SBRT stands for Stereotactic Body Radiation Therapy, a radiation therapy approach which delivers high dose radiation to a target within the body, in either a single treatment session or up to  approximately five treatment sessions (each session is typically referred to as a “fraction”).

The first term in the acronym, “stereotactic” refers to precise three dimensional localization of a tumor target.  The incorporation of the second term in the acronym, “body,” is of historical derivation.  Stereotactic radiation therapy was first invented for the treatment of brain tumors with tools like the Gamma Knife - which has been in practice for a half century.  Extension of stereotactic high-dose radiotherapy techniques to tumor targets outside of the brain and cranium is relatively novel, an advent of the past decade.   Thus the use of the term “body” delineates that the technique is being applied to extracranial (non-brain) tumors.

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    The ASTRO (American Society of Therapeutic Radiation Oncologists) was held in early November in San Diego.  Here’s a little info on one of the highlight presentations.

    The group from William Beaumont Hospital in Detroit (Welsh and colleagues, Abstract #1088), presented a very interesting analysis comparing patients with early stage lung cancer in their own institution treated with the more extensive lung surgery of a lobectomy (removing one third of the right lung or half of the left lung), wedge resection (a much smaller surgery), and stereotactic body radiotherapy (SBRT).  SBRT is a non-interventional form of radiation that delivers very high doses of radiation to small areas with a high degree of precision and accuracy.  This was a retrospective report evaluating the results of these patients.  The lobectomy patients performed the best, but this might be explained by these patients having better lung function, and fewer other co-existing medical problems.  The patients that were treated with wedge resection and SBRT tended to be the more fragile than patients treated with a lobectomy.  The patients treated with SBRT had significantly better local control (92%) than the patients treated with a wedge resection (75%).   Overall, then, this suggests that among patients who aren’t optimal candidates for a full lung surgery, SBRT may be a very strong choice.

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I recently heard a fascinating presentation by Dr. Paul Okunieff, a leader in radiation oncology.  Dr. Okunieff recently relocated to my home state to become the director of the University of Florida Shands Cancer Center.   He discussed his pioneering work on treating patients with just a few sites of metastatic cancer (a condition known as oligometastatic disease, oligo meaning “few”) with stereotactic body radiotherapy (SBRT).   I will admit that I have never been a fan of chasing after metastatic disease with radiation.   After hearing Dr. Okunieff’s presentation, though, I definitely felt that his approach was worth pursuing in larger clinical trials.

Prior to the 1970s, with very limited chemotherapy options, local therapies (such as surgery or radiation) were pursued more frequently for metastatic cancers.   Even today, for metastatic tumors with few effective chemotherapies (such as melanomas and sarcomas), removal of multiple metastases may be performed.   For colon cancer, resection of liver or lung metastases can lead to long-term survival in some patients.   Resections of solitary brain metastases have long been undertaken, including for patients with lung cancers.   However, most oncologists would understandably object to local therapy (either surgery or radiation) in a patient with lung cancer and 2 metastatic deposits in the contralateral lung and 2 in the liver.   The argument is that metastatic cancer is a systemic disease: if we can see 2 metastases, there are probably hundreds of micrometastases that we cannot see on scans.   If we use local therapy, it’s like playing whack-a-mole: as soon as one metastasis is destroyed, another will pop up and so on and so on…

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Vivek Mehta, Radiation Oncologist, on radiation approaches for early stage and locally advanced NSCLC.

Transcript: V Mehta Interview I Transcript

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   As I described in my last post, stereotactic body radiotherapy (SBRT) is a technique of treating lesions in the lung with a high dose of radiotherapy.  Usually the treatment is administered in 3-5 fractions.  Several institutions have reported very good results using this technique.

   Recently, some centers have started reporting the long term follow up of these patients.  As an example, Usematsu and colleagues from Japan reported at this year’s ASTRO that 131 patients with biopsy proven stage I NSCLC were treated with SBRT using between 5-10 fractions.  Only 5 of the 131 patients demonstrated local progression.  The 5 and 10 year overall survival rate was 54% and 48%., with a 5 and 10 year cancer-specific survival rate was 78% of 74%, respectively.  Remember, the significant difference between the overall survival and cancer-specific survival in this setting is because many patients treated with SBRT are medially inoperable because of competing medical problems.  Illustrating this factor, the 5 and 10 year overall survival rate of medically operable patients (who had refused surgery) was 72% and 65%, respectively.

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   Stereotactic Body Radiation Therapy is a technique designed to deliver a very high dose of radiation to a target lesion in the lung.  There are a variety of platforms that are used to deliver this type of treatment including Imaged Guided Linear Accelerators and the Cyberknife.

   Increasing evidence suggests that this technique might be very effective at eradicating the disease in the areas treated.

   Recently, however, there have been reports of complications associated with this treatment approach.  Unfortunately, complications associated with treatment are often underreported because it is more interesting to report positive data then negative data.

   At the recent meeting at the American Society for Therapeutic Radiation and Oncology (ASTRO, the main US-based radiation oncology professional society), the incidence of severe pain and rib fracture were reported in a combined series from the University of Virginia and the University of Colorado.  Dunlap and colleagues (abstract here) reported that 13 of the 31 patients with lesions that were with 1.5 cm of the chest wall underwent high dose stereotactic radiotherapy either experienced chest wall pain or rib fracture.  Most patients who experienced rib fracture or chest wall pain experienced it around 7 months.  When they evaluated the plans after the fact, they identified the risk of rib fracture or chest wall pain to be associated with high dose radiation in the region of the rib.  This series suggested that if the volume of the chest wall that received over 30 Gy was greater than 40 cc the risk of complications approached 50%.  Although this series is somewhat small, there is the suggestion that if one can use techniques to limit the high dose region that overlaps the rib/chest wall region the risk of rib fracture or chest wall pain will be less.

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One emerging alternative to standard radiation therapy for medically inoperable patients with early stage NSCLC is stereotactic body radiation therapy (SBRT). This technique requires fixation and very precise treatment planning for a brief course of radiation that targets a more limited radiation field. One key issue with SBRT is that it presumes you don’t need to do extensive radiation to lymph node areas around the primary tumor — this is a big topic, but the evidence generally suggests this to be true, that we really need to focus more on treating the disease we see with stronger and more precise radiation, rather than get too distracted by the potential presence of microscopic regional disease in lymph nodes that appear normal on scans (abstract here, for example).

Our standard radiation dose of 60-66 Gray (the unit of radiation administration) for NSCLC is based on remarkably little evidence and goes back several decades. In fact, we know that similar or lower doses of RT are very effective in eradicating microscopic disease and laryngeal cancers that measure just a few millimeters, but radiation that is routinely administered in the 70 Gray and higher range are fair to good at treating smaller tumors like prostate and cervical cancers, both of which generally falling in the range of a few cm. In contrast, radiation for NSCLC lung lesions are often in the 5-10 cm range, and radiation in the 60 Gy range just isn’t that effective for such large and not especially radiosensitive tumors.

Newer techniques allow us to potentially deliver one or just a few fractions of very high dose radiation to a precisely limited area, thus reducing the risk of damage to surrounding areas and the need to administer radiation over many fractions over several weeks (radiation at low doses over many weeks takes advantages of the fact that normal non-cancer cells can recover better from radiation-induced DNA damage, leading to our routines of small doses accumulating over many weeks). By giving very high doses to a very defined area, stereotactic radiation becomes similar to a non-invasive form of surgery, leading to it being marketed as “gamma knife” or “cyber knife” (if you actually see any knives during these procedures, you should be concerned). This line of study was pioneered in the field of treating brain lesions, where the skull can serve as a reference system and the entire area can be immobilized with a fixed frame screwed into the skull (temporarily). These strategies are now very widely used for primary brain tumors or metastases to the brain from other sites.

But there are new techniques that allow introduction of the previously brain-based approach to body lesions as well. One of the less technical ones is to have a device that compresses the abdomen to minimize the ability of the diaphragm to move up and down and change the shape of the lungs:

(Click on image to enlarge)

That white arc is where a patient’s abdomen is, and the vertical screw clamps down on the abdomen to limit motion. You may also note the presence of a metal frame on either side of the chest to hold it in place as well. It may seem medieval, but this is a potential step forward in treating cancer. Read the rest of this entry »