Radiation Therapy Options for Osteosarcoma
WHAT IS STEREOTACTIC RADIATION THERAPY FOR OSTEOSARCOMA?
Nonsurgical alternative methods for limb salvage such as stereotactic radiation therapy (SRT) can be considered in dogs who are not deemed suitable candidates for amputation. In the published literature about this technique in dogs, the reported outcome and survival was similar to dogs who underwent treatment with amputation followed by chemotherapy.
Typical protocol involves a CT scan the week prior to generate the radiation treatment plan. After the radiation treatment plan has been generated, the use of a biosphosphonate 24-72 hours prior to the first dose of radiation therapy is recommended. The current SRT protocol utilizes 3 doses of radiation on 3 consecutive days. Chemotherapy (usually carboplatin) is administered at the time of the first or second radiation therapy treatment and is continued every 21 days for a total of 4-6 doses of chemotherapy.
Pathologic fracture is the most common complication following this procedure. This is mostly due to the amount of preexisting tumor associated osteolysis and the amount of postirradiation bone necrosis. Typically smaller and more blastic lesions are better candidates for this procedure over large and more lytic lesions. Pathologic fracture rates can range from 30-45%. Other side effects include hair loss, pigmentation of the underlying skin, and dermatitis (skin burn from radiation). Long term side effects from radiation include fibrosis and necrosis within the radiation site.
WHAT IS PALLIATIVE RADIATION AND HOW IS IT EFFECTIVE FOR OSTEOSARCOMA?
The goal of palliative radiation therapy is to address the pain and swelling associated with the primary tumor and we see relief in up to 70% of patients for some period of time. This therapy is given either as 2 consecutive treatments on back-to-back days, or once weekly for 4 treatments. Palliative radiation may have some anti-tumor benefit, however these effects are likely short-lived with minimal to no tumor control noted, and no benefit provided to lower the risk of metastasis. Side effects of this therapy are rare however the treatments do involve low-level anesthetic events.
Without chemotherapy, survival times using palliative radiation therapy, with the addition of bisphosphonates (used to strengthen the bone) is generally around 3-4 months. The addition of chemotherapy may contribute some anti-tumor benefit, potentially lower the risk of or delay the onset of metastasis, and extend some patient survival times.