CyberKnife for Kidney Lesions

Stereotactic Radiosurgery/Stereotactic Body Radiotherapy for RCC

Radiosurgery and stereotactic body radiotherapy have been extensively applied against renal cell carcinoma (23-27). Paradoxically, although the response of metastatic RCC brain lesions to conventional radiotherapy has been virtually nil, the long-term response rate of RCC brain metastases to radiosurgery exceeds 90% in some series (24,25,26). The addition of conventional whole brain radiotherapy to stereotactic radiosurgery does not appear to improve the intracranial local control or recurrence-free survival in RCC patients with intracranial metastatic lesions (25,26).

Highly successful stereotactic radiotherapy results have been described for both primary and metastatic RCC all over the body by the Radiumhemmet group, with only 3 documented recurrences among 162 treated RCC lesions, using a variety of treatment regimens of 3-4 large stereotactic radiotherapy treatments (23). Similarly, spinal metastatic RCC lesions have been successfully radiosurgically ablated in a single treatment with CyberKnife® in 89% of cases, a figure that seems even more impressive when one considers that the majority of these lesions had already recurred after “conventional” spinal radiotherapy prior to their CyberKnife® radiosurgical treatment (27).

In summary, it appears that RCC is far more sensitive to ablative (1-5 treatments using large dose per treatment) radiotherapy/radiosurgery approaches than it is to “conventionally fractionated” radiotherapy (10-30 smaller radiation treatments).

Precise Ablation of Focal Kidney Lesions

The kidney is another organ that moves with respiration, limiting the accuracy of conventional or even stereotactic radiotherapy approaches against malignant lesions within the kidney itself, resulting in a large fuzzy margin between the high dose and low dose radiotherapy zone. This seriously limits the ability to safely delivery an ablative radiation regimen to a primary kidney lesion, even with sophisticated radiotherapy techniques.

CyberKnife® Synchrony® Respiratory Tracking System overcomes this problem by locking onto implanted gold fiducial markers that are easily placed within the kidney under CT guidance, and correlates their position with the respiratory cycle as determined by optical tracking, tracking the targeted lesion with 1.5 mm accuracy throughout the entire breathing cycle. This allows a much smaller applied margin compared with other radiation delivery systems – virtually surgical in its precision.

Targeting Angles

Traditional radiotherapy systems target the lesion from a relatively small number of fixed positions. In contrast the CyberKnife® device allows literally hundreds of targeting angles to be selected, increasing the ability to conform the ablative dose to the target lesion within the kidney, while better sparing the adjacent kidney and surrounding normal gastrointestinal tissues.

The accuracy of this model has been validated in a study of pig kidneys, in live animals treated with CyberKnife® radiosurgery, whose kidneys were then evaluated pathologically, revealing total destruction of all cellular elements within the focally targeted zone by 8 weeks post-treatment, with preserved kidney tissue adjacent to the sharply marginated target zone annihilation.

Conclusion

Treatment of renal cell carcinoma (RCC) is highly successful in early stage cases and sometimes results in prolonged disease-free survival even in patients with metastatic lesions (1-6). There is a trend toward kidney sparing surgery in patients with small tumors, and increasing use of nonsurgical ablative approaches (1,3,4,5, 7-11).

While there is some evidence that RCC is “resistant” to conventional radiotherapy doses (14), particularly for brain lesions (12,13,16), there is a substantial body of literature demonstrating local control rates in excess of 90% for renal cell carcinoma lesions targeted with stereotactic radiosurgery or large dose per treatment (hypofractionated) stereotactic radiotherapy (23-27).

As the only system capable of tracking respiratory-induced moving targets such as the kidney with radiosurgical precision, CyberKnife® appears uniquely capable of ablating focal tumor lesions within the kidney itself, in RCC patients for whom surgery is not an option (28).  Due to its robust dose sculpting and target tracking capability, CyberKnife® radiosurgery is also appropriately applied to ablate a range of locally recurrent, unresectable and metastatic RCC lesions (23-27).

Case Studies:

Spinal Cord Metastasis (L-1 from Renal Cell Carcinoma)
Peter Gerszten, M.D., Steve Burton, M. D. - UPMC
Posterior Fossa Metastatic Renal Cell Carcinoma
Debra Freeman, M.D., Paul D. Dernbach, M.D. - NCH

Bibliography

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