Fracture rate and time to fracture in dogs with appendicular osteosarcoma receiving finely fractionated compared to coarsely fractionated radiation therapy: A single institution study

Abstract

Background Radiation therapy (RT) is used for local pain alleviation in dogs with appendicular osteosarcoma (OS), especially among dogs that are poor surgical candidates for amputation. However, many historical reports of fractionated protocols lack time to fracture and fracture rates. Objectives The primary objectives of this retrospective study were to determine fracture rate and time to fracture of dogs receiving RT (coarse or fine fractionated) for appendicular OS. Secondary objectives were to evaluate tolerability and disease outcome measures. Methods Fifty‐one dogs that received RT as part of treatment for appendicular OS were available for evaluation. Forty‐five received coarse fractionation (C‐RT, 8 or 6 Gy per fraction protocols [C‐RT8 or C‐RT6]) while the remaining six received fine fractionation (F‐RT). Results The overall pathologic fracture rate was 37%. Pathologic fracture rate was significantly higher for dogs that received F‐RT (5/6, 83%) compared to dogs that received C‐RT (12/40, 30%, p = 0.021). In the 17 dogs that fractured, the overall median time to fracture was 57 days. For all dogs, the median progression free interval (PFI) and median overall survival time (OST) were 90 and 140 days, respectively. In a very small cohort of dogs (n = 7) treated with zoledronate and RT, fracture rate was 0% and extended survival times were noted. Conclusions In conclusion, C‐RT is recommended over F‐RT due to lower risk of pathologic fracture and similar PFI. Prospective evaluation of combined C‐RT and zoledronate, especially for dogs with poor surgical candidacy, is warranted for the treatment of canine appendicular osteosarcoma.

Configuration of pathologic fractures in dogs with osteosarcoma following stereotactic body radiation therapy: A retrospective analysis

“…The rate of pathologic fracture in the present study was found to be very similar to the rate of pathologic fracture in previous studies: 39% in the present study versus 38% and 37% in 2 other studies 28,29 . All studies had similar cohorts of dogs based on median age (8.3 vs. 8.5 and 8 years old) and weight (43.2 vs. 41.1 and 48.2 kg).…”

“…In one of the other studies, dogs also received radiation therapy but not SBRT. 29 The most significant difference between the present study and the other study 28 is that tumour sites were treated with SBRT in the present study whereas patients in the other study were treated for pain with typically 2 or more of the following: opioids, tramadol, NSAIDs, gabapentin, neurotoxins and amantadine and only one dog receiving palliative RT. 28 The rate of fracture varied between the studies for some anatomic sites or bones whilst others were similar.…”

“…All studies had similar cohorts of dogs based on median age (8.3 vs. 8.5 and 8 years old) and weight (43.2 vs. 41.1 and 48.2 kg). In one of the other studies, dogs also received radiation therapy but not SBRT 29 . The most significant difference between the present study and the other study 28 is that tumour sites were treated with SBRT in the present study whereas patients in the other study were treated for pain with typically 2 or more of the following: opioids, tramadol, NSAIDs, gabapentin, neurotoxins and amantadine and only one dog receiving palliative RT 28 .…”

“…in the present study versus 38% and 37% in 2 other studies. 28,29 All studies had similar cohorts of dogs based on median age (8.3 vs. 8.5 and 8 years old) and weight (43.2 vs. 41.1 and 48.2 kg). In one of the other studies, dogs also received radiation therapy but not SBRT.…”

“…29 The two studies 28,29 grouped all femoral and tibial fractures for each bone irrespective of the location within the bone (distal vs. proximal). Compared to the present study, the other two studies 28,29 reported femur fracture rates of 57% and 60% versus 27%, and tibia fracture rates of 53% and 25% versus 47%.…”