Renal Cancer is Not Radioresistant: Slowly but Continuing Shrinkage of the Tumor After Stereotactic Body Radiation Therapy

Abstract

Purpose: To evaluate the safety and efficacy of stereotactic body radiation therapy for primary lesion of renal cell carcinoma with long-term and regular follow-up of tumor size and renal function.

Methods: This prospective study included 13 patients treated with stereotactic body radiation therapy for primary lesion of stage I renal cell carcinoma between August 2007 and June 2016 in our institution. Diagnosis of renal cell carcinoma was made by 2 radiologists using computed tomography or magnetic resonance imaging. A dosage of 60 Gy in 10 fractions or 70 Gy in 10 fractions was prescribed. The higher dose was selected if dose constraints were satisfied. Tumor response on imaging examination, local progression-free rate, overall survival, and toxicity were assessed.

Results: The mean follow-up period was 48.3 months (range: 11-108 months). The tumors showed very slow but continuous response during long-term follow-up. Three cases (23.1%) showed transient progression during the short follow-up. The mean duration until the day on which partial response was confirmed among the partial or complete response cases was 22.6 months (95% confidence interval, 15.3-30.0 months). Local progression-free rate was 92.3% for 3 years and overall survival rate 91.7% for 2 years and 71.3% for 3 years. Twelve cases (92.3%) had impaired renal function at baseline. Renal function decreased slowly and mildly in most of the cases, but 2 cases of solitary kidney showed grade 4 or 5 renal dysfunction.

Conclusion: All renal tumors decreased in size slowly but continuously for years after stereotactic body radiation therapy. Renal cancer can be treated radically with stereotactic body radiation therapy as a radiosensitive tumor, but careful attention should be given in cases with solitary kidney.

Keywords: kidney cancer; primary lesion; stereotactic body radiation therapy (SBRT); toxicity; tumor response.

Figure 1.

Case presentation. A, The dose distribution of case 1 treated with SBRT using static multiport. B, Follow-up CT examinations showed tumor response of partial response. The tumor showed very slow but continuing response. SBRT indicates stereotactic body radiation therapy; CT, computed tomography.

Figure 2.

Tumor size change in percent of pre-SBRT is shown. Most tumors demonstrate very slow response. Three cases increased temporally and showed tendency to decrease in size. Only one case relapsed about 1 year after SBRT. SBRT indicates stereotactic body radiation therapy.

Figure 3.

Survival analyses. The survival analyses using Kaplan-Meier method. Local progression-free rate was 92.3% for 3 years. Overall survival was 91.7% for 2 years and 71.3% 3 years.

Figure 4.

Comparison of CKD grade. Comparison of eGFR (mL/min/m²) between pre-SBRT and post-SBRT. Grade of CKD are also colored. In most of cases, the serum creatinine level decreased after SBRT but mildly. One grade 5 event was reported, but the association between treatment and death was unclear because it occurred 9 years after treatment. CKD indicates chronic kidney disease; eGFR, estimated glomerular filtration rate; SBRT, stereotactic body radiation therapy.