Palliative Radiation

Palliative external beam radiation therapy (PRT) can be used to control symptoms that cannot be relieved surgically or by other means. In the case of osteosarcoma, it may be indicated for patients who are not candidates for amputation.  It might also be indicated for treatment of painful bone metastases (spread to other bones) even after amputation, under specific circumstances. The goal of PRT is to provide relief of symptoms, not to cure the cancer.

Ask your radiation oncologist if a bone scan is necessary before starting the PRT, to look for other bone areas that might be involved, even without symptoms.  You should also ask about the possibility of combining the PRT with chemotherapy if your dog is not a candidate for amputation.

PRT is particularly useful to alleviate pain from osteosarcoma (bone cancer).  It is usually combined with pain medications and bisphosphonates.  Approximately 65 percent of patients will show a moderate to significant improvement in symptoms, and the effects can last for several weeks to several months.  It may begin to have effect several days after the first treatment, or it may take a few weeks before improvement is noted.

PRT delivers radiation over a period of time.  The treatment plan should be discussed with the radiation oncologist, regarding frequency and interval between treatments.  Each treatment procedure requires general anesthesia.

Aside from the potential side effects of anesthesia, side effects from PRT are usually limited to the area involved by radiation.  The side effects usually begin several weeks after starting treatment and can last for several weeks thereafter. The skin area that receives PRT will be pink or even red, with loss of hair and possibly some flaking or dryness of the skin.  This is known as “radiation dermatitis.” It can look like a severe sunburn or even a blistering rash. Topical medications prescribed by the veterinarian may help, and preventing the dog from licking, rubbing or scratching the treated area will also be of benefit.   Eventually the skin will become very dark, even black and there may be some hair re-growth. Long-term side effects such as risk of non-healing wounds usually occur after a year but are much less common due to the life expectancy of most dogs with osteosarcoma treated with PRT.

It is unusual for dogs to develop nausea or vomiting from PRT, unless part of the abdomen is involved in the radiation field.   If PRT is being recommended for bones involving the head/skull, there can be side effects involving the eyes or mucous membranes and salivary glands of the mouth.  These side effects should be discussed in detail with your radiation oncologist.

Please note:  PRT cannot be used in conjunction with artemisinin, an herb that is sometimes used in the management of osteosarcoma.  If your dog is currently getting PRT, artemisinin should not be started for several months after completing the therapy. If your dog is currently taking artemisinin and you are considering PRT, the artemisinin must be stopped for at least several weeks.

Stereotactic Radiosurgery

Stereotactic radiosurgery (SRS) uses imaging techniques and multiple radiation beams focused within the tumor to precisely deliver the beams directly into the tumor.  This enhances the radiobiological effect on the tumor and minimizes damage to normal tissues such as skin.

It also provides reduction in pain, excellent local tumor control, can

treat all anatomic sites, and requires less anesthesia than traditional radiation therapy.  In addition, SRS can also be administered with adjuvant chemotherapy. Unfortunately not all veterinary treatment facilities offer SRS.

Prior to starting SRS, bisphosphonates will be administered.   The most common complication is pathologic fracture, which could be related to prior bone damage from the tumor itself, or the effect of radiation on the bone.  

Survival time with the use of SRS is comparable to the currently accepted standard of care for limb osteosarcoma (amputation followed by chemotherapy).