A Challenger to Proton Therapy?

Within the last 15 years, proton therapy has become a significant part of cancer treatment within the US. The number of installations has grown to 15 and the expectation is that there will be a total of 27 in operation by 2017, with these facilities attaining revenues in excess of $1 billion. With the marketing advantages and the high reimbursement rates associated with proton therapy, critics equate the growth to a “medical arms race” with hospitals vying for dominance within their region.

Development of a proton therapy center is a major undertaking by an institution. Construction and installation of a proton therapy site costs in a range from $100-$225 million and can take upwards of three years to complete. The justification for the facility is the belief that proton therapy provides a more accurate delivery of radiation treatment. Additionally, the proton therapy reimbursement rate is approximately double that of traditional radiation treatment making it a more lucrative treatment which could offset the cost over time. However, the debate remains in the healthcare community as to whether proton therapy has proven to be a more effective treatment. Clinical studies at various institutions are currently underway studying treatment outcomes.

Massachusetts General Hospital, Linac 4 Fit-Out

Traditional treatment is delivered as photon radiation (x-rays or gamma rays and electrons) via a linear accelerator, gamma knife or cyber knife system. The accelerator shapes the beam as they exit the gantry to conform to the shape of the tumor. With traditional radiation treatment, the beams must travel through normal tissue to arrive at the targeted tumor, damaging the healthy tissue in the process. Proton therapy treatment utilizes particle radiation via protons. They release their energy only after traveling a certain distance and due to the large mass of protons, there is little lateral side scatter and therefore the beam does not broaden, stays targeted on the tumor shape and delivers only low-dose side-effects to surrounding tissue. The precise nature in which tumors can be targeted with less effect on adjacent healthy tissue makes proton therapy appear to be a better radiation delivery method, especially for sensitive area such as the eye, brain and spinal cord.

While the debate continues over the improved effectiveness of proton therapy, there is new technology is on the horizon that could dramatically change the discussion. An integrated MR-Linear Accelerator is being developed by two separate groups, with the goal to create a system that leverages the advantages of each component. MR technology is the superior imaging technology for soft tissue. Using the high-quality images generated from the MR, the hybrid device will be able to monitor the accurate location of tumors in real time while the radiation treatment generated by the Linac system is ongoing. This will enable clinicians to precisely locate, size and treat a tumor in real time, even if the tumor is moving. The ability to monitor tumors during treatment is the ground-breaking component of the system as both traditional and proton therapy rely on CT imaging prior to treatment.

Development of shielding systems to protect each technology from the other’s interference will be the fundamental challenge to the hybrid technology development. RF noise, or electromagnetic interference, from the Linac can reduce the quality of the MR image plus MR images can also be affected by currents induced in the MR coils by the megavoltage photon radiation. Likewise, the magnetic fields generated by the MR unit can impact the delivery of the radiation beams of the Linac. Additionally, the speed of MR imaging will need to be increased in order to accurately image the entire volume of a tumor in real time.

Two teams have developed a prototype MR-Linac hybrid device. The first is a consortium led by Philips Research and Elekta that includes several leading radiation oncology centers located worldwide. The other team is the Cross Cancer Institute in Edmonton, Canada, who recently installed a prototype device into an existing linear accelerator vault. Each team has indicated that they have successfully acquired high-quality MRI images, contoured the target, tracked and then irradiated it. Each team anticipates clinical studies will commence in 2015 once granted by the associated regulatory agencies. With this competitive environment, it will be a race to the market to see who can get jurisdictional approval for standard treatments.

The significance of this development is that advanced cancer treatment has the potential to become more widely available, both in terms of installation and cost of procedure. If existing vaults can be renovated to accept the new devices, cost and speed of completion will mean that they will be on line rapidly and could be well within the budget range of most healthcare systems. For example, the Cross Cancer Institute installed their prototype device into an existing 20’ by 20’ vault within the available maze and entry door arrangement.

The question remains whether or not, in five years, proton therapy will be even considered a preferred method of cancer treatment or if it will be considered archaic in light of real-time imaging and treatment. It will also be interesting to see if those facilities which are jumping on the bandwagon now and investing in proton therapy centers will be able to re-coupe the cost of construction and installation sufficiently. In the “medical arms race”, each facility will have to weigh the options and gamble on how fast the hybrid MR-Linac – or the next best thing – will be developed.

Resources:
“Is Proton Beam Therapy for Prostate Cancer Worth the Cost?” Durado Broosks, MD, American Cancer Society, February 20, 2013
“Elekta, Philips Research to Create MRI-Guided Radiation Therapy” Imaging Technology News, November 2, 2012
“Elekta and Philips Establish Research Consortium to Leverage a Breakthrough in Cancer Care with Integration of a Linear Accelerator and MR Imaging” Connected Care, Elekta blog, October 25, 2012
“Hybrid Linac-MRI Technology Developed to Image and Treat Tumors” MedImaging, August 14, 2009
“27 US Proton Therapy Centers Expected by 2017” Imaging Technology News, March 14, 2014

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