A mask used in radiation therapy shows laser lines for targeting cancer cells in the brain...Adobe
Every year, doctors get better tools to fight cancer. Engineered cancer-killing cells, immunotherapies, targeted drugs, and more are helping clinicians cure more patients. Increasingly, though, oncologists are trying to use less radiation, long one of the main pillars of cancer therapy. In some cases, they are even keeping certain patients with low-risk tumors off radiation entirely.
“We are in an era of radiation omission or de-escalation,” said Corey Speers, vice chair of radiation oncology at the University Hospitals Seidman Cancer Center and Case Western Reserve University. “Radiation is perhaps one of the most precise and most effective cancer therapies we have, so it will always play an important role in cancer management, but there are situations now on an individual patient basis where radiation may not be needed.”
Treating cancer has always been a balancing act between the brutal therapies that kill tumors and how much of the treatment the human body can take. At their worst, the side effects of chemotherapy, radiation, and surgery can leave lasting damage, disrupt key bodily functions, or permanently disfigure a patient. So doctors have always wondered just how much of a therapy they could dial back without sacrificing any efficacy.
That’s been true for medicines and surgery as well, said Abram Recht, a radiation oncologist . “People have been looking at reducing the intensity of surgery, radiation, and systemic therapy for a long time, and there’s always been controversy about it,” Recht said. “The balance has always been the question — is reducing the intensity of treatment going to impact the long-term effectiveness?…Continue reading…
By Angus Chen
Source: Radiation, mainstay of cancer treatment, begins a fade-out – STAT
Critics:
Exposure to ionizing radiation is known to increase the future incidence of cancer, particularly leukemia. The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. The most widely accepted model posits that the incidence of cancers due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5% per sievert; if correct, natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second.
Additionally, the vast majority of non-invasive cancers are non-melanoma skin cancers caused by ultraviolet radiation (which lies on the boundary between ionizing and non-ionizing radiation). Non-ionizing radio frequency radiation from mobile phones, electric power transmission, and other similar sources have been investigated as a possible carcinogen by the WHO‘s International Agency for Research on Cancer, but to date, no evidence of this has been observed.
According to the prevalent model, any radiation exposure can increase the risk of cancer. Typical contributors to such risk include natural background radiation, medical procedures, occupational exposures, nuclear accidents, and many others. Some major contributors are discussed below. Radon is responsible for the worldwide majority of the mean public exposure to ionizing radiation. It is often the single largest contributor to an individual’s background radiation dose, and is the most variable from location to location.
Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics, and basements. It can also be found in some spring waters and hot springs. Epidemiological evidence shows a clear link between lung cancer and high concentrations of radon, with 21,000 radon-induced U.S. lung cancer deaths per year—second only to cigarette smoking—according to the United States Environmental Protection Agency. Thus in geographic areas where radon is present in heightened concentrations, radon is considered a significant indoor air contaminant.
Residential exposure to radon gas has similar cancer risks as passive smoking. Radiation is a more potent source of cancer when it is combined with other cancer-causing agents, such as radon gas exposure plus smoking tobacco. In industrialized countries, Medical imaging contributes almost as much radiation dose to the public as natural background radiation. Collective dose to Americans from medical imaging grew by a factor of six from 1990 to 2006, mostly due to growing use of 3D scans that impart much more dose per procedure than traditional radiographs.
CT scans alone, which account for half the medical imaging dose to the public, are estimated to be responsible for 0.4% of current cancers in the United States, and this may increase to as high as 1.5-2% with 2007 rates of CT usage; however, this estimate is disputed. Other nuclear medicine techniques involve the injection of radioactive pharmaceuticals directly into the bloodstream, and radiotherapy treatments deliberately deliver lethal doses (on a cellular level) to tumors and surrounding tissues.
It has been estimated that CT scans performed in the US in 2007 alone will result in 29,000 new cancer cases in future years. This estimate is criticized by the American College of Radiology (ACR), which maintains that the life expectancy of CT scanned patients is not that of the general population and that the model of calculating cancer is based on total-body radiation exposure and thus faulty.
In accordance with ICRP recommendations, most regulators permit nuclear energy workers to receive up to 20 times more radiation dose than is permitted for the general public. Higher doses are usually permitted when responding to an emergency. The majority of workers are routinely kept well within regulatory limits, while a few essential technicians will routinely approach their maximum each year. Accidental overexposures beyond regulatory limits happen globally several times a year.
Astronauts on long missions are at higher risk of cancer, see cancer and spaceflight. Some occupations are exposed to radiation without being classed as nuclear energy workers. Airline crews receive occupational exposures from cosmic radiation because of reduced atmospheric shielding at altitude. Mine workers receive occupational exposures to radon, especially in uranium mines. Anyone working in a granite building, such as the US Capitol, is likely to receive a dose from natural uranium in the granite.
Nuclear accidents can have dramatic consequences to their surroundings, but their global impact on cancer is less than that of natural and medical exposures. The most severe nuclear accident is probably the Chernobyl disaster. In addition to conventional fatalities and acute radiation syndrome fatalities, nine children died of thyroid cancer, and it is estimated that there may be up to 4,000 excess cancer deaths among the approximately 600,000 most highly exposed people.
Cancer is a stochastic effect of radiation, meaning it is an unpredictable event. The probability of occurrence increases with effective radiation dose, but the severity of the cancer is independent of dose. The speed at which cancer advances, the prognosis, the degree of pain, and every other feature of the disease are not functions of the radiation dose to which the person is exposed.
This contrasts with the deterministic effects of acute radiation syndrome which increase in severity with dose above a threshold. Cancer starts with a single cell whose operation is disrupted. Normal cell operation is controlled by the chemical structure of DNA molecules, also called chromosomes. When radiation deposits enough energy in organic tissue to cause ionization, this tends to break molecular bonds, and thus alter the molecular structure of the irradiated molecules.
Less energetic radiation, such as visible light, only causes excitation, not ionization, which is usually dissipated as heat with relatively little chemical damage. Ultraviolet light is usually categorized as non-ionizing, but it is actually in an intermediate range that produces some ionization and chemical damage. Hence the carcinogenic mechanism of ultraviolet radiation is similar to that of ionizing radiation.
Unlike chemical or physical triggers for cancer, penetrating radiation hits molecules within cells randomly. Molecules broken by radiation can become highly reactive free radicals that cause further chemical damage. Some of this direct and indirect damage will eventually impact chromosomes and epigenetic factors that control the expression of genes. Cellular mechanisms will repair some of this damage, but some repairs will be incorrect and some chromosome abnormalities will turn out to be irreversible.
Related contents:
- The 2007 Recommendations of the International Commission on Radiological Protection”.
- “IARC classifies radiofrequency electromagnetic fields as possibly carcinogenic to humans”
- “Cell Phones and Cancer Risk Fact Sheet – NCI”.
- “Facts about Radon”.
- “A Citizen’s Guide to Radon”.
- Chapter 14: Ionizing Radiation”.
- Ionizing radiation exposure of the population of the United States : recommendations of the National Council on Radiation Protection and Measurements.
- Computed tomography–an increasing source of radiation exposure”.
- Projected cancer risks from computed tomographic scans performed in the United States in 2007″.
- “Thousands of New Cancers Predicted Due to Increased Use of CT”. Medscape.
Radiation Accidents: Occurrence, Types, Consequences, Medical Management, and the Lessons to be Learned”. - “Radiation in the Environment”
- Health Effects of the Chernobyl Accident and Special Health Care Programmes: Report of the UN Chernobyl Forum Health Expert Group
- Japanese Officials on Defensive as Nuclear Alert Level Rises”.
- Report: Emissions from Japan plant approach Chernobyl levels”.
- Chronic Cs-137 incorporation in children’s organs”.
- Overview of Dose Assessment Developments and the Health of Riverside Residents Close to the “Mayak” PA Facilities, Russia”.
- “Global Inventory and Distribution of 238-Pu from SNAP-9A”.
- “Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses”.
- Fractionated Low-Dose Radiation Exposure Leads to Accumulation of DNA Damage and Profound Alterations in DNA and Histone Methylation in the Murine Thymus
- “Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses”.
- Repair of x-ray-induced DNA double-strand breaks in specific Not I restriction fragments in human fibroblasts: joining of correct and incorrect ends”.
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