当前位置： SCI文献检索 > PHYSICS IN MEDICINE AND BIOLOGY期刊下所有文献 > Spatial resolution of 2D ionization chamber arrays for IMRT dose verification: single-detector size and sampling step width.

Spatial resolution of 2D ionization chamber arrays for IMRT dose verification: single-detector size and sampling step width.

Abstract：

:The spatial resolution of 2D detector arrays equipped with ionization chambers or diodes, used for the dose verification of IMRT treatment plans, is limited by the size of the single detector and the centre-to-centre distance between the detectors. Optimization criteria with regard to these parameters have been developed by combining concepts of dosimetry and pattern analysis. The 2D-ARRAY Type 10024 (PTW-Freiburg, Germany), single-chamber cross section 5 x 5 mm(2), centre-to-centre distance between chambers in each row and column 10 mm, served as an example. Additional frames of given dose distributions can be taken by shifting the whole array parallel or perpendicular to the MLC leaves by, e.g., 5 mm. The size of the single detector is characterized by its lateral response function, a trapezoid with 5 mm top width and 9 mm base width. Therefore, values measured with the 2D array are regarded as sample values from the convolution product of the accelerator generated dose distribution and this lateral response function. Consequently, the dose verification, e.g., by means of the gamma index, is performed by comparing the measured values of the 2D array with the values of the convolution product of the treatment planning system (TPS) calculated dose distribution and the single-detector lateral response function. Sufficiently small misalignments of the measured dose distributions in comparison with the calculated ones can be detected since the lateral response function is symmetric with respect to the centre of the chamber, and the change of dose gradients due to the convolution is sufficiently small. The sampling step width of the 2D array should provide a set of sample values representative of the sampled distribution, which is achieved if the highest spatial frequency contained in this function does not exceed the 'Nyquist frequency', one half of the sampling frequency. Since the convolution products of IMRT-typical dose distributions and the single-detector lateral response function have no or very small frequency contributions beyond 0.1 mm(-1), the mathematical approach introduced by Nyquist and Shannon shows that the sampling frequency of 0.2 mm(-1) is appropriate. Overall it is shown that the spatial resolution of the 2D-ARRAY Type 10024 is appropriate for the dose verification of IMRT plans. The insights obtained are also applied in the discussion of other available two-dimensional detector arrays.

journal_name

Phys Med Biol

journal_title

Physics in medicine and biology

authors

Poppe B,Djouguela A,Blechschmidt A,Willborn K,Rühmann A,Harder D

doi

10.1088/0031-9155/52/10/019

subject

Has Abstract

pub_date

2007-05-21 00:00:00

pages

2921-35

issue

eissn

0031-9155

issn

1361-6560

pii

S0031-9155(07)40995-2

journal_volume

pub_type

杂志文章

在线工具

Spatial resolution of 2D ionization chamber arrays for IMRT dose verification: single-detector size and sampling step width.