Kilby and colleagues (1) review the rapidly evolving applications of SRS and SBRT using the Cyberknife VSI Robotic radiosurgery system discussing its enhanced dosimetric accuracy and inverse treatment planning algorithms in targeting a variety of tumor locations throughout the body. The authors provide a detailed review of geometric accuracy involving both phantom tests and patient data. In addition, Kilby et al propose that the technical advancements on the CyberKnife® VSI have allowed for more extended fractionation schemes similar to those seen with IMRT.

The histolopathological effects of severely hypofractionated therapy, the hallmark of SRS/SBRT, is also detailed in a case report of a prostate cancer patient treated with SBRT by Oermann et al (2). Their histopathological evaluation of prostatic tissues treated with SBRT offers some insight on an area of little known tissue effects and represents an area ripe for clinical investigation.

A corollary review by Katz (3) summarized the clinical outcomes to date. Emerging data in over 300 patients appears to suggest treatment efficacy and more importantly, absence of long-term high-grade treatment toxicities of SBRT. In addition, Bolzicco and colleagues (4) also report promising biochemical control with little toxicity in an early clinical experience with prostate cancer. In patients with hepatocellular carcinoma (HCC), aggressive local therapy is necessary if curative intent is the goal. Increasingly, SBRT has been used as either an adjuvant to surgery, radiofrequency ablation or as primary therapy. The clinical outcomes reported by Louis et al (5) appear to confirm the efficacy of this approach with local control rates in excess of 90% in patients not otherwise eligible for other conventional approaches.

Complex tumors involving the cranial base represent challenges for the neurosurgeon and radiation oncologist. Incomplete resections are sometimes unavoidable in order to avoid injury to critical neurovascular structures. The residual mass lesions are often adjacent to radiation sensitive structures such as the optic chiasm and thus have proved challenging for radiation dose planning. Paravati and colleagues (6) describe a corridor based approach to skull base tumors using a combination of a novel, minimally-invasive endoscopic endonasal approach to benign and malignant tumors of the base of skull combined with traditional open approaches when needed, followed by adjuvant fractionated stereotactic radiosurgery (fSRS). The experience of 39 patients with a variety of benign and malignant histologies showed control rates of approximately 90% and progression-free survival of nearly 20 months. Based on their response rates and minimal adverse events, the authors concluded that this corridor based surgical approach followed by fSRS was a safe and effective management strategy for skull based tumors. We believe this first of a 2-part special edition of TCRT focusing on robotic stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) using the CyberKnife® platform will serve to inform the readers of the novel approaches to some of the most challenging tumors encountered in the modern oncologic practice.

References

1. Kilby, W., Dooley, J. R., Kuduvalli, G., Sayeh, S., Maurer, C. R., Jr. The CyberKnife Robotic Radiosurgery System in 2010. Technol Cancer Res Treat 9, 433-452 (2010).
2. Oermannn, E. K., Slack, R. S., Hanscom, H. N., Lei, S., Suy, S., Park, H. U. et al. A Pilot Study of Intensity Modulated Radiation Therapy with Hypofractionated Stereotactic Body Radiation Therapy (SBRT) Boost in the Treatment of Intermediate- to High-Risk Prostate Cancer. Technol Cancer Res Treat 9, 453-462 (2010).
3. Katz, A. J. CyberKnife Radiosurgery for Prostate Cancer. Technol Cancer Res Treat 9, 463-472 (2010).
4. Bolzicco, G., Favretto, M. S., Scremin, E., Tambone, C., Tasca, A., 4. Guglielmi, R. Image-Guided Stereotactic Body Radiation Therapy for Clinically Localized Prostate Cancer: Preliminary Clinical Results. Technol Cancer Res Treat 9, 473-477 (2010).
5. Louis, C., Dewas, S., Mirabel, X., Lacornerie, T., Adenis, A., Bonodeau, F., Lartigau, E. Stereotactic Radiotherapy of Hepatocellular Carcinoma: Preliminary Results. Technol Cancer Res Treat 9, 479-487 (2010).
6. Paravati, A. J., Heron, D. E., Gardner, P. A., Snyderman, C., Ozhasoglu, C., Quinn, A., Burton, S. A., Seelman, K., Mintz, A. H. Combined Endoscopic Endonasal Surgery and Fractionated Stereotactic Radiosurgery (fSRS) for Complex Cranial Base Tumors—Early Clinical Outcomes. Technol Cancer Res Treat 9, 489-498 (2010).