Daniel Malatek, PA-C
Physician Assistant
Department of Radiation Oncology – GI Service
The University of Texas MD Anderson Cancer Center
Hi. My name is Daniel Malatek. I'm a Physician Assistant at the University of Texas MD Anderson Cancer Center and I work in the Radiation Oncology Department, GI Service. Today, we're going to talk about the role of radiation therapy in the treatment of colorectal cancers.
The objectives of this lesson are to discuss the foundational concepts in radiation therapy; describe how radiation therapy is delivered; and recognize the role of radiation therapy in the treatment of colon cancer, rectal cancers, and recurrent colorectal cancers.
There are three types of radiation therapy that are delivered by external beam. The first is photons. They're high energy x-rays that are produced by linear accelerators and the most commonly used form of energy for treatment. Electrons are produced by linear accelerators as well. They have a less of a depth of penetration so they're only used for specific circumstances. Protons are also an available treatment with rad --- external beam radiotherapy. But it is only available at a few select centers of which the University of Texas MD Anderson Cancer Center is one.
This is a picture of a linear accelerator commonly used today and a treatment room or vault as it's called that patients go into to receive their treatment.
Now, prior to linear accelerators, radiation therapy was most commonly delivered with a radioactive source or radioactive material of which Cobalt 60 was most commonly used. It's now mostly only used in third world countries who can't afford linear accelerators. But it is also the radiation source for gamma knives. And we won't speak much about gamma knives, but they're specialized radiation treatment machines that can deliver a very high dose of radiation therapy to a very small specific area. The side effects of Cobalt 60 are the same as radiation from linear accelerators, except the side effects are usually worse.
Now, there's two other ways that radiation therapy can be delivered and that's called brachytherapy and intraoperative radiation therapy. This involves the placement of radioactive materials. This is either temporary or permanently placed. Iridium-192 is mostly used for temporary placement and radioactive gold, palladium, or iodine is mostly used for permanent placement.
Here's a picture of a radioactive seed – one there and one there. They're very small, less than --- or about a millimeter in diameter.
Now, "What're the indications for radiation therapy in the treatment of colorectal cancer?" It can be used for definitive treatments, either neo-adjuvantly or adjuvantly. It can be used intraoperatively. It's used for local control of disease, treatment of recurrent cancers, and also for palliative treatments, including metastatic lesions.
Now, its role in colon cancer is limited. It's usually indicated when there is perforation of tumor through the colon, if there's an incomplete surgical resection with tumor left behind, or a patient is not a surgical candidate. It still will give local control of disease and it still can treat recurrent disease. And also, again, can be used for metastatic lesions from a colon primary.
Now, for rectal cancers, radiation therapy provides a more primary definitive role. It's commonly delivered preoperatively now, but, in the --- the not too distant future, it was used postoperatively quite commonly as well. Again, local control of disease, including for recurrence, is obtained with radiation therapy. And it gives the surgeon a better chance of tumor resection with sphincter preservation at the time of surgery as well. When it's used postoperatively in rectal cancers, it's used for local control.
Now, the dose of radiation therapy that's delivered when it's done preoperatively is a total dose of 50.4 Gray in 28 fractions. The first 45 Gray is given in 25 fractions to the whole pelvis that's at risk for disease, including the lymph nodes. And then an additional 5.4 Gray boost is given in 3 fractions to the tumor only. Again, this is for local control and to hopefully have a better sphincter preservation during surgery. And then surgery is performed approximately eight weeks after the completion of treatments.
This is a picture of typical radiation therapy treatment plan, one section of it. And, the red is the tumor being treated. The purple line is the area being treated to 45 Gray and the blue line is the area that's getting the total dose of 50.4 Gray.
Now, radiation can also be delivered inter --- intraoperatively as we mentioned earlier. When done so, 10 to 15 Gray is delivered to the tumor bed. It's delivered with brachytherapy, radiation seeds that are radioactive are used and they're temporary placed at the site of tumor. A high dose can be delivered by giving radiation therapy this way because normal tissues can be moved out of the way, lead shields placed to prevent doses of radiation from getting to normal tissues which cause side effects.
Now, when used postoperatively for colorectal cancers, a dose of 45 Gray in 25 fractions to the pelvis is usually delivered. And then there's an optional boost that can be given at the discretion of the physician and then for each patient's particular case to a dose of 5.4 Gray up to 9 Gray that's delivered in 3 to 5 fractions to the tumor bed. It's usually delivered four to six weeks after surgery once the patient has recovered from surgery. Their incision should be completely healed prior to starting radiation therapy because rad --- radiation can cause delayed wound healing. And once again, it's used for local control.
Now, there are special cases when radiation can be used definitively without surgery. However, it's not recommended. And the only reason you would usually want to consider it, is if the patient was not a surgical candidate. The radiation can be delivered either by external beam radiation or brachytherapy.
Now, retreatment of cancer that's reoccurred in a radiation treatment field is usually not recommended. The body that's received radiation therapy always remembers that fact and there's a greater risk of acute and late side effects if that area again receives radiation therapy. However, MD Anderson Cancer Center is one of the few centers that has been retreating patients with great success over the past five to seven years. Treatment can be delivered with either external beam or brachytherapy or both. When an area that's received previous radiation therapy is treated, smaller treatment fields are used to help minimize the risks of side effects, both acute and late. Smaller doses are given and usually the dose is --- daily dose is divided up into twice per day fractions.
Now, when delivered with brachytherapy again, definitively or intraoperatively, radioactive seeds are used. They're placed temporarily or permanently and temporary seeds are most commonly used intraoperatively, where permanent seeds are most commonly used for unresectable tumors.
So, in summary, radiation therapy is an integral part of the treatment of colorectal cancers. It is usually a safe and effective treatment for proven local control of tumors. It can render tumors more amendable to resection and reduce the risk of recurrence. In select patients, it can be used for retreatment as well. Thank you. This is --- is the end of my talk. And your feedback is appreciated.
The Role of Radiation Therapy in the Treatment of Colorectal Cancer video
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