Intensity-modulated radiotherapy and chemotherapy for canine right atrial tumors: A retrospective study of seven dogs.

Most primary cardiac tumors in dogs are located in the right atrium/atrial appendage, with hemangiosarcoma being the most common. The aims of this retrospective, case series were to describe outcomes for seven dogs with right atrial tumors treated with hypofractionated intensity-modulated radiotherapy and concurrent vinblastine and propranolol. One dog had a complete response, four dogs had partial responses and two dogs had stable disease after treatment. Effusions resolved in all dogs. Median progression-free survival was 290 days. Five dogs died from metastatic disease, one dog from unrelated neoplasia, and one dog is alive. Median overall survival was 326 days. Three dogs with confirmed hemangiosarcoma survived 244, 326, and 445 days. Two dogs developed clinically significant, but nonfatal, cardiac arrhythmias. One dog that received three courses of radiation had subclinical myocardial and arterial fibrosis at necropsy. Hypofractionated chemoradiotherapy was well tolerated and may provide clinical benefit in dogs with right atrial tumors.

Evaluation of mega-voltage CT images for completed radiotherapy treatments for dogs and cats reveals uncommon but potentially consequential dose deviation in thoracic and abdominal tumors.

As advanced delivery techniques such as intensity-modulated radiation therapy (IMRT) become conventional in veterinary radiotherapy, highly modulated radiation delivery helps to decrease dose to normal tissues. However, IMRT is only effective if patient setup and anatomy are accurately replicated for each treatment. Numerous techniques have been implemented to decrease patient setup error, however tumor shrinkage, variations in the patient's contour and weight loss continue to be hard to control and can result in clinically relevant dose deviation in radiotherapy plans. Adaptive radiotherapy (ART) is often the most effective means to account for gradual changes such as tumor shrinkage and weight loss, however it is often unclear when adaption is necessary. The goal of this retrospective, observational study was to review dose delivery in dogs and cats who received helical radiotherapy at University of Wisconsin, using detector dose data (D2%, D50%, D98%) and daily megavoltage computed tomography (MVCT) images, and to determine whether ART should be considered more frequently than it currently is. A total of 52 treatment plans were evaluated and included cancers of the head and neck, thorax, and abdomen. After evaluation, 6% of the radiotherapy plan delivered had clinically relevant dose deviations in dose delivery. Dose deviations were more common in thoracic and abdominal targets. While adaptation may have been considered in these cases, the decision to adapt can be complex and all factors, such as treatment delay, cost, and imaging modality, must be considered when adaptation is to be pursued.

Adjustment of multi-leaf collimator parameters in 4-MV and 6-MV IMRT: A study of veterinary clinical cases.

Background: For optimal treatment, it is important to maintain optimal multi-leaf collimator (MLC) transmission in intensity-modulated radiation therapy (IMRT). However, adjustment of transmissions has not been reported in veterinary medicine. Aim: To demonstrate that appropriate MLC parameter adjustment for IMRT using 4- and 6-MV energy can reduce the need for quality assurance revalidation in real companion animal clinical cases. Methods: The MLC parameters (leaf transmission and leaf offset) of the treatment planning system were adjusted by evaluating seven plans (10 × 10 cm, 3ABUT, DMLC, 7segA, FOURL, HDMLC, and HIMRT) and 20 preclinical cases (10 cases each in 4- and 6-MV groups). Subsequently, 101 IMRT plans of 88 cases (77 dogs and 11 cats) were evaluated for absolute dose of plan target volume (PTV) and organs at risk (OAR) and were analyzed for the relative dose distribution by gamma analysis (3%/3 mm, >10%) using EBT3 film. Results: After adjustment of the MLC parameters (leaf transmission and leaf offset, 4 MV: 0.008 and 0, 6 MV: 0.005 and 0, respectively), the data from 101 plans (4 MV: 64 plans and 6 MV: 37 plans) treated with IMRT showed PTV <3%, OAR <5%, and gamma analysis pass rates ≥95% in all cases. Conclusion: Clinically meaningful dose distributions can be created even with a limited validation device if the treatment parameters are adjusted appropriately, even for tumors in canines and felines, where the irradiation field is small, the target is adjacent to the OAR, and the target is often superficial.

Dose-escalated simultaneously integrated boost radiation protocol fails to result in a survival advantage for sinonasal tumors in dogs.

The prognosis for canine sinonasal tumors remains rather poor despite definitive-intent radiotherapy (RT). Theoretical calculations predicted improved outcomes with simultaneously integrated boost (SIB) protocols. With the hypothesis of clinically detectable differences in outcome between groups, our retrospective study evaluated prognostic variables and outcome in dogs treated with regular versus SIB RT. Dogs with sinonasal tumors treated with either a regular (10 × 4.2 Gy) or new SIB protocol (10 × 4.83 Gy to macroscopic tumor) were included. Information regarding signalment, tumor stage, type, clinical signs, radiation toxicity, response, and outcome was collected. Forty-nine dogs were included: 27 treated regularly and 22 treated with SIB RT. A total of 69.4% showed epistaxis, 6.1% showed epileptic seizures, 46.9% showed stage IV tumors, and 6.1% showed lymph node metastases. Early toxicity was mostly mild. Late grade 1 skin toxicity (alopecia/leucotrichia) was seen in 72.1% of dogs, and a possible grade 3 ocular toxicity (blindness) was seen in one dog. Complete/partial resolution of clinical signs was seen in 95.9% of patients as best clinical response and partial remission was seen as best imaging response in 34.7%. The median progression-free survival (PFS) was 274 days (95% CI: 117-383) for regular and 300 days (95% CI: 143-451) for SIB RT, which was not significantly different (P = 0.42). Similarly, the median overall survival (OS) was 348 days (95% CI: 121-500) for regular and 381 days (95% CI: 295-634) for the SIB RT (P = 0.18). Stratified by protocol, the hazard ratio of stage IV versus stage I-III tumors was 2.29 (95% CI: 1.156-4.551, P = 0.02) for OS but not PFS. All dogs showed acceptable toxicity. In contrast to theoretical predictions, however, we could not show a statistically significant better outcome with the new protocol.

Adaptive radiation therapy using weekly hypofractionation for thymoma treatment: A retrospective study of 10 rabbits.

Radiation therapy (RT) is being utilized more commonly for rabbit thymomas due to high perioperative mortality rates with surgery. Median overall survival times reported for rabbit thymomas treated with a variety of RT protocols and techniques range from 6 months to greater than 2 years. As thymomas are radiation-responsive tumours and may shrink rapidly after RT, adaptive radiotherapy (ART) is often warranted. The purpose of this single-institution retrospective case series was to investigate the tumour volume reduction during RT, the frequency of replanning during RT, and survival time in rabbit thymomas treated using intensity-modulated/image-guided radiation therapy (IMRT/IGRT) and a weekly hypofractionated protocol delivering a total dose of 30 Gy. Ten rabbits met the inclusion criteria from October 2014 to October 2019. The median progression-free survival was 561 days and the median overall survival was 634 days (range: 322-1118 days). The tumour volume gradually decreased with each RT fraction. On post-hoc analysis, only the first RT fraction was associated with a significant GTV reduction (of more than 50% on average, p < .001). All subsequent RT fractions did not further reduce the GTV significantly (p > .06). Hypofractionated RT using a weekly protocol of 5 fractions of 6 Gy is a reasonable option to treat rabbit thymomas and replanning should be anticipated. The results of this study support the use of RT to rapidly relieve thymoma-induced dyspnoea in rabbits.

Retrospective assessment of radiation toxicity from a definitive-intent, moderately hypofractionated image-guided intensity-modulated protocol for anal sac adenocarcinoma in dogs.

A recent calculation study predicted acceptable toxicity in pelvic organs at risk for a new definitive-intent, moderately hypofractionated radiation therapy (RT) protocol (12 x 3.8 Gy), when used with image-guided intensity-modulated radiation therapy (IG-IMRT). We hypothesized this protocol to result in clinically acceptable radiation toxicities. Dogs diagnosed with and irradiated for anal sac adenocarcinoma (ASAC) were retrospectively assessed. Eleven dogs were included, six had prior surgery. Before any therapy, staging according to Polton et al. resulted in the following distribution: stage 1 (n = 1), stage 2 (n = 1), stage 3a (n = 6), stage 3b (n = 3). We scored radiation toxicities at the end of therapy, at weeks 1, 3 and every 3 months after RT according to Veterinary Radiation Therapy Oncology Group radiation toxicity criteria. Clinical follow-up was maintained on regular intervals combined with computed tomography (n = 3). Median follow-up time for dogs still alive was 594 days (range: 224-972 days). Within 1 week post treatment, eight dogs (73%) developed grade 2 and four dogs (36%) grade 1 acute toxicity in the perianal region. All acute toxicities resolved or improved to grade 1 within 3 weeks after treatment. Late toxicity, for example, chronic colitis/diarrhoea, ulcerations, strictures or myelopathies was not observed in any patient. Five dogs were euthanized 105, 196, 401, 508 and 908 days after RT and six dogs were still alive, one in spite of progressive disease. The median progression-free survival was 908 days (95%CI: 215; 1602). The previous theoretically described definitive-intent, moderately hypofractionated protocol using IG-IMRT for the treatment of advanced ASAC showed clinically acceptable acute and late toxicities.

Use of imaging-guided intensity-modulated stereotactic body radiation therapy to treat a well-differentiated hepatocellular carcinoma in a dog.

CASE DESCRIPTION: A 14-year-old 5.6-kg (12.3-lb) castrated male Toy Poodle was evaluated because of high serum activities of alkaline phosphatase and alanine aminotransferase and the presence of a hepatic mass. CLINICAL FINDINGS: Abdominal CT revealed a large (approx 6.8 × 7.1 × 6.5-cm) soft tissue mass along the midline of the liver. The mass either originated from the papillary process of the caudate lobe or the left medial liver lobe. TREATMENT AND OUTCOME: A partial liver lobectomy was performed, and approximately a third of the mass was successfully removed and submitted for histologic examination. Consultation with the oncology service was advised to determine whether radiation therapy could be used to treat the residual disease. On 5 consecutive days, the dog underwent imaging-guided intensity-modulated radiotherapy-stereotactic body radiation therapy (4 Gy/treatment) with a simultaneous integrated boost to the center of the tumor. The dog received a base dose of 20 Gy that was then boosted to 28 Gy. In the 10-month period after completion of radiation therapy, the hepatocellular mass continued to decrease in size, and overall improvements in the dog's serum liver enzyme abnormalities were evident. CLINICAL RELEVANCE: There are few treatment options for dogs with incompletely excised hepatocellular carcinomas. On the basis of the positive outcome in this case, radiation therapy could be useful following incomplete surgical removal of hepatocellular carcinomas in dogs.

Safety and efficacy of a nonmyeloablative pretransplant conditioning regimen using total lymphoid irradiation with volumetric modulated arc therapy in healthy dogs: A pilot study.

Allogeneic hematopoietic cell transplantation (HCT) has been an effective treatment for human patients with haematological malignancies (Baron & Storb, 2006; Bair et al., 2020; Copelan et al., 2019). However, the optimal pretransplant conditioning treatment is unclear in canine allogeneic HCT. This pilot study aimed to evaluate the safety and efficacy of total lymphoid irradiation (TLI) with volumetric modulated arc therapy (VMAT) for a nonmyeloablative HCT conditioning. Six healthy dogs were treated with 8 or 12 Gy TLI using VMAT. Haematological and physical changes were recorded over 8 weeks. To assess the effect of peripheral lymphocyte condition, lymphocyte subset and proliferative ability were examined. At the end of the experiment, necropsy was performed. All dogs showed mild-to-moderate neutropenia and thrombocytopenia, and these haematological changes resolved spontaneously. One dog treated with 8 Gy TLI developed transient cutaneous infection. No major complication was seen in the other seven dogs. Myelocytes and erythroblast cytopenia of bone marrow were detected in two dogs treated with 12 Gy TLI. This study is the first report of TLI using VMAT in dogs, and results suggest that this regimen is a feasible nonmyeloablative treatment.

Patterns of local residual disease and local failure after intensity modulated/image guided radiation therapy for sinonasal tumors in dogs.

BACKGROUND: Most dogs with sinonasal tumors (SNT) treated with radiation therapy (RT) died because of local disease progression. HYPOTHESIS/OBJECTIVES: Our hypothesis is that the majority of local failure and residual disease would occur within the radiation field. ANIMALS: Twenty-two dogs with SNT treated with RT. METHODS: Retrospective cohort study. INCLUSION CRITERIA: dogs with SNT receiving 10 daily fractions of 4.2 Gy with intensity modulated radiation therapy (IMRT)/image guided radiation therapy (IGRT) and follow-up cone beam computed tomography (CBCT). Each CBCT was registered with the original radiation planning CT and the gross tumor volume (GTV) contoured. The GTV was classified as residual (GTVr) or a failure (GTVf). The dose statistic for each GTV was calculated with the original IMRT plan. For GTVf, failures were classified as "in-field," "marginal," or "out-field" if at least 95, 20-95, or less than 20% of the volume of failure was within 95% (D95) of the total prescription dose, respectively. RESULTS: There were 52 follow-up CBCT/CTs. Overall there was a GTVr for 20 dogs and GTVf for 16 dogs. The majority of GTVr volume was within the original GTV. GTVf analysis showed that 75% (12/16) were "in-field," 19% (3/16) were "marginal" and 6% (1/16) were "out-field." CONCLUSION AND CLINICAL IMPORTANCE: In-field failures are the main pattern for local recurrence, and there is evidence of radioresistant subvolumes within the GTV.

Nasal angiofibroma treatment outcome using intensity-modulated radiation therapy in a dog.

A 6-year-old dog presented with a modified Adams stage 3 angiofibroma of the right nasal cavity, causing fluid accumulation along the right frontal sinus. Treatment consisted of step-and-shoot intensity-modulated radiation therapy in 12 daily treatments of 3.5 Gy, for a total dose of 42 Gy to 95% of the planning target volume. The dog developed self-limiting grade 2 oral mucositis which resolved within 2 weeks of course completion. A recheck exam 668 days after treatment confirmed a stable disease response by RECIST and a tumor volume decrease of 55.4%.

A combined protocol with piroxicam, chemotherapy, and whole pelvic irradiation with simultaneous boost volumetric modulated arc radiotherapy for muscle-invasive canine urinary transitional cell carcinoma: First clinical experience.

The aims of this pilot study were to evaluate the feasibility and efficacy of high-dose hypofractionated volumetric modulated arc radiotherapy (VMAT) applied to whole pelvic region radiotherapy (WPRT) with multilevel simultaneous integrated boost (MLSIB) combined with piroxicam and chemotherapy for the treatment of canine transitional cell carcinoma (TCC) of the lower urinary tract with muscle invasion TCC. Twelve dogs were enrolled, according to stage, in two groups: group 1, TCC confined to the urinary tract; group 2, TCC with metastasis. The planning target volume dose was tailored from 36 to 42 Gy in 6 fractions. All dogs were prescribed piroxicam and radiosensitizing carboplatin, and six received chemotherapy after radiotherapy. Serial follow-ups with computed tomography and magnetic resonance imaging were performed. Disease control and toxicity effects were evaluated according to the Response Evaluation Criteria in Solid Tumors and Veterinary Radiation Therapy Oncology Group criteria. The treatment was well tolerated, and no high-grade side effects were reported. The median overall survival times for groups 1 and 2 were 1,230 and 150 days, respectively. A considerable percentage of patients in group1 (50%) were still alive at the time of writing this paper, and a longer follow-up could enable a more accurate survival analysis. This preliminary analysis shows that VMAT applied to the WPRT with MLSIB is an effective and safe option for dogs with lower urinary TCC, although the presence of metastases worsens the prognosis.

Reducing margins for abdominopelvic tumours in dogs: Impact on dose-coverage and normal tissue complication probability.

Image-guided, intensity modulated radiation therapy (IG-IMRT) reduces dose to pelvic organs at risk without losing dose coverage to the planning target volume (PTV) and might permit margin reductions potentially resulting in lower toxicity. Appropriate PTV margins have not been established for IG-IMRT in abdominopelvic tumours in dogs, and herein we explore if our usual PTV 5 mm margin can be reduced further. Datasets from dogs that underwent IG-IMRT for non-genitourinary abdominopelvic neoplasia with 5 mm-PTV expansion were included in this retrospective virtual study. The clinical target volumes and organs at risk (OAR) colon, rectum, spinal cord were adapted to each co-registered cone-beam computed tomography (CBCT) used for positioning. New treatment plans were generated and smaller PTV margins of 3 mm and 4 mm evaluated with respect to adequate dose coverage and normal tissue complication probability (NTCP) of OAR. Ten dogs with a total of 70 CBCTs were included. Doses to the OAR of each CBCT deviated mildly from the originally planned doses. In some plans, insufficient build-up of the high dose-area at the body surface was found due to inadequate or missing bolus placement. Overall, the margin reduction to 4 mm or 3 mm did not impair dose coverage and led to significantly lower NTCP in all OAR except for spinal cord delayed myelopathy. However, overall NTCP for spinal cord was very low (<4%). PTV-margins depend on patient immobilization and treatment technique and accuracy. IG-IMRT allows treatment with very small margins in the abdominopelvic region, ensuring appropriate target dose coverage, while minimizing NTCP.

Definitive-intent intensity modulated radiotherapy for modified-Adams' stage 4 canine sinonasal cancer: A retrospective study of 29 cases (2011-2017).

Dogs with sinonasal tumors with cribriform plate lysis (modified Adams' stage 4) treated with non-conformal definitive radiotherapy (RT) have short median survivals of 6-7 months. Intensity-modulated radiotherapy with its greater conformality and tumor dose homogeneity may result in more favorable outcomes. Dogs with epithelial or mesenchymal sinonasal tumors and CT evidence of cribriform lysis that received 10 daily fractions of 4.2 Gray using IMRT by helical tomotherapy were included in this single-institution retrospective case series study. Dogs with distant metastasis, previous treatment, or concurrent chemotherapy were excluded. Based on CT, tumors were divided into two groups: cribriform plate lysis only (stage 4a) or intracranial extension (stage 4b). Twenty-nine dogs were included, 23 with carcinoma and six with sarcoma. Eight dogs had stage 4b tumors; two presented with neurologic signs. Two dogs had lymph node metastasis at diagnosis, one confirmed and one suspected. Radiation dose distributions were standardized and patient positioning for RT was verified daily using on-board megavoltage CT. All evaluable dogs had improvement of clinical signs. Median progression free survival was 177 days (95% CI, 128-294 days). Median overall survival was 319 days (95% CI, 188-499 days). Radiotherapy was well tolerated. The most common side effect was grade 1 or 2 oral mucositis. Two dogs that received additional treatment at progression (stereotactic RT [1]; surgery [1]) developed significant late effects. Image-guided definitive-intent IMRT may improve survival in dogs with modified Adams' stage 4 sinonasal tumors and is associated with low morbidity. Intracranial tumor extension was not prognostic in this cohort of uniformly treated dogs.

Outcome of a dog undergoing definitive-intent intensity-modulated radiation therapy for an intranasal ganglioneuroma.

An 11-year-old intact male Shiloh Shepherd was presented for evaluation of epistaxis, decreased nasal airflow, and destructive caudal nasal lesion identified using CT. Histopathologic evaluation of the nasal mass was consistent with a ganglioneuroma. The dog was treated with 10 × 4.2 Gy using IMRT technique. Post radiation therapy (RT), improvement in clinical signs were noted. Tumor progressed in size based on CT evaluation at 49 days, 3, and 6 months post-treatment. A grade 2 oral mucositis was the only RT side effect noted. Radiation therapy as described above was completed without evidence of high-grade radiation toxicities and has potential to improve clinical signs but failed to induce tumor response.

Definitive-intent intensity-modulated radiation therapy provides similar outcomes to those previously published for definitive-intent three-dimensional conformal radiation therapy in dogs with primary brain tumors: A multi-institutional retrospective study.

Radiotherapy with or without surgery is a common choice for brain tumors in dogs. Although numerous studies have evaluated use of three-dimensional conformal radiotherapy, reports of definitive-intent, IMRT for canine intracranial tumors are lacking. Intensity-modulated radiation therapy has the benefit of decreasing dose to nearby organs at risk and may aid in reducing toxicity. However, increasing dose conformity with IMRT calls for accurate target delineation and daily patient positioning, in order to decrease the risk of a geographic miss. To determine survival outcome and toxicity, we performed a multi-institutional retrospective observational study evaluating dogs with brain tumors treated with IMRT. Fifty-two dogs treated with fractionated, definitive-intent IMRT at four academic radiotherapy facilities were included. All dogs presented with neurologic signs and were diagnosed via MRI. Presumed radiological diagnoses included 37 meningiomas, 12 gliomas, and one peripheral nerve sheath tumor. One dog had two presumed meningiomas and one dog had either a glioma or meningioma. All dogs were treated in the macroscopic disease setting and were prescribed a total dose of 45-50 Gy (2.25-2.5 Gy per fraction in 18-20 daily fractions). Median survival time for all patients, including seven cases treated with a second course of therapy was 18.1 months (95% confidence of interval 12.3-26.6 months). As previously described for brain tumors, increasing severity of neurologic signs at diagnosis was associated with a worse outcome. Intensity-modulated radiation therapy was well tolerated with few reported acute, acute delayed, or late side effects.

Ocular and periocular radiation toxicity in dogs treated for sinonasal tumors: A critical review.

Visual impairment from radiation-induced damage can be painful, disabling, and reduces the patient's quality of life. Ocular tissue damage can result from the proximity of ocular organs at risk to irradiated sinonasal target volumes. As toxicity depends on the radiation dose delivered to a certain volume, dose-volume constraints for organs at risk should ideally be known during treatment planning in order to reduce toxicity. Herein, we summarize published ocular toxicity data of dogs irradiated for sinonasal tumors from 36 publications (1976-2018). In particular, we tried to extract a dose guideline for a clinically acceptable rate of ocular toxicity. The side effects to ocular and periocular tissues were reported in 26/36 studies (72%) and graded according to scoring systems (10/26; 39%). With most scoring systems, however, toxicities of different ocular and periocular tissues are summed into one score. Further, the scores were mostly applied in retrospect and lack volume- and dose-data. This incomplete information reflects the crux of the matter for radiation dose tolerance in canine ocular tissues: The published information of the last three decades does not allow formulating dose-volume guidelines. As a start, we can only state that a mean dose of 39 Gy (given in 10 x 4.2 Gy fractions) will lead to loss of vision by one or both eyes, while mean doses of <30 Gy seem to preserve functionality. With a future goal to define tolerated doses and volumes of ocular and periocular tissues at risk, we propose the use of combined ocular toxicity scoring systems.

Outcome of intensity-modulated radiation therapy-based stereotactic radiation therapy for treatment of canine nasal carcinomas.

Stereotactic radiation therapy (SRT) has emerged as a convenient definitive treatment modality in veterinary medicine, but few studies exist evaluating outcome with treatment for canine nasal tumors, and no studies report the treatment of one single tumor histotype. This retrospective, observational study evaluates toxicity, response, and survival in 17 dogs with nasal carcinomas treated with SRT. Dogs received a median of 3000 centigray in three fractions via 6-MV linear accelerator. Eighty-eight percent of patients (n = 15) demonstrated clinical benefit. Of dogs with repeated CT imaging (n = 10), 60% (n = 6) achieved a partial response and 10% (n = 1) achieved a complete response. Median progression-free survival (PFS) was 359 days. Median survival time (MST) was 563 days. Among dogs evaluable for acute toxicity, 50% (n = 10) developed low grade toxicity (grade 1, n = 4; grade 2, n = 1). No patients developed grade 3 toxicity. 16 dogs (87%) evaluable over the long term developed signs consistent with possible late toxicity. The majority of late toxicities were mild (alopecia, hyperpigmentation, and leukotrichia n = 10; ocular discharge and keratoconjunctivitis sicca n = 5). Thirty-seven percent of patients (n = 6) developed seven possible grade 3 late toxicities (blindness, n = 3; fistula, n = 1; seizures, n = 3), which were difficult to distinguish from progressive disease in most patients. Of the prognostic factors evaluated (demographics, tumor stage, dosimetric data, epistaxis, facial deformity, clinical response, image-based response, nonsteroidal anti-inflammatory drugs, and chemotherapy), only clinical response was a positive prognostic factor on MST (P < .00). No factors were found to be significantly associated with PFS.

Using biologically based objectives to optimize boost intensity-modulated radiation therapy planning for brainstem tumors in dogs.

Irradiated brain tumors commonly progress at the primary site, generating interest in focal dose escalation. The aim of this retrospective observational study was to use biological optimization objectives for a modeling exercise with simultaneously-integrated boost IMRT (SIB-IMRT) to generate a dose-escalated protocol with acceptable late radiation toxicity risk estimate and improve tumor control for brainstem tumors in dogs safely. We re-planned 20 dog brainstem tumor datasets with SIB-IMRT, prescribing 20 × 2.81 Gy to the gross tumor volume (GTV) and 20 × 2.5 Gy to the planning target volume. During the optimization process, we used biologically equivalent generalized equivalent uniform doses (gEUD) as planning aids. These were derived from human data, calculated to adhere to normal tissue complication probability (NTCP) ≤5%, and converted to the herein used fractionation schedule. We extracted the absolute organ at risk dose-volume histograms to calculate NTCP of each individual plan. For planning optimization, gEUD(a = 4)  = 39.8 Gy for brain and gEUD(a = 6.3)  = 43.8 Gy for brainstem were applied. Mean brain NTCP was low with 0.43% (SD ±0.49%, range 0.01-2.04%); mean brainstem NTCP was higher with 7.18% (SD ±4.29%, range 2.87-20.72%). Nevertheless, NTCP of < 10% in brainstem was achievable in 80% (16/20) of dogs. Spearman's correlation between relative GTV and NTCP was high (ρ = 0.798, P < .001), emphasizing increased risk with relative size even with subvolume-boost. Including biologically based gEUD values into optimization allowed estimating NTCP during the planning process. In conclusion, gEUD-based SIB-IMRT planning resulted in dose-escalated treatment plans with acceptable risk estimate of NTCP < 10% in the majority of dogs with brainstem tumors. Risk was correlated with relative tumor size.

Definitive-intent intensity-modulated radiation therapy for treatment of canine prostatic carcinoma: A multi-institutional retrospective study.

No standard of care is currently recognized for treatment of canine prostatic carcinoma (PC). This retrospective study assesses outcome following definitive-intent, intensity-modulated radiation therapy (RT) in dogs with PC. Medical records review was performed, including 18 patients from four institutions undergoing definitive-intent intensity-modulated radiotherapy to treat PC. Diagnosis was incidental in 7/18 (39%) patients. Five dogs (28%) had evidence of metastasis to loco-regional lymph nodes at diagnosis. Seventeen patients received concurrent non-steroidal anti-inflammatory drugs; 15/18 (83%) patients received maximally-tolerated dose (MTD) chemotherapy, with variable drugs and protocols employed. Total prescribed radiation dose ranged from 48 to 54 Gy (median 50 Gy) delivered as daily doses of 2.5-2.8 Gy. One patient was euthanized prior to completing radiotherapy. Acute toxicity was observed in nine patients; Grade 1-2 diarrhoea was the most common toxicity observed. Suspected late toxicity (urethral stricture, ureteral stricture and hindlimb oedema) was observed in three patients. Median event-free survival (EFS) following RT was 220 days, and median overall survival was 563 days. Local progression occurred in seven patients at a median of 241 days. Median overall survival was significantly longer in incidentally diagnosed dogs (581 vs 220 days in symptomatic dogs, P = .042). EFS was significantly longer in patients treated with MTD chemotherapy (241 vs 25 days, P < .001), and significantly shorter in patients presenting with evidence of metastatic disease (109 days) vs those without (388 days, P = .008). These findings suggest that definitive-intent radiotherapy is a valuable treatment option for local control of canine PC with moderate risk of toxicity.

A case report of total skin photon radiation therapy for cutaneous epitheliotropic lymphoma in a dog.

BACKGROUND: Total skin electron beam radiation therapy (TSEBT) is an effective treatment for primary diffuse cutaneous lymphomas in humans. While several techniques exist, they all require significant commitment of staff time and resources. In veterinary medicine, canine-specific techniques and strategies have been adapted and delivered but deemed not "realistically" clinically implementable given the time commitment of over 2.5 h plus per fraction or have been relegated to palliative intent. Leveraging these technologies of helical tomotherapy and 3D printing, we developed and clinically implemented a radiotherapeutic treatment strategy for the management of medically refractory diffuse cutaneous lymphoma in the dog. CASE PRESENTATION: A 13.5-year-old female spayed Bichon Frise presented to the Oncology service at Texas A&M University, College of Veterinary Medicine due to the progression of diffuse cutaneous epitheliotropic lymphoma (CEL) that had failed medical management. Twenty-seven gray were delivered to the patient with a treatment time requirement under 40 min including real time monitoring of anesthesia during setup and treatment. A partial response was noticeable after four fractions and the tumor completely regressed progressively over the entire treated area by the end of therapy. A grade 1 lethargy, fatigue, weight loss, and oral mucositis and grade 2 alopecia, nail/claw changes, pruritus, scaling, anorexia, and diarrhea were noted during treatment. Additionally, a grade 3 thrombocytopenia developed after fraction eight requiring a treatment interruption of 6 weeks and prescription modification prior to treatment continuation and completion. From the beginning of total skin photon radiation therapy (TSPT) treatment until the time of the patient was euthanized unrelated to cutaneous epitheliotropic lymphoma (123 days), only one new lesion on the head was identified and confirmed by histopathology within the treated fields. CONCLUSIONS: The proposed technique is an acceptable alternative to TSEBT that is actually clinically implementable within a palliative or definitive setting and clinical constraints, however further testing and refinement is needed to reduce hematological complications and to confirm and expand on preliminary findings.