The effects of local irradiation on circulating lymphocytes in dogs receiving fractionated radiotherapy

Response of Canine Soft Tissue Sarcoma to Stereotactic Body Radiotherapy

Canine soft tissue sarcoma (STS) has served as a preclinical model for radiation, hyperthermia, experimental therapeutics, and tumor microenvironmental research for decades. Stereotactic body radiotherapy (SBRT) demonstrates promising results for the control of various tumors in human and veterinary medicine; however, there is limited clinical data for the management of STS with SBRT. In this retrospective study, we aimed to define overall efficacy and toxicity of SBRT for the treatment of macroscopic canine STS to establish this preclinical model for comparative oncology research. Fifty-two canine patients met inclusion criteria. Total radiation dose prescribed ranged from 20-50 Gy delivered in 1-5 fractions. Median progression-free survival time (PFST) was 173 days and overall survival time (OST) 228 days. Best overall response was evaluable in 46 patients, with 30.4% responding to treatment (complete response n = 3; partial response n = 11). For responders, OST significantly increased to 475 days vs. 201 days (P = 0.009). Prognostic factors identified by multivariable Cox regressions included size of tumor and metastasis at presentation. Dogs were 3× more likely to progress (P = 0.009) or 3.5× more likely to experience death (P = 0.003) at all times of follow up if they presented with metastatic disease. Similarly, every 100-cc increase in tumor volume resulted in a 5% increase in the risk of progression (P = 0.002) and death (P = 0.001) at all times of follow up. Overall, 30.8% of patients developed acute toxicities, 7.7% grade 3; 28.8% of patients developed late toxicities, 11.5% grade 3. Increased dose administered to the skin significantly affected toxicity development. SBRT serves as a viable treatment option to provide local tumor control for canine macroscopic STS, particularly those with early-stage disease and smaller tumors. The results of this study will help to define patient inclusion criteria and to set dose limits for preclinical canine STS trials involving SBRT.

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.

Treatment of genitourinary carcinoma in dogs using nonsteroidal anti-inflammatory drugs, mitoxantrone, and radiation therapy: A retrospective study

Background

Locoregional tumor control and prolonged survival for dogs with genitourinary carcinoma (CGUC) reportedly are achievable using treatment with radiotherapy (RT) with or without adjunctive chemotherapy and nonsteroidal anti‐inflammatory drugs (NSAIDs).

Objectives

To characterize event‐free and overall survival after treatment of CGUC using NSAIDs, mitoxantrone (MTX), and a standardized RT protocol (57 Gy in 20 fractions).

Animals

Fifty‐one client‐owned dogs treated between 2008 and 2017.

Methods

Dogs were retrospectively categorized into treatment groups: (a) first‐line concurrent chemoradiotherapy (≥1 dose of MTX started within 1 month of RT); (b) first‐line chemotherapy (MTX administered for >1 month before RT without tumor progression); (c) RT as a salvage procedure (MTX, surgery or both with subsequent locoregional tumor progression before RT). Treatment‐induced toxicoses, event‐free survival (EFS), and overall survival times (OSTs) were recorded. The influence of demographics, staging, and treatment‐related factors on survival was assessed using Cox proportional hazards modeling.

Results

Median EFS and OST for all dogs were 260 and 510 days with no significant differences among groups 1 (n = 39), 2 (n = 4), and 3 (n = 8). Both EFS and OST were shorter in dogs with moderate to severe clinical signs (P < .001 and P < .001, respectively); OST was shorter in dogs with prostatic involvement (P = .02). Permanent urinary incontinence developed in 16 dogs (31%) at a median of 70 days postirradiation; other toxicoses were mild and self‐limiting.

Conclusions and Clinical Importance

Mild clinical signs and lack of prostate involvement were associated with favorable prognosis for survival. Client education regarding the risk of urinary incontinence is warranted.

Impact of radiotherapy on circulating lymphocyte subsets in patients with esophageal cancer

Radiotherapy (RT) can affect the immune function of patients with cancer. The purpose of this study was to investigate the effect of RT on lymphocyte and its subsets in patients with esophageal cancer (EC).All patients received RT with a mean dose of 5369 cGy (gray). Blood parameters were measured in 31 patients on 3 occasions (before, at the end of radiotherapy, and at 3 months follow-up). The whole blood count and lymphocyte subsets were measured and correlated with short time efficiency and radiation dose parameters.White blood count (WBC) and lymphocyte count (ALC) were greatly decreased at the end of radiotherapy, and the percentages of CD3+, CD3+CD8+ T cells were significantly increased, on the other hand, a decrease in the CD4/CD8 ratio was observed. The percentages of CD3-CD16/56+NK cells and CD19+ B cell were decreased at the end of RT compared with prior RT. The percentages of CD3+ T cells before RT and the WBC and ALC count after RT can be used as prognostic indicators for survival. The PTV dose can cause significant changes in lymphocytes count after RT. CD3+T cells after RT were significantly correlated with mean heart dose and heart V50.Our study identified that RT causes changes in lymphocyte subsets, and these changes may indicate differences in immune function between individuals. Radiotherapy plan should be designed to minimize normal tissue dose to reduce the impact on WBC and lymphocytes.

The effects of local irradiation on circulating lymphocytes in dogs receiving fractionated radiotherapy

Localized radiation therapy can be an effective treatment for cancer but is associated with localized and systemic side effects. Several studies have noted changes in complete blood count (CBC) parameters including decreases in the absolute lymphocyte count (ALC) and increases in the neutrophil:lymphocyte ratio (NLR). These changes could reflect immunosuppression and may contribute to decreased efficacy of immunotherapies used to treat cancer. We hypothesized that dogs would demonstrate decreased ALCs during a course of radiotherapy. A retrospective study was conducted on 203 dogs receiving definitive-intent radiotherapy. Demographic information, CBC values and details of the radiotherapy protocol were collected. The mean lymphocyte count pre-treatment was 1630.68 cells/μL (SD ± 667.56) with a mean NLR of 3.66 (SD ± 4.53). The mean lymphocyte count mid-treatment was 1251.07 cells/μL (SD ± 585.96) and the mean NLR was 6.23 (SD ± 4.99). There was a significant decrease in the mean lymphocyte count by 351.41 lymphocytes/μL (SD ± 592.32) between pre-treatment and mid-treatment (P < .0001), and a corresponding significant increase in the mean NLR of 0.93 (P = .02). Lymphopenia grade increased in 33.5% of dogs and was significant (P = .03). The ALC decrease was not correlated with the volume irradiated (P = .27), but correlated with the irradiated volume:body weight ratio (P = .03). A subset of patients (n = 35) with additional CBCs available beyond the mid-treatment time point demonstrated significant and sustained downward trends in the ALC compared with baseline. Although severe lymphopenia was rare, these decreases, especially if sustained, could impact adjuvant therapy for their cancer.