Palliation of Clinical Signs in 48 Dogs With Nasal Carcinomas Treated With Coarse-fraction Radiation Therapy
Data from 48 dogs with nasal carcinomas treated with palliative radiation therapy (PRT) were retrospectively reviewed. Factors potentially influencing resolution of clinical signs and survival after PRT were evaluated. Clinical signs completely resolved in 66% of dogs for a median of 120 days. The overall median survival time was 146 days. Duration of response to PRT was shorter in dogs that had clinical signs for <90 days before PRT. Survival times were shorter in dogs that had partial or no resolution of clinical signs after PRT than in dogs that had complete resolution of clinical signs.
Introduction
Malignant neoplasms of the nasal cavity and paranasal sinuses cause local soft-tissue and bony destruction, resulting in clinical signs such as epistaxis, sneezing, facial deformity, and upper-airway dyspnea.1–12 Without therapy, progression is fairly rapid. The reported median survival times for 16 dogs with various intranasal neoplasms were 10.5 weeks from the initial onset of clinical signs and 3.5 weeks from presentation to a veterinary facility.4 In a recent study of 139 dogs with untreated nasal carcinomas, survival times ranged from 7 to 1114 days (median 95 days).12
Treatment options for dogs with nasal carcinoma include surgery, external-beam radiation therapy (RT), brachytherapy, immunotherapy, and chemotherapy.1–15 External-beam RT has become the treatment of choice for nasal tumors, because historical evidence suggests that surgery or chemotherapy alone rarely provides long-term tumor control.1–11,14 Unfortunately, even with treatment, most dogs with nasal carcinomas are eventually euthanized because of local disease progression and worsening of clinical signs.
Nasal tumors are most often seen in older dogs (median age approximately 10 years),3,6,7,11,13 and many affected dogs have concurrent diseases that contribute to overall morbidity. Concurrent illness also makes decisions about treatment increasingly difficult for both the owner and the veterinary oncologist. In some cases, advanced local disease or the presence of metastasis makes the clinician hesitant to recommend a definitive course of RT because of the potential for adverse effects in a dog with a poor long-term prognosis. For these dogs, a palliative course of RT may be considered to minimize hospitalization, the number of anesthetic episodes, and adverse effects normally associated with definitive RT.
The goal of palliative radiation therapy (PRT) is to improve quality of life while minimizing treatment-associated morbidity. Radiation therapy can decrease pain associated with bony lysis, inflammation, or tissue compression caused by tumors. Improvement of clinical signs may also prolong life, although this is not the primary goal of PRT.16–18
Information regarding use of PRT protocols in dogs with sinonasal cancer is lacking. The purpose of the current study was to evaluate the clinical characteristics and outcomes of dogs with nasal carcinomas treated with PRT.
Materials and Methods
Criteria for Case Selection
Patient records from eight contributing institutions were reviewed for the period between 1996 and 2005. Dogs that had histologically confirmed nasal or paranasal carcinomas treated with PRT were included in the study, as well as those that had been treated with nonsteroidal antiinflammatory drugs (NSAIDs), steroids, or antibiotics before or concurrently with PRT. Dogs that had inadequate follow-up or that had received previous RT, chemotherapy, or surgery were excluded.
Case Data
Data abstracted from medical records included 1) patient characteristics, such as age, weight, breed, presence of clinical signs, duration of clinical signs, and treatments before diagnosis; 2) diagnostic information, such as results of imaging methods and histopathological diagnosis; 3) treatment data, including reason for PRT, radiation source, dose per fraction, number of fractions administered, schedule for RT, and description of the radiation treatment field; and 4) follow-up data, including adverse effects associated with PRT, medications administered during and after completion of PRT, response to PRT (including resolution of clinical signs and response duration), survival time, and cause of death. Follow-up information was obtained from existing records or telephone interviews with the referring veterinarian and/or owner.
Information was obtained, when available, on the results of staging procedures, including cytological examination of regional lymph nodes, radiography of the thorax and abdomen, and ultrasonography of the abdomen. Systemic staging was performed according to clinician preference. Clinical tumor staging was based on results of computed tomography (CT) or magnetic resonance imaging (MRI), with tumors categorized according to a published classification system for sinonasal tumors.1 Clinical staging was not assessed when CT or MRI findings were unavailable.
Statistical Analysis
Duration of clinical signs before PRT was defined as the interval between the onset of clinical signs (as reported in the medical record) and the initiation of radiotherapy. For dogs in which clinical signs resolved completely, response duration was defined as the interval between the final dose of PRT and recurrence of clinical signs. Dogs in which clinical signs did not resolve completely were not included in analysis of response duration. Survival time was defined as the time from the end of PRT until death from any cause. Dogs that were free of clinical signs or alive at the last follow- up were included in analyses until the last day of follow- up, and then they were censored. Additionally, dogs that received a second course of PRT were censored from survival analyses at the time the second course was begun.
Risk factors were analyzed as possible predictors of response to PRT or survival. These risk factors included duration of clinical signs before the initiation of PRT (<90 days versus ≥90 days), Adams’ stage (stages 1 and 2 versus stages 3 and 4), total radiation dose (<24 Gy versus ≥24 Gy), dose per fraction (<8 Gy versus ≥8 Gy), complete resolution of clinical signs during or after PRT (yes versus no), and use of antiinflammatories (NSAIDs or steroids) with or without antibiotics during and after PRT (yes versus no).
Chi-square and Fisher’s exact testsa were used to screen categorical data for associations with complete resolution of clinical signs. The Kaplan-Meier product-limit method was used to estimate response duration and survival curves for each potential risk factor. These curves were then compared using the logrank test for censored data. Multivariable survival analysis using the Cox proportional-hazards method was performed to evaluate the joint effects of potential risk factors on response duration and survival. Variables with P values ≤0.05 in the univariable analysis were initially considered in the multivariable analysis, with stepwise backward elimination used for final model selection. In the final analysis, P values ≤0.05 were considered significant.
Results
Medical records of 65 dogs with nasal carcinomas were retrospectively evaluated for inclusion in the study. Ten dogs that had inadequate follow-up were excluded, as were seven dogs that had received chemotherapy concurrent with or after PRT. Of the remaining 48 dogs, 23 were male (19 castrated) and 25 were female (24 spayed). Weights ranged from 4 to 50 kg (median 24 kg, mean 24 kg). Age ranged from 5 to 15 years (median 11 years, mean 11 years). Nine dogs weremixed breeds, and 39 were purebreds (composed of 19 different breeds). The most common breeds were Labrador retrievers (n=7), golden retrievers (n=6), and beagles (n=4).
The duration of clinical signs before evaluation was known for 44 dogs and ranged from 7 to 730 days (median 90 days, mean 142 days). Clinical signs included epistaxis (n=40, 83%), sneezing (n=31, 65%), nasal discharge (n=26, 54%), facial deformity (n=19, 40%), upper-airway dyspnea (n=16, 33%), and ocular abnormalities (n=13, 27%). Most dogs had more than one clinical sign at presentation. Ocular abnormalities included decreased ocular retropulsion, third eyelid protrusion, exophthalmos, and epiphora. One dog with minimal signs related to the nasal cavity was presented for evaluation of ataxia, acute-onset blindness, and seizures.
Of the 39 (81%) dogs treated empirically for nasal signs before sinonasal neoplasia was diagnosed, 11 (28%) had partial or complete resolution of signs after treatment. Dogs were treated with NSAIDs (n=11), steroids (n=16), antibiotics (n=23), or combinations of these medications (n=10) before PRT. In most cases, the resolution of clinical signs resulting from these treatments lasted <1 month.
In 11 (23%) dogs, mandibular lymph nodes ipsilateral to the tumor were aspirated. The records did not indicate whether these lymph nodes were enlarged at diagnosis, but no dogs had cytological evidence of lymph node metastasis. Thoracic radiographs were taken in 47 (98%) dogs and were unremarkable except for a presumed primary lung tumor seen in one dog.
Information on tumor staging was available for 42 cases. Stages were based on retrospective evaluation of CT (n=41) or MRI (n=1) reports, and they were categorized as T1 (n=4), T2 (n=6), T3 (n=10), or T4 (n=22).1
The reasons for treating patients with PRT (as opposed to definitive therapy) were documented in 40 (83%) cases. In 14 (35%) dogs, the extent of local disease was listed as the cause for recommending PRT. In 24 (60%) cases, owners requested PRT because of concerns about cost, potential for toxicity, or travel/hospitalization associated with definitive RT. In two (5%) dogs, PRT was recommended because of concurrent diseases, including cardiac arrhythmias and the presence of a presumed primary lung tumor.
Dogs were treated with a course of PRT using standard protocols of each institution. After general anesthesia was induced, dogs were treated with megavoltage radiation using either a linear accelerator (n=32) or a Cobalt-60 teletherapy unit (n=16). Treatment planning was based on CT/MRI scans (n=42) or on skull radiographs and anatomical landmarks (n=6). Computer-based treatment plans were used for most cases in which advanced imaging was available. Dogs were treated with parallel opposed beams (n=43), single dorsal beams (n=4), or three or more orthogonal beams (n=1). Blocks and wedges were used at the discretion of the radiation therapist but were not used in most cases. Ipsilateral mandibular lymph nodes were not irradiated in any dogs. The total radiation dose ranged from 16 to 40 Gy (median 24 Gy). Dose per fraction ranged from 4 to 10 Gy (median 8 Gy) [see Table]. Oral medications (including steroids, NSAIDs, and/or antibiotics) to help control clinical signs related to the nasal tumor or other conditions (e.g., osteoarthritis) were administered to 16 dogs during and/or after completion of PRT.
In 47 (98%) of the 48 dogs, the planned course of treatment was completed. The dog in which the course of therapy was not completed was euthanized after two of the three planned treatments, because the owner perceived a lack of response.
In 39 (81%) dogs, at least one eye was irradiated. In 11 (28%) of these 39 dogs, ocular medications (including eye lubricants, topical cyclosporine, or antibiotic ointments) were prescribed during and/or after completion of PRT.
Because of the retrospective nature of this study, grading the adverse effects of RT using standardized schemes was not possible.19 Information on adverse effects during or after completion of PRT was available for 40 dogs, and acute adverse effects were reported in 14 (35%) dogs.Acute toxicities were generally mild and included (listed in order of decreasing frequency) oral mucositis, conjunctivitis, pitting edema in the irradiated field, dermatitis, and uveitis. Many dogs had multiple concurrent adverse effects. Asymptomatic alopecia, leukotrichia, and hyperpigmentation of the skin in the irradiated field were common in dogs that survived >3 months after PRT.
The incidence of acute ocular toxicity was difficult to discern, because some dogs were treated prophylactically with eye lubricants and topical ocular medications (e.g., antiinflammatory or antibiotic ointments/drops) during PRT and for 2 to 4 weeks after. Chronic ocular toxicities (i.e., conditions necessitating medications for >4 weeks after PRT) were reported in five (13%) of the 39 dogs that had at least one eye irradiated. Chronic toxicities included conjunctivitis, corneal ulceration or perforation, loss of vision, keratoconjunctivitis sicca, severe mucoid ocular discharge, cataract formation, blepharospasm, and uveitis. Most dogs that experienced chronic ocular toxicity had multiple concurrent ocular side effects.
One dog developed lymphadenomegaly, cytological evidence of mandibular lymph node metastasis, and recurrence of nasal signs 256 days after completion of the initial course of PRT. This dog was treated with a second course of PRT, in which both the nasal cavity and lymph node were irradiated.
Two dogs developed evidence of systemic metastasis after PRT. One of these had been treated for a stage T11 nasal adenocarcinoma and developed coughing and exercise intolerance 70 days after PRT. Thoracic radiographs revealed a multifocal nodular pattern consistent with metastasis, but this was not confirmed cytologically or histologically. The other dog, which had been treated for a stage T31 nasal adenocarcinoma, developed recurrence of nasal signs and cytological evidence of metastatic carcinoma to the liver, spleen, ribs, and scapulae 390 days after PRT.
Seizures were reported in four dogs 80 to 240 days (median 135 days) after PRT. Only one of these dogs had a history of seizure activity before PRT. Three of these dogs had been treated for stage T41 tumors (including brain invasion), and one had a stage T31 tumor. After the onset of seizures in one dog, a repeat CT scan confirmed progressive brain invasion by the tumor.
Response to PRT was evaluated in all dogs based on a retrospective review of medical records. In 32 (66%) of the 48 cases, clinical signs had completely resolved by the end of PRT or soon after. The remaining 16 dogs had only partial (n=12) or no (n=4) response to therapy. Dogs with partial or no response were combined in the data analysis.
No association was found between resolution of clinical signs and any of the analyzed risk factors. Thirty dogs experienced complete resolution of clinical signs but subsequently relapsed, while two remained free of clinical signs 113 and 883 days after PRT. Analysis of censored survival curves suggested a median response duration of 120 days (mean 209 days, range 20 to 1238 days [Figure 1]). One year after treatment, 10% of dogs were free of clinical signs; 2 years after treatment, 6% were free of clinical signs.
The only risk factor significantly associated with shorter response duration was the duration of signs before diagnosis. Dogs that had <90 days of nasal signs before diagnosis were 4.1 times more likely to have a relapse (95% confidence interval [CI] 1.6 to 10.6, P=0.004). In these nine dogs, the median response duration was 80 days, versus 150 days in dogs that had ≥90 days of clinical signs before diagnosis (n=20, P=0.001) [Figure 2].
During the follow-up period, 36 dogs died. Twelve dogs were censored from survival analysis; three were alive 691, 783, and 883 days after PRT, and nine were censored at the time of repeat irradiation. Analysis of censored survival curves indicated that the overall median survival time was 146 days (mean 284 days, range 0 to 1238 days) [Figure 3]. One year after treatment, 25% of dogs were alive; 2 years after treatment, 9% were alive.
Risk factors significantly associated with shorter survival during univariate analysis were duration of clinical signs for <90 days before diagnosis (P=0.044) and lack of resolution of clinical signs after PRT (P<0.0001). In multivariate analysis, only “complete resolution of clinical signs” remained significant. Dogs that did not have complete resolution of clinical signs after PRT were three times more likely to die (95% CI 1.4 to 6.5, P=0.006) than dogs in which clinical signs resolved completely. The median survival time for dogs that did not have complete resolution of clinical signs (n=16) was 42 days, versus 255 days for dogs in which clinical signs resolved completely after treatment (n=32, P<0.0001) [Figure 4].
Eleven (23%) dogs that completely responded to the first course of PRT were treated with a second course of PRT when clinical signs recurred. The second course of PRT was initiated 70 to 573 days (median 171 days; mean 215 days) after the first course was completed. Dosing schedules were the same as the first course of PRT for 13 of 15 dogs. One of the remaining dogs received two additional 8-Gy doses at 6 and 22 months after the first treatment, and the other received two additional 8-Gy doses 1 week apart at an unknown interval after the first treatment. Nine (82%) of 11 dogs had a complete response to the second course of PRT. Duration of response varied, but it was >100 days in seven dogs.
Discussion
Definitive treatment for canine nasal tumors using external-beam RT consists of total radiation doses of 36 to 57 Gy divided into 10 to 19 fractions. Survival times after definitive RT range from 7 to 23 months, with 1-year survival rates of 37% to 60% and 2-year survival rates of 17% to 48%.1,3–11 Factors associated with longer survival include low stage,1,3 age <10 years,11 lack of metastasis to regional lymph nodes or lungs,7 lack of facial deformity, and complete resolution of clinical signs.6 In the present study, the overall median survival time was 146 days, with 25% of dogs alive at 1 year and 9% alive at 2 years after PRT. The shorter survival times for the dogs in the current study may be related to 1) more advanced-stage nasal disease than in previous studies; 2) a lower total radiation dose (i.e., median of 24 Gy in this study) compared to previous studies; 3) a fractionation schedule that could favor tumor repopulation (i.e., once-weekly treatments); and 4) a higher prevalence of dogs with concurrent illness compared to that reported in previous studies.
The shorter survival time in the authors’ study may have also been related to owner-specific factors. In this study, 60% of dogs were treated with PRT (instead of a definitive course of RT) at the owners’ request; many of these owners were specifically seeking therapies unlikely to result in adverse effects. Possibly, the owners of these dogs had less tolerance for the morbidity associated with treatment and/or lack of response to treatment, and they may have elected euthanasia sooner than owners of dogs in other studies.
The only factor significantly associated with survival time in this study was resolution of signs after PRT. The median survival time for dogs that did not have complete resolution of clinical signs was 42 days, versus 255 days for dogs that had complete resolution of signs after treatment. This finding is comparable to that of a 2001 study of dogs treated with orthovoltage RT, in which dogs with resolution of signs after RT had a median survival time of 476 days, versus 133 days for dogs with continued clinical signs.6
Few published studies of RT for canine nasal tumors address either the likelihood of response to treatment or the response duration, because at least some nasal signs persist long term in many dogs after treatment. Only one study addressed this issue objectively; in that study, 24 dogs were treated with Cobalt radiation for nasal carcinomas, and CT scans were performed at 1, 3, 6, and 12 months after treatment. The duration of local control was longer in the 11 dogs with marked tumor regression on CT (389 days) than in dogs without tumor regression (161 days).20 Other factors associated with longer response include surgical excision of the tumor before RT4 and low tumor stage.1,3
In the authors’ study, the complete response rate to PRT was 66%, with an overall response duration of 120 days. Response duration was assessed through careful examination of medical records and discussion with owners and referring veterinarians. However, it is possible that response rates were over- or underestimated because of the retrospective nature of the study.
The only factor significantly associated with longer response was “duration of clinical signs for ≥90 days before diagnosis.” It is likely that such tumors grew slowly, making them more responsive to PRT because of adequate oxygenation and a lack of tumor cell repopulation between fractions.21 Conversely, tumors resulting in a rapid onset of clinical signs may have been less sensitive to radiation because of hypoxic areas within the tumor (related to rapid growth) that allowed continued tumor growth and shorter symptom-free interval.
To date, only two other studies have evaluated treatment responses in dogs with nasal cancer after PRT or coarse radiation-fractionation schemes.2,4 In a retrospective study of 56 dogs with various histological types of sinonasal neoplasia, PRT was administered with a linear accelerator in four weekly 9-Gy fractions.2 Treatment plans and tumor stage determination were based solely on skull radiographs. Clinical signs improved by the end of PRT in 95% of these dogs, but most (89%) dogs were eventually euthanized as a result of their tumors. The median survival time from the last day of PRT was 212 days (range 38 to 386 days), with a 1-year survival rate of 45% and a 2-year survival rate of 15%.2 There was no difference in survival between dogs that had carcinomas versus sarcomas or between stages of disease. In another report, 12 dogs with a variety of tumor types that were staged using skull radiographs were treated with PRT administered in four weekly, 9-Gy fractions.4 In these dogs, the median survival time was 441 days (range 301 to 1400 days), with 58% alive 1 year after PRT and 13% alive 2 years after PRT. No difference was seen in survival of dogs with different tumor types. In these reports (as in the present study), toxicities were mild, with most dogs responding to therapy. The longer median survival times and 1- and 2-year survival rates reported in these earlier studies may be because a larger portion of dogs had less advanced tumors than dogs in the present study. However, direct comparisons are difficult, because tumors in earlier studies were staged using skull radiographs rather than cross-sectional imaging.
The primary goal of PRT is to alleviate discomfort, not necessarily to prolong survival.22–24 Therefore, assessing outcomes after PRT is difficult, especially in veterinary patients. Patient response to PRT should ideally be measured both qualitatively and quantitatively. In people, response is assessed via questionnaires regarding mobility, pain, analgesic use, and overall improvement before, during, and after treatment.22–24 In one published study of PRT in dogs with various advanced-stage malignancies, 24 dogs were treated with 8-Gy fractions on days 0, 7, and 21—for a total dose of 24 Gy.16 Owners were asked to complete questionnaires that assessed the appetite, activity level, and lameness of their dog. Analgesic requirements, weight of the dog, and tumor response were also recorded before, during, and after therapy. Twenty (87%) of 23 dogs experienced partial or complete pain relief, and most owners felt that their pet had an improved quality of life and that they would consider the same treatment for another pet.16 Unfortunately, this type of information can rarely be obtained when reviewing records in a retrospective manner.
Prospective studies using detailed questionnaires addressing owner and clinician perceptions of patient status would improve the authors’ knowledge about responses to RT. Quantitative measurements of response should include measurement of the primary and metastatic tumor and evaluation of disease-free interval and survival time. Although the goal of PRT is not necessarily to prolong survival, improved quality of life may lead to longer survival. Many animals undergoing PRT might otherwise be euthanized because of the severity of their clinical signs. Hopefully, evaluation of both response duration and overall survival time gives a reasonable estimate for meaningful (i.e., good quality of life) survival. In the authors’ study, survival time was significantly affected only by response to therapy. Dogs that did not have a response to PRT were likely euthanized because of continued clinical signs and disease progression.
Palliative RT uses less intense dosing schedules and a lower total radiation dose than definitive RT, resulting in fewer acute adverse effects.16–18 In the present study, 35% of dogs had acute RT toxicity, which was generally mild and resolved with supportive care. This toxicity rate is lower than that reported for canine patients treated with definitive RT for nasal tumors, although differences in toxicity grading and follow-up make it somewhat difficult to compare results of this study to those of definitive RT studies.
Retrospective studies permit only limited assessment of toxicity. Ideally, prospective evaluations during treatment could be documented using a published toxicity scheme.19 Both acute and chronic toxicities possibly are underestimated in this study because of inconsistent follow-up and incomplete medical records.
The reported occurrence of acute ocular, cutaneous, and oral adverse effects in dogs treated with definitive RT protocols is 67% to 95%, 92%, and 81% to 95%, respectively. 1,6,9 Chronic ocular toxicity was seen in 13% of the dogs in the present study, which is lower than the 39% to 76% reported after definitive RT for nasal tumors;1,3,6,9,11,25 but concern is still warranted given the increased morbidity and cost associated with ocular toxicity from PRT.
The ideal fractionation scheme for PRT has yet to be determined. Studies have not consistently revealed a dose-response relationship in people treated with coarse-fraction-ation schemes for metastatic bone cancer.22–24 Few veterinary studies have examined the effect of fractionation on outcome in palliative protocols, and in the present study no significant differences were seen in outcomes for dogs treated with different total doses or doses per fraction. Most published fractionation schemes for PRT in dogs are similar to those reported here and involve weekly treatments for 2 to 4 weeks using 8 to 10 Gy per treatment—for a total dose of 16 to 30 Gy.16,26–28 The advantages of a once-weekly treatment schedule include a decreased number of anesthetic episodes and decreased incidence of acute adverse effects (compared with daily therapy), because normal tissues have time to repair between treatments.
The disadvantages of a weekly protocol include the possibility of repopulation and repair of tumor cells and an increased chance of late-occurring adverse effects in susceptible tissues (e.g., muscle, nerve, and bone) as the dose per fraction is increased.21,29 Late adverse effects may include fibrosis and necrosis of tissues and (rarely) secondary tumor formation at the irradiated site.29 These effects are usually not seen until ≥1 year after radiation and are therefore uncommon in treated animals, which often do not survive this long after a course of PRT.
The occurrence of late side effects can be minimized by decreasing the fraction size.29 As an example, one of the treatment protocols in this study used five consecutive, daily 4-Gy fractions. Daily treatments allow little time for tumor cells to repair and repopulate, which may result in improved response. The lower dose per fraction (compared with most palliative protocols that use 8 to 10 Gy per fraction) decreases the chance of late side effects.29 In addition, the lower total dose (20 Gy) in this protocol may allow normal tissues to tolerate re-treatment if clinical signs recur. Clinicians might otherwise be hesitant to recommend re-treatment after protocols using higher total doses of radiation. Further studies to determine the ideal dosing scheme for PRT in dogs are indicated.
Eleven (23%) of the dogs in this study received a second course of PRT. All these dogs completely responded to the first course of PRT and were re-treated after relapse of clinical signs. Controlled studies on repeated irradiation are lacking in the veterinary literature. In one study, 51 dogs and cats with various tumors were given a second course of RT after an initial definitive course. A total of 86% had partial or complete response at 2 months after the second course of RT, and 41% were alive 1 year later.30 Complications after reirradiation have not been documented in the present study, although most dogs are deceased.
Clinicians and owners of dogs with nasal cancer may seek either alternatives to RT or synergistic therapies that may enhance quality of life and prolong survival compared with RT alone. Options include chemotherapy, pain medications, steroids, NSAIDs, and surgery. Chemotherapy has shown some potential for treatment of primary and metastatic sinonasal cancer, although large prospective studies have yet to be performed.14,31 Cyclo-oxygenase-2 (COX-2) inhibitors may alleviate pain and clinical signs, may have antineoplastic properties, and may act as radiation sensitizers. 31–33 In a recent study of dogs with nasal cancer, survival times were longer for dogs treated with definitive RT followed by nasal cavity exenteration than for dogs treated with RT alone, although the surgical group had substantial postoperative morbidity.34 In addition to these adjunct therapies, improvements in RT treatment planning and delivery (such as 3D conformal RT and intensity-modulated RT) are increasingly available in veterinary medicine.35 The goals of these therapies are to improve dose distribution throughout the tumor volume and to decrease adverse effects in adjacent normal structures.
Conclusion
The goal of PRT is to improve the patient’s quality of life while minimizing treatment-associated morbidity. In most dogs of this study, clinical signs resolved completely and usually with only mild signs of toxicity. The symptom-free intervals and overall survival times for nasal cancer cases treated with PRT are shorter than those in published results for definitive RT. Palliative RT should be considered as a treatment option in dogs with advanced local, metastatic, or severe concurrent disease that precludes definitive therapy. Hopefully the ongoing study of canine nasal cancer will result in decreased side effects, improved patient comfort, and prolonged survival.
SPSS 10; Statistical Analytical Software, Chicago, IL
![Figure 1—. Response duration for 32 of 48 dogs with nasal tumors in which clinical signs resolved completely after palliative radiation therapy. The overall median response duration was 120 days (95% confidence interval [CI] was 93 to 146 days). Vertical markers represent censored data.](/view/journals/aaha/44/3/119_fig1.jpeg)
![Figure 1—. Response duration for 32 of 48 dogs with nasal tumors in which clinical signs resolved completely after palliative radiation therapy. The overall median response duration was 120 days (95% confidence interval [CI] was 93 to 146 days). Vertical markers represent censored data.](/view/journals/aaha/44/3/full-119_fig1.jpeg)
![Figure 1—. Response duration for 32 of 48 dogs with nasal tumors in which clinical signs resolved completely after palliative radiation therapy. The overall median response duration was 120 days (95% confidence interval [CI] was 93 to 146 days). Vertical markers represent censored data.](/view/journals/aaha/44/3/inline-119_fig1.jpeg)
Citation: Journal of the American Animal Hospital Association 44, 3; 10.5326/0440116
Citation: Journal of the American Animal Hospital Association 44, 3; 10.5326/0440116
Citation: Journal of the American Animal Hospital Association 44, 3; 10.5326/0440116
Citation: Journal of the American Animal Hospital Association 44, 3; 10.5326/0440116
Response duration for 32 of 48 dogs with nasal tumors in which clinical signs resolved completely after palliative radiation therapy. The overall median response duration was 120 days (95% confidence interval [CI] was 93 to 146 days). Vertical markers represent censored data.
The median response duration was 80 days (95% CI 51 to 109 days) (dashed line) for nine dogs with nasal carcinomas and clinical signs for <90 days before diagnosis, versus 150 days (95% CI 115 to 185 days) for 20 dogs with clinical signs present for ≥90 days before diagnosis (solid line) (P=0.001).
Overall survival time for 48 dogs treated with palliative radiation therapy for sinonasal carcinomas. The median survival time was 146 days (95% CI 114 to 178 days).
The median survival time was 42 days (95% CI 3 to 81 days) (dashed line) for 16 dogs in which clinical signs did not resolve, versus 255 days (95% CI 29 to 481 days) for 32 dogs in which clinical signs resolved completely after palliative radiation therapy (solid line) (P<0.0001).
