Abstract
BACKGROUND: The incidence of kidney cancer diagnosis has been increasing over the last years. Surgical resection and local ablation are primary treatment options for localized disease. However, many patients are deemed medically inoperable, technically high risk for surgery or local ablation, or ultimately decline these procedures. Stereotactic body radiation therapy (SBRT) using conventional x-rays has recently been shown to improve outcomes for patients with primary renal cell carcinoma (RCC) in terms of local control and toxicity. However, this treatment may be associated with a significant decline in kidney function that necessitates additional intervention including dialysis in some patients. Proton therapy possesses unique properties that allow the bulk of the energy to be released at the tumor (Bragg peak) while sparing nearby healthy tissues, particularly the remaining ipsilateral and contralateral kidneys. METHODS: SPARE is a single arm, phase II study. Nineteen patients will be recruited and followed for 2 years. Eligible criteria include a biopsy confirmed diagnosis of primary RCC, if feasible, medically inoperable, technically high-risk patients for surgery or local ablative procedures, or decline surgery or ablation, and no clinical or radiographic evidence of metastatic disease. Radiotherapy treatment planning is undertaken using four dimensional computed tomography scanning to incorporate the impact of respiratory motion. Treatment must be delivered using a proton based SBRT using 40–42 Gy in 3–5 fractions. The primary endpoint is the change in Kidney function following proton based SBRT. The secondary endpoints are local control, toxicity profile, progression and overall survival. DISCUSSION: SPARE study represents the first trial to our knowledge evaluating the use of proton based SBRT for treatment of primary RCC. We aim to assess the efficacy and toxicity of this approach and to compare our results to historical outcomes established by previous trials. Proton therapy with its unique properties may be able to spare more ipsilateral and contralateral healthy kidney tissue, thus preserving kidney function superior to photon SBRT particularly in patients with challenging situations including patients with a solitary kidney, large tumors close to nearby organs or poor baseline kidney function. TRIAL REGISTRATION: Clinicaltrials.gov NCT06376669, registered April 19, 2024.