Charge collection efficiency, underlying recombination mechanisms, and the role of electrode distance of vented ionization chambers under ultra-high dose-per-pulse conditions.

PURPOSE: Investigating and understanding of the underlying mechanisms affecting the charge collection efficiency (CCE) of vented ionization chambers under ultra-high dose rate pulsed electron radiation. This is an important step towards real-time dosimetry with ionization chambers in FLASH radiotherapy. METHODS: Parallel-plate ionization chambers (PPIC) with three different electrode distances were build and investigated with electron beams with ultra-high dose-per-pulse (DPP) up to 5.4 Gy. The measurements were compared with simulations. The experimental determination of the CCE was done by comparison against the reference dose based on alanine dosimetry. The numerical solution of a system of partial differential equations taking into account charge creations by the radiation, their transport and reaction in an applied electric field was used for the simulations of the CCE and the underlying effects. RESULTS: A good agreement between the experimental results and the simulated CCE could be achieved. The recombination losses found under ultra-high DPP could be attributed to a temporal and spatial charge carrier imbalance and the associated electric field distortion. With ultra-thin electrode distances down to 0.25 mm and a suitable chamber voltage, a CCE greater than 99 % could be achieved under the ultra-high DPP conditions investigated. CONCLUSIONS: Well-guarded ultra-thin PPIC are suited for real-time dosimetry under ultra-high DPP conditions. This allows dosimetry also for FLASH RT according to common codes of practice, traceable to primary standards. The numerical approach used allows the determination of appropriate correction factors beyond the DPP ranges where established theories are applicable to account for remaining recombination losses.

Monte Carlo verification of IMRT treatment plans on grid.

The eIMRT project is producing new remote computational tools for helping radiotherapists to plan and deliver treatments. The first available tool will be the IMRT treatment verification using Monte Carlo, which is a computational expensive problem that can be executed remotely on a GRID. In this paper, the current implementation of this process using GRID and SOA technologies is presented, describing the remote execution environment and the client.

Remote radiotherapy planning: the eIMRT project.

In this paper, we present the eIMRT project which is currently carried out by diverse institutions in Galicia (Spain) and the USA. The eIMRT project will offer radiotherapists a set of algorithms to optimize and validate radiotherapy treatments, both CRT- and IMRT-based, hiding the complexity of the computer infrastructure needed to solve the problem using GRID technologies. The new platform is designed to be independent from the medical accelerator models, scalable and open. Having a web portal as client, it is designed in three layers using web services, which will allow users to access the platform directly from any front-end and client. It has three main components, namely remote characterization of linear accelerators for Monte Carlo and convolution/superposition (C/S) dose-calculation techniques, remote Grid-enabled radiotherapy treatment planning optimization and verification and data depository.