Ionization Chamber Readout Circuit for High-Current Radiotherapy
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Solution Overview
Problem
Existing circuit solutions for acquiring signals from ionization chambers in charged particle beam calibration for external radiotherapy are limited by the amplitude of current they can manage, particularly in applications with pulsed accelerators like synchrocyclotrons, where instantaneous currents exceed those handled by linear accelerators by several orders of magnitude, leading to saturation issues.
Innovation Solution
A circuit arrangement with multiple channel branches connected in parallel, featuring current-to-frequency converters and counters, and an adder-tree structure that sums outputs from sets of channel registers, allowing selection via a multiplexer to prevent saturation by distributing current across multiple branches, thereby extending the manageable current range from microamps to hundreds of microamps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single channel branch is used to readout ionization chamber signals, then the circuit is simple, but the current management range is limited and saturation occurs at high currents
Solution Approach 1:
The readout circuit is divided into multiple parallel channel branches, each capable of independently processing signals from ionization chambers. This segmentation allows the system to distribute high currents across multiple branches, preventing saturation in any single branch while maintaining the ability to handle both low and high current regimes effectively
2Reliability
If multiple channel branches are used in parallel, then the current management range is extended, but the device complexity increases
Solution Approach 1:
Multiple channel branches are combined through parallel connection to a common readout path. Each branch processes signals independently but contributes to the overall current management capability. The merging of multiple branches allows the system to achieve extended current management range while sharing common resources such as power supply and readout electronics
3Adaptability or versatility
If the circuit is designed for high current applications, then pulsed accelerator applications are supported, but low current measurement precision may be compromised
Solution Approach 1:
The circuit incorporates dynamic range adjustment capabilities through gain control mechanisms that can adapt to different current levels. For low current measurements, the circuit switches to high-gain mode to maintain precision, while for high current applications including pulsed accelerators, it transitions to low-gain mode to prevent saturation. This dynamic adaptation allows the same circuit to maintain measurement precision across multiple orders of magnitude
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables the circuit to handle higher current ranges without saturating, achieving a wider dynamic range and linearity, with relative channel gains remaining uniform, and supports precision measurements in both high and low current regimes, including those encountered in pulsed accelerator applications.
Implementation Method 1
at least one ionization-chamber sensor, which includes a plurality of sensor channels
Implementation Method 2
said channel branches comprising respective current-to-frequency converters and counters
Data Source
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AI summary
A circuit arrangement for acquisition of signals from an apparatus for measuring beams of charged particles for external radiotherapy, in particular protons, carbon ions, and other ion species, emitted by particle accelerators, comprising at least one ionization-chamber sensor (10), which includes a plurality of sensor channels (20), said circuit arrangement (200; 500) comprising a plurality of channel branches (B0,..., B63; BR0,..., BR63) in parallel designed to be connected to said sensor channels (20) for receiving respective measurement signals (i) therefrom, said channel branches (B0,..., B63; BR0,..., BR63) comprising respective current-to- frequency converters (210) and counters (220) for supplying count values (CT), representing a charge associated to a given channel (20), to a multiplexer (250; 550). According to the invention, said channel branches (BR0,..., BR63) supply their own outputs (CT0,..., CT63) directly to said multiplexer (550) and to an adder structure (240) comprising at least one first column (2401) of adders (2411) that adds up the values at the outputs (CT0,..., CT63) of the channel branches (Br0,..., BR63) to supply sum values (CT_100,..., CT_115, CT_200,..., CT_203, CT_300) at outputs thereof, said multiplexer (550) being configured for selecting, from the direct outputs (CT0,..., CT63) of the channel branches (BR0,..., BR63) and the outputs (CT_100,..., CT_115, CT_200,...,CT_203, CT_300) of the adder structure (240), a signal to be supplied to a readout electronics (400) for reading the channels (20), in particular in order to enable the channels necessary for detecting a given peak excursion via the multilayer-ionization-chamber sensor (10) without saturating.