Radiation
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Loading ...Some patients with small and early stage lung cancer are not able to undergo a surgical resection because of other medical conditions that might make an operation too risky. In this patient population, radiotherapy alone has often been the primary treatment.
Radiation is a very effective treatment modality for patients with any type of cancer. Most patients that have received treatment with radiotherapy in this situation receive conventionally fractionated radiotherapy. Conventionally fractionated radiotherapy means that the radiotherapy is delivered daily Monday through Friday. Most patients receive between 6.5 and 7.5 weeks of treatment. It is usually between 33 and 37 fractions (individual treatments) of radiotherapy. The outcomes with this type of treatment are generally pretty good. The published outcomes from this type of treatment range from 30% to 81%, which is a large range. Part of the explanation for this range is that there is such a tremendous variation in the patients included in the medically unresectable category. Some of these patients are quite healthy with the exception of some reason that they can’t undergo surgery. Other patients have really fragile lung function and oxygen dependent. There is some suggestion that the control of the tumor is better with higher doses of radiotherapy. There is also the suggestion that with improved technologies and newer treatment that the outcomes will continue to improve.
It is quite common for surgeons to compare the surgical treatment of early stage lung cancer with radiotherapy alone and point to improved outcomes. Unfortunately, this is not an accurate comparison. The published surgical experience is based on an analysis of pathologically staged specimens. This means that when a surgeon reports outcomes on the resection of a 2 cm tumor, the size of the tumor is based on the surgical specimen and the measurement by the pathologist. Surgery also gives the chance to find lymph nodes that are involved microscopically but weren’t noted on scans. Most of the time, the CT images (clinical staging) underestimate the size of the tumor that is measured by a pathologist after surgery, and it may understage nodal involvement. This means that when you compare outcomes with radiation alone to the results with surgery for a similar stage, you’re likely actually including many higher stage patients on the radiation arm who are going to do less well.
There is emerging interest in the role of stereotactic radiosurgery for the treatment of early stage lung cancer. Stereotactic radiosurgery means the delivery of a very high dose of radiotherapy in just 1 to 5 treatments. The dose of radiotherapy that is delivered is often biologically equivalent to 7 or more weeks of daily radiotherapy. The early experience with this approach in Japan and the US suggest that control rates in excess of 90+% can readily be achieved. The toxicity of this approach is reasonable in most instances.
Posted in: Radiation therapy
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Thank you for the very understandable explanations, Dr Mehta. Wow, I wonder how intense the body reactions to stereotactic radiosurgery in lung cancer are, such as pneumonitis, fibrosis, all the esophageal/gastric effects. Are they about the same or intensified?
Foxy
foxy
I’ll try to flag down Dr. Mehta to weigh in, but I’d say that the side effects of stereotactic radiosurgery are often pretty minimal, since it’s a very focal treatment, unlike conventional radiation, which administers radiation to a much wider area because it needs to provide a margin around a less precisely localized tumor. Dr. Mehta has treated and followed many more of these patients than I have, but my patients have generally had very mild side effect issues after stereotactic radiosurgery.
-Dr. West
Usually, the volume of tissue that is being treated with stereotactic radiosurgery is very small. Because the beams are coming from so many different entry points, the dose is effectively “spread out” over a lot of normal tissue. Of course, all of these beams overlap at the target which is where the dose is concentrated. If one evaluates the dose of radiation beyond the target, one will find that there is a very “rapid dose fall off.” This means that 5 mm away from the target the dose might be 50% of the prescribed dose and 10 mm away it might only be 10% of the prescribed dose.
The side effects from radiation are almost always based on the dose delivered to the volume of tissue exposed. So if your target that is treated is more than 1-2cm away from the organ you are interested in, there is very little risk to that organ. On the other hand if the target is within or adjacent to that organ you might have a potentially devastating side effect.
If one treats a small lung lesion in that is located in the periphery of the lung, there will be no dose to the esophagus or spinal cord for example. In terms of the risk of fibrosis or pneumonitis, this risk will be based on how big the target is. Most publications indicate that the risk of pneumonitis is very low after this procedure.
I agree with Dr. West. In my experience, the side effects are pretty mild and usually very tolerable.
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