The future of radiotherapy in small animals - should the fractions be coarse or fine?

Update in Veterinary Radiation Oncology: Focus on Stereotactic Radiation Therapy

Stereotactic radiotherapy (SRT) involves the precise delivery of highly conformal, dose-intense radiation to well-demarcated tumors. Special equipment and expertise are needed, and a unique biological mechanism distinguishes SRT from other forms of external beam radiotherapy. Families find the convenient schedules and minimal acute toxicity of SRT appealing. Common indications in veterinary oncology include nasal, brain, and bone tumors. Many other solid tumors can also be treated, including spinal, oral, lung, heart-base, liver, adrenal, and prostatic malignancies. Accessibility of SRT is improving, and new data are constantly emerging to define parameters for appropriate case selection, radiation dose prescription, and long-term follow-up.

Use of Cold Atmospheric Plasma in the Treatment of Squamous Cell Carcinoma: in vitro Effects and Clinical Application in Feline Tumors: A Pilot Study

Cold atmospheric plasma (CAP) has shown promising results against squamous cell carcinoma (SCC) in both in vivo and in vitro assays, mainly in humans and mice. Its applicability for treatment of feline tumors, however, remains unknown. This study aimed to evaluate the anticancer effects of CAP on a head and neck squamous cell carcinoma (HNSCC) cell lineage and against a clinical case of cutaneous SCC in a cat. Control and treatment groups employing the HNSCC cell line (SCC-25) were used, the latter exposed to CAP for 60 seconds, 90 seconds, or 120 seconds. The cells were subjected to the MTT assay nitric oxidation assay and thermographic in vitro analyses. The clinical application was performed in one cat with cutaneous SCC (3 sites). The lesions were treated and evaluated by thermographic, histopathological, and immunohistochemical examinations (caspase-3 and TNF-alpha). Treatment of the SCC-25 cells for 90 seconds and 120 seconds resulted in a significant nitrite concentration increase. Decreased cell viability was observed after 24 hours and 48 hours, regardless of exposure time. However, the cell viability reduction observed at 72 hours was significant only in the 120 seconds treatment. In vitro, the temperature decreased for all treatment times, while the plasma induced a slight increase in mean temperature (0.7°C) in the in vivo assay. Two of the 3 clinical tumors responded to the treatment: one with a complete response and the other, partial, while the third (lower lip SCC) remained stable. Both remaining tumors displayed apoptotic areas and increased expression of caspase-3 and TNF-alpha. Adverse effects were mild and limited to erythema and crusting. The CAP exhibited an in vitro anticancer effect on the HNSCC cell line, demonstrated by a dose-dependent cell viability reduction. In vivo, the therapy appears safe and effective against feline cutaneous SCC. The treatment did not result in a clinical response for 1 of 3 lesions (proliferative lower lip tumor), however, a biological effect was still demonstrated by the higher expression of apoptosis indicators.

Use of a cyclical hypofractionated radiotherapy regime ('QUAD shot') for the treatment of feline sinonasal carcinomas

OBJECTIVES

Radiation therapy is the treatment of choice for cats with sinonasal carcinomas. Different protocols have been described in the literature, though a clear consensus regarding the optimal protocol is lacking. The aim of the study was to describe the tolerability, efficacy and outcome of cats treated with a cyclical hypofractionated protocol.

METHODS

Cats with histologically diagnosed sinonasal carcinomas in a single institution were retrospectively included. All patients were treated with a cyclical hypofractionated protocol ('QUAD shot' regime). Cats were treated with 4 Gray (Gy) delivered in four fractions within 48 h, with a minimum of 6 h between two treatments, and repeated every 3-4 weeks for a total dose of 48 Gy in three cycles.

RESULTS

Seven cats met the inclusion criteria. Nasal discharge and sneezing were the most common presenting complaints. All cats presented with advanced stage of disease with CT examination (three with modified Adams stage 3 and four with stage 4). Clinical improvement was seen in six cats. Five cats had a follow-up CT; one had a complete response, two had partial responses, one had stable disease and one had progressive disease. Two cats were still alive at the time of writing while four were euthanased owing to tumour-related causes. The median overall survival time was 460 days. The 1-year survival time was 80% and the 2-year survival time was 0%. Severe acute or late toxicity was not reported.

CONCLUSIONS AND RELEVANCE

This is the first report of a cyclical hypofractionated protocol in the veterinary literature that can provide prolonged survival in cats with advanced stage sinonasal carcinoma. Its use should be considered in patients when prolonged hospitalisation can be detrimental to quality of life, while still delivering a therapeutic total dose of radiation therapy.

Stereotactic radiotherapy (10 Gy X 3) for canine nonlymphomatous intranasal tumors is associated with prolonged survival and minimal risk of severe radiotoxicity

OBJECTIVE

To describe oncologic outcomes following administration of a uniform stereotactic radiotherapy protocol (SRT; 10 Gy X 3) for canine intranasal tumors and to identify whether any clinical or dosimetric factors were predictive of event-free or overall survival time (EFST or OST).

ANIMALS

129 dogs.

PROCEDURES

In this single-institution retrospective study, the medical records database was searched for canine nonlymphomatous intranasal tumors treated with 10 Gy X 3 SRT between August 2013 and November 2020. Findings regarding adverse effects and outcomes were analyzed overall, for dogs grouped on the basis of life stage (mature adult, senior, or end of life), and for treatment-related or tumor-related variables to identify potential predictors of outcome.

RESULTS

After SRT, most dogs clinically improved with minimal acute radiotoxicity. The median EFST was 237 days; median OST was 542 days. Receipt of other tumor-directed therapies before or after SRT was associated with improved EFST in senior dogs (hazard ratio [HR], 0.416) and improved OST in mature adult (HR, 0.241) and senior dogs (HR, 0.348). In senior dogs, administration of higher near-minimum radiation doses was associated with improved EFST (HR, 0.686) and OST (HR, 0.743). In senior dogs, chondrosarcoma was associated with shorter OST (HR, 7.232), and in dogs at end of life, having a squamous cell or transitional carcinoma was associated with worse EFST (HR, 6.462).

CLINICAL RELEVANCE

This SRT protocol results in improved quality of life and prolonged OST for dogs of all life stages. Radiation protocol optimization or use of multimodal therapy may further improve outcomes.

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.

Canine comparative oncology for translational radiation research

PURPOSE

Laboratory and clinical research are essential for advancing radiation research; however, there is a growing awareness that conventional laboratory animal models and early-phase clinical studies in patients have not improved the low success rates and late-stage failures in new cancer therapy efforts. There are considerable costs and inefficiencies in moving preclinical research into effective cancer therapies for patients. Canine translational models of radiation research can fill an important niche between rodent and human studies, ultimately providing valuable, predictive, translational biological and clinical results for human cancer patients. Companion dogs naturally and spontaneously develop cancers over the course of their lifetime. Many canine tumor types share important similarities to human disease, molecularly and biologically, with a comparable clinical course. Dogs receive state-of-the-art medical care, which can include radiotherapy, experimental therapeutics, and novel technologies, offering an important opportunity for radiobiology and radiation oncology research. Notably, the National Cancer Institute has developed the Comparative Oncology Program to promote this area of increased research interest.

CONCLUSION

In this review, the benefits and limitations of performing translational radiation research in companion dogs will be presented, and current research utilizing the canine model will be highlighted, including studies across research areas focusing on common canine tumor types treated with radiotherapy, comparative normal tissue effects, radiation and immunology research, and alternative radiation therapy approaches involving canine cancer patients.

Treatment of nasal tumours in dogs: a review

Nasal tumours are common neoplasms in dogs and often represent a diagnostic and therapeutic challenge due to their confined location within the nasal cavities. The main goal of this review is to extract the most relevant information from a wide and often confusing evidence-based medicine on the treatment of canine nasal tumours and conclude with current recommendations. This report highlights the different therapeutic modalities available and describes their technical aspects, interests and limitations. Megavoltage radiotherapy, as the most recent treatment and standard of care, is particularly examined, especially the different types of radiotherapy units, the main protocols used and their advantages and limits. Newer and non-conventional treatments are also discussed.

Impact of radiation dose and pre-treatment pain levels on survival in dogs undergoing radiotherapy with or without chemotherapy for presumed extremity osteosarcoma

The purpose of this bi-institutional retrospective study was to determine whether survival for dogs with extremity osteosarcoma (OS) is improved through the use of stereotactic radiotherapy (SRT; a single fraction of 25 Gy, or 36 Gy total given in three consecutive daily fractions) plus chemotherapy, vs lower dose conventionally planned and delivered hypofractionated radiotherapy (CHRT; 14-20 Gy total in 1-2 consecutive daily fractions) plus chemotherapy. We also sought to determine whether baseline pain severity influences oncologic outcomes following radiotherapy for canine extremity OS. The medical records of 82 dogs undergoing radiotherapy for confirmed or presumed OS were reviewed. In dogs receiving combinations of both chemotherapy and radiotherapy, survival was significantly longer with SRT vs CHRT (median overall survival time: 350 vs 147 days; P = .031). In a univariate analysis, dogs with pulmonary metastases and high pain at the time of irradiation had short overall survival times; use of high radiation doses and chemotherapy were associated with improved survival. Separate multivariable models were built to assess the predictive nature of various factors that might influence event-free or overall survival in dogs treated with radiotherapy, with or without chemotherapy; for dogs treated with both chemotherapy and radiotherapy, overall survival times were significantly longer when baseline pain scores were 'low' (vs 'high'; hazard ratio: 0.258; P = .030), radiation doses were high (hazard ratio: 0.943; P = .034). Neither pain nor radiation dose were associated with survival in dogs treated with radiotherapy, without chemotherapy.

Significant advances in veterinary oncology - 60 years on

The first edition of the Journal of Small Animal Practice published in February 1960, contained a paper entitled "Recent Treatments of Malignant Neoplasia" by Dr Larry Owen. Now we have reached the 60th anniversary of JSAP, that article provides a baseline from which to review subsequent advances in veterinary oncology, which now includes worldwide networks that have resulted in veterinary oncology becoming the multidisciplinary speciality that it is today. There certainly have been many advances in understanding of the pathology and epidemiology of animal cancers and in methods of diagnosis and treatment. However, the subject has become so large and diverse that not all aspects can be covered in detail here. It should also be acknowledged that there are still many gaps in knowledge in this field and that, because of a lack of randomised clinical trials, the evidence base for what is often regarded as "standard of care" is weak.

Changes in target volume during irradiation of canine intranasal tumors can significantly impact radiation dosimetry

Nasal tumor size can change during radiation therapy (RT). The amount of peritumoral fluid (eg, mucohemorrhagic effusions) can also fluctuate. How often this occurs and the magnitude of change are unknown. Likewise, there are no data which describe dosimetric effects of these changing volumes during a course of RT in veterinary medicine. This study addresses that gap in knowledge. Using pet dogs with nasal tumors, three CT image sets were created. Different Hounsfield units were applied to the gross tumor volume (GTV) of each image set: unchanged, -1000 (AIR), -1000 (to the portion of the GTV that actually underwent volume reduction during clinical RT; REAL). Two plans were created: 18-fraction three-dimensional conformal RT (3DCRT) and three-fraction intensity-modulated stereotactic RT (IM-SRT). For nearby normal tissues and GTV, near-maximum doses (D_2% and D_5% ) and volumes receiving clinically significant doses were recorded. To verify "AIR" results, thermoluminescent dosimeters recorded dose in cadavers that were irradiated using both 3DCRT and IM-SRT plans. "AIR" scenario had ≤1.5 Gray (Gy) increases in D_2% and ≤3.2 cc increases of volume. "REAL" scenario had ≤0.97 Gy increases in D_5% and ≤0.55 cc increases of volume at clinically relevant doses. Both were statistical significant. Results suggest that near-complete resolution of GTV warrants plan revision.

Update in Veterinary Radiation Oncology: Focus on Stereotactic Radiation Therapy

Stereotactic radiotherapy (SRT) involves the precise delivery of highly conformal, dose-intense radiation to well-demarcated tumors. Special equipment and expertise are needed, and a unique biological mechanism distinguishes SRT from other forms of external beam radiotherapy. Families find the convenient schedules and minimal acute toxicity of SRT appealing. Common indications in veterinary oncology include nasal, brain, and bone tumors. Many other solid tumors can also be treated, including spinal, oral, lung, heart-base, liver, adrenal, and prostatic malignancies. Accessibility of SRT is improving, and new data are constantly emerging to define parameters for appropriate case selection, radiation dose prescription, and long-term follow-up."

Owners' perception of their dogs' quality of life during and after radiotherapy for cancer

OBJECTIVES

To determine the owners' perception of dogs' quality of life before, immediately after and 6 weeks after radiotherapy treatments for a variety of neoplasms and assess owner satisfaction over their decision to treat.

MATERIALS AND METHODS

Questionnaires were given to owners whose dogs completed a radiotherapy treatment at a referral radiation oncology centre. Questionnaires were given at three time points: before treatment, on the last day of treatment and more than 6 weeks after the treatment was finished. Owners were asked questions regarding their perception of radiotherapy and the quality of life of their pets before, during and after treatment with radiation therapy. Quality of life was scored from 1 (could not be worse) to 10 (could not be better).

RESULTS

Seventy-one owners met the inclusion and exclusion criteria. Results showed that 6 weeks or more after treatment, most owners were happy that they had chosen to treat their dogs (92%) and would treat another pet again, if indicated (88%). Across the three time points, median quality of life perception score was 9.

CLINICAL SIGNIFICANCE

Radiotherapy was well tolerated by owners and dogs in this study. The great majority of clients were happy to have pursued radiotherapy, would choose to do it again (if indicated) and would recommend it to a friend.