Page 561 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 25 Tumors of the Skeletal System 539

Nonsurgical Limb Salvage H H
Intracorporeal and Extracorporeal Intraoperative
VetBooks.ir Radiation Therapy
Intraoperative RT (IORT), using either an intracorporeal or extra-
corporeal approach, for limb sparing has been utilized in a small
number of canine OSA patients 225,226 as well as human patients
with extremity bone tumors. 227–229 This limb salvage technique
involves a surgical approach to the bone with osteotomy proxi-
mal or distal to the affected site (depending on the anatomic loca-
tion of the tumor) and reflection of normal soft tissues from the
tumor affected bone. The neurovascular bundle, muscle, and skin
are retracted away from the affected bone, and the tumor is piv- 8.56 cm 8.57 cm
oted from the site on the intact joint tissue. The patient is then
transported to the radiation suite and a single dose of 70 Gy is F F
then delivered to the tumor, taking care to spare the distracted
neurovascular bundle. The irradiated bone is then anatomically • Fig. 25.9 Dose color wash map of radiation distribution for stereotactic
replaced and surgical fixation of the osteotomy is achieved with radiation therapy of distal radius osteosarcoma lesion showing a steep
either dynamic compression plating or an interlocking nail sys- dose gradient drop off between tumor volume and normal tissues.
tem. One advantage of IORT for limb salvage over LSS is that it
can be used to preserve limb and joint function in anatomic sites MST was 9.7 months. Of the patients with complete medical
that are not amenable to LSS with arthrodesis of the adjacent joint records, 63% developed pathologic fracture at a median of 5.9
(e.g., proximal humerus). 162 Patients treated with IORT had good months. Acute and late skin toxicities developed in 58% and 16%
limb function in the immediate postoperative period; however, of dogs, respectively. Involvement of subchondral bone appeared
complications related to surgery or RT led to implant revisions to be predictive of shortened time to fracture.
in 69% of cases within 5 to 9 months of initial surgery, including Many veterinary radiation oncology facilities currently offer
four amputations. Pathologic fracture of the irradiated bone was SRT for OSA. SRT protocols for the treatment of OSA typically
the most common complication. Additionally, local tumor recur- involve two to three fractions with doses ranging from 8 to 13 Gy
rence occurred in four dogs and infection in four dogs. A modi- per fraction, and the most common protocol is three fractions of
fication of this technique includes complete temporary removal 10 Gy. These fractions are delivered daily or, less commonly, every
of diaphyseal tumors, performing extracorporeal IORT, and then other day.
reimplantation and stabilization of the irradiated bone segment. In an orthotopic, athymic, rat model inoculated with canine
In situ radiation of distal femur and any tibial tumors can be per- OSA cells, three fractions of 12 Gy SRT was shown to induce
formed without osteotomy. The disease-free and overall limb and complete tumor necrosis in 92% of rats treated. 232 Previous
joint salvage rates for extracorporeal IORT as assessed at the time canine studies have indicated that therapies which induce more
of death or data analysis were 46% and 54%, respectively. The than 80% local tumor necrosis are associated with an increase in
MST for dogs with appendicular sarcoma treated with limb- and local tumor control. 233 The same athymic rat model also indicated
joint-sparing extracorporeal IORT was 298 days. that zoledronic acid combined with parathyroid hormone could
increase bone volume after SRT. Many oncologists advocate the
Stereotactic Radiation Therapy use of bisphosphonates before or after SRT. As SRT is a local-
SRT or stereotactic radiosurgery (SRS) offer the ability to deliver ized therapy, adjuvant chemotherapy is recommended to delay the
high dose RT to the tumor volume with relative sparing of the onset of metastatic disease. Chemotherapy can also be considered
surrounding normal tissues by use of accurate patient immobili- as a radiation sensitizer as reported in the studies of single frac-
zation, image guidance, and a rapid dose fall-off from the tumor tion SRS for canine OSA. 231 Radiation recall (recurrence of acute
margins (Fig. 25.9). In this respect, it is a refinement of the IORT skin toxicities after initial resolution) has been observed in some
technique that avoids the need for surgical exposure. A nonsurgical patients treated with adjuvant DOX chemotherapy.
limb salvage technique using a single fraction SRS was developed Pathologic fracture is the most frequent complication associ-
at the University of Florida, and initial results were reported in 11 ated with SRT and SRS. Fracture is postulated to be due to the
dogs. 230 Adjuvant carboplatin chemotherapy was used in six dogs amount of preexisting tumor associated osteolysis and postirra-
immediately before RT for its potential radiosensitization action diation bone necrosis resulting in loss of dynamic bone remodel-
in addition to its conventional cytotoxic effects, and five dogs were ing and healing capacity after SRT. Smaller, more blastic lesions
treated with SRS alone. Four dogs developed pathologic fractures may be better candidates for SRT limb salvage than larger, more
and one dog developed infection. Acute effects to the skin were lytic lesions. There is some evidence that lysis of subchondral
generally mild to moderate; however, one dog developed an open bone may be associated with a higher rate of fracture. 231 Patho-
skin wound 3 months after treatment, and another dog developed logic fracture has been treated by internal fixation, external
a full thickness skin wound under a splint used during the treat- coaptation, or amputation. 112 Preemptive stabilization has also
ment of a pathologic fracture. Limb use in the dogs treated with been used for more concerning lesions or those with evidence
SRS and chemotherapy was excellent. The overall MST was 363 of pathologic fracture at the time of SRT (Fig. 25.10). 111 In
days. In a follow-up retrospective study, the same group reported a recent study, seven dogs underwent surgical stabilization for
the outcome of 46 patients treated with a similar single fraction fractures documented at the time of SRT, and 11 dogs were sta-
SRS technique (median prescribed dose 30 Gy). 231 Forty-five dogs bilized preemptively. Infection occurred in 15 dogs and was con-
received conventional maximal tolerated dose chemotherapy. The sidered a major complication in 13 of these dogs and ultimately