A modified barium swallow study (MBSS), also called a videofluoroscopy swallowing study uses ionising radiation to assist the clinician in visualising swallowing biomechanics from the oral cavity to the oesophagus. This procedure is currently one of the best methods used by speech and language therapists in particular, to assess a patient’s swallowing and to guide swallowing rehabilitation. Whilst the radiation exposure from the procedure is generally known to be very small, there is little known about the quantifiable risk in terms of any potential excess cancer risk to patients. The authors therefore wished to obtain a quantifiable estimate of organ doses and the corresponding carcinogenic radiation risk for the MBSS. In this study, 53 consecutive patients underwent the complete modified barium swallow impairment profile (MBSImP) protocol comprising 13 swallow trials. The authors used a software program and specific models to calculate dose to the relevant major organs/tissues. They compared the doses to published data available in the ‘Biological Effects of Ionizing Radiation Report VII’ (BEIR VII, 2006) to estimate cancer risk. Three factors determine risk: average radiation absorbed dose (mGy), age, and sex of the individual at time of exposure. The BEIR VII report provides data for males and females at various age ranges. The results showed that the highest organ dose was to the thyroid (1.7mGy). Only four other organs received doses exceeding 0.1mGy: lung (0.24mGy); red bone marrow (0.27mGy); liver (0.14 mGy) and oesophagus (0.43mGy). The median total effective dose for a typical MBSS was 0.27mSv.
In terms of excess cancer risk for exposed patients, 20-year old females had a reported risk of 32 cases in a million and males of 11 in a million. The risk decreased for patients at 60 years of age with risk for males being 4.9 cases in a million and females at 7.2 in a million.
In younger patients, exposure to the thyroid contributed most to risk but this falls with age. In the oldest males, the red bone marrow (leukemia) was the largest contribution to cancer risk, whilst in the oldest females, lung cancer contributed most to total carcinogenic risk. This paper confirms that excess cancer risk per unit effective dose (% Sv) for the MBSS is generally low. Useful data that quantifies excess cancer risk is made available for clinicians and researchers who may wish to use the information when making risk-benefit judgments or when explaining potential risks to patients.
