The 6-MV beams used in this study had been commissioned for stereotactic radiosurgery dosimetry. Although the VMAT plans were optimized with a 2-mm dose grid to speed up the optimization process, the final dose distributions were calculated in a 1-mm dose grid to ensure comparable accuracy to that of the GK dose calculations.In this study, we generated comparison VMAT and IMPT plans for patients with skull-base or large intracranial lesions that had been treated with GKE to a median dose of 24 Gy in 3 fractions. Our goals were to meet the critical OAR dose constraints of the GKE plans and to quantitatively evaluate VMAT and IMPT plan quality for SRT. To the best of our knowledge, no such findings have been published comparing GK, VMAT and IMPT for FSRS of the head and neck. We found that VMAT and IMPT plans could achieve similar or lower doses to critical OARs compared with the GKE plans, with comparable target coverage. VMAT and IMPT offered more dose-homogeneous plans and significantly shorter delivery time . By contrast, the GKE plans had a higher GI and less low-dose spillage than did VMAT or IMPT, indicating less irradiation of normal tissues.This difference in favor of GKE compared with VMAT and IMPT was the most pronounced for the treatment of smaller tumors. In instances where the dose for single-session radiosurgery would exceed the tolerance of a nearby critical structure, FSRS is preferred. Before the wide availability of LINAC-based SRT systems, the Extend system was used on a GK unit to avoid the need for repeated head frame placement. The measurement system consists of a repositioning digital check tool attached to the Extend frame , which can position a patient to within 1.0 mm of the reference position. With a calculated mean interfractional radial setup difference of 0.64 ± 0.24 mm and an intrafractional positional difference of 0.47 ± 0.3 mm, the overall setup and immobilization uncertainty of GKE is between 1.0 and 2.0 mm. Use of the Extend system on a LINAC with only a reposition check tool confers a mean 3D positional displacement of 1.3 mm for patient setup, and so a 2-mm uncertainty margin for patients treated with the GKE system is typically used to ensure adequate coverage.
Today, LINACs such as the TrueBeam STx are used for frameless FSRS and can achieve sub-millimeter imaging setup accuracy, comparable to that of the GKE system. Advantages of LINAC systems are their integrated volumetric imaging system, easy verification of daily patient treatment positioning before and during treatment,flood tray and their ability to detect and correct setup errors before and during treatment. Thus for VMAT, use of a 2-mm PTV should ensure adequate target coverage while still accommodating machine uncertainties. Indeed, several studies have shown that a practical margin of <1.5 mm on the TrueBeam STx is sufficient because of the accuracy of measured isocenter and multi-leaf collimator positioning, a coincidence of kV and MV imaging isocenters that is within 1.0 mm, and geometric margins that are within ~1.2 mm. Two dosimetric studies have compared GK with LINAC-based VMAT for single-session treatment of intracranial lesions; in these studies, McDonald et al. and Thomas et al. found comparable target coverage and conformity for treating patients with multiple brain metastases. Our results for FSRS for skull base tumors demonstrate that VMAT can achieve the same or even steeper dose drop-off towards priority critical organs such as the brainstem and optic apparatus compared with the GKE . This was typically achieved by placing the isocenter between the target volume and the critical OAR , axial image for VMAT plan and subsequently using a half-beam block technique with a non-coplanar arc. Proton beam therapy may also be well suited for skull base FSRS. Published dosimetric comparisons of IMRT/VMAT and IMPT for patients with head and neck tumors treated with conventional fractionation have suggested that IMPT has better conformity. To our knowledge, studies evaluating proton-based FSRS for skull-base or head and neck tumors have not been reported. Here, we used a 2-mm PTV for VMAT and a 2-mm “optimization target volume” for IMPT. Although our results indicate that proton beam therapy for skull base FSRS is feasible, uncertainties in addition to patient setup and machine mechanical limitations should be considered. Of particular importance are particle beam range uncertainties, which are influenced by factors such as CT artifacts, conversion of Hounsfield units to stopping powers, or changes in patient geometry . Thus, a limitation not addressed in this study is the potential requirement for a relatively larger “PTV” margin for proton SRT. An uncertainty of 3.5% + 1 mm is often considered during proton treatment planning for conventionally fractionated treatments. We observed that IMPT plans showed excellent sparing of normal tissues, with a sharp gradient index and minimal low-dose bath for larger and superficially located targets . Improved CT image quality, accurate patient setup verification, and high-quality treatment plans that are less sensitivity to the aforementioned uncertainties continue to be sought for proton radiotherapy to minimize overshoot.
A clear advantage of VMAT and IMPT over GKE is the significantly shorter delivery time. The typical treatment time for each fraction with VMAT on a TrueBeam machine was less than 10 minutes, including the delivery time from the first beam to end of treatment, gantry and couch setup, and imaging verification between beams. The delivery time for IMPT was mainly based on total number of the spot and layers. The overall treatment time may be up to 20 min when 3 – 4 beams are used. A marked difference between the GKE and the VMAT or IMPT plans was observed in dose heterogeneity, in that the HI of GKE plans was significantly greater than that for VMAT or IMPT . The difference in the HI between GKE and VMAT/IMPT was not influenced by tumor size or location. GKE plans showed a superior GI and better low-dose-volume index , indicating a sharper dose falloff outside the target. In fact, the R20-50 for GKE was only about half that of VMAT and IMPT plans, because the GK unit produces less lateral scattering of lower energy radiation and has shorter distances from source and collimator to focus. Despite these differences in machine capabilities, we found that with inverse planning, VMAT could achieve similar or lower doses to OAR without loss of coverage; moreover the dose gradient at the OAR-target boundary can be further optimized for steeper drop-off if necessary. By contrast, IMPT achieved slightly lower coverage with similar OAR constraints, and the dose gradient was often not as favorable as that of VMAT, perhaps because the spot size of the proton system at our institution is larger than 1 cm; this could also explain the marked increase in the low-dose bath and higher GI for small and centrally located lesions for IMPT plans . Currently, stereotactic application of protons may be more appropriate for superficial targets if the same radiation treatment and plan quality can be maintained. The Extend involves use of a vacuum-sealed, custom prosthesis that locks onto the teeth and can be challenging to tolerate. At our institution, use of this system requires that the patient have good performance status, at least 3 intact teeth, and no gag reflex. We did not use the Extend frame for LINAC- or IMPT-based FSRS. If we had, the repositioning check tool would have been used before each treatment to correct interfractional setup error. Thus use of our current thermoplastic head and neck immobilization system with LINAC- or IMPT-based FSRS may have involved setup differences. Further comparisons of the two systems are needed with regard to intrafractional translational and rotational restriction of patients, particularly for skull base targets, which are often adjacent to the neuro-optic apparatus. In addition, it is unclear if the differences in low-dose bath we observed among VMAT, IMPT, and GKE are clinically significant for FSRS.
A previous study of 130 patients with head and neck cancer treated with conventionally fractionated IMRT indicated that radiation-induced nausea and vomiting were significantly associated with mean doses to particular nausea-associated regions. Clinical studies are needed to determine the clinical impact, if any, of the low-dose bath and differences in the other dosimetric variables found in this study for FSRS for head and neck tumors.Microwave irradiation may be helpful in this context. Microwave irradiation has recently been a very active research due to the many advantages of nonthermal effects such as reaction promotion, nucleation induction, and diffusion facilitated by the molecular vibration of polar molecules. We hypothesized that the precipitation reaction and diffusion characteristics through semipermeable membrane of chemical garden could be modulated or explained via various microwave properties. In addition, precipitation of chemical garden may suggest a new application of microwave irradiation and suitable operating conditions for highly functional inorganic materials of hollow tubes. The concentration of aqueous solution is essential for solving the diffusion and precipitation challenges of chemical garden phenomena. In this study, we varied the concentration and microwave power to understand the microwave effect. We used a microwave reactor equipped with an in-situ observation system to capture the dynamic growth behavior of the tree-like pattern.Lead is a naturally occurring heavy metal that exists at low concentrations in the environment. Throughout human history, Pb’s prolific use has facilitated its relocation, concentration, and subsequent threat to human health. Through the phase-out of Pb use in products such as gasoline and paints, the amount of Pb used in the United States has generally declined since the mid-1970’s.However, the residual effects of the Pb use in these and other industries have increased the levels of environmental Pb to which the average person is exposed. Leaded gasoline emissions and Pb paint peeling in older buildings can result in suspension and further deposition of Pb on nearby surfaces. Though Pb exists in various compounds, ebb and flow tray as a basic element it does not readily degrade in the environment and binds tightly to soils, therefore, contributing to its persistence as an environmental human health risk. Drinking, eating, and breathing particles containing Pb in any concentrations can result in acute or chronic Pb poisoning.
Many urban area soils are disproportionately contaminated with Pb from particulate dispersal via leaded gasoline emissions and Pb paint on older buildings. Older homes and neighborhoods adjacent to heavily trafficked roads are often historically associated with marginalized and low-income communities. In these communities and others, urban gardening is experiencing a resurgence in neighborhoods and schools as an educational tool for food, environmental, and nutrition literacy and self-sufficiency; therefore, an understanding of the state of soil contamination is vital to reduce or eliminate unnecessary food chain transfer of soil Pb to urban communities. Unfortunately, garden produce such as leafy greens and root vegetables have heavy-metal tolerance traits and can grow uninhibited by Pb and subsequently accumulate the heavy metal in their tissues. The United States does not regulate Pb and other contaminants in produce. However, China released a standard for maximum levels of contaminants in foods in 2018. Per this regulation, the maximum concentration of Pb allowed for Brassica vegetables and leafy greens is 0.3 ppm of total fresh weight. For reference of “acceptable” soil Pb limits, The U.S. Environmental Protection Agency set maximum bare soil Pb concentrations in federally funded project sites. Bare soil play areas and high-contact areas for children are limited to 400 ppm Pb. The rest of the yard is allowed 1200 ppm Pb. Various Cooperative Extension publications cite the 400 ppm EPA value of as the maximum soil Pb concentration considered safe to grow vegetables in soil. At any concentration above 400 ppm, an expensive remediation solution is excavation and removal of contaminated soils. Alternatively, the University of Connecticut Extension Service recommends growing vegetables in raised beds as a reasonable reduced risk option for avoiding Pb accumulation in garden vegetables particularly leafy greens and root vegetables. These recommendations are consistent with those presented by other extension services throughout the country, specifically from Kentucky State, Oregon State, UMass Amherst and the University of Delaware.