In June, a 13.5-year-old female spayed Bichon Frise presented to the Oncology service at Texas A&M University, College of Veterinary Medicine & Biomedical Sciences due to the progression of diffuse CEL. Approximately 8 months before presentation, the patient was seen at Pennsylvania State University, College of Veterinary Medicine and conservatively managed with antibiotic therapy for a mildly erythematous and pruritic, noduloplaque skin rash over her right caudal thorax. Concurrently while on therapy, several new multi-focal ulcerative lesions presented. Skin scrapes and a punch biopsy were performed and findings confirmed (dermatopathologist’s histopathological description consistent with, no special stains were submitted) epitheliotropic lymphoma. In April, the patient was started on L-asparaginase/CCNU/Prednisone/Denamarin protocol with subjective clinical improvement. At the client’s request, the patient was referred to Hope Veterinary Specialist to concurrently participate in a clinical trial utilizing monoclonal T cell therapy in combination with traditional chemotherapy. In May, CCNU was delayed secondary to hepatotoxicity. While on CCNU break, several new ulcerative lesions were noted on the right thorax, right ventral tail base, right perianal and vulvar region, and ventral thorax. The patient was started on Cyclophosphamide/Hydroxydaunorubicin/Vincristine/Prednisone (CHOP) receiving only one administration of vincristine prior to being switched to a modified Mechlorethamine/Vinblastine/Procarbazine/Prednisone (MOPP-based) protocol after continued disease progression. After the patient received two cycles of the modified MOPP-based protocol with no apparent response, the client was referred to Texas A&M University for participation in the leukotoxin (Leukothera®) clinical trial. On presentation the physical exam was unremarkable with the exception of the skin which revealed a sparse and patchy hair coat, multiple to generalized distribution of raised plaques with overlying scales and ulceration, a generalized erythema, and erosion of the oral mucosa and mucocutaneous junction. Complete blood count (CBC), coagulation panel, and urinalysis collected by void were relatively unremarkable with no significant abnormalities. Serum chemistry panel (CHEM) demonstrated an elevated cholesterol (297 mg/dl), ALT (325 U/L), and ALKP (420 U/L). Three-view thoracic radiographs identified mild left atrial enlargement with no evidence of cardiogenic pulmonary edema and no evidence of pulmonary neoplasia identified. Sonographic assessment of the abdomen revealed liver enlargement consistent with steroid hepatopathy, renal dystrophic mineral and possible calculi, and bladder calculi and possible cystitis. Fine-needle aspiration of mandibular, superficial cervical, popliteal, and inguinal lymph nodes indicated reactive lymphoid hyperplasia. Due to the patient’s prior and persistent hepatotoxicity secondary to CCNU, they were excluded from participation at the time of initial evaluation. At the client’s perseverance, lack of response to prior therapy, and progressive disease, the patient was referred from medical oncology to radiation oncology for TSPT. Delivery of radiation therapy commenced approximately 30 days (30 days) after initial presentation with no additional staging prior to start. An indexible nylon Vac-Lok™ cushion (CIVCO Medical Solutions, Coralville, Iowa) immobilization system and an in-house, canine-specific bite block fixation device were used to rigidly immobilize the head and neck, body, and limbs. For 3D mold generation, a computed tomography (CT) image set of the whole body was acquired. The entire patient was scanned in a large bore (80 cm) CT scanner (Siemens Somatom Definition AS). The image set was transferred to a VelocityAI (Varian Medical Systems Inc., Palo Alto, CA.) workstation for contouring. To generate the initial 3D mold scaffold, the patient’s surface was contoured and expanded 10 mm into air. To prepare the 3D mold scaffold for final printing, the 3D mold contour was then transformed into a 3D mesh using 3DSlicer [], segmented into four separate interconnected shell components using Meshmixer (Autodesk, San Rafael, CA.) converted to a stereolithographic file for 3D printing using Simplify3D (Cincinnati, OH.), and sent to re:3D (Austin, TX.) for manufacturing/printing. The mold was fabricated using polylactide (PLA) filament with a mass density of approximately 1.09 g/cm− 3 and an infill percentage of 100. For helical tomotherapy treatment planning (v. 4.0.4. Tomotherapy, Inc., Madison, WI) a CT image set of the patient’s whole body encased within the 3D printed mold was acquired. The image set was transferred to a VelocityAI workstation for target and normal tissue contouring. Lungs, heart, liver, kidneys, spleen, intestines, stomach, bladder, brain, spinal cord, eyes, estimated bone marrow cavities (cervical vertebrae/caudal skull, thoracic vertebrae/ribs/sternum, abdominal vertebrae/pelvis, brachium and scapula, and femur) thyroids, and lenses (among other volumes) were contoured as organs at risk (OAR). The clinical target volume (CTV) included the entire body surface and extended 3 mm subcutaneously. To account for setup variability and the impact of respiratory motion, the CTV was expanded 2 mm isotropically to form the planning target volume (PTV). Three constraint contours (10 mm, 15 mm, and 20 mm expansions inward from the subcutaneous side of the PTV) not representing OARs or target structures but used strictly as planning tools for dose optimization were generated for dose constraints to the core of the body. Initially, 27 Gy delivered in 15 fractions, 4 times per week were prescribed to 92% of the PTV. Normal tissue dose constraints where based on previously reported clinical tolerances to various OARs. The field width, pitch, and modulation factor used for treatment planning optimization were 5.0 cm, 0.430, and 3.5 respectively. Dose volume histograms and isodose lines were evaluated for the target and individual OARs. Normal tissue toxicity from treatment was evaluated and scored according to the Veterinary Cooperative Oncology Group – Common Terminology Criteria for Adverse Events v1.1 []. Due to hematological toxicity after fraction 8, a treatment interruption was instituted to allow for recovery and the prescription and frequency was modified. The remaining 7 fractions had the dose per fraction reduced from 1.8 Gy to 1.4 Gy (plan not shown) and to compensate for the loss of biological effect from fraction size and treatment break, the number of remaining fractions was increased from 7 to 9. Patient positioning and setup was verified by onboard volumetric megavoltage CT (MVCT) system integrated in the helical tomotherapy machine. Daily MVCT scans (approximately 3 cGy to the body regions for each daily scan) were performed cranially from the level of the eyes caudally to the rear limbs. Image fusions were evaluated by the radiation oncologist and any appropriate translational shifts were applied to the patient’s setup prior to treatment delivery. The patient was pre-medicated with butorphanol (0.2 mg/kg IV) and induced slowly to effect with propofol (2–4 mg/kg IV) for each treatment. The patient was intubated and placed on Sevoflurane (2.5–3%) in oxygen. Intravenous fluids (Lactated Ringers Solution) were provided through the cephalic catheter throughout anesthesia (6 ml/kg/hr). Manual ventilation was provided until the patient had been fully positioned within the body mold then the patient was switched to mechanical ventilation at 17 breaths/min, 10 ml/kg and inspiratory pressure of 19 cm H20 (Hallowell Ventilator). Monitoring included a pulse oximeter probe on the tongue, oscillometric blood pressure cuff on the forelimb, ECG patches on the ventral paw pads and side stream EtCO2 (Vetrends MAX multi-parameter monitor). The body mold did not extend past the proximal forelimb or distal to the hock to allow placement of the IV catheters, ECG patches and oscillometric cuff. Weekly NOVAs (Waltham, MA) were run prior to the start of each week of radiation therapy to ensure patient candidacy for anesthesia. Due to the localization of the disease to the skin only (as determined by prior staging) and the obesity of the patient, an ASA physical status score of 3 was initially assigned. Patient-specific delivery quality assurance was performed in a solid-water phantom native to the system using Radiochromic EBT3 film (Ashland, Covington, KY.) and ionization chamber measurements to verify the planned fraction delivered dose (not shown). Relative planar dose profiles and absolute point dose measurements were compared to calculated planar isodose profiles and point doses. Tolerance for the plan to be deemed acceptable was +/− 3% for measured point doses and gamma value </= 1 for 90% of all points lying within the 30% isodose line using search criteria of 3% and 3 mm. Six nanoDot™ (Landauer, Glenwood, IL) dosimeters were placed along the dorsal and ventral surfaces of patient midline as secondary in vivo verification of dose received to the surface of the skin. Several types of dosimeters could have been considered for in vivo measurements, but the size, ease of appositional placement, processing, and independent accuracy of nanoDot™ thermoluminescent dosimeters made them ideal. Additionally, the uncertainty in dose inherent to the dosimeters is well under the variation that classical TSEBT patients experience day to day and patient to patient variation [, ]. Twenty-seven gray were delivered to the patient from July 13th, 2015 to September 23rd, 2015. A partial response was noticeable after four fractions and the tumor completely regressed over the entire treated area by the end of therapy. No follow-up histology for pathological response was performed at the request of the client. Grade 1 lethargy, fatigue, weight loss, and oral mucositis and grade 2 alopecia, nail/claw changes, pruritus, scaling, anorexia, and diarrhea were noted during and within a couple weeks of treatment. Additionally, grade 3 thrombocytopenia developed after fraction eight requiring a treatment interruption of 6 weeks and prescription modification prior to treatment continuation and completion. No clinically relevant abnormal liver or renal functions and, although not specifically assayed, there was no clinical sign of thyroid or pituitary axis dysfunction detected during or after treatment and the follow-up period prior to the event leading up to the time of euthanasia. Supportive measures were provided and all toxicities except alopecia and thrombocytopenia which fluctuated between grade 1 and grade 2 fully resolved without further incident. Transient pyoderma was noted on follow-up examines after treatment. From the beginning of TSPT treatment until the time the patient was euthanized unrelated to CEL (complications associated with acute pancreatitis) on November 13th, 2015 (approximately 123 days), only one new lesion on the head was detected and confirmed by histopathology within the treated field. The min, mean, and max doses of TSPT to various OARs are presented in Table. The surface dose to the skin as verified by the placement of six nanoDot™ dosimeters along the dorsal and ventral surface of the patient are listed in Table. Ventral placement of the dosimeters prior to the first treatment fraction is demonstrated in Fig..