Four-Fraction Radiation Therapy for Macroscopic Soft Tissue Sarcomas in 16 Dogs
A retrospective study of 16 dogs with macroscopic soft tissue sarcomas was performed to evaluate response to a four-fraction radiotherapy protocol (prescribed dose of 32 Gy). Radiation was well tolerated with minimal side effects. The overall response rate was 50%, with seven partial responses and one complete response. The median time to progression was 155 days, and the median survival time was 309 days. Coarsely fractionated radiation therapy may be a reasonable palliative option for dogs with unresectable soft tissue sarcomas, although the response is relatively short-lived.
Introduction
Palliative (i.e., coarsely fractionated) radiation therapy (RT) has been used for provisional pain relief and improvement of dysfunction in both people and animals suffering from primary or metastatic neoplasia.1,2 The use of coarsely fractionated RT in veterinary medicine has principally been tailored toward management of canine osteosarcoma and melanoma, but some interest has been shown in similar protocols for temporary control of various advanced malignancies and their associated pain.1 “Definitive” RT remains the ideal approach for those animals in which long-term control may be achieved, while palliative therapy is usually reserved for dogs in which curative measures are not feasible.3–5
The radiation dose and fractionation scheme often depend on the reason for the therapy, the general health status of the dog, the volume of tissue to be treated, the relative sensitivity of the tumor type, and the critical organs or tissue that may be included in the treatment field.6 Toxicity is directly related to the tissue irradiated and increases with the overall volume of irradiated tissue, the overall delivered dose, and the dose per fraction. 6 Acute side effects primarily depend on the overall radiation dose, the duration of the protocol, and the fraction size.5–7 Late radiation side effects depend particularly on fraction size and less so on overall duration. 5–7 Large fraction sizes of radiation are particularly damaging to slowly dividing or nondividing normal tissue, such as connective tissue, nervous tissue, muscle, and bone.5–7 Toxicity to these late-responding tissues typically shows up >3 to 6 months after radiation, and it is dose dependent. This radiation damage is irreversible, progressive, and permanent, because the connective tissue structure and normal vasculature are compromised.6,7,9
Curative radiation protocols generally consist of relatively low doses per fraction (1.8 to 3.0 Gy) delivered daily for many weeks.6 However, it is difficult to lower the dose per fraction to ≤2.0 Gy in veterinary medicine because of the prolonged treatment time required to reach a tumoricidal dose.8 Such long treatment regimens would require excessive anesthesia (i.e., dogs are anesthetized for each fraction of radiation) and hospitalization. This has led to a compromise in which dogs are treated with a regimen with slightly higher doses per fraction.
Coarsely fractionated or “palliative” RT is typically reserved for controlling the discomfort, localized hemorrhage, and tumor progression associated with incurable cancer. 2,10 Typical protocols involve large radiation doses (5 to 10 Gy) delivered as a few fractions once or twice weekly. Examples of coarse-fractionated protocols include (but are not limited to) four fractions of 8 Gy each delivered once per week, five fractions of 4 Gy given daily or once per week, and one fraction of 10 Gy or six fractions of 5 to 6 Gy delivered at a rate of one fraction per week.
Many incurable tumors are sizeable, requiring treatment of a large radiation field. Administration of higher dose fractions to a large volume of tissue increases the risk of late radiation side effects.5,10,11 Lower doses per fraction are preferred for palliative therapy, so as to preserve normal tissue structure and function.5,8 Unfortunately, some veterinary facilities have access to a radiation treatment center for only 1 to 2 days per week. Delivery of a small fraction size once per week is unlikely to lead to a durable response, because tumor cells have a significant amount of time to repair damage and to proliferate between treatments.5,8 Therefore, large doses of radiation are often delivered to optimize killing of tumor cells, with the increased risk of late radiation toxicity accepted as a part of treatment.27 Concern for clinically significant late effects can be addressed by delivering lower doses of radiation, such as 4 Gy given daily in five fractions. However, most dogs receive palliative therapy to improve quality of life, not to prolong life, and they may not live long enough to experience permanent effects.
A protocol using larger dose fractions also decreases the frequency of anesthesia. Dogs with advanced heart disease, renal insufficiency, or widespread metastasis may benefit from a course of RT that minimizes the frequency of general anesthesia, particularly if the tumor is causing only localized discomfort.2,27 Coarsely fractionated RT may offer short-term relief without compromising life expectancy, which is generally reduced by systemic disease, regardless of the treatment chosen for the cancer.2,10,27
Soft tissue sarcomas represent a histologically diverse group of mesenchymal tumors that tend to behave similarly. 10 Typical locations include the skin and subcutaneous tissues, although sarcomas can arise from any mesenchymal tissue in the body.10 These tumors are generally locally invasive and have microscopic projections that extend through the pseudocapsule, thereby predisposing to local recurrence after conservative surgical excision.10,12
Treatment of soft tissue sarcomas has included surgery alone, RT alone, chemotherapy, or a combination of modalities. 13–24 Marginal surgical resection followed by postoperative RT yields the best results, providing a median survival time of 1851 days and a time to local recurrence of >798 days.24 In some cases, this aggressive approach is not possible because of tumor location or size or because of concurrent disease. Palliative RT may offer some benefit in this setting, with the goal being to delay tumor progression and improve quality of life.
The purpose of this retrospective study was to assess the efficacy of a four-fraction palliative RT protocol in dogs with macroscopic soft tissue sarcomas.
Materials and Methods
Study Animals
The RT database at the University of Wisconsin-Madison Veterinary Medical Teaching Hospital (UW-VMTH) was searched for all dogs that had been started on a course of palliative RT for macroscopic soft tissue sarcoma. Cases were included if they met the following criteria: adequate staging (including histopathological diagnosis and tumor measurements), intent to treat with four-fraction RT, and sufficient follow-up information. Medical records were reviewed for signalment, laboratory data (including complete blood count [CBC], serum biochemical profile, urinalysis, histopathological tumor diagnosis), clinical staging, pretreatment tumor volume, treatment methods (radiation protocol, overall duration of radiation, chemotherapy, surgery, and any other medications), radiation side effects, underlying reason for the owner seeking RT, owner satisfaction, and tumor response to RT.
Responses and Toxicities
Side effects for dogs treated after October 2001 were formally graded according to the Veterinary Radiation Therapy Oncology Group acute RT morbidity scoring scheme,25 and results were recorded for each dog throughout therapy and at follow-up with UW-VMTH. This same scoring scheme for acute and late toxicity was also retrospectively applied (based on notations within the medical record) to all dogs treated before October 2001, even though a standardized scoring scheme was not in effect at that time.
Tumor size was measured at the initial consultation, at the administration of each fraction, and at various intervals after RT had been completed. Tumor measurements were not always recorded by the same individual. Tumor volume was calculated according to the formula v = π/6(lwh), in which l, w, and h represent diameters in three mutually orthogonal planes. Individual dimensions were recorded at the time of each radiation treatment, but tumor volume was more consistently recorded during follow-up. Therefore, volume estimates were used for evaluation of response.
A “complete response” was defined as complete disappearance of all measurable tumor. A “partial response” was defined as >50% reduction in tumor volume. “No response” was defined as <50% reduction and ≤25% increase in tumor volume. Progressive disease was defined as a >25% increase in tumor volume. Overall response rate was defined as the percentage experiencing complete or partial response.
Follow-up information was obtained through rechecks at UW-VMTH, through standardized satisfaction postcards sent to owners after RT, or through telephone communication with owners and/or referring veterinarians. Postcards provided information on owner satisfaction with the RT, recovery from side effects, time to recurrence, and survival time. No formal recheck schedule was consistently followed, but the recommended follow-up schedule was 2 to 4 weeks after therapy and then every 2 to 3 months thereafter, unless problems arose.
The “progression-free” interval was defined as the time between the start of RT and documented progression. If the date of tumor progression was unknown, then dogs were censored from progression-free analysis at the point of last known nonprogressive follow-up. Survival times were calculated from the start of RT until documented date of death. Dogs were censored from survival analysis if their deaths were unrelated to the tumor, if they were lost to follow-up, or if a cause of death was unknown.
Statistics
The median progression-free interval and survival time were calculated using the Kaplan-Meier product-limit method.26 Response to treatment and tumor size were evaluated for their association with these outcomes. Differences in progression-free interval and survival time between groups were compared using the logrank test. A two-sided Fisher’s exact test was used to compare the likelihood of response associated with receiving or not receiving concurrent chemotherapy and larger versus smaller (than the median) tumor volume. Statistical calculations were performed using a commercial statistical software package.b A P value <0.05 was considered significant in all analyses.
Results
The database included 18 dogs with soft tissue sarcoma treated with palliative RT between March 1995 and January 2002. Results of complete blood work, urinalysis, thoracic radiographs, and histopathology were available for all dogs. Additional diagnostics included computed tomography (CT) scan (n=4), abdominal ultrasound (n=5), magnetic resonance imaging (MRI) (n=1), echocardiogram (n=1), and skull (n=2) or pelvic (n=1) radiographs. Two of the 18 dogs were excluded from the study because of incomplete medical records.
Of the 16 dogs included in this study, 12 were neutered males and four were spayed females. The ages ranged from 3 to 15 years, with a median of 10 years and a mean (± standard deviation [SD]) of 9.9 (±3) years. Breeds included golden retriever (n=3), Labrador retriever (n=3), mixedbreed dog (n=3), Siberian husky (n=2), German shepherd dog (n=2), Shetland sheepdog (n=1), toy poodle (n=1), and Doberman pinscher (n=1).
Tumor Characteristics
Soft tissue sarcomas consisted of various histiotypes located in several areas of the body [see Table]. Pretreatment tumor volumes ranged from 5.65 cm3 to 1754 cm3, with a median of 81 cm3 and a mean (± SD) of 260 (±449) cm3. Records indicated that 12 of the 16 owners had sought therapy because of pet discomfort related to the sarcoma. The reason behind palliative therapy was not specifically documented in the other four cases, but medical records suggested that these four tumors were treated to slow the progression of the tumor and to alleviate presumed discomfort. In all cases, potentially curative therapy was offered to the owners. Such therapy included amputation, body wall resection, complete surgical excision, and/or definitive RT. All owners declined definitive treatment and elected palliative therapy.
Treatment Protocol
The RT protocols consisted of manual methods using single or parallel opposed fields, with a 3-cm margin surrounding the palpable edge of the tumor (if possible). Computed tomography scans were used when available to help estimate field size and depth of treatment, but true image-based computer planning was not performed. When feasible, critical structures such as eyes, nasal planum, and lungs were blocked from inclusion in the field. For appendicular sites, a narrow portion of tissue was spared to decrease the risk of radiation-induced lymphatic obstruction. The total dose of radiation prescribed to the tumor was 32 Gy to isocenter, delivered as one 8-Gy fraction on days 0, 7, 14, and 21. All fractions were administered using a cobalt teletherapy unit.a
Other Therapies
In addition to four-fraction RT, 12 dogs received other therapy before, during, or after RT [see Table]. Tumors continued to progress in all 12 dogs in the face of therapy given before RT. Three dogs had received concurrent doxorubicin/ cyclophosphamide chemotherapy at standard dosages at 3-week intervals for four cycles. Medical records of these three dogs suggested that chemotherapy was administered to help improve tumor response to RT. Further therapy at the time of tumor progression consisted of piroxicam (n=3), investigational Phenstatin phosphate chemotherapy (n=1), endostatin gene therapy and genetically modified Salmonella (n=1), additional radiation (n=2), or chemotherapy (n=1).
Response to Treatment
Radiation therapy was given to 15 of the 16 dogs on days 0, 7, 14, and 21. The remaining dog (case no. 7; see Table) became clinically ill secondary to neutropenia induced by chemotherapy, so the first and second fractions of radiation were delivered 2 weeks apart. Two of the 16 dogs had achieved a partial response by the fourth radiation dose, and one dog had stable disease at that time. Radiation was well tolerated, with all dogs continuing to display normal or subjectively improved attitudes, appetites, and energy levels.
Mild, acute side effects were noted during therapy. Grades of acute toxicity were assigned prospectively to one hospitalized dog (using standardized toxicity criteria), but all other cases were graded retrospectively. Two dogs developed grade-1 skin desquamation; three dogs developed grade-2 moist desquamation; and three dogs developed grade-2 oral mucositis. All eight of these dogs were rechecked within 2.5 weeks of completion of RT, at which time all acute side effects had resolved. Four of the eight dogs were reevaluated at the UW-VMTH, and the remaining four were evaluated by referring veterinarians.
Each of the 16 dogs was evaluated at some point after therapy by a referring veterinarian, with five of the 16 dogs rechecked at 14 to 19 days after completion of therapy. Of the 16 cases, 13 were also reevaluated at the UW-VMTH at some time period between 2 weeks (four dogs) and 8 months (one dog) after treatment. Recheck evaluations were recommended at regular intervals (i.e., 2 weeks, then 1 month, then every 3 months), but few dogs were consistently returned for evaluation, and the level of follow-up varied. For example, of the 13 dogs reevaluated at UW-VMTH, one was evaluated at 2 and 4 weeks; two were evaluated at 1 month, with repeat evaluations at 2-month intervals; and one was evaluated at 3 and 5 months. All other cases were rechecked at UW-VMTH no more than once.
The overall objective response rate was 50% and included seven partial and one complete response. Three dogs experienced a 30% to 40% reduction in tumor size but did not fully meet the criteria for objective response. The remaining five dogs had static tumors that did not change measurably in size. None of the dogs developed progressive disease during the course of therapy, and eight dogs experienced stable disease for a median of 140 days.
The dog that experienced a complete response had been diagnosed with a cutaneous hemangiosarcoma located over the left ventral thorax. This dog received chemotherapy concurrent with RT. The tumor did not progress for 224 days, but the dog was euthanized at 253 days because of local recurrence and ulceration of the tumor.
Nine of the 16 owners were pleased with the clinical responses achieved through treatment, with three owners reporting significant improvement of lameness in their dogs. One owner expressed mild displeasure associated with the side effects (oral mucositis) but did not regret the decision to pursue RT. In the remaining cases, owner satisfaction was not documented.
No variables were statistically associated with response to RT. All three dogs treated with concurrent chemotherapy achieved an objective response, but this finding was not statistically significant (P=0.10), likely due to the small sample size. The small sample size also precluded the statistical evaluation of whether treatment before RT affected the response rate.
The median progression-free interval was 155 days, with a range of 72 to 460 days [see Figure]. Four dogs were censored from progression-free analysis because of lack of follow- up regarding date of documented progression. Six (48%) dogs were progression free at 6 months, and two (16%) dogs were still progression free at 1 year.
Twelve (75%) dogs were alive at 6 months, and six (37%) dogs were still alive at 12 months. The overall median survival time was 309 days, with a range of 73 to 600 days [see Figure]. Three dogs were censored from survival analysis at the time of death from causes completely unrelated to the tumor. Among these three deaths, one dog with a truncal hemangiopericytoma died acutely after collapsing; one dog treated for a forelimb hemangiopericytoma was euthanized for paraparesis and fecal incontinence; and one dog with a forelimb hemangiopericytoma died secondary to unregulated diabetes mellitus and hyperadrenocorticism.
The median survival time of the eight dogs responding to RT was 218 days, and the median survival time of dogs not responding was 416 days. This difference was not statistically significant (P=0.34). The three dogs that received concurrent doxorubicin and cyclophosphamide experienced survival times of 253 days, 309 days, and 373 days.
Discussion
This is the first report describing the response to a four-fraction protocol in dogs with measurable soft tissue sarcomas. The literature on coarse-fractionated RT for soft tissue sarcomas is sparse, although various reports have emerged in the past 13 years. A recent report described a coarse-fractionated protocol consisting of three 8-Gy fractions given either weekly or on days 0, 7, and 21.30 Fifteen dogs with either fibrosarcoma or hemangiopericytoma were treated, and 13 (87%) of the 15 dogs achieved stable disease for a median of 263 days.30 Only one partial response was noted in this study. Time to progression and survival time were longer in this study (263 days and 332 days, respectively)30 than in the authors’ study (155 days and 309 days, respectively), but this may be an artifact caused by favorable case selection in the former study and by more severe, refractory disease in this study’s population of dogs. The median tumor volume in this study was 81 cm3, while that in the previous report was 75 cm3.30 In addition, only five tumors in the previous report had been surgically resected, and 10 were treated solely with primary coarse-fractionated radiotherapy. 30 Recurrent tumors may be more difficult to treat, and many of the dogs in the authors’ study had received other forms of treatment before RT, which is often the case with advanced malignancies.10
In another report, 16 dogs were irradiated for advanced nonskeletal tumors (including melanomas and sarcomas) using three fractions of 8 Gy each.1 The protocol was tolerated very well, with quick pain relief and minimal side effects. These dogs survived for up to 557 days after treatment.1
In the authors’ study, 50% of dogs responded to therapy, and dogs remained progression free for a median of approximately 5 months. Limb function was definitively improved after RT in three dogs; two of these dogs were partial responders, but the third dog did not have a measurable response. All dogs tolerated RT well, with minimal and acceptable acute side effects. Late effects were not noted in any of the 16 dogs. However, the median survival time was 10 months, and late effects may not have become clinically apparent within that time period.
The authors chose a protocol consisting of 8-Gy fractions administered once weekly, based on a recommended fractional dose of 8 Gy for optimal palliation of bone metastasis in people.28,29 Use of this fractionation scheme has been standard practice at UW-VMTH, even though a 0-7–21-day protocol has been used in previous studies.1,30 A dose of 8 Gy is estimated to kill approximately 70% to 80% of the tumor population.27
Radiation protocols can be compared using a formula known as the “biological equivalent dose” (BED), which estimates effective doses to tissues.5 Assuming α/β ratios of 10 for acute effects and 3 for late effects, the BED for the authors’ four-fraction protocol is 57.6 Gy10 for acute effects and 117.3 Gy3 for late effects. By comparison, using 8-Gy fractions in the published 0–7–21-day protocol for advanced malignancies and soft tissue sarcomas yields BEDs of 43.2 Gy10 for acute effects and 88 Gy3 for late effects.1,30 These findings suggest that the authors’ four-fraction protocol may have greater efficacy against acutely responding tissue such as tumor, but that late-responding tissues will also be more affected (i.e., greater probability of late side effects).
Coarsely fractionated protocols can certainly cause significant late tissue damage and (if used inappropriately) can eventually impact quality of life during a durable response.5,7 However, some radiation oncologists may be less concerned with late effects when dealing with palliative therapy, because dogs undergoing such treatment do not live long enough to experience late radiation effects. None of the dogs in this study suffered any reported late effects (even given the higher effective dose for late-responding tissues), which was most likely a result of the relatively short survival time. The incidence of late effects possibly would have been higher if the dogs had survived longer.
Applying the BED formula to a published definitiveradiation protocol of 19 fractions of 3 Gy each yields effective doses of 74 Gy10 for acute effects and 114 Gy3 for late effects.24 This definitive protocol, which is prescribed to cure microscopic disease, yields a higher effective dose for acute effects (tumor) and a lower BED for late effects than the protocol the authors used to treat bulky, nonresectable soft tissue sarcomas. This highlights the fact that coarsefractionated protocols are not meant to replace definitive, protracted RT because of the potential negative impact on normal structures associated with palliative, coarse-fractionated procedures.
Large soft tissue sarcomas can cause significant discomfort and impairment in normal function. Analgesics are often used to maintain quality of life when other therapeutic options are not feasible. Curative surgery with or without RT may not be feasible because of tumor size and location. Alternative management methods for nonresectable soft tissue sarcomas are needed. Preoperative, definitive radiation protocols may prove beneficial by shrinking the tumor to a resectable volume. Additionally, amputation may be curative for dogs with low- or intermediate-grade soft tissue sarcomas of the distal limb.
The use of chemotherapy for soft tissue sarcoma is somewhat controversial, because chemotherapy in combination with radiation has not been shown to definitively improve response or survival, although it may provide palliation in the case of measurable tumors.10,16,31 The use of chemotherapy in combination with palliative RT has not been assessed but may potentially delay onset of systemic disease and improve/maintain quality of life in the case of metastatic tumors. An alternative view is that chemotherapy has the potential to make animals ill, and it may not significantly impact the disease process underlying patient discomfort.
Limitations of this study included the small sample size, the lack of a control group, the observational (i.e., nonrandomized) and retrospective design, and variable use of adjuvant therapies. Only 16 dogs were evaluated, and these could not be compared to a similar group of dogs that did not receive RT. Bias (e.g., confounding or selection bias) is also a potential problem in any observational study (especially a retrospective one), although it is difficult to determine if such bias actually occurred. Owners of dogs in profound discomfort with advanced disease may be less likely to opt for RT, and it is possible that the dogs in the authors’ study population were healthier than the average dog with soft tissue sarcoma. In other instances, definitive treatment of operable tumors may be declined for various reasons. In these cases, coarsely fractionated RT serves as palliative therapy for dogs experiencing poor quality of life, rather than as a true substitute for definitive treatment.
It is not known whether the 16 dogs in this study would have survived as long as they did without palliative therapy. However, early euthanasia was a real possibility in these cases, given that most (11 of 16) owners sought treatment for deteriorating quality of life. The retrospective nature of this study made it difficult to adequately evaluate pain relief and return to function among treated dogs, given that tumor size and response to therapy were documented more thoroughly than resolution of discomfort.
The authors also may not have captured the full range of improvement among treated dogs. Some tumors can take months to shrink, so it is possible that tumor volume may have continued to decrease even among dogs that did not achieve an objective response during the study and followup periods. Tumor volume was not consistently measured during reevaluation, but it is clear from time-to-progression data that any additional shrinkage was temporary.
As with any retrospective study, the authors did not have control over numerous treatment-related variables, frequency of reevaluation, etc. One source of concern is the fact that most dogs were treated with a wide variety of additional therapies before or after RT. However, only three dogs had concurrent chemotherapy that might have affected assessment of response to RT. While variable chemotherapeutic regimens, investigational agents, and prior surgical excisions were performed before RT, a 50% response rate was still achieved.
It is impossible to know with certainty whether pretreatment had a substantive impact on response or progressionfree interval. Various treatment regimens, such as gene therapy or prior surgery, certainly may have altered tumor blood supply or gene expression. Such concurrent treatments may have also modulated “bystander effects” associated with RT, thereby modifying inherent tumor response to ionizing radiation. Chemotherapy may act in conjunction with RT, so it is also conceivable that dogs receiving chemotherapy had improved responses to RT. In this regard, it should be noted that the three dogs receiving concurrent doxorubicin and cyclophosphamide had survival times equal to or better than the median. Interestingly, all three dogs had objective antitumor responses. The role of concurrent chemotherapy would be an interesting subject for a future prospective study, but its role in the present set of dogs cannot be determined.
Another issue of concern is that dogs were treated with manual setups based on visual assessment of the tumor. Image-based planning (generally CT-based) allows better determination of the targeted tumor volume, and it may help limit the volume of surrounding normal tissue that is irradiated. 32 Computerized treatment planning was not performed in any of the dogs in this study, although CT images were used to help estimate tumor volume. Computerized tomography was done in 25% of dogs for evaluation of invasiveness and as a guide for potential surgery. Imaging was not done in the remaining 75% of dogs. It is possible that visual and palpable evaluation underestimated the extent of tumor in these dogs, even given the 3-cm margin. Computerized treatment planning individualized for each dog may have improved local control.
The effect of postradiation treatments on overall survival is impossible to evaluate effectively. Radiation therapy may cause cellular damage and death for months after delivery, and it is theoretically possible that additional postradiation therapies acted synergistically to enhance tumor control. However, the fact remains that the 50% response rate among the dogs in this study was not durable beyond a median of 5 months.
Interestingly, dogs experiencing stable disease had a median survival time of 416 days, while partial/complete responders survived for only a median of 218 days. This difference was not significant, so it may have been a chance occurrence. However, it should be noted that four of the nonresponders had tumors located on the extremities. Perhaps tumors on the extremities were better compensated for than tumors located on the trunk or within the oral cavity. Alternatively, such tumors possibly were innately less proliferative than other tumors.
Conclusion
Aggressive local therapy remains the standard of care for treatment of soft tissue sarcomas and often involves a combination of surgery and definitive RT. However, results of this study support the use of coarsely fractionated RT as a viable therapeutic option for soft tissue sarcomas, if definitive treatment (e.g., surgery with or without curative RT) is not elected or is not expected to improve local control. Furthermore, RT delivered as four weekly fractions may be attractive to some owners because of the fewer number of visits and less time required for hospitalization.
Such short-course, high-dose protocols result in a relatively high risk for late radiation side effects. This fact should be considered and explained to owners, particularly in cases where animals may be better served by protocols intended to provide a cure. However, clearly nonresectable, large, bulky tumors may respond well to coarse-fractionated RT over the short term. The coarse-fraction protocol was well tolerated by all dogs in this study and may offer an opportunity for temporary relief of pain and return to function. The ideal protocol to achieve good local control and amelioration of clinical signs has yet to be determined.
Theratron 780; Atomic Energy of Canada, Kanata, Ontario, K2K 1X8, Canada
Prism 4.0b; GraphPad Software, San Diego, CA 92130
Citation: Journal of the American Animal Hospital Association 44, 3; 10.5326/0440100
Progression-free interval and overall survival time for dogs with soft tissue sarcomas treated with radiation therapy. Three dogs were censored from progression-free interval analysis because of lack of follow-up pertaining to date of documented progression. Four dogs were censored from survival analysis at the time of death because of causes of death unrelated to their tumors.
