Intensity‐Modulated and Image‐Guided Radiation Therapy for Treatment of Genitourinary Carcinomas in Dogs

Abstract

Background: External beam radiation therapy can be used to treat pelvic tumors in dogs, but its utility is limited by lack of efficacy data and associated late complications.Hypothesis/Objectives: The objective of this study was to assess local tumor control, overall survival, and toxicosis after intensity-modulated and image-guided radiation therapy (IM/IGRT) for treatment of genitourinary carcinomas (CGUC) in dogs.Animals: 21 client-owned dogs. Methods: A retrospective study was performed. Medical records of dogs for which there was intent to treat with a course of definitive-intent IM/IGRT for CGUC between 2008 and 2011 were reviewed. Descriptive and actuarial statistics comprised the data analysis.Results: Primary tumors were located in the prostate (10), urinary bladder (9), or urethra (2). The total radiation dose ranged from 54-58 Gy, delivered in 20 daily fractions. Grade 1 and 2 acute gastrointestinal toxicoses developed in 33 and 5% of dogs, respectively. Grade 1 and 2 acute genitourinary and grade 1 acute integumentary toxicoses were documented in 5, 5, and 20% of dogs, respectively. Four dogs experienced late grade 3 gastrointestinal or genitourinary toxicosis. The subjective response rate was 60%. The median event-free survival was 317 days; the overall median survival time was 654 days. Neither local tumor control nor overall survival was statistically dependent upon location of the primary tumor.Conclusions and Clinical Importance: IM/IGRT is generally well-tolerated and provides an effective option for locoregional control of CGUC. As compared with previous reports in the veterinary literature, inclusion of IM/IGRT in multimodal treatment protocols for CGUC can result in superior survival times; controlled prospective evaluation is warranted.

A pilot study of toceranib/vinblastine therapy for canine transitional cell carcinoma

“…When radiation was combined with mitoxantrone and piroxicam in one study, the reported response rate of 22% was not significantly different compared to the use of mitoxantrone and piroxicam alone [25]. More recently, the use of image guided intensity modulated radiation (IG/IMRT) with or without adjunctive chemotherapy in one study reported a median survival time of 614 days [26]. In addition, adjuvant low-dose palliative radiation therapy resulted in a 61% objective response rate, with 100% of dogs experiencing clinical benefit (CR, PR, SD) within 6 weeks of radiation therapy [27].…”

Outcome and prognostic factors in medically treated canine prostatic carcinomas: A multi‐institutional study

“…There is limited literature regarding efficacious treatment of canine PC. As most dogs are euthanized due to local obstructive disease, research has focused on local treatment such as complete or partial prostatectomy, photodynamic therapy and radiation therapy (RT), either in the form of intraoperative,intensity‐modulated or image‐guided RT …”

Lower Urinary Tract Cancer

“…Dogs with larger tumors invading locoregionally or with evidence of metastasis (ie, more advanced stage) have a less favorable prognosis with shorter survival times or shorter time to obstruction. 2,7,47 Dogs at an increased risk for metastasis include younger dogs (increased risk of lymph node metastasis), dogs with prostate involvement (increased risk of distant metastasis), and dogs with larger tumors (increased risk for both nodal and distant metastasis). 2,47 Many publications describe heavily pretreated dogs or dogs that go on to receive other treatments, which makes survival data for dogs with this tumor challenging to summarize.…”

“…However, this modality is not suitable for dogs with distant metastatic disease, and owners should be counseled about risks of side effects, as discussed. 47 Palliative radiation therapy may be used to relieve severe clinical signs, urethral obstruction, or pain from bone metastases. The risk of late side effects to the gastrointestinal and urinary tract is theoretically considerable with palliative protocols, but clinically not of great concern because of the palliative intent-most patients do not live long enough to experience late side effects.…”

“…With treatment, reported MST range from approximately 3 to 4 months to up to 1.8 years for dogs with disease Lower Urinary Tract Cancer confined to the prostate treated with IMRT. 47 Therapy is generally aimed at relieving clinical signs and improving comfort with long-term tumor control not expected in most cases.…”