Radiation therapy is given in a series of treatments that encompass several weeks. This schedule helps protect normal tissue by spreading out the total dose of radiation.
The treatment area is designed to include all of the cancer and as little normal tissue as possible.
The total dose used and the number of treatments depends on many factors. These factors include
- the size and location of the cancer (i.e. which normal tissues will be within the treatment area)
- the general health of your pet
- the type of cancer present
The most important consideration is the total amount of radiation that can be administered to a patient without compromising the ability of healthy tissue to heal. The treatment area may be marked with ink to enable the treatment to be directed to the same area every time. Please maintain the marks as directed.
Definitive or Curative Intent radiation therapy is given in a series of small daily dose treatments that encompass several weeks. This type of radiation is chosen when there is potential for long term control. This schedule helps protect normal tissue by spreading out the total dose of radiation. Most patients receive treatments on a Monday-Friday schedule for a total of 16-21 treatments over a course of approximately 1 month. There are some exceptions to this generalization, which will be discussed with you if it applies to your pet. Weekends are reserved as a rest period during which normal tissues have an opportunity to recover from the treatment. At times, more extensive rest periods are required.
Palliative radiation therapy is less intensive and is given in larger fractions of radiation 1-2 times a week for a total of 3-6 weeks. The intent of palliative radiation is to alleviate any pain or clinical signs such as reducing pressure, bleeding, or pain. Palliative radiation therapy is not considered a cure but is used to improve the patient’s quality of life and does not have long term control.
Veterinary patients are anesthetized for each dose of radiation to insure they remain absolutely still during the treatment. Because of the anesthesia required, they should not be feed after 10pm the night before treatments, but water may be provided throughout the night. Pets may be sleepy for several hours following each treatment.
The patient is monitored by the nurse anesthetist throughout the whole procedure. Electrocardiogram, blood pressure, and respiration are monitored using sophisticated equipment. A wide selection of modern anesthesia drugs accommodates each patient’s individual requirements and provides a quick recovery from anesthesia. This allows radiation to be safely administered five days a week.
We rely heavily on owner feedback as to how your pet is doing. If for any reason you do not feel they are recovering well, please let us know and we will be happy to adjust the anesthetic protocol as best we can. Something unique to PennVet is our use of SVAP’s (subcutaneous venous access ports) to administer anesthesia.
Patients may stay in the hospital from Monday through Friday, or come in for each treatment. We do not offer boarding on weekends as we would like them to be home and with their families.
Outpatient treatments take approximately two hours. The first day of treatment is typically the longest as we work to match the CT scan and make any necessary adjustments. The anesthesia protocol will also be determined at this point.
In the case of daily treatments we would also place the SVAP as a minor surgical procedure. Please plan on the first treatment day being the longest.
Here at Penn Vet we like to spoil our patients with love, attention, and of course the occasional treats. If there are any dietary discretions please let us know and bring appropriate treats or food for them.
Subcutaneous Venous Access Port (SVAP)
Something unique to us at PennVet is our use of SVAPs (Subcutaneous vascular access ports). They are long-term, surgically placed intravenous catheters that reduce the time, trauma, and discomfort associated with the placement of multiple short term catheters.
Venous access is necessary in order to ensure the patient’s safety during the multiple anesthesias required for animals undergoing radiation therapy. In many animals, there is difficulty maintaining this access throughout the course of therapy with multiple short term catheters (often in one of the limbs), because blood vessels can become scarred, collapsed, and inflamed when they are repeatedly used. SVAPs not only ensure a simple, non-stressful method to gain venous access, but they also minimize the need to use multiple veins, thereby preserving these vessels for future use (such as for blood tests, anesthesia, fluid supplementation, or drug therapy).
The SVAP consists of a long, thin, soft, flexible tube that is placed into a large vein (usually in the neck), and an attached reservoir that sits in a pocket under the skin (typically around the shoulder blade area) where drugs can be given or blood samples withdrawn. Placement and removal of the SVAPs require a brief surgical procedure lasting about 45 minutes each. Typically, the SVAP will be placed during the first radiation treatment and removed at the last treatment.
Minimal maintenance is required for SVAPs. The fur will be clipped around the area of the SVAP which when placed in the neck with be roughly half of the neck from the base of the ear to the tip of the shoulder. There will be two small incisions, one over the jugular vein and one just adjacent to the port itself. These areas should be checked for redness, swelling and discharge, and you should discourage your pet from licking, chewing or rubbing at the sites. Stitches, when present, are removed in 7-10 days. If the SVAP will not be used for a period of time, you will need to have a brief visit at PennVet to have the catheter “flushed” and “locked” every 2-3 weeks in order to prevent a clot from blocking the tubing and making it unusable. During the course of treatment, this maintenance will be performed at each visit.
Most complications associated with SVAPs are mild and easily managed, and consist mainly of soreness and swelling around the incisions for a few days. There is a small chance of localized infection, which is treated with antibiotics, but which may occasionally require removal of the SVAP. Serious complications are rare, and may include generalized infection and blood clots.
Vascular access ports have been used for over 20 years in the treatment of human cancer patients, and their use is increasing in veterinary medicine. Overall, the benefits of SVAPs outweigh the potential complications for most animals undergoing radiation therapy, and have become a standard procedure at Ryan Hospital.