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Extracorporeal ablation of small renal tumors using CyberKnife™ radiosurgery
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Extracorporeal ablation of small renal tumors using CyberKnife™ radiosurgery
Fernando Korkes, MD, Irving Kaplan, MD, Lakshmi N. Shanmugham, MD, Salvatore A. La Rosa, MS, William C. Dewolf, MD, Mark Hong, MD, Andrew A. Wagner, MD.
Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
Introduction:
Standard fractionated radiation is an impractical approach for treatment of kidney lesions due to excessive dose to normal kidney and surrounding organs. New hypofractionated stereotactic radiosurgery (HSR) techniques allow delivery of very high doses of radiation in a single fraction and have been shown to control renal cell carcinoma (RCC) metastases in the CNS. The CyberKnife can deliver HSR to primary RCC with minimal dose to surrounding normal tissue.
Material and Methods:
Initially, patients undergo percutaneous biopsy of the tumor and placement of 3 gold fiducial seeds in the tumor and normal kidney. A treatment plan is created using sophisticated 3-dimensional imaging software that allows for a 3mm margin around the tumor volume and <50% radiation dose at all points > 1cm away from the target. Sensors are placed on the patient and monitor movement during treatment (e.g. breathing). The movement of the fiducials (and thus the treatement plan) is tracked in real time by the CyberKnife thus allowing for ablation of abdominal tumors in unanesthetized patients with sterotactic precision. Patients were prospectively evaluated for acute and subacute radiation-induced morbidity. Abdominal imaging was performed every 3 months following treatment.
Results:
To date, fourteen patients have been treated for mean tumor size 4.1 cm (range 1.7-6.3 cm) in maximum diameter with no RTOG Grade II toxicity. With a maximum of one year follow-up, there has been no tumor progression or increase in creatinine. Tumor volume has decreased a mean of 9%, 11%, 28%, and 44% at 3, 6, 9, and 12 month follow-up imaging, respectively. The figure (figure 2b and c) demonstrates treatment of a 3cm left renal tumor. A total of 195 separate 15 mm radiation beams were used to treat the lesion (left figure). The target volume was the tumor with a uniform 3 mm margin (middle and right figures). A total dose of 21 Gy was delivered in three fractions of 7 Gy each to this patient.
Conclusion:
Using CyberKnife, ablative doses of radiation can safely be delivered to renal tumors while limiting dose to normal tissue. Prior to large-scale clinical application, more information is needed regarding the effect of HRS on normal renal parenchyma and urothelium. Additionally, optimal dosimetry for RCC is yet to be determined. Based on the potential of CyberKnife to deliver completely non-invasive ablative HRS to renal tumors, a phase I/II study is underway.
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