Radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. It can be further divided into two categories: ionizing and nonionizing radiation. Ionizing radiation occurs when these particles or waves carry enough energy to free electrons from atoms. Gamma rays, x-rays, and the higher ultraviolet part of the electromagnetic spectrum are ionizing, whereas the lower ultraviolet part of the electromagnetic spectrum, visible light (including nearly all types of laser light), infrared, microwaves, and radio waves are considered nonionizing radiation. Ionizing radiation is utilized in various types of imaging modalities including x-rays, CT, positron emission tomography (PET), angiography, and radionuclide imaging. In medical imaging, the amount of ionizing radiation deposited or absorbed per unit mass of tissue is classified as the absorbed dose and measured in grays (Gy). One gray is defined as the absorption of 1 J per kg of radiation to the target tissue.¹ The equivalent dose, or the actual quantity of absorbed dose imparted to the target tissue to cause a biologic effect, is dependent on the type of radiation and amount absorbed. The risk of induction of cancer from an equivalent dose is highly dependent on the receiving organ, as different tissues and organs have unique radiation sensitivities. The tissue-weighted sum of all equivalent doses to the irradiated tissue/organs exposed is known as the effective dose. It is measured in sieverts (Sv). One sievert is defined as the absorption of 1 J per kg of biologic tissue. For reference, a single posteroanterior (PA) chest radiograph imparts an effective dose of 0.03 mSv to the lungs, breasts, esophagus, and stomach, whereas a CT scan of the chest delivers more than 200× that dose (7 mSv).²,³

Radiation exposure can be harmful to human tissues in both small and large doses, and its effects are categorized into two groups: deterministic effects and stochastic effects. Deterministic effects (nonstochastic) are described by a cause and effect relationship between radiation dose and damage, whereby the severity of the deterministic effect increases as the exposure dose increases. A radiation dosage threshold exists and, when exceeded, cell damage and death may occur. Previous studies have shown radiation doses of 2 Gy and 12 Gy to the skin can cause deterministic effects of erythema and necrosis, respectively. A dose of 4 Gy to the eyes may cause cataracts if received over a period of less than 3 months.⁴

Stochastic effects occur when low doses of radiation result in damage or mutation at a molecular level in a linear fashion. No threshold exists, but rather the risk of detrimental effects increases as the radiation dosage increases. For example, the risk of cancer from a single spine CT scan imparting an effective dose of 6 mSv is approximately 1:3,300.⁵

Minimally invasive procedures have become more common as spine technology and techniques have evolved. However, limited direct anatomic visualization during MISS often warrants generous use of imaging modalities for incision localization, instrumentation placement, and deformity correction. Large C-arm fluoroscopy is the most commonly used imaging modality for most minimally invasive procedures. However, there are alternative options that may help reduce the cumulative radiation exposure to the surgical staff and patients.

Lumbar diskectomy has been traditionally performed through an open midline surgical approach using either loupes or a microscope. Intraoperative fluoroscopy or plain film x-ray is often utilized to determine the correct operative level. The senior author typically uses two radiographs, one of which is used for determination of the incision and the other for confirmation of the level after the exposure is complete. During this process, the surgeon and the operative team can stand either behind a lead shield or in a separate substerile room to minimize radiation. In contrast, MIS approaches using tubular retractors often require the surgeon to be present holding the dilator or retractor during fluoroscopic imaging. Mariscalco et al. compared the radiation exposure between the surgeons who performed open versus MIS diskectomy and found the mean exposure to the thyroid, chest, and hand were 10 to 20 times higher in the MIS group. For example, while a single-level open microdiskectomy had a mean radiation exposure of 0.16 ± 0.22 mR to the thyroid and 0.21 ± 0.23 to the chest, the MIS counterpart had mean exposures of 1.72 ± 1.52 mR and 3.08 ± 2.93 mR to the thyroid and the chest, respectively.¹² It should also be noted that during open cases, surgeons who were standing in the substerile room were exposed to radiation as well, with an average exposure of 0.2 mR per case.¹² Given the cumulative effect of radiation exposure on overall cancer risk, surgeons should be aware that localization imaging alone is not inconsequential.