Scoliosis is a relatively common disorder with pathologic spinal curves greater than 20° occurring in approximately 2-4% of children aged six to fourteen
. To date, the gold standard for identifying and monitoring scoliosis has been standing anteroposterior (AP) and lateral scoliosis x-ray films, with systematic radiographic imaging performed throughout the individual’s course of treatment. As such, significant advances have been made in current diagnostic techniques: in general, adolescents are exposed to less radiographic imaging, and newer imaging techniques (e.g., 3-phase x-ray machines and high-speed x-ray films) decrease radiation exposure. It should be noted that the rates of cancer secondary to radiation exposure are not specific to scoliosis patients or x-rays. Numerous studies have documented the increase in ionizing radiation exposure and the corresponding risk of cancer in individuals with tuberculosis who require frequent lung radiographs to ensure infection progression, as well as patients who were exposed to atomic bomb radiation
However, there is an increasing awareness of the potential oncogenic effect of radiation exposure. Ronckers et al. studied patients diagnosed with scoliosis between 1912 and 1965 who were exposed to significant ionizing radiation in their adolescent years
. The median value for cumulative dose for the breast alone was 10–15 cGy (centi-Gray radiation unit, where one Gray is the absorption of one Joule of energy of ionizing radiation). In a child, neuropsychiatric damage is possible at 1,800 cGy, and endocrinologic dysfunction of the pituitary gland is seen at approximately 2,000 cGy
. Ronckers et al. followed 5,513 females who were exposed to an average of 22.9 radiographs per person during treatment and follow-up of scoliosis. Overall, the risk of mortality was 46% higher than the general population, with cancer identified as the primary cause of 23% of these deaths. In terms of frequency, breast cancer was most common, followed by lung and then ovarian cancer. Surprisingly, an increased risk was not identified in terms of developing thyroid cancer or leukemia, both of which were predicted to have increased risk secondary to radiation exposure.
A key aspect of this study was that the risk of death secondary to breast cancer corresponded with the number of x-rays involving breast radiation exposure. It was found that women with 25–49 x-rays involving breast exposure were 1.4 times more likely to die of breast cancer than women with fewer than 25 x-rays, and women with more than 50 x-rays were 2.7 times more likely to die of breast cancer. In addition, the number of xrays paralleled the amount of actual radiation exposure, with an increased rate of breast cancer in women exposed to higher than 20 cGy of radiation compared to women exposed to 0–9 cGy of radiation. These findings were not replicated in the analyses of the relationship between radiation and lung cancer. One possible explanation is that the lungs are exposed to only a fraction of the radiation doses that breast tissue is exposed to. The study also noted a significantly decreased risk of cervical cancer, which is likely due to the fact that some females with scoliosis suffer from sexual dysfunction. Several specific aspects of the group followed in Ronckers et al. are noteworthy: women with scoliosis smoked slightly less than the general public but included the same number of heavy smokers, and had higher rates of sexual dysfunction (thus reducing HPV transmission and cervical cancer risk while increasing breast cancer cases because nulliparous women are at higher risk). Additionally, if women with scoliosis are not physically able to withstand aggressive cancer treatment, the numbers associated with mortality may be skewed. In summary, the relationship between radiation dosage and cancer itself is a key element in the study that supports a correlation between breast cancer and radiation exposure.
Another key study by Nash et al. followed 13 females with idiopathic adolescent scoliosis
. AP and lateral films were measured over a 3-year period, during which the females were part of a treatment program for back brace curvature reduction. This Milwaukee-based program estimated that each patient had 22 films taken during the 3-year course. The study showed that the increased risk for leukemia was 3.4%, stomach and upper gastrointestinal cancers was 1.3%, lung cancer was 7.5%, and breast cancer secondary to the radiation exposure was 110%. This risk is reduced to only 3.8% if posteroanterior (PA) films are taken rather than AP films. The fact that these numbers were so drastically altered by adjusting the mechanics of the radiographic imaging led to the study’s recommendation to use PA films rather than AP films. Gialousis et al. also found that the PA approach could reduce the increased risk of breast cancer in females treated for scoliosis
A study by Levy et al., which concluded that the effects of radiation exposure depend on certain variables
, looked at 2,039 patients who were at least 9 years old between 1965 and 1979. The study found that, for several different types of full-spinal radiographs, the doses of radiation were 50% lower for adolescents compared to adults. This reduced dose is due to increased intensity and energy of the x-ray to compensate for the larger body size of adult patients. In an AP view, the thyroid gland and breast were most exposed, but the PA view nearly eliminated thyroid radiation exposure. It should be noted that the PA view did increase exposure to lungs in women and bone marrow in both sexes; however, both of these malignancies are known to have less risk per dosage of radiation exposure. Further, the study explains that both severity of the scoliotic curve and whether the patient had surgery are important factors that increased radiation exposure in this specific cohort. In essence, more severe curvatures require more images to track the progression of the curve. If the patient was older when diagnosed, the number of radiographs was reduced because they were not exposed to as much monitoring via imaging. Overall, the mean number of radiographs taken was 12 for females and 10 for males. For females, patients diagnosed under the age of 13 who had curves less than 20° had a lifetime cancer risk of 65 per 100,000. Females under the age of 13 who had surgical intervention for the curvature had an overall lifetime risk of cancer of 238 per 100,000. The numbers were less drastic for men, as the incidence of breast cancer was clearly negligible. Again, as seen in Nash et al., the greatest increased risk of any one particular cancer is breast cancer, and substituting AP imaging with PA imaging again reduces the risk. It should be noted that the study did find an increase in females having gastrointestinal malignancies from the PA angle imaging technique.
After following 5,573 patients who had diagnostic testing for scoliosis, Doody et al. also showed that the risk of breast cancer in females is increased. This study also pointed out the importance of age and that females who were exposed between the ages of 10–11 had a greater risk of cancer with a greater dose–response relationship when compared to females exposed at an older age
A review of these studies creates some consistent conclusions, despite varying calculations of risks of cancer and assumptions of radiation exposure per x-ray and over a lifetime. First, PA films should replace AP films, when possible, to reduce excess radiation to both the thyroid and breast tissue. This specific positioning is most important in females because of the specific increased risk of breast cancer from the radiation exposure. Second, while many of the original studies discussing the harmful effects of radiation produced dramatic results, they were using outdated techniques of radiation; current diagnostic procedures are less damaging than previously thought. Third, the earlier the exposure in a patient’s life, the more harmful; therefore, delayed imaging may be of benefit in terms of radiation exposure. Delayed imaging may, however, hinder the ultimate treatment of the scoliosis. Finally, while there is an overall increased risk of cancer, if the images are taken as infrequently as possible and if positioning encourages the safety of the patient, the risks to the patient can be minimized. Imaging should be done as necessary to provide the best patient care possible, balancing both risks and benefits. Any disparities in calculations or risk calculations are likely due to the lack of standard measurement of radiation as well as differences for each x-ray machine and the positioning of every individual patient.