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