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Radiation, surgery and chemotherapy are our main weapons in the fight against cancer. Similar to a standard radiology unit, our linear accelerator, located at VSH Cary, produces radiation when it is in use. The main difference is that the accelerator produces more powerful radiation which can be focused superficially or deeply on the tumor. |
| There are no radioactive substances used during treatment nor does the room or patient become radioactive. If not used carefully, radiation can be indiscriminate in its effect on the body, causing changes both to normal and cancerous tissues. Our success lies in focusing the radiation while limiting exposure of the normal surrounding tissue. |
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Just as with an oral or IV drug, the dose of radiation to a tumor must be calculated. This three dimensional picture was created on a radiation therapy workstation using two dimensional images imported from our CT scanner. The picture shows the dorsal surface of a dog’s head with the neck to the right and nose to the left. The scan stopped midway through the nose allowing us to see the turbinates within the nasal passages as well as the oral cavity.
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Dr. Dave Ruslander has rotated the image so that we are looking at the ventral surface of the neck with the nose pointing upwards. The green and red areas on the patient’s skin correlate to differing amounts of radiation received. The shape of the green area corresponds to the collimation of the radiation beam. For superficial tumors, a metal mold can be created with a cut-out corresponding to the shape of the tumor. This metal mold helps shield normal tissue. |
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The planning computer also shows cross sections of the patient. The green area in the middle of the computer image is a thyroid tumor. The other colored areas and lines within the cross section correlate to differing amounts of radiation exposure. The colored lines outside of the patient show the path of the radiation beams which will be used to treat the tumor. Deep tumors are typically treated from four directions so that the beams overlap at the tumor site.
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| This cross sectional view of the patient also allows Dr. Ruslander to look at radiation exposure of sensitive tissues such as the brain, spinal cord and lungs. The computerized data from the planning station is used to set the proper radiation beam angle and amount of radiation delivered from the linear accelerator. |
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Technicians bring the patients into the accelerator room and use either a short acting IV anesthetic or isoflurane via mask to induce them. Therapy is not painful but it does require the patient to be perfectly still during radiation exposure. An immobile patient also allows reproducibility since treatments are given as frequently as once a day for three weeks (21 treatments). |
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Radiation can produce some acute side effects such as desquamation of the skin as noted in this cat. Acute effects are seen in body tissues with a relatively high cellular turnover rate (skin, bone marrow, mucosal surfaces). These skin changes are not burns and in general aren’t painful. Because the barrier function of the skin can be compromised in some patients, we monitor for infection and treat with oral and topical antibiotics and anti-inflammatories.
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One chronic effect of radiation which can occur is a change in the color of the hair coat as in this German Shepherd. Owners are informed prior to therapy that this change is only cosmetic.
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Radiation patients are typically back to normal within an hour of the cessation of anesthesia and can be treated on an outpatient basis rather than admitted for long term hospitalization. This patient with osteosarcoma of the distal radius has been extubated for ten minutes. The markings on the patient help the nursing staff position the limb in the same manner for repeated treatments.
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