High dose, local stereotactic radiosurgery (SRS) shows promise for treating small renal tumors in select patients for whom nephrectomy carries unacceptable risks, according to researchers.
Michael Staehler, MD, of Grosshadern Hospital at the University of Munich in Germany, and colleagues prospectively assessed the short-term safety and efficacy of the Cyberknife system in 40 patients (35 male) with a median age of 64. The patients were diagnosed with renal cell carcinoma or transitional cell carcinoma during the period of 2007 to 2011. A majority of patients had a sole remaining kidney following a prior nephrectomy. Their tumors were less than 4 cm in diameter, qualifying them for the outpatient radiation treatment.
The Cyberknife robotic radiosurgery system consists of a 6-MV accelerator mounted on a computer-controlled robotic manipulator with 6 axes. During the treatment session, X-ray cameras provided real-time images of the patient’s kidney and surrounding areas to avoid. Gold fiducials, implanted near the tumor via ultrasound prior to treatment, accurately pinpointed the target.
To account for kidney motion during breathing, an external camera array also tracked infrared markers on the patient’s chest. Together, the internal and external information provided coordinates for locating the tumor continuously and for focusing the radiation beam within 1 mm. All lesions were treated with a 25 Gy dose in a single fraction to the 70% isodose.
At 9 months after treatment, 98% of the 45 total tumors were controlled, according to results published in The Journal of Urology (2015;193:771-775). The researchers observed shrinkage of 38 tumors, including complete remission in 19. None of the patients needed a nephrectomy.
Renal function remained stable, and no patient required immediate dialysis. The median creatinine clearance was 70.3 mL/min/1.73m2 following treatment compared with 76.8 mL/min/1.73m2 at baseline.
Side effects were minimal and included erythrodermia, fatigue, and nausea.
“In view of the short overall followup these initial findings should be regarded with caution before definitive clinical conclusions can be drawn. However, they demonstrate the promising, short-term effects of high dose SRS on tumor size and local control,” the researchers stated.
SRS provided results similar to other ablative techniques. It has no anatomical limitations and can reach tumors near the ureter. Unlike cryoblation and radiofrequency ablation, SRS requires no analgesia or invasive access beyond fiducial placement.