A facility for the research, development, and translation of advanced technologies for ion-beam therapies

Abstract

This article describes the updated GSI radiotherapy research facility (Cave M) located at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. This facility was upgraded by modernizing the beamline that supported a pilot project in carbon ion cancer therapy in Europe from 1997 to 2008. Descriptions are provided of the modernized beamline, related hardware components and treatment delivery system. The performance specifications and general characteristics for each major component are described, along with example pre-clinical test results of selected components. These upgrades to Cave M allow for investigating novel therapy methods. The radiotherapy research facility is located on a beamline of the heavy ion synchrotron (Schwer-Ionen-Synchrotron, or SIS-18) accelerator complex, capable of delivering 0.1 to 2 GeV/u charged particle beams, ranging from protons to uranium. This beamline contains components for fast beam gating, aborting, focusing, scanning, monitoring, and shifting the range of the beam. The beam scanning magnets, position detectors, and beam monitors are described, along with tests of functionality and performance. A dose delivery system (DDS) was adapted from a clinical unit at the National Centre for Oncological Hadrontherapy (CNAO), Pavia, Italy, and consists of modular real-time hardware and software. The DDS was modified to enable research on adaptively-managed patient motion through the use of libraries of 4D-optimized radiation treatment plans, an unsolved problem of importance for treating moving tumors. The system is modular and is designed to support future research studies, such as high dose rate (Flash) radiotherapy and radioactive ion beams. A series of validation tests confirmed the functionality and performance of various key components and systems. For example, an end-to-end test revealed that dosimetric spatial homogeneity of over 95% was achieved for square treatment fields. More generally, all performance characteristics that were tested satisfied anticipated clinical requirements.

Dosimetric Validation of a System to Treat Moving Tumors Using Scanned Ion Beams That Are Synchronized With Anatomical Motion

“…Our study had several limitations. At the time of these experiments at GSI, our beam gating system (based on radiofrequency knockout extraction) could not yet fully gate the beam ( 21 ), and the accelerator system could not yet provide beams of multiple energies in any one delivery. We discuss both of these limitations in detail here.…”

“…This system was implemented in a research version of the dose delivery system (DDS) that is used clinically at the National Center for Oncological Hadrontherapy (CNAO) ( 20 ). It was similarly implemented in the radiotherapy research facility (Cave M) at GSI ( 21 ).…”

“…Therefore, all plans were delivered with a nominal beam energy of 280 MeV/u. As a provisional means to produce multiple beam energies and ranges within a single delivery, we used a binary range shifter comprising polyethylene (PE) plastic slabs ( 21 , 22 ). The treatment plans contained beam energy codes, that specified the needed beam energy for each slice of the treatment plan.…”

“…Treatment deliveries were repeated twice for each setup: once to irradiate a 2D ionization chamber (IC) array detector (Octavius 1500XDR; PTW, Freiburg, Germany) and again to a stack of six radiochromic films (EBT3 Gafchromic; International Specialty Products, Wayne, NJ). The 2D IC array detector was placed within a 5 mm thick PMMA holder, and 6 films, were slotted into the films stack, between 10 mm slabs of PMMA ( 21 ). The 2D IC array detector, containing ICs filled with air at ambient pressure, was set to integral mode to measure total delivered dose.…”

“…We used an established formalism to calibrate the IC array detector ( 13 , 21 , 29 ). These are briefly reviewed here for the convenience of the reader.…”