Cross calibration method used for online beam monitoring detector in three-dimensional spot scanning beam distribution

A calibration method and detector technology, applied in instruments, measuring devices, scientific instruments, etc., can solve problems such as large uncertainty and systematic errors, too many equipment and detectors, and cumbersome processes, and achieve accurate implementation, improvement and improvement. Distribution technology, the effect of improving work efficiency

Inactive Publication Date: 2013-10-16

INST OF MODERN PHYSICS CHINESE ACADEMY OF SCI

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AI-Extracted Technical Summary

Problems solved by technology

[0012] The purpose of the present invention is to overcome the deficiencies of the prior art, to provide a cross-calibration method for on-line beam monitoring detectors in three-dimensional point scan...

Abstract

The invention belongs to a calibration method for a detector used for monitoring ion beam radiation. The cross calibration method used for the online beam monitoring detector in three-dimensional spot scanning beam distribution includes the following steps: (1) measuring response of a large-area parallel-plate ionization chamber to monoenergetic ion pen-shaped beams; (2) forming a calibration field with a diameter of 80 to 120 mm through spot scanning and measuring accumulated dose of a mini-size absolute dose ionization chamber in the center of the dose calibration field; (3) establishing a mapping relation between a central reading and a central dose; (4) calibrating practically. The cross calibration method used for the online beam monitoring detector in the three-dimensional spot scanning beam distribution provided by the invention has advantages that (1) frequency of using a complicated scanning system is reduced and experiment errors and uncertainty of dose calibration in the spot scanning beam distribution are reduced; (2) a complicated conventional method is replaced with the simple and quick method, so that online beam monitoring detector calibrating time is reduced and working efficiency is improved; (3) ion beam three-dimensional spot scanning beam distribution technology is improved and developed, so that convenience is made for adjusting and controlling exposure doses of different scanning spots in an exposure area for realizing three-dimensional intensity modulated irradiation.

Application Domain

X/gamma/cosmic radiation measurment

Technology Topic

Ion beam depositionParallel plate +6

Image

Examples

Experimental program(5)
Effect test(1)

Example Embodiment

[0042] Example 1: see figure 1 , figure 2 and image 3 , a cross-calibration method for online beam monitoring detectors in three-dimensional point scanning beam distribution, comprising the following steps:

[0043] (1) The response of a large-area parallel-plate ionization chamber to a single-energy pencil beam with an energy of 250 MeV/u was measured by using the Bragg Peak Chamber34070 produced by PTW Company (the sensitive volume diameter of the detector is 8.4 cm);

[0044] During measurement, set a fixed set of counts MU (1×10 4 , 2×10 4 , 3×10 4 , 4×10 4 ), the readings in the dosimeter when the single-energy pencil beam acts on the large-area parallel-plate ionization chamber in turn are 8.86, 18.86, 28.86, and 38.86, respectively, which are recorded as the central reading D spot; experimental setup see figure 2.

[0045] (2) According to the fixed counting MU set in step (1), scan point by point at the incident depth of 6.8mm to form a calibration field with a diameter of 100mm, and measure the cumulative dose of the micro-absolute dose ionization chamber in the dose calibration field;

[0046] When measuring, the fixed count MU described in step (1) is 1×10 4 , 2×10 4 , 3×10 4 , 4×10 4 , each scanning point in each group is set with an equal MU, and the single-energy ion pencil beam described in step (1) is scanned point by point to form a calibration field with a diameter of 100 mm, the scanning step is 3 mm, and the micro absolute dose ionization chamber is set At the beam axis, the measured cumulative physical absorbed doses at the center of the calibration field of each group are 2.893Gy, 5.467Gy, 7.912Gy, and 10.863Gy, respectively, which are recorded as the center dose D. center; experimental setup see image 3.

[0047] (3) Under the fixed count MU and beam current parameters described in step (1), for the same ion pencil beam, establish the center reading D spot with central dose D center The mapping relationship between , this mapping relationship can be expressed as:

[0048] D center =f(D spot ),

[0049] In this example it is expressed as:

[0050] D center =0.2635×D spot +0.4952,

[0051] Of which: D spot is the center reading, f(D spot ) is the central dose value;

[0052] The mapping relationship between the two is used as the benchmark for the actual operation of the cross-calibration of the online beam monitoring detector in the point scan, and is the key to the double-ion chamber cross-calibration method;

[0053] (4) Actual calibration, set a fixed set of counts MU (1×10 4 , 2×10 4 ) to obtain the center reading of the current ion beam (energy 300MeV/u) (8.16, 16.7), experimental setup see figure 2; Calculate the central dose value when the current pencil beam scan forms the dose field according to the mapping relationship obtained in step (3). is 2.645Gy, 4.896Gy, according to the point scanning dose calibration algorithm, the current energy of the online beam monitoring detector can be calculated as E 0 The ion beam dose calibration factor CF (E 0 ):

[0054] CF ( E 0 ) = f ( D spot ′ ) ρΔxΔy M S E 0 ( z )

[0055] Where: ρ is the density of the medium (water: 1g/cm 3 ), is the stopping power of the ion beam at the measurement depth z (the stopping power of the 300MeV/u carbon ion beam at the measurement depth of 6.8mm is 12.8keV/μm), Δx and Δy are the point scans in two orthogonal directions in the transverse direction, respectively The step size (3mm), M is used to control the reading (ie MU) of the line beam monitoring detector at each scanning point during the scanning of the control point.

[0056] The above steps constitute a double ion chamber cross-calibration method for the online beam monitoring detector in the ion beam three-dimensional spot scanning beam distribution.

Example Embodiment

[0057] Example 2: see figure 1 , the center reading D spot with central dose D center The establishment of the mapping relationship between them is achieved by analyzing the response data of the large-area parallel-plate ionization chamber 4 to the ion pencil beam 1 and the response data of the micro-sensitive volume ionization chamber 5 to the dose calibration field 7 to establish a standard relational database. .

Example Embodiment

[0058] Example 3: see figure 2 , the large-area parallel plate ionization chamber 4 measures the single-energy pencil beam 1 device including a scanning magnet 2 arranged downstream of the single-energy ion pencil beam 1 to control and ensure the single-energy ion pencil beam 1 along the beam transport line For collimation distribution, an online monitoring detector 3 is arranged on the beam axis 6 , and a large-area parallel plate ionization chamber 4 is arranged at the end of the beam axis 6 . It is required to ensure that the beam is vertically irradiated to the large-area parallel plate ionization chamber 4 after passing through the online monitoring detector 3 along the beam axis 6 .

PUM

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Classification and recommendation of technical efficacy words

reduce time consumption
reduce system error

Cross calibration method used for online beam monitoring detector in three-dimensional spot scanning beam distribution

AI-Extracted Technical Summary

Problems solved by technology

Abstract

Image

Examples

Example Embodiment

Example Embodiment

Example Embodiment

PUM

Description & Claims & Application Information

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