Page 657 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 29 Tumors of the Male Reproductive System 635

using fluoroscopy or digital radiography and stents are typi- with PCA were treated with intraoperative orthovoltage ther-
cally selected to extend approximately 1 cm proximal and distal apy. 247 Nine of the dogs were prescribed 20 Gy to 30 Gy to the
166,237–239
The use of digital radiography to
prostate with an MST of 114 days, although the range extended to
to the obstruction.
VetBooks.ir guide stent placement is relatively new and may require more 750 days. 247 It is probable that with advances in RT planning and
237
delivery involving the routine use of 3D conformal RT (CRT) or
cautious placement.
Stents can be ordered in various diam-
eters and are recommended to be 10% greater than the diam- intensity-modulated RT (IMRT) with image-guided RT (IGRT)
eter of healthy-appearing urethra. The procedure is considered to confirm target positioning, local disease may be better targeted
palliative and complications include incontinence (which may and controlled (Fig. 29.8). A recent retrospective study described
be severe in 25% of cases), stranguria, reobstruction, and stent definitive-intent IMRT/IGRT in 21 dogs with genitourinary
migration. 166,237–239 Although the literature reporting outcome carcinomas that were prescribed 54 to 58 Gy in 20 fractions to
for dogs treated with stenting and chemotherapy is still matur- the primary target volume. 248 Ten dogs had prostatic carcinomas
ing, studies suggest that the addition of NSAIDs with or without completed treatment and had an event-free survival time of 317
chemotherapy may be beneficial. 238 days; the overall event free survival time and overall survival time
PDT may be a viable option for some dogs with minimally reported for all 21 dogs was 317 days and 654 days, respectively. 248
invasive PCA, although its availability is not widespread. 240 PDT Although multimodality therapy and NSAIDs were not standard-
remains predominantly investigational at this time, although sev- ized, results support further prospective evaluation of RT for long-
eral reports have suggested that the dog provides a good model to term control. Given the potential for durable tumor control after
support clinical applications for novel treatments for PCA. 241–246 RT, it will be important to monitor for late radiation toxicity, as
Challenges in delivering homogeneous doses may limit the utility approximately 20% of dogs developed manageable grade 3 late
of PDT in advanced tumors. toxicity (including urethral, ureteral, and rectal stricture), despite
RT may be useful in the palliation of clinical signs related to the small fraction size. 248 It is unclear if improving local control
local PCA and to painful skeletal metastases, although optimal with RT will alter the time or pattern of metastasis but prospective
dose and fractionation are unknown. In an older study, 10 dogs efforts to elucidate the role of RT are warranted.

A B

C

• Fig. 29.8 Precontrast (A) and postcontrast (B) films of a dog with a large, mineralized, and heterogeneous
prostatic carcinoma causing dorsal deviation and compression of the colon. The blue outline represents
the gross tumor volume. (C) Radiation dose distribution illustrated with colored isodose lines around the
prostate on an axial CT image.