Palliative Radiation Therapy -An Incredibly Valuable Tool

When dealing with cancer care in veterinary patients, palliative care is a significant part of what we do.  When I look back over the number of radiation patients that I have treated over the past 10 years with radiation, approximately 65% of these patients were treated with palliative radiation.  This is higher than the numbers reported for people where approximately 50% of patients receiving radiation are treated in a palliative fashion.  However, the goals for palliative radiation may be very different in people versus animals.

In people, palliative care refers strictly to treating a clinical sign or a symptom but in animals there are many reasons why pet owners might choose palliative care.  Palliative radiation may be a more feasible option for our veterinary patients because it typically involves fewer treatments (meaning fewer anesthesia episodes), fewer side effects, and lower costs to the client.

Palliative radiation usually involves between three and six treatments of radiation delivered over a three to four week period.  Side effects with these doses tend to be mild to non-existent.  In some cases a single treatment may be enough to help make an animal feel better.  These protocols are designed to limit the adverse effects on a patients quality of life, in the short term.

The primary use of palliative radiation is for the treatments of pain.  Palliative radiation has been used to successfully treat pain in dogs with appendicular osteosarcoma.  Treatment protocols range from two treatments of 10 Gy each to 4 or more treatments.  Approximately 75-90% of dogs achieve significant pain control within a week of the first treatment, sometimes within days (Knapp-Hoch, et all JAAH 2009, Green et al JAAHA 2002, Ramirez et al VRUS 1999).  This pain control lasts for approximately three months on average.

john1Figure 1  Image of an osteosarcoma of the distal radius.  Palliative radiation results in pain control in 75-90% of dogs, usually within one week of the first treatment.

 

 

 

 

 

 

 

 

 

However, palliative radiation can also be used to treat pain or discomfort from any tumor.  Pain control can occur with different tumor types (Bateman, et al JVIM 1994) Tumors that are inflamed will often “dry up” with palliative radiation, resulting in much less irritation.  For dogs and cats with oral tumors, palliative radiation can often control pain enough to help the animal eat better for a period of time.  Finally, in some cases when animals are having difficulty breathing, eating, defecating, urinating etc, such as advanced thymoma or other thoracic masses, enlarged cervical lymph nodes, or any tumor that interferes with an animals normal function, palliative radiation may help provide temporary relief.

Nasal tumors can often be effectively treated with palliative radiation.  Definitive radiation for nasal tumors often results in severe side effects and decreases quality of life for a significant period of time.  Newer radiation techniques such as intensity modulated radiation or stereotactic radiation have been beneficial for preventing some of these side effects.  However, for owners who cannot afford to put their pets through these treatments, palliative radiation can be very effective.  One study showed that palliative radiation for nasal carcinoma in dogs can result in tumor control for over 7 months and survival of almost a year (11 months) (Cancedda et al VRUS 2015)

john2Figure 2. Before (left) and 6 months after (right) images from a CT scan of a dog with a nasal carcinoma treated with palliative radiation

 

 

 

 

 

Another new use for palliative radiation has been either as a primary treatment or as adjuvant therapy for dogs and cats with incompletely excised soft tissue sarcomas and nasal tumors.  A number of studies have shown that patients with these tumors who can not have surgery can have a good survival with palliative radiation alone (Lawrence ,et al JAAHA 2008, Poirier, et al In Vivo 2006, Sones et al Vet Radiol Ultrasound 2013).

There are a number of potential uses for palliative radiation for animals.  While most of these are aimed at “the relief of animal suffering” as it is written in the veterinarian’s oath, some can provide months of quality time for dogs and cats with cancer.

Submittted by Dr. John Farrelly DVM, MS,

ACVIM (Oncology), ACVR (Radiation Oncology)

Radiation Oncologist/Medical Oncologist at The Veterinary Cancer Center

References

Green EM, Adams WM, Forrest LJ. Four fraction palliative radiotherapy for osteosarcoma in 24 dogs.  J Am Anim Hosp Assoc. 2002 Sep-Oct;38(5):445-51.

Knapp-Hoch HM, Fidel JL, Sellon RK, Gavin PR. An expedited palliative radiation protocol for lytic or proliferative lesions of appendicular bone in dogs.  J Am Anim Hosp Assoc. 2009 Jan-Feb;45(1):24-32.

Ramirez O 3rd, Dodge RK, Page RL, Price GS, Hauck ML, LaDue TA, Nutter F, Thrall DE. Palliative radiotherapy of appendicular osteosarcoma in 95 dogs. Vet Radiol Ultrasound. 1999 Sep-Oct;40(5):517-22.

Bateman KE, Catton PA, Pennock PW, Kruth SA. 0-7-21 radiation therapy for the palliation of advanced cancer in dogs.  J Vet Intern Med. 1994 Nov-Dec;8(6):394-9.

Cancedda S, Sabattini S, Bettini G, Leone VF, Laganga P, Rossi F, Terragni R, Gnudi G, Vignoli M. Combination of radiation therapy and firocoxib for the treatment of canine nasal carcinoma.  Vet Radiol Ultrasound. 2015 May-Jun;56(3):335-43.

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