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Stereotactic Body Frame
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The Department of Radiation Oncology at the Indiana University School of Medicine is one of only a small number of sites in the nation that have the capability to perform stereotactic conformal radiotherapy in the chest and abdomen. The concept of extremely precise radiation delivery as popularized in radiosurgery treatments to the brain can also be used to treat certain lesions in the chest and abdomen when appropriate. Stereotactic conformal radiotherapy using the stereotactic body frame allows dose escalation with minimal exposure to surrounding normal tissues. The stereotactic body frame allows for precise and reproducible localization of tumors located in the chest, abdomen, or pelvic regions. With this technology, treatments typically requiring weeks to months to perform with conventional radiation therapy can be performed in two or three fractions. The stereotactic body frame is coupled to an extremely sophisticated 3-D conformal treatment planning system that exploits the localization characteristics of the frame itself. As with the Gamma Knife radiosurgery unit, indications for the stereotactic body frame in treatment of malignant lesions outside the brain continue to expand. Questions and answers regarding the early stage medically inoperable lung cancer protocol opened at Indiana University Medical Center on February 2, 2000. The protocol involves the use of stereotactic body radiotherapy, a method of precisely directing more potent radiation doses toward a tumor with considerable more sparing of surrounding normal tissue than conventional radiation techniques. Eligible patients must have previously untreated stage I lung cancer (early stage cancer that has not spread to lymph nodes or to distant organs) and have pre-existing medical problems making them unsuitable candidates for surgical removal of the tumor. To our knowledge as well as to the knowledge of the manufacturer of the equipment, this is the first U.S. formal trial of stereotactic body radiotherapy for primary lung cancer. While much credit for this technology should go to the Swedes as noted below, the unique aspects of this trial are the patient population (patients with "curable" lung cancer) and the intensity modulated radiotherapy (developed in-house for this application at Indiana University). How exactly does stereotactic body radiotherapy work and what are its advantages over traditional radiation therapy? Stereotactic treatments involve directing therapies, in this case focused beams of radiation, toward a target in three-dimensional space using a computer assisted guidance. The three dimensional space is defined by a frame that immobilizes the patient and sets reference coordinates. The concepts of stereotaxis were originally developed by a Swedish neurosurgeon, Lars Leksell, for precisely guiding needles through the brain toward abnormalities for biopsy or therapy. Dr. Leksell subsequently used the same concepts to build the Gamma Knife, which is a machine used to perform radiosurgery on brain abnormalities. Stereotactic radiation treatments in the brain are characterized by optimal immobilization, millimeter precision in targeting and treatment delivery, and rapid falloff of dose to surrounding sensitive normal tissue. Gamma Knife radiosurgery, used for both benign and malignant brain tumors as well as vascular malformations and functional disorders, has been one of the biggest medical success stories of the 20th century. In the case of treating brain metastases from cancers arising elsewhere in the body, control rates with a single Gamma Knife treatment are reported around 90%. Translating the Gamma Knife technology to the body has not been straightforward due mostly to problems with inherent organ motion and patient immobilization. We want our patient's heart to beat and we want them to breathe, and the bowels will churn-- all potentially moving tumor targets. The system we are using to reduce the magnitude of these problems again was invented and developed by Swedish doctors, Drs. Ingmar Lax and Henric Blomgren, at the Karolinska Hospital. They have been treating patients with metastases to the lungs, liver, and retroperitoneum using this system for several years. Metastases are tumors that originated in a separate organ, such as the colon, breast, etc., and spread to other distant organs. These patients are typically not curable with modern medicine including chemotherapy. In 1997, our group at Indiana University traveled to Stockholm to train with Drs. Blomgren and Lax. When we returned we began treating metastases in a similar fashion. We have not previously treated patients with primary lung cancer limited to the original site, and at that time of our training in Sweden, neither had Drs. Blomgren and Lax. Primary early stage lung cancer is ideally treated with surgery. If the tumor has not metastasized, the cure rate is 50-60% for stage I. Because of significant medical problems like emphysema, heart disease, stroke, and diabetes, some patients could not tolerate a surgery to remove lung for lung cancer. These patients may be offered conventional radiation therapy. Cure rates with conventional radiation are typically 20%, with some reports slightly higher. Many patients in the U.S. don't take either treatment option and are simply followed. Many of these patients will eventually die of lung cancer. Conventional radiation therapy is delivered with technology that actually treats dramatically larger volumes of normal tissue to high dose than the cancer volume itself. Because of the large volumes of normal lung and other tissues like heart and esophagus exposed, the treatment must be prolonged or fractionated. Conventional radiation therapy involves 20-35 daily treatments given as an outpatient over 4-7 weeks. Typically, the amount of radiation ultimately delivered is limited by the tolerance of normal tissue. Unfortunately, most patients treated this way will eventually recur resulting in the poor survival data. With the stereotactic body radiotherapy we have the ability to exclude normal tissue from high doses of radiation. We also can better concentrate the radiation within the tumor in order to afford more tumor kill. The protocol involves only 3 outpatient treatments, which owes to the fact that large doses are given with each session. There is increasing evidence that large doses are more biologically effective, as indicated by the Gamma Knife experience. What types of equipment does the procedure involve? e.g. is Computed radiography used to image the patient? The patient lies in a stereotactic immobilization frame equipped with an abdominal press that minimizes tumor motion caused by breathing while the patient still breathes using more chest wall expansion rather than the diaphragm. The patient has a scan in this position using computed tomography (CT). Images are transferred to a treatment planning computer where the slices can be reconstructed in 3-D to give a representation of the patient, both internally and externally. The tumor is targeting and a dose plan is created. As part of the 3-D treatment planning approach, we have developed a separate method of intensity modulating each beam of radiation. Intensity modulation allows the dose within the target to be maximum near the center where cells are known to be most resistant to radiation and still fall off very rapidly to surrounding normal tissue. This dose distribution is again similar to those generated by the Gamma Knife. Our method of intensity modulation involves milling custom tissue compensators for each beam for each patient. These tissue compensators are made of a lead alloy and are placed in front of each beam prior to treatment. The treatment is carried out using a modern linear accelerator which generates high-energy photons (electromagnetic radiation). Numerous beams (typically around 7) are aimed at the tumor using the stereotactic guidance system coupled with room lasers. Each treatment takes about 45 minutes. -Can you give me the names of the companies which manufactured the various equipment used in your study - (e.g. the imaging modality and the device for administering intensity modulated photon radiation)? Elekta Instruments, Stockholm, manufactures the stereotactic frame. Our 3-D conformal dose planning system is called Render 3-D produced by Precision Therapy International, Atlanta. Our intensity modulation system was internally developed at Indiana University Medical Center. Can you give me more details concerning the trial set-up? e.g. How many patients will be involved? The phase I study (dose escalation toxicity study to determine the maximum safe amount of radiation for these rather debilitated patients) will accrue a maximum of 25 patients with 3 patients on each dose level. Several weeks will be required for observation between each dose cohort level to observe for toxicity. Once the maximum tolerated dose is determined, as many as 35 more patients will be studied in the phase II portion of the study. This phase will serve to confirm the toxicity data and make some estimation about the efficacy of the treatment. The trial does not involve a randomized treatment assignment in either phase. How long is the trial expected to last? 2-4 years. What will the follow-up involve? Routine interval examinations with chest x-ray and pulmonary function tests every 3 months for 5 years. I assume from the press release, the patients will undergo 3 outpatient treatments; how long will each treatment last? About 45-60 minutes Is the trial being financed by industry, and if so by whom? The trial is not industry sponsored and our department will bear the cost of data management. Insurance companies or patients will be billed for radiation treatments and computer planning. Can you put a figure on how many early lung cancer patients in the US are NOT candidates for surgery and will be candidates for this new treatment? The figure is not precisely known. Dr. Mark Williams, a pulmonologist and the trial's principal investigator, estimates that around 10,000 to 20,000 patients are diagnosed each year in the U.S. who would be eligible for this trial. The protocol is testing patients with the poorest tolerance of treatment. If the results are encouraging, others with marginal pulmonary functional could be given this therapy as an option without a need for a similar phase I and II study (the toxicity in healthier patients could only be less). Eventually as more centers acquire this technology, a randomized study could be performed comparing various treatment options for larger patient populations. Is radiation therapy currently the ONLY treatment for these patients? Yes, conventional radiotherapy is the only non-surgical treatment with a confirmed cure rate. Your press release says that in 1997 IU did the first treatment for a patient whose cancer has spread to the lung. Please let me correct this statement. I.U. did the first treatment IN THE US for a patient whose cancer had spread to the lung. This occurred in 2/97. The Swedes had treated similar metastatic patients dating back to 1991. How successful was that treatment? The tumor was controlled, but the patient died later of tumor recurrence elsewhere in the body. Interestingly, we have treated several patients with what seemed to be very hopeless metastatic disease refractile to chemotherapy. While these were a very select group of patients, we have a few patients out more than two years with no evidence of further progression. This experience constitutes why we have so much optimism for the current trial. How many similar patients has it been performed on? We've treated about 20 patients with lung metastases as of February 2000. Is this new treatment being evaluated for other forms of cancer e.g. prostate? please expand. We have a protocol at our center for recurrent pelvic cancers from GYN and GI sources (rectal, cervix, endometrial, etc.). We don't have a protocol for prostate cancer and to date we have not treated any patients for primary prostate cancer. Has the procedure been widely accepted by the medical community as a treatment for this population, or is it still too early to say? It is not widely accepted in the U.S. despite encouraging publications on metastases from Karolinska Hospital. Interestingly, the Gamma Knife was not embraced in the U.S. when it was introduced in 1987 despite 20 years of published encouraging results from Europe. This is why we are conducting a formal study on protocol rather than ad hoc treatments. A few other centers have been treating patients in the U.S. with a similar system for stereotactic guidance. Some of these centers have made rather bold and exaggerated claims about their experience and the success rates. What is necessary is carefully conducted scientific study rather than anecdotal experience. Hopefully, the protocol treatment will help patients, and the results of the trial will be considered legitimate by the medical community. These things take time. Inquiries regarding the protocol should be directed to: Web sites featuring this protocol include: http://www.wired.com/news/technology/0,1282,34165,00.html http://www.sciencedaily.com:80/releases/2000/02/000207074209.htm
[Keywords: stereotactic conformal radiotherapy, chest, abdomen, lung cancer] |
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