Platforms for SBRT besides CyberKnife

In another thread, Hopeful & Optomistic said...
Allen,I wonder, have there been studies comparing Accuray Cyberknife results with other platforms. I am most interested in knowing how Novalis compares with Cyberknife.

While CyberKnife (CK) is probably the most popular platform for SBRT, it has been done on a number of different platforms. In fact, my RO, Dr. King was the first one to use CK for prostate cancer at Stanford, but then came to UCLA where he does it on the Novalis Tx RapidArc platform, on which I was treated. He has found that RapidArc, besides being much faster, also gives him a more conformal and more homogeneous plan.

This study found that the dosimetry is pretty much the same between the two:

Stereotactic Body Radiotherapy in Prostate Cancer: Is Rapidarc a Better Solution than Cyberknife?

This study bears out what Dr. King said about more homogeneous dose delivery with RapidArc, and found better penile bulb sparing:

Dosimetric Comparison of Robotic Radiosurgery [CyberKnife] and VMAT [RapidArc] for Hypofractionated Prostate Radiation Therapy

This study compared RapidArc, Tomotherapy and CyberKnife SBRT plans and also found that RapidArc and Tomotherapy gave more homogeneous plan, dose to bladder and rectum were lower too:

Stereotactic Body Radiation Therapy (SBRT) for Low-Risk Prostate Cancer: A 3 Way Comparison Between Modulated Arc, Helical Tomotherapy, and Robotic Radiosurgery Plans

All of these differences seem minor or only slight improvements to me. The critical capabilities are:
• to deliver a highly comformal plan with sub-millimeter accuracy
• to track and respond to intra-fractional prostate motion or stabilize it
• to deliver a lot of radiation quickly

I think it will encourage wider use if ROs can repurpose their existing equipment for SBRT. SBRT will replace IMRT for all purposes except salvage radiation after RP failure, so it is good that the older equipment can be used. Aside from platforms from Varian (RapidArc) and Accuray (CK and Tomo), Elekta has their SBRT Axesse system. There are two new platforms that are ideal for SBRT -- Brainlab's Vero system and ViewRay with an integrated MRI.

The highest volume SBRT RO that I'm aware of is Dr. Alan Katz in NYC. He has treated over 600 men at all risk levels and on several different platforms - CyberKnife, RapidArc and Tomotherapy.

There is an SBRT registry that accumulates data on all SBRT-treated patients and includes data on the platform used. I don't expect that the platform will ever be shown to make a discernable difference in outcomes, however. There are much more important considerations (e.g., total dose, margin, detection and control of intrafractional motion, dose homogeneity, degree of hypofractionation, dose to other organs, etc.).

I believe that SBRT is the treatment of the future, costing significantly less than IMRT with less time spent in treatment with comparable or better results. SBRT also compares favorably with surgery in many ways.

Over time the excellence of SBRT treatment will improve as acceptance becomes more and more widespread, and additional studies are published in prestigious journals.