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Saturday, July 19, 2008

Radiation Risks Associated with Prostate Cancer

[Updated June 5, 2011]

Some of this material was previously part of Advice to the Newly Diagnosed but has been expanded and so placed here on a separate page.

The Nature of Radiation Risk

Radiation involves health risks which increase with (1) increasing dosage of radiation received and number of times that radiation was received, (2) youth when received, i.e. the risk varies inversely with age when radiation was received -- the younger one is the greater the risk as being younger means more years of remaining life during which cancer from the radiation can develop (3) the amount of time since exposure -- the increase in risk is approximately linear in the first 10 years. See Hall citation below and (4) the existence of family history of prostate cancer which may increase the risk of radiation. (See the references to the Nottingham research below for this last point.) (5) "Some patients with nonmalignant systemic diseases, like collagen vascular disease (CVD), hypertension, diabetes mellitus, and inflammatory bowel disease (IBD), tolerate radiation therapy poorly. Although the mechanisms of each of these disease processes are different, they share a common microvessel pathology that is potentially exacerbated by radiotherapy." [PMID: 11961197] [Full Text].

In the future it may be possible to determine which patients are at greatest risk for radiation toxicity by examining their lymphocyte levels. [PMID: 19167839] .

Diagnostic Imaging

Radiation

A June 2008 epidemiological study done by Nottingham researchers based on 431 young-onset prostate cancer cases and matched controls found risks of 2x, 5x and 14x between the development of prostate cancer and X-ray exposure 5, 10 and 20 years earlier and also found a 2x risk for barium enenmas 5 years prior relative to controls not so exposed. The study author cautioned that "Although these results show some increase in the risk of developing prostate cancer in men who had previously had certain radiological medical tests we want to reassure men that the absolute risks are small and there is no proof that the radiological tests actually caused any of the cancers." [Science Daily] [PMID: 18506189].

Martin and Semelka in a 2007 Medscape article reviewing the BIER VII report and other materials write that a low radiation dosage is regarded to be under 100 mSv. Chest X-rays involve 0.1 mSv, CT Scans of the pelvis and abdomen involve 10 to 20 mSv and a full body PET or CT scan involves 25 mSv. Organ specific radiation from a CT scan is typically 20 to 30 mSv. In comparison, they write that atomic bomb survivors receiving radiation exposure of up to 100 mSv (with mean of 29 mSv) and organ specific exposure of 5 to 125 mSv experienced heightened rates of cancer. (For additional data see wikipedia and for even more in depth information down to the figures for specific models of equipment see Shrimpton et al, 2003.) They point out that ultrasound and MRI are safer than methods which use ionizing radiation such as CT Scans; however, MRI is contraindicated for people with embedded metal such as pacemarkers and sometimes stents and cochlear implants and even metallic jewellry although sometimes an MRI of lower tesla rating can be used instead (although that would also imply an image that is less clear). Also see this 2007 New York Times article and the American College of Radiology (ACR) patient safety information and white paper [summary].

A study presented at the April 2009 American Roentgen Ray Society meeting based on 100 physician surveys in various specialties found that 63% of physicians underestimated radiation exposure from abdominal-pelvic CT scans and only 20% thought that radiation risk was a part of disclosure. See this PSA Rising article.

Radiation exposure of diagnostic imaging

Estimating Mortality from CT Scans Using data from a large insurance database, in [Table 1] of [Full Text] published in Dec 2009 Archives of Internal Medicine, Berrington de Gonzalez et al estimated the risk of dying from CT scans to the abdomen at 5, 3 and 2 deaths for men age 30, 50 and 70 respectively per 10,000 CT scans. They further estimated that 29,000 excess cancers and 15,000 deaths in the US would occur due to the radiation exposure from CT scans performed in 2007 alone. The cancer and mortality numbers were based on CT scans to any part of the body, not just pelvic CT scans that might be done for urology, and excluded CT scans conducted after a diagnosis of cancer or scans performed in the last 5 years of life.

Actual Measured Dosages. A second study [Full Text] in the same Dec 2009 Archives of Internal Medicine issue examined the 11 most common types of CT studies in 1119 adult patients at 4 San Francisco Bay hospitals and concluded that actual dosages being given are substantially higher and more variable than previously thought:
We documented higher and more variable doses than what is typically quoted from the most common types of diagnostic CT studies performed in clinical practice. For example, the median effective dose of an abdomen and pelvis CT scan (the most common type of CT examination performed in the United States12) is often quoted as 8 to 10 mSv. Yet we found that the median dose of a routine abdomen and pelvis CT scan was 66% higher, and the median dose of a multiphase abdomen and pelvis CT scan was nearly 4-fold higher. Furthermore, we found substantial variation in doses within and across institutions, with a mean 13-fold variation between the highest and lowest dose for each CT study type included. Thus, depending on where an individual patient received imaging and the specific technical parameters used, the effective dose received could substantially exceed the median. While some of this variation may be clinically indicated to accommodate patients of different size or the specifics of the clinical question that was being addressed, the variation in effective dose was dramatic and of greater magnitude than widely considered acceptable, particularly considering that the patients were already stratified within relatively well-defined clinical groups. The variation in dose across the 4 clinical sites reflects site-specific methods of choosing different technical parameters to answer the same clinical question.
The data is shown in [Table 2] of that paper which shows that median dosages of actual measurements for routine abdomen-pelvis CT scans with contrast were 16mSv per scan ranging from 10mSv - 20mSv equating to about 220 chest radiographs. In [Table 4] they estimate one death per 660 pelvic CT scans given to men age 60.

Bone Scan. The gamma radiation from a bone scan -- this is a test where one is injected with a radionucleotide, a radioactive substance that accumulates in the bone, and a few hours later the patient is scanned with a gamma camera to detect "hot spots". The radiation dose is 4 mSv according to information on the National Health System (UK) site.

Contrast-Induced Nephropathy

. Contrast-induced nephropathy, i.e. kidney damage due to the use of contrast agents taken by the patient to improve the images from diagnostic imaging, is a possible complication of imaging which is distinct from the radiation risk itself. "The risk of contrast-induced nephropathy is less than 10% in patients with normal baseline renal function. In patients with a creatinine clearance of 10 to 20 mL/min, the incidence of adverse renal effects is 80% to 90%." [Goldfarb, 2005] Risk assessment prior to such administration is performed. A brief overview of contrast-induced nephropathy can be found in this article by George Herbert. More details can be found in [Rudnicki, 2006] and [Medscape review]. A 2008 meta-analysis of prevention methods concluded that "N-Acetylcysteine is more renoprotective than hydration alone. Theophylline may also reduce risk for contrast-induced nephropathy, although the detected association was not significant. Our data support the administration of N-acetylcysteine prophylaxis, particularly in high-risk patients, given its low cost, availability, and few side effects." [Annals of Internal Medicine, 2008].

Radiation Treatment

Radiation as a treatment, as opposed to using it as an imaging diagnostic, was also reported to lead to higher rates of bladder, colorectal and lung cancer in [link] although from the same link the investigator stated that: "the absolute risk associated with the development of secondary malignancies in patients exposed to external beam radiation therapy is quite small".

Hall (2006) [Full Text] [PMID: 16618572] estimates that: "Induced cancers increase with time after radiotherapy and in elderly patients amount to approximately 1.5% by 10 years after treatment. This figure may be doubled by new techniques, such as intensity-modulated radiotherapy. In older patients, for example patients with carcinoma of the prostate, doubling the second cancer incidence from 1.5% to 3% may be acceptable if it is balanced by a substantial improvement in local tumor controlled and reduced acute toxicity. These improvements have not yet been documented in control clinical trials."

Although the radiation of nearby healthy tissue is reduced in IMRT, the overall increase in radiation from IMRT is due to the greater effect of leakage as IMRT employs more radiation units. It would be possible to shield such radiation but only at substantial cost. Again, from Hall: "An alternative strategy is to replace X-rays with protons. However, this change is only an advantage if the proton machine employs a pencil scanning beam. Many proton facilities use passive modulation to produce a field of sufficient size, but the use of a scattering foil produces neutrons, which results in an effective dose to the patient higher than that characteristic of IMRT. The benefit of protons is only achieved if a scanning beam is used in which the doses are 10 times lower than with IMRT." (A broader comparison of proton therapy with IMRT can be found in [PMID: 18619120] [Full Text] and is also listed under the tag "Proton vs. IMRT" on the Treatment Comparison line under Links in the right margin.)

Calculating Lifetime Exposure

The radiation dosage calculator will estimate your lifetime radiation exposure in mSv given the types and numbers of exposures.

More Info


The Joint Task force of the American College of Radiology and the Radiological Society of North America in collaboration with the American Association of Physicists in Medicine and the American Society of Radiologic Technologists have created the Image Wisely campaign and web site with the objective of lowering the amount of radiation used in medically necessary imaging studies and eliminating unnecessary procedures. See Image Wisely.

This chart compares the radiation from various sources in a way that allows you to develop an understanding of radiation magnitudes.

The World Health Organization (WHO) has recently classified cell phones as possibly carcinogenic to humans. (See [press release - pdf]. On this page you can enter your cell phone make, e.g. Motorola, and find out how much energy it emits: http://www.computerworld.com/s/article/9217287/What_s_your_cell_phone_s_maximum_radiation_level_Interactive_database#form . (Their assessment relates to brain cancer and not prostate cancer.)

1 comment:

maack1@cox.net said...

Certainly interesting information that should be noted by patients and discussed with their radiological oncologist when radiation of any form is being proposed. Thanks for sharing and thanks for the time consuming work I know must go into maintaining your informative website.
Charles (Chuck) Maack
Prostate Cancer Advocate
Wichita, Kansas Chapter, Us TOO Intl., Inc.