The Johns Hopkins colorectal health care team may recommend radiation therapy as part of the treatment for colorectal cancer. Radiation can be administered two ways, either as external radiation therapy, or as intraoperative radiation therapy which is administered as during a surgical procedure.
The Goals of Radiation Therapy
The benefits of radiation therapy for patients with colorectal cancer include: killing and eliminating cancer cells and tumors; shrinking tumors; and, preventing cancer cells from growing and dividing. The DNA of a malignant cell is more susceptible to radiation damage than a normal cell. Radiation used before surgery to shrink a tumor can provide the best chance of successful tumor removal during surgery. Radiation administered after surgery can eliminate remaining cancer cells.
For colon cancer, radiation therapy is used mainly for fixed lesions (lesions that are adherent to structures adjacent to the colon, such as the abdominal wall or the bladder), and for metastatic disease (secondary cancer), such as tumors that have traveled through the lymphatic system or bloodstream to the liver, lung or brain.
For rectal cancer, combined radiation therapy and chemotherapy are often used as a pre-surgery (neoadjuvant) therapy, and/or as a post-surgery (adjuvant) therapy. Neoadjuvant radiation is used to shrink tumors prior to surgery, which may help to decrease the chances that a permanent colostomy will be required. Radiation treatment is commonly recommended in situations where the rectal tumor has grown through the wall of the bowel or has spread into nearby lymph nodes.
Radiation therapy is typically combined with chemotherapy, such as the drug, 5-FU. Adding chemotherapy to the radiation therapy improves the effectiveness of the treatment by making the tumor cells more sensitive to the radiation. This sensitivity allows the radiation to do more damage to the tumor cells. Administering the radiation and chemotherapy prior to surgery has been shown to improve the effectiveness of the surgical treatment (Sauer, et al.), and, also, to decrease the risk of side effects.
External radiation therapy (Figure 1) is delivered via a machine, such as a Linear Accelerator or Tomotherapy machine, that makes high energy X-rays or photons, which can be targeted to areas inside the patient. The type of machine used is dependent upon the location of the cancer. Treatments are generally given daily, Monday through Friday, for five to six weeks. When multiple beams of radiation are used to deliver radiation to the rectal tumor and adjacent lymph nodes we call this intensity modulated radiation therapy (IMRT) (Figure 2). IMRT uses computer programming to deliver a pricise three-dimensional dose of radation directly to the tumor and the immediately surrounding tissue. one version called TomTherapy combines radiation with computerized tomography (CT) imaging. This procedure maps the size and shape of the tumor to be treated, sparing surrounding tissue from radiation.
|Figure 1. Standard three field radiation plan. A: horizontal cut-away view as seen from top of body (axial) B: vertical cut-away view as seen from left side of body (sagittal) C: vertical cut-away view as seen from front of body (coronal). The planning treatment volume of radiation outlined in red and the prescription isodose lines are labeled in the upper left corner of each image.|
|Intensity Modulated Radiation Therapy (IMRT). A) axial B) coronal views C) sagittal views. Patient is positioned supine. After CT simulation, nodes at risk and the primary tumor plus a margin are treated with multiple modulated beams to deliver focused radiation while limiting dose to normal adjacent structures. |
In certain circumstances, radioactive substances may be placed directly into the tumor (an implant), or, into an adjacent body cavity (intracavity radiation). With this type of treatment (brachytherapy), the radioactive substance is administered for one day, or a week, or permanently. Brachytherapy is often administered in conjunction with surgery, or, as an additional treatment combined with external radiotherapy.
Another possible treatment approach is called intraoperative radiation therapy (IORT), in which a dose of radiation is delivered directly to the affected tissues inside the body during the surgical procedure (Figure 4). With IORT, a high dose of radiation can be focused on the remaining tissue surrounding a tumor while limiting the dose to adjacent normal tissues. Not all patients are appropriate for IORT. Prior to being selected for IORT you will need to be seen in the consultation with a surgeon and radiation oncologist who specializes in colorectal cancer.
In addiation to IORT, chemotherapy and/or radiation may need to be used before or afer surgery. In other cases no furhter radiation treatment is required tfollowing IORT, making it a much more convenient approach for delivering therapy. Unlie X-ray radation, IORT radiation affects less normal tissue because it is delivered at the time of surger through catheters. After the radation is delivered, the catheters and radiation are removed from your body and no radiation is left behind. The form of IORT most commonly used at Johns Hopkins is high dose brachytherapy, which is also called HDR-IORT.
Johns Hopkins is one of the few institutions in the country using high dose rate (HDR) brachytherapy for the treatment of recurrent malignancies, after previous radiation treatment has been performed. HDR is delivered locally to the previously irradiated tumor at the time of surgery. Delivering HDR radiation locally decreases toxicities to other structures. It can also be used after neoadjuvant radiation is delivered for T4 rectal cancer.
|Figure 4. HDR-brachytherapy involves placement of catheters in the tumor bed following en bloc resection of the rectal cancer. The catheters are often placed into a silicone flap that can be cut to conform to the tumor bed (A). After adjusting the wires to the appropriate length (B), the flap is placed into the operative field with the appropriate shielding (C). A wire with a single iridium source (I-192) at the end then passes through the catheters imbedded into the flap at evenly spaced 1-cm intervals to deliver the radiation. |
Side Effects of Radiation Therapy
Patients can expect some common side effects during and after radiation therapy (including radiation therapy administered in combination with chemotherapy). The specific side effects and severity of each depends on the individual patient, the body part being treated, and the dose of radiation required. Some patients experience no side effects or mild ones, while other patients experience more severe reactions. Side effects include: bloating, constipation, diarrhea, fatigue, gas, loss of appetite, mouth sores, nausea, skin changes, sore throat, taste changes, and vomiting. The Johns Hopkins health care team closely monitors side effects as well as the progress of the cancer treatment itself.
Radiation therapy clinical trials are currently underway at Johns Hopkins to improve treatment options and outcomes for patients with colorectal cancer.