RaySearch and Mevion are working to develop a new approach for enhancing the delivery of FLASH proton therapy on Mevion's S250i Proton Therapy System with HYPERSCAN

RaySearch, Mevion explore new approach for delivering FLASH proton therapy

October 27, 2021
by John R. Fischer, Senior Reporter
RaySearch Laboratories and Mevion Medical Systems are developing advanced treatment planning approaches to deliver FLASH therapy on Mevion’s S250i Proton Therapy System with HYPERSCAN.

FLASH therapy is an advanced form of radiotherapy currently under investigation. It is designed to deliver a noninvasive, ultra-high dose of radiation in less than one second to treat tumors effectively, while sparing healthy tissue. For their endeavor, RaySearch and Mevion are focused on FLASH intensity modulated proton therapy, an approach that alters proton beams to conform to the shape of tumors. It then applies multiple small proton beams to varying levels of intensity to precisely destroy the tumor.

FLASH therapies require sufficient dose coverage for large tumor volumes, which often are hundreds of cubic centimeters. Combined with the complexity of target shapes and constraints for surrounding organs at risk, this makes single-field FLASH treatments unlikely to provide acceptable dosimetric distribution relative to conventional treatment plans. To address this, Mevion and RaySearch have developed a "merged-field" technique that basically stitches together smaller fields to allow for FLASH doses to be delivered at a rate where the large volume is covered while surrounding organs are spared. Each of the smaller fields are a few cubic centimeters and can be modulated in size and weight with this approach and delivered over a non-FLASH timescale.

"Our collaboration with RayStation will build upon this technique to develop the temporal and spatial modeling necessary to facilitate optimal target conformality and normal tissue sparing," Daniel Owen, R&D clinical engineer at Mevion, told HCB News.

The approach starts out by applying adjacent intensity-modulated small volumes at FLASH dose rates separately and then combining the individual small volumes to create a single large volume that can apply treatment effectively, while still sparing normal tissue. It is expected to combine both IMPT and FLASH into one delivery system, with each volume applied at FLASH dose rates that complement Mevion’s system.

The collaboration will focus on the calculation of FLASH weighted dose distributions including optimization and consideration of tissue type dependencies. For its part, RaySearch will utilize its Monte Carlo dose calculation system to come up with a final dose calculation and to determine optimal use of the technique with Mevion’s system. “We are now excited to explore how RayStation can create optimal FLASH plans for the HYPERSCAN system and to further deepen our partnership,” said Kjell Eriksson, chief science officer of RaySearch.

Mevion is currently studying approaches to deliver FLASH dose rates to a larger volume of several hundred cubic centimeters or more, which is a common irradiation volume for typical cancer patients. It previously used the FLASH effect in a preclinical trial with its S250i proton accelerator. In this trial, the FLASH effect was delivered at the Bragg peak, which plots the energy loss of ionizing radiation as it travels through matter and occurs immediately before protons, Alpha-rays and other ion ray particles come to rest.

The treatment was applied to mice, with the goal being to increase their survivability by delivering doses at FLASH rates that would be lethal if applied at conventional rates. By hitting the Bragg peak, Mevion succeeded in applying the rapid doses to the tumor, while sparing healthy tissues within the FLASH field. Its use of pulse proton beams instead of electron beams demonstrated the opportunity to investigate the application of FLASH at clinically significant depths.

Mevion’s S250i proton accelerator is equipped with Direct Beam Delivery (DBD) system architecture, which has a beam line where transmission efficiency does not drop below 70%. This enables a Bragg peak FLASH effect at ultra-high dose rates. HYPERSCAN enables faster and sharper delivery of therapeutic radiation to tumors while sparing healthy tissue.

RaySearch and Mevion have previously developed advanced treatment planning capabilities for HYPERSCAN pencil-beam scanning and Adaptive Aperture pMLC.