PART II: PROFESSOR REISER'S PERSONAL HIGHLIGHTS AND VIEWS ON RADIATION DOSE
Jana Ivanidze: Dose exposure and new ways to reduce it are heavily discussed these days, especially because of the growing availability of CT scanners and the lower threshold to send a patient to the CT scanner in the western countries. What do you think can be done to combine that maximum use with a risk as low as possible?
Professor Reiser: To begin with, let me say that we should look at the dose exposure problem from a relativistic perspective. The increase in exposure dose was higher in the United States than in Europe. This has to do with more strict regulations here in Europe. For instance, a CT-based tumor screening (for primary prevention) is forbidden here, while many commercial companies offer it in the States. Here in Europe a clear clinical indication is the prerequisite for a CT screening. Nevertheless the exposure dose has risen in Europe as well in the last years. Due to these upward shifts in exposure doses we have witnessed an increase in equivalent dose from 1.6 to 1.7 mSv in the general population. If you now calculate the rate of tumor induction, you end up with scary numbers, but this is only part of the whole picture. If you take a look at who is usually undergoing CT scans, you will realize that CT is used in particular for the acutely ill and for oncologic patients. In the oncologic patient group the question of possible secondary tumor induction through diagnostic CT becomes a lot less important at second glance, because these patients often have a shortened life expectancy due to their primary illness and often receive chemotherapy and radiation therapy simultaneously, which causes a lot more damage to the DNA than diagnostic CT.
Jana Ivanidze: More specifically, where, in your opinion, does exposure dose reduction only play an insignificant role and in which clinical settings can we seek specific ways to achieve a reduction in exposure dose?
Professor Reiser: There are different possibilities but you have to weigh the benefits of a rapid and precise diagnosis against the benefits of a lower exposure dose. In the polytraumatized patient for instance, both survival and rehabilitation rate are much better if a multisclice detector CT is used in the early diagnostic phase – also known as the “golden hour of shock” (as shown by a study from the German Society for Trauma Surgery), where we find ourselves in a situation where dose reduction becomes less important. We find ourselves in a similar situation with the acute stroke patient where “time is brain”: using very rapid and precise diagnostic tools followed by optimized therapy, we can save life-important areas in the brain from ischemia.
I thus think that CT certainly has it’s main applications in the acute patient and the oncologic patient, and that in both cases considerations of exposure dose become subordinate to life-saving diagnostic and therapeutic options. I would expect that in future we will have even broader indications for CT, despite all the exposure dose considerations.
Having said that, we should of course seek ways to reduce exposure dose. One way is a careful consideration of indication, i.e. in young females. Whenever MRI is a possible evidence-based alternative, it should be seriously considered. Another important term here is the so-called ALARA-principle (As Low As Reasonably Achievable), which keeps exposure dose low by modulating it until a level where a reasonable (not optimal, but adequate) imaging quality is achieved. The third way of dose reduction is a serious consideration whether CT screenings are justified in individual cases. In principle there are four situations where CT screening is an option to consider. The first one is lung cancer screening. Here the dose can be dramatically reduced by a careful choice of the screening population. In 2009 a big study will come out that examines the consequences of lung cancer screening for patient survival. The general consideration is now that the smaller the discovered tumor the higher the survival rate, but this is yet to be proved. As is well-known, the risk populations for lung cancer (which should be screened), are long-term smokers and asbestos-exposed people. In the latter case, the incidence peak of asbestos-cause lung cancer is expected for 2025, so we are currently not in a good position for screening.More to come... [to be continued in the next part of this exclusive interview!] This article is brought to you by Jana Ivanidze, radRounds, 2008.