Palliative radiation therapy
Palliative radiation therapy proto-cols are delivered with the intent of alleviating pain or another side effect associated
with an incurable tumor. Palliative radiation therapy typically is reserved for animals with a decreased quality of life and
that likely would not benefit from a more aggressive definitive course of radiation treatment.
Radiation therapy protocols are defined as definitive or palliative based on the total radiation dose and fractionation scheme.
Definitive protocols typically involve the delivery of 2.25 to 3.20 Gy per fraction on a Monday-through-Friday basis for a
total of 16 to 25 treatments and a total dose of 48 to 63 Gy.
Palliative radiation protocols typically involve the administration of a larger dose per fraction, but a fewer total number
of fractions and lower total radiation dose. A variety of palliative protocols exist. One of the most commonly used protocols
is 8 Gy per fraction, given once weekly for four consecutive weeks for a total dose of 32 Gy. Another involves 5 Gy per fraction
once daily for five consecutive days for a total dose of 25 Gy.
Palliative protocols typically are associated with minimal to no acute adverse effects, such as moist desquamation of the
skin or oral mucositis. The larger dose per fraction does increase the risk for late adverse effects, but most animals receiving
palliative radiation therapy typically do not live long enough to develop late effects.
Palliative radiation therapy has been studied most thoroughly for the treatment of canine osteosarcoma. Approximately 75 percent
to 90 percent of dogs experience pain relief based on an improvement in lameness. The median time from when radiation therapy
is initiated to when lameness improves is around 14 days (range, one to 60 days). Median duration of analgesia is around two
to four months, but individuals have enjoyed considerably longer periods of pain relief. Palliative radiation therapy also
has been effectively used to treat oral tumors, nasal tumors, thyroid carcinomas and soft-tissue sarcomas.
Prednisone can be used as a chemo-therapy drug for some forms of cancer. When dogs with lymphoma are treated with single-agent
prednisone, approximately half will attain either a partial or complete remission. Remissions usually are transient, though,
and survival times typically are around one to two months. Prednisone can be used for cats with lymphoma; survival times usually
are less than one month. Canine mast-cell tumors can be treated palliatively with single-agent prednisone. Approximately 20
percent of dogs will enjoy a partial or complete remission. Response durations are variable, but usually persist for a few
weeks to a few months.
It is critical to reach a definitive diagnosis of cancer before placing an animal on a palliative course of steroids.
While response rates to prednisone are low, the responses that do occur can be quite dramatic, particularly for dogs with
lymphoma. It is not uncommon for an owner to change his or her mind and request that more aggressive therapy be initiated
after seeing a marked response to prednisone.
However, reaching a definitive diagnosis once the animal is in a partial or complete remission can be difficult or impossible,
and it is below current standards of care to initiate aggressive cytotoxic chemotherapy without a definitive diagnosis of
Additionally, before starting a course of palliative steroids, owners always should be counseled that if they decide to pursue
more aggressive chemotherapy at a future time, pretreatment with steroids can induce multi-drug resistance mechanisms that
diminish the efficacy of chemotherapy.
The anti-inflammatory effects of prednisone can be very beneficial as well. Tumors often can induce an inflammatory response,
and this secondary peritumoral inflammation and edema can have a significant clinical impact. For example, in dogs and cats
with brain tumors, an anti-inflammatory course of prednisone can dramatically improve clinical signs for up to a few months.
Prednisone can reduce the congestion and stertorous breathing often seen in animals with nasal tumors, as well as the coughing
associated with pulmonary metastasis. Prednisone also can help maintain quality of life by improving appetite and energy level.
Palliative care is about quality of life. Alleviate anything that is hindering quality of life, and try to prevent future
hindrances from arising. There is no single best palliative treatment plan. The plan chosen will depend on the tumor type,
the tumor location, the patient's clinical signs and the owner's goals.
Because there are so many variables, close communication between the veterinary staff and the owner is vital. The owner sees
his or her animal in its own environment every day and therefore will recognize subtle changes more quickly. This feedback
can be used by the veterinary staff to modify the palliative treatment as needed.
At the same time, this feedback will help strengthen the bond between the owner and veterinarian, a bond that becomes even
more important when quality of life can no longer be maintained and the conversation turns to euthanasia. The strong trust
that has been fostered will allow the owner to realize that you have his or her animal's best interest at heart and take comfort
in the knowledge that everything was done to provide his or her family member with the best possible quality of life for as
long as possible.
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: firstname.lastname@example.org