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A novel technique for calculating the particles emerging from a radiotherapy machine head using a transport matrix technique.

IP.com Disclosure Number: IPCOM000020087D
Original Publication Date: 2003-Oct-24
Included in the Prior Art Database: 2003-Oct-24
Document File: 2 page(s) / 49K

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The aim of external radiotherapy treatment is to deliver a curable dose to local cancerous tissue in a patient while keeping the dose in healthy tissues as low as possible in the shortest time possible. In order to design the patient treatment delivery correctly, it is essential to calculate the dose distribution throughout the target volume and within normal tissue as accurately as possible. There are two main methods of achieving this. One is the use of Monte Carlo techniques simulate the production of radiation particles and their interactions within patients. The other is to use deterministic methods. The deterministic methods are used, even though the Monte Carlo techniques are seen as accurate, due to the relative speed of calculation. The Monte Carlo techniques take too long in a clinical environment. A new way of calculating the dose distribution is disclosed which is comparable in quality to the Monte Carlo techniques but in a much shorter time.

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  A novel technique for calculating the particles emerging from a radiotherapy machine head using a transport matrix technique.

In order to design the patient treatment dose correctly, it is essential to calculate the dose distribution coming from the treatment machine head as accurately as possible. Most treatment-planning systems are based on 2-dimensional semi-empirical algorithms and the use of experimentally obtained central axis isodose data. Currently, Monte Carlo simulation is arguably the most accurate method to simulate radiation transport and predict doses in complex machine systems. The advantage of the Monte Carlo method, compared to deterministic methods, has been the ability to deal accurately with any complex geometry. The main disadvantage is the extremely long computing times that are required in order to obtain a dose distribution with good statistical accuracy .

    Monte Carlo uses particle-by-particle methods to simulate a radiation treatment wherein the more particle histories that are tabulated, the better is the representation of the actual dose. Since high resolution, high accuracy calculations can require tracking of as many as 100 million incident particles, the time required to calculate dose can be prohibitively long. With the advent of movable multi leaf collimators and intensity-modulated radiotherapy this time problem has become even more important.

    Using transport, T, matrix techniques it is possible to pre-calculate the photon spectrum for each component of the radiotherapy head. The spectra for each component is then saved in a database and the whole head can be calculated by summing together the individual component. The advantage of the T matrix is that this can be pre-calculated for each beam modifier and then once all the modifiers have been chosen the compound T matrix can be calculated by multiplying the T matrices together. If the order or type of beam modifier is changed then this process is repeated. Once this...