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Radiotherapy and Chemotherapy
Published in R James A England, Eamon Shamil, Rajeev Mathew, Manohar Bance, Pavol Surda, Jemy Jose, Omar Hilmi, Adam J Donne, Scott-Brown's Essential Otorhinolaryngology, 2022
Although 70 Gy in 35 fractions (overall treatment time, 46 days/7 weeks) is one of the most common radiotherapy dosing schedules, prior to chemoradiation's being accepted as standard treatment, several different fractionation schemes had been studied. Acceleration is a reduction in the overall treatment time below the standard 46 days. Hyperfractionation is use of <2 Gy per fraction, and hypofractionation is use of >2 Gy per fraction. Altered fractionation may be required if radiotherapy appointments are missed, for example. Dose escalation is an increase in the total physical dose above 70 Gy.
Dose Fractionation in Radiotherapy
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Gordon Steel, Catharine West, Alan Nahum
Accelerated fractionation means reducing the overall duration of radiation therapy while using a conventional fraction size. The aim is to reduce the impact of tumour-cell proliferation during treatment. As with hyperfractionation, to deliver the prescribed total dose within a short overall time (without increasing dose per fraction), more than one fraction per day must be given.
Radiation Response of Human Tumors
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
The radiation response of tumors can be modified by the dose rate, fractionations, LET, and radiosensitizing and radioprotective agents. The dose rate used in the clinical range does not significantly influence the tumor response. In general, the higher the dose rate, the greater the damage. At a lower dose rate (5 rads/min), cells repair. In tumor therapy, fractionation is more effective than a single dose, because greater amounts of radiation can be delivered, and because reoxygenation of the tumor cells occurs between fractions. In those tumors where the presence of hypoxic cells become the limiting factor in the control of tumor growth, the use of high-LET radiation may be useful for when (1) the RBE is higher than that of X-rays, and (2) the OER is lower than that of X-rays. Among high-LET radiations, fast neutrons and negative pions appear to be most effective. Some important radiosensitizing agents that have been of some value in the treatment of tumors are triethylene melamine (TEM) (retinoblastoma), actinomycin D (Wilm’s tumor), methotrexate (squamous cell carcinoma of head and neck), hydroxyurea (head and neck cancers), 6-mercaptopurine (acute and chronic myelogenous leukemia), and 5-fluorouracil (carcinoma of gastrointestinal tract). The efficiency of neutron capture therapy in human tumors has not been encouraging.
Postoperative Radiotherapy for Cutaneous Melanoma in Patients at High Risk of Local-Regional Recurrence after Surgery Alone
Published in Cancer Investigation, 2022
Nicolette R. Drescher, Robert J. Amdur, Christopher G. Morris, Christiana M. Shaw, Peter T. Dziegielewski, William M. Mendenhall
We report excellent local-regional control rates with both hypofractionated and conventional radiotherapy schedules without a significant difference in control contradicting the historical thought that melanoma cells are radioresistant. Of note, however, only 29 patients (22%) in our cohort were treated with conventional fractionation. In 1990, investigators at MD Anderson described a hypofractionated schedule 30 Gy over 5 fractions in 2.5 weeks (17). Since that publication, we have adopted this hypofractionated treatment schedule as standard treatment for cutaneous melanoma when logistically feasible. Hypofractionation is preferred due to patient convenience owing to the shortened treatment time and low risk of acute and late toxicity. Conventional fractionation schedules are preferred when the disease is close to critical structures, requires large treatment fields and includes the scalp (5).
Preliminary pre-clinical studies on the side effects of breast cancer treatment
Published in International Journal of Radiation Biology, 2021
Camila Salata, Carlos E. deAlmeida, Samara C. Ferreira-Machado, Regina C. Barroso, Liebert P. Nogueira, Andrea Mantuano, Arissa Pickler, Carla L. Mota, Cherley B. V. de Andrade
It is important to highlight most of the research about the mechanisms of RIHD has been performed mostly with a high-dose rate single high dose of radiation to the heart, or a limited number of fractions. While these radiation protocols seem to cause similar late cardiac remodeling, there is few data available from animal models to determine whether fractionated sections as used in the clinic cause cardiovascular effects similar to single high-doses (Boerma et al. 2016). Boria and Perez-Torres compared fractionated and single doses mice models of radiation necrosis. They found that all fractionation schemes produced radiation necrosis comparable to what would be achieved with single fraction doses (Boria and Perez-Torres 2019). The single fraction animal model is frequently used as it causes less animal stress due to manipulation and anesthesia (as all the animals are anesthetized during irradiation), and avoids possible confounds due to the potentially limited reproducibility of positioning for focal treatments.
Radiation-Induced Optic Neuropathy: Literature Review
Published in Neuro-Ophthalmology, 2021
Fabrício Gomes Ataídes, Samuel Flávio Braga Reis Silva, Julianna Joanna Carvalho Moraes De Campos Baldin
According to Seregard et al.25 the damage to the optic nerve is related to the total dose, volume of optic nerve irradiated and fractionation. It has already been shown that the anterior visual pathway does not tolerate cumulative doses greater than 50 Gy and fractional doses greater than 2 Gy. In addition, it is reported that the increase in the incidence of RION is proportional to the increase of these doses.2,23,26–30 However, more recent data indicate that a single dose less than 12 Gy will induce RION in 1% of patients.31,32 Data also suggest that no patient receiving less than 8 Gy to the anterior optic pathways will develop RION, but the frequency rises steeply to 78% when the dose is 15 Gy or more following stereotactic radiosurgery, whose the security dose is less than 8–10 Gy.6,25 Fractionation significantly reduces radiation toxicity and for doses at <1.8 Gy per fraction, radiation damage increases markedly first when the total dose is more than 60 Gy.25 A similar increase in radiation toxicity is evident for single doses above 12 Gy.33