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In-Room Imaging Devices Used for Treatment
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
MVCT images inherently have poor subject contrast due to the use of x-rays in the megavoltage range. However, using megavoltage x-rays for imaging does have the advantage of eliminating artefacts normally caused when high-Z materials are imaged with kilovoltage x-ray beams. Additionally, there is only one x-ray source and one detector, in-line with the treatment beam, providing easier access to the patient by the radiation technologists and simplifying QA, as the image is directly referenced to the beam.
Proton Therapy
Published in Harald Paganetti, Proton Therapy Physics, 2018
The first medical application of ionizing radiation, using X-rays, was reported in 1895 [1,2]. In the following decades, radiation therapy became one of the main treatment options in oncology [3]. Many improvements have been made with respect to how radiation is administered considering biological effects, e.g., the introduction of fractionated radiation therapy in the 1920s and 1930s. In addition, technical advances have been aimed, for instance, at reducing dose to healthy tissue while maintaining prescribed doses to the target or increasing the dose to target structures with either no change or a reduction of dose to normal tissue. Computerized treatment planning, advanced imaging and patient setup, and the introduction of megavoltage X-rays are examples of new techniques that have impacted beam delivery precision during the history of radiation therapy. Another way of reducing dose to critical structures is to take advantage of dose deposition characteristics offered by different types of particles.
Megavoltage Competition in Academia and Industry
Published in Barbara Bridgman Perkins, Cancer, Radiation Therapy, and the Market, 2017
Investigators using GE’s 1 MeV device at New York’s Memorial Hospital found—discouragingly—that most of the first 300 patients treated on the machine were dead 5 years later.3 Many of the cancers were advanced to begin with, but the radiotherapists had hoped that their new high-powered machine would benefit that very population. Another Memorial Hospital study observed that megavoltage X-ray treatments played a significant palliative role for some cancers but concluded that “so far this study does not lend encouragement to the hope that million volt roentgen therapy may lead to a high percentage of five year survivals.”4
Radiation therapy techniques in the treatment of skin cancer: an overview of the current status and outlook
Published in Journal of Dermatological Treatment, 2019
Ali Pashazadeh, Axel Boese, Michael Friebe
Megavoltage X-ray systems generate photons with energies more than 1 MeV. These high-energy photons are produced through the use of a linear accelerator. Electrons that are accelerated using the oscillating electric potential of the linear beamline collide with the target and produce energetic photons. In clinical applications, the energy of 4–25 MV is the typical range of voltage for photons. Physics of the interaction of high-energy photons with tissue indicate that the lethal dose can be deposited in the deep-seated target while the dose delivered to the first layers of the skin tissue is not significant. Therefore, this range of photon energy is suitable for treating lesions that are located in the tissue deep. In skin cancer therapy, where most of the tumors are superficial, MV X-ray systems are of very limited application.
Proton scanning and X-ray beam irradiation induce distinct regulation of inflammatory cytokines in a preclinical mouse model
Published in International Journal of Radiation Biology, 2020
Steffen Nielsen, Niels Bassler, Leszek Grzanka, Jan Swakon, Pawel Olko, Michael R. Horsman, Brita Singers Sørensen
X-ray reference irradiation was performed at Aarhus University Hospital. Reference radiation for the long-term study group was orthovoltage X-rays. Dose was delivered using a 240 kV Philips X-ray machine with a 2.3 Gy/min dose rate. Dosimetry was performed using an ionization chamber (TM31010, PTW-Freiburg). Megavoltage X-rays were used as reference radiation for the acute study group. A 6 MV clinical linear accelerator (Varian) was used for irradiation with a 6.4 Gy/min dose rate at the target site. Irradiations were performed at similar time of day for both proton and X-ray groups to avoid any possible variation in circadian rhythm. The fixation of the mice and the experimental set-up was the same for all radiation types. Control mice were sham-irradiated.
Feasibility study on the use of gold nanoparticles in fractionated kilovoltage X-ray treatment of melanoma
Published in International Journal of Radiation Biology, 2018
An external megavoltage X-ray beam can reach lesions of most tumors located deep inside the human body. Superficial radiation therapy is widely used in non-melanoma skin cancer treatment with a fractionated regime (Mcgregor et al. 2015). However, radiation therapy is not commonly applied to treat melanoma because of its high radioresistance. Fractionated X-ray therapy has yet to be considered for melanoma treatment. Furthermore, melanoma cells are resistant to chemotherapy (Chen and Gottesman 2005; Chen et al. 2009). Surgical excisions may cause a serious deformity on lesions. If feasible, then radiation treatment would be preferable to surgery on facial lesions for cosmetic and functional purposes (Sinesi et al. 1987).