Hypofractionated radiotherapy in nine dogs with unresectable solitary lung adenocarcinoma

Abstract

Although lung lobectomy is the most common treatment option for dogs with solitary lung tumors, surgery often cannot be performed at the time of diagnosis. In this retrospective, case series study, we described the effects of hypofractionated radiotherapy for tumor mass reduction in nine dogs with solitary lung adenocarcinoma that were later considered for surgical resection, and we assessed the tolerability of the radiation protocol. Tumors were deemed unresectable by the attending veterinarian. The dose prescription was 7.0‐12.0 Gy/fraction in four to seven fractions, administered weekly for a total dose of 40‐50 Gy. Treatment planning prioritized normal tissue dose constraints. The median interval between the last radiotherapy session and maximum tumor size reduction was 56 (range: 26‐196) days, with six and three dogs exhibiting a partial response and stable disease, respectively. Although acute and late radiation‐induced toxicity to the skin and/or lungs developed in all nine dogs, it was self‐limiting or improved with short‐term anti‐inflammatory treatment. Tumor progression after initial size reduction was confirmed in three dogs at 62, 126, and 175 days, respectively, after the last radiotherapy session. Seven of the nine dogs underwent lobectomy a median of 68 days after radiotherapy when tumors were in partial response or stable disease or at the time of progression, and five received systemic chemotherapy concurrent with or after radiotherapy. These findings suggest that hypofractionated radiotherapy for canine solitary lung adenocarcinoma is useful when the tumor is large or when surgery cannot be performed immediately after diagnosis.

Retrospective study evaluating the efficacy of stereotactic body radiation therapy for the treatment of confirmed or suspected primary pulmonary carcinomas in dogs

“…In that study, all dogs experienced acute and late toxicity with 44% of dogs alive at 1 year and 5/9 (55%) eventually succumbing to their lung adenocarcinoma 2 . Acute toxicity included 89% of dogs with Grade 1 or 2 toxicity of the lung and 33% exhibiting Grade 1 toxicity of the skin 2 . Late toxicity was seen in 22% with all exhibiting Grade 1 toxicity of the lung and one also experiencing Grade 1 toxicity of the skin 2 .…”

“…A previous publication evaluated a weekly hypofractionated three‐dimensional conformal radiation therapy (3D‐CRT) in dogs with unresectable lung adenocarcinoma to reduce the size of pulmonary tumours to allow for surgery to follow 2 . In that study, all dogs experienced acute and late toxicity with 44% of dogs alive at 1 year and 5/9 (55%) eventually succumbing to their lung adenocarcinoma 2 . Acute toxicity included 89% of dogs with Grade 1 or 2 toxicity of the lung and 33% exhibiting Grade 1 toxicity of the skin 2 .…”

“…Stereotactic body radiation therapy (SBRT) utilizes high, precisely delivered doses of radiation therapy administered over a short time to target tumours as an alternative to surgery. A previous publication evaluated a weekly hypofractionated three‐dimensional conformal radiation therapy (3D‐CRT) in dogs with unresectable lung adenocarcinoma to reduce the size of pulmonary tumours to allow for surgery to follow 2 . In that study, all dogs experienced acute and late toxicity with 44% of dogs alive at 1 year and 5/9 (55%) eventually succumbing to their lung adenocarcinoma 2 .…”

“…2 Acute toxicity included 89% of dogs with Grade 1 or 2 toxicity of the lung and 33% exhibiting Grade 1 toxicity of the skin. 2 Late toxicity was seen in 22% with all exhibiting Grade 1 toxicity of the lung and one also experiencing Grade 1 toxicity of the skin. 2 With SBRT, a more conformal radiation approach than 3D-CRT, it would be anticipated that the toxicity profile should be less and the radiotherapy more ablative with the high dose intensity protocol.…”

Vinorelbine as First-Line Treatment in Stage IV Canine Primary Pulmonary Carcinoma

“…Surgical excision is the treatment of choice; however, the diagnosis is often made at advanced clinical stages when the tumour has already invaded neighbour structures and/or has metastasized, making palliative strategies a more realistic option. In a recent study [ 10 ], the effect of hypofractionated radiotherapy as neoadjuvant therapy for canine solitary lung adenocarcinoma was described. Results were encouraging in terms of tumour response; although acute and late radiation-induced toxicity were common, it was manageable with short-term anti-inflammatory treatment.…”