Random Repainting for Scanned Ion Beam Interplay Effect Mitigation
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Solution Overview
Problem
Conventional proton therapy systems face challenges in achieving uniform dose distribution due to scanning direction and speed, leading to under-dose and over-dose patterns caused by motion uncertainties, which current repainting techniques fail to adequately mitigate.
Innovation Solution
A random repainting technique is introduced, where spot locations for proton beam applications are selected at random, and the radiation plan is adjusted to align with the target area's movement, using a particle accelerator, gantry, treatment nozzle, and sensor devices to ensure precise and uniform dose delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional repainting techniques are used to deliver prescribed dose distribution, then treatment can be delivered to moving targets, but under-dose and over-dose patterns occur due to motion parameters and scanning direction
Solution Approach 1:
The patent implements dynamic repainting by randomly varying the scanning start position and scanning direction for each energy layer. This dynamic approach adapts the fixed raster scanning pattern to account for target motion, ensuring that the accumulated dose distribution remains uniform even when the target moves during treatment. The randomization parameters include different starting positions along the scanning path and different scanning directions (e.g., left-to-right vs. right-to-left), which are selected based on the monitored motion characteristics.
Solution Approach 2:
The patent changes key scanning parameters dynamically: the start position of the scan, the scanning direction, and the energy layer sequence are all varied randomly according to the target's motion parameters. This parameter variation prevents the systematic under-dosing and over-dosing that occurs with fixed scanning patterns, as the dose accumulation becomes less sensitive to motion-induced positioning errors.
2Productivity
If fixed raster scanning pattern is used for spot scanning, then delivery path is predetermined for each energy layer, but interplay effects cause dose distribution artifacts
Solution Approach 1:
The patent transforms the static raster scanning pattern into a dynamic one by introducing random variations in start position and scanning direction for each energy layer. This maintains the efficiency of predetermined scanning paths while eliminating the systematic artifacts caused by the interplay between fixed scanning and target motion. The dynamic adjustments are calculated based on real-time motion monitoring data.
Solution Approach 2:
The patent performs preliminary calculations of random repainting parameters based on expected or measured motion characteristics before treatment delivery. The motion parameters (amplitude, frequency, direction) are determined in advance, and the corresponding random scanning variations are pre-computed to optimize dose uniformity. This preliminary action allows the system to maintain high delivery efficiency while preparing the adaptive scanning pattern.
3Manufacturing precision
If steep dose gradients are used at target border for intensity-modulated particle therapy, then dose conformity is enhanced, but robustness to uncertainties decreases
Solution Approach 1:
The patent applies dynamic repainting with randomized scanning parameters to deliver the steep dose gradients required for intensity-modulated particle therapy. By varying the start position and scanning direction randomly, the system maintains the high dose conformity of steep gradients while reducing sensitivity to motion uncertainties. The randomization effectively smooths out the interplay effects that would otherwise amplify uncertainties at steep dose boundaries.
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 random repainting technique significantly reduces interplay effects, improving dose conformity and reducing the need for additional target margins, resulting in a more efficient and uniform dose distribution compared to conventional methods.
Implementation Method 1
a particle accelerator such as a cyclotron or synchrotron is used to generate a beam of ions from, for example, an internal ion source located in the center of the cyclotron. The ions in the beam are accelerated (via a generated electric field)
Implementation Method 2
the beam of accelerated ions is subsequently 'extracted' and magnetically directed through a series of interconnecting tubes (called a beamline)
Implementation Method 3
Particle therapy works by providing energetic ionizing particles to target tissue (e.g., a tumor). These particles are used to destroy or damage the DNA of tissue cells.
Data Source
AI summary
Interference of dose application in scanned ion beam therapy and organ motion, also called interplay effect, may lead to dose deviations at target volumes. Current repainting methods are susceptible to artifacts due to a predominant scanning direction, ranging from fringed field edges to under and overdosed regions (hot and cold spots). To overcome the difficulties inherent in the repainting techniques of conventional proton therapy systems, new random repainting techniques are described herein for mitigating the under-dose and/or over-dose pattern inherent in existing repainting techniques using a random repainting approach that randomly selects spot locations within the target area.