory thresholds were not different between constipated and healthy women. CONCLUSIONS: Among healthy and constipated women, a greater anal resting pressure is correlated with greater opening pressure and lower maximum volume during distention, and, hence, provides a surrogate marker of anal distensibility. The difference (opening-resting pressure), which reflects anal relaxation during distention, is correlated with anal relaxation during evacuation. Anal resting pressure and distensibility were comparable in healthy and constipated women.

Experimental validation of a new COMS-like 24 mm eye plaque for the treatment of large ocular melanoma tumors.

PURPOSE: A new Collaborative Ocular Melanoma Study (COMS)-like 24 mm eye plaque was experimentally characterized using physical and dosimetric measurements in preparation for clinical usage. The new eye plaque will enable surgeons and radiation oncologists to accommodate patients who have larger ocular melanoma tumors. METHODS AND MATERIALS: Physical measurement of the Modulay radius of curvature was performed using a FARO Edge, and the base thickness of the Silastic insert was measured with a depth gauge and Vernier caliper. Dosimetric measurements, using Gafchromic film, were used to determine the absolute dose as a function of the depth along the plaque's central axis, profiles as a function of polar angle, and basal coverage at the inner sclera. The measured results were compared with a theoretical model, which incorporated the plaque's heterogeneities using a modified TG-43 formalism. RESULTS: The Modulay radius of curvature measured 14.7 mm (specification = 14.55 mm). The Silastic base thickness measured 0.9 mm (specification = 1.0 mm). For a 24 mm plaque fully loaded with 1.27 U 125I model 2301 seeds, the dose rate at a prescription depth of 5 mm from the inner sclera was measured to be 36 cGy U-1 hr-1. The basal coverage for the same prescription depth was 17.9 mm. The experimental measurements were in close agreement with the theoretical predictions. CONCLUSIONS: The new 24 mm COMS-like plaque was experimentally validated for clinical use. Physical and dosimetric measurements for the 24 mm plaque agreed with nominal specifications and theoretical predictions. The 24 mm plaque provides greater basal coverage and lower surface doses than existing COMS plaques.

Gravity Flow in Proposed Enteral Tube Small-Bore Connectors.

BACKGROUND: Enteral nutrition (EN) misconnections have been identified as a serious and potential deadly problem. An international effort led by EN industry leaders has developed a small-bore enteral connector (ENFit) that in theory will reduce the frequency of misconnections. Despite the potential benefit of preventing misconnections, the full impact of adoption of the ENFit connector is unknown. To assess the impact of transitioning to ENFit on our home EN (HEN) patients, the current study evaluated gravity feeding comparing 2 proposed small-bore connectors to the legacy (current connector) using various commercial formulas. METHODS: Six commonly used enteral formulas in our facility with varying density and viscosity were tested in triplicate. Forty milliliters of formula was poured into a syringe connected to an ENFit or legacy (current) feeding connector attached to varying French size tubes. The time it took formula to flow through the connectors was recorded, and the test was repeated in triplicate. RESULTS: All formulas took significantly longer to flow through the first ENFit connector compared with the legacy connector ( P < .05). The second ENFit connector demonstrated similar flow dynamics to the legacy connector. CONCLUSIONS: There is wide variability in the flow dynamics in ENFit connectors with significant potential impact on many facets of HEN, including medicine delivery, blenderized feeds, venting, and compliance with EN due to increased time to administer feeds. We highly recommend additional testing of flow dynamics, including gravity flow, as ENFit tubes are being developed and adopted.

Seed coordinates of a new COMS-like 24 mm plaque verified using the FARO Edge.

A 24 mm COMS-like eye plaque was developed to meet the treatment needs of our eye plaque brachytherapy practice. As part of commissioning, it was necessary to determine the new plaque's seed coordinates. The FARO Edge, a commercially available measurement arm, was chosen for this purpose. In order to validate the FARO Edge method, it was first used to measure the seed marker coordinates in the silastic molds for the standard 10, 18, and 20 mm COMS plaques, and the results were compared with the standard published Task Group 129 coordinates by a nonlinear least squares match in MATLAB version R2013a. All measured coordinates were within 0.60 mm, and root mean square deviation was 0.12, 0.23, and 0.35 mm for the 10, 18, and 20 mm molds, respectively. The FARO Edge was then used to measure the seed marker locations in the new 24 mm silastic mold. Those values were compared to the manufacturing specification coordinates and were found to demonstrate good agreement, with a maximum deviation of 0.56mm and a root mean square deviation of 0.37 mm. The FARO Edge is deemed to be a reliable method for determining seed coordinates for COMS silastics, and the seed coordinates for the new 24 mm plaque are presented.

Engineering analysis and development of the spheroid reservoir bioartificial liver.

A significant demand exists for a liver support device such as a Bioartifical Liver (BAL) to treat patients experiencing acute liver failure. This descriptive paper outlines the design and development of two of the key components of the Mayo Spheroid Reservoir Bioartificial Liver (SRBAL) system. One of the components is the multifunctional Spheroid Reservoir and the other is Multi-shelf Rocker. The Spheroid Reservoir provides an environment to support the viability and functionality of the hepatocyte spheroids at very high cell densities. The Spheroid Reservoir is the biologically active component of this extracorporeal liver support device. Since the Spheroid Reservoir is designed to support 200-400 grams of hepatocyte spheroids, a method to quickly produce large quantities of spheroids is required. The Multi-Shelf Rocker fulfills the production requirement by allowing the culturing of up to six liters of hepatocyte suspension in a conventional laboratory incubator. The SRBAL is designed to provide life sustaining liver-like function to patients in acute liver failure.