Radiation Therapy for Pancreatic Cancer
Radiation therapy or radiotherapy uses high-energy rays to damage or kill cancer cells by preventing them from growing and dividing. Similar to surgery, radiation therapy is a local treatment used to eliminate or eradicate visible tumor. Radiation therapy is not typically useful in eradicating cancer cells that have already spread to other parts of the body. Radiation therapy may be externally or internally delivered. External radiation delivers high-energy rays directly to the tumor site from a machine outside the body. Internal radiation, or brachytherapy, involves the implantation of a small amount of radioactive material in or near the cancer.
Radiation therapy is an important treatment modality for patients with advanced pancreatic cancer, but is rarely used alone. Optimal treatment of patients with pancreatic cancer often requires more than one therapeutic approach. Thus, it is important for patients to be treated at a medical center that can offer multi-modality treatment involving radiation oncologists, surgeons, medical oncologists, medical gastroenterologists and nutritionists.
The role of radiation therapy alone for the treatment of pancreatic cancer is limited. Radiation therapy is usually given with chemotherapy, which can improve the average duration of survival for patients with localized and locally advanced disease.
External Beam Radiation Therapy
Radiation therapy is delivered to the pancreas and surrounding lymph nodes from a machine outside the body, called a linear accelerator, or from a shielded repository of a powerful isotope, such as cobalt 60. External beam radiation therapy is most often administered in conjunction with chemotherapy. In some instances, patients with advanced disease are treated with radiation therapy alone for palliation. Conventional radiation therapy is administered over a course of 5-7 weeks. The Radiation Therapy Oncology Group (RTOG) is actively involved in improving radiotherapy techniques for pancreatic cancer. The RTOG has evaluated higher dose radiation delivered on a twice-a-day basis as well as low-dose liver irradiation in clinical trials. Definite improvement with these approaches awaits results of further study. Technical advances in treatment planning of radiation therapy are allowing more precise targeting of radiation to the cancer.
Three-dimensional conformal radiation therapy can precisely target radiation to the areas of where cancer cells may be located, and therefore minimize side effects from radiation to normal structures such as the liver, stomach and kidneys. Because many patients develop areas of cancer cells in the liver, low-dose radiation therapy aimed at the entire liver has been used in an attempt to destroy cancer cells.
Side Effects of Radiation Therapy
Although patients do not feel anything while they are receiving radiation treatment, the effects of radiation gradually build up over time. Many patients experience fatigue as treatment continues. Loose stools or diarrhea is also common.
Strategies to Improve Treatment
While some progress has been made in the treatment of pancreatic cancer, the majority of patients still succumb to cancer and better treatment strategies are clearly needed. Future progress in the treatment of pancreatic cancer will result from continued participation in appropriate clinical trials. There are several areas of active exploration aimed at improving the treatment of pancreatic cancer.
Neoadjuvant Therapy: The use of radiation therapy and chemotherapy to shrink the cancer before surgery is referred to as “neoadjuvant therapy.” Patients with cancers that are “borderline” resectable may benefit from partial shrinkage of the cancer, which may allow a greater chance for complete removal of the cancer. Neoadjuvant therapy has been evaluated in clinical trials in an attempt to increase the likelihood of complete removal of pancreatic cancer with surgery. While it is currently unclear whether neoadjuvant therapy improves survival rates, there are several potential advantages to administering neoadjuvant therapy before attempting surgical removal of the cancer.
The side effects following surgery to remove pancreatic cancer are substantial and may delay the administering of post-operative (adjuvant) therapy. Approximately 25% to 33% of patients are unable to receive chemotherapy or radiation treatment following surgery. Additionally, some patients experience very rapid growth (recurrence) of pancreatic cancer following surgery. By administering neoadjuvant therapy, all patients are able to receive therapy for their cancer, while patients unlikely to benefit from treatment due to rapid growth of the cancer are spared the complications of surgery. Patients who experience cancer regression following neoadjuvant therapy are more likely to have their remaining cancer completely removed with surgery. Efforts are currently underway to determine the best combination of chemotherapy and radiation that will result in maximal shrinkage of the cancer before surgery.
Intraoperative Radiation Therapy (IORT): Intraoperative radiation therapy (IORT) is a single dose of radiation therapy that is delivered directly to the area of surgery during the operation. IORT is performed in specially-equipped operating rooms. During IORT, the radiation doctor can see the area being treated and move sensitive normal structures, such as the small bowel, away from the radiation beam. Results from some studies evaluating IORT indicate that cancer may recur less often in the area of the surgery.
Three-dimensional Conformal Radiation Therapy: Three-dimensional conformal radiation therapy can precisely target radiation to the areas where cancer cells may be located and therefore, minimize side effects from radiation to normal structures such as the liver, stomach and kidneys. Because many patients develop areas of cancer cells in the liver, low-dose radiation therapy aimed at the entire liver has been used in an attempt to destroy cancer cells.
Brachytherapy: Brachytherapy is the placement of a radioactive isotope, such as iridium 192, within the pancreas or by infusing other isotopes attached to biological compounds into a vein.
Placement of isotopes directly into the cancer at the time of surgery in patients with locally advanced disease may be effective in controlling local spread. Placement of isotopes through a laparoscope has also been performed on an outpatient basis with palliation of obstructive symptoms with minimal side effects.
Colloidal phosphorus-32 is a radioactive substance that spontaneously emits rays of radiation that can destroy cancer cells. Colloidal phosphorus-32 can be administered directly into the pancreas. This allows delivery of very large doses of low energy radiation directly to the cancer cells in the pancreas without affecting the whole body. To maximize the chance of destroying the cancer, doctors have combined the colloidal phosphorus-32 with a standard treatment approach for pancreatic cancer using external beam radiation therapy and chemotherapy. In one report, 5 patients with locally advanced non-resectable pancreatic cancer were treated with this approach. The therapy was well tolerated and all 5 patients experienced regression of their cancer. Three patients have now survived without local cancer progression over 24 months from initiation of therapy and 1 patient is approaching 36 months. Colloidal phosphorus-32 utilized in combination with other treatment strategies may represent a new treatment option for patients with pancreatic and other difficult to cure cancers. However, further clinical studies to determine the best way to incorporate the colloidal phosphorus-32 into treatment programs will be necessary.