Traditional Linear Accelerators
W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald in Handbook of Radiotherapy Physics, 2021
The transmission waveguides in the microwave radiation system are filled with a dielectric gas. The most common gas for this purpose is sulphur hexafluoride (SF6). The gas pressure system is sealed but can be topped up from a pressurised cylinder of liquid gas, permanently installed in the linac. The sealed system usually operates with a pressure of around 25 psi.* A pressure relief valve is essential to ensure that the pressure does not exceed ~35 psi, which could damage the RF-vacuum ceramic windows. Because of minor leaks within the gas pressure system, the pressure should be checked daily and if necessary, topped up from the cylinder. Sulphur hexafluoride is not toxic but is a heavier-than-air asphyxiant. Precautions should therefore be taken if the cylinder leaks.
Posterior relaxing retinotomy
A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha in Vitreoretinal Surgical Techniques, 2019
Alturki et al15 described the results of posterior retinotomy in 15 consecutive patients with complicated retinal detachment. Of these, 11 patients had PVR, 2 had trauma, and 2 had an inflammatory retinopathy. The retina was tamponaded with silicone oil in 14 patients. Three patients had short-term tamponade with perfluoroperhydrophenanthrene followed by silicone oil injection. One patient received sulfur hexafluoride gas. With a minimum follow-up of 6 months, 80% of the retinas remained attached – which is similar to results reported for anterior retinotomy (63–82%).8,12–;14 Visual acuity improved in 53%, remained unchanged in 20%, and decreased in 27%. Of the 11 eyes that had stable or improved vision, 5 (45%) achieved 20/400–20/25 vision, 5 achieved count fingers perception, and 1 remained stable at hand motion perception.
X-Ray Tubes and Linear Accelerators
Eric Ford in Primer on Radiation Oncology Physics, 2020
One detail to note about the linac is that, like the X-ray tube, most components are maintained at very low vacuum pressures. This is to prevent sparking or arcing associated with high voltages. (If there is no gas in the RF system there are no atoms to ionize and carry the current of a spark.) However, the microwave generation system is an exception to this. It is, instead, filled with sulfur hexafluoride (SF6) gas at high pressure. This is less costly than a low-pressure vacuum and easier to maintain, though it should be noted the SF6 is toxic. There is a glass window between the microwave system and waveguide to separate the SF6 region from the vacuum region, and there is a ceramic window to separates out the klystron/magnetron.
Preparation of targeted theranostic red blood cell membranes-based nanobubbles for treatment of colon adenocarcinoma
Published in Expert Opinion on Drug Delivery, 2023
Tahoora Ghasemzadeh, Maliheh Hasannia, Khalil Abnous, Seyed Mohammad Taghdisi, Sirous Nekooei, Negar Nekooei, Mohammad Ramezani, Mona Alibolandi
Micro and nanobubbles (called MB and NB, respectively) are core–shell self-assembled nanoparticles comprising gas core and shell layer with various types of shell such as polymer, lipid, protein, and so on. In two recent decades, theranostic MB/NBs have been widely applied as innovative imaging and therapy approaches for cancer treatment while providing real-time monitoring of tumor physiology by their gaseous core as ultrasound contrast agents (UCAs) [15]. Perfluorocarbon and sulfur hexafluoride (SF6) gases have been widely implemented as UCAs due to their acceptable safety and lack of toxicity and poor water solubility. Stability of these inert gases in microbubbles coated with lipid could enhance their plasma circulation time, reduce their size distribution, and maintain their physical stability [16]. SonoVue is an FDA-approved UCA comprising microbubbles based on phospholipid, filled with SF6, offering pronounced characteristics such as low solubility, good safety, great echogenicity, prominent stability, and endurance against pressure [17].
Vitreomacular disorders: a review of the classification, pathogenesis and treatment paradigms including new surgical techniques
Published in Clinical and Experimental Optometry, 2021
Mali Okada, Daniel Chiu, Jonathan Yeoh
Pneumatic vitreolysis is the technique of injecting intravitreal expansile gas with the goal of cleaving the vitreous adhesion and inducing complete PVD. The proposed advantage is that as it is an intravitreal injection, treatment can be given in the office setting. It is also less expensive compared to both ocriplasmin and vitrectomy. Pneumatic vitreolysis was first introduced in 1995 as treatment for impending or small macular holes.39 In the original study by Chan et al., 10 of the 11 patients with VMT (classified as stage 1A/1B in the original Gass classification), demonstrated release of the vitreous attachment on slit lamp examination after injection of 0.3 to 0.5 ml of 100% perfluoropropane (C3F8) gas. Other studies have also investigated use of other expansile gases, such as sulphur hexafluoride (SF6), with variable success.40,41 More recently, a larger retrospective study of patients with isolated VMT reported success rates of 80.0% for inducing PVD, when treated with pneumatic vitreolysis using 0.3 ml C3F8.42 Adverse events reported for pneumatic vitreolysis in previous studies are low but include progression to FTMH, development of retinal tears and retinal detachment.42,43 Although pneumatic vitreolysis remains a promising option, high-quality prospective trials data have so far been lacking and the timing can be up to six months for VMT resolution to occur.44
Pneumatic retinopexy: a review of an essential technique in vitreoretinal surgical care
Published in Expert Review of Ophthalmology, 2022
Ian Shao, Arjan S. Dhoot, Marko M. Popovic, Paola L. Oquendo, Hesham Hamli, Peter J. Kertes, Rajeev H Muni
In clinical practice, the inert gases sulfur hexafluoride (SF6) and perfluoropropane (C3F8) are often used, with the former being more favorable. SF6 has a doubling of size within the first 24–48 hours, and lasts an average duration of 12 days within the eye after injection. In comparison, C3F8 quadruples in volume after injection, however, its longer average duration of 38 days is longer than necessary and may result in undesirable outcomes [10–13,15]. Furthermore, it takes 3–4 days for the C3F8 gas bubble to reach its maximal volume which is less ideal than the 36 hours it takes for SF6. If a larger bubble is required, we prefer sequential SF6 gas injections separated by a few days.
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