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Improvement of I'mRT MatriXX in terms of spatial resolution and large area acquisition for patient-specific intensity-modulated radiotherapy verification.

Oinam AS, Singh L, Sharma SC, Goswami P - J Med Phys (2009)

Bottom Line: After an analysis of the dose linearity and spatial resolution of this 2D array (I'mRT MatriXX), the signal sampling time of 200 ms was selected for data acquisition.Multiple-sequence acquisitions at the nearest 4 positions with the shift of half of the distance between the centers of two adjacent ion chambers increase the spatial resolution up to four times when used with this I'mRT MatriXX.It is found that the convolution method can also be used to improve the IMRT dose verification with the same parameters of the passing criteria significantly, viz., up to 99.87% agreement, by smoothening the treatment planning system profile.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, PGIMER, Chandigarh, India.

ABSTRACT
2D array of ionization chambers can be used for both absolute and relative dose verification of patient-specific intensity-modulated radiotherapy (IMRT) quality assurance. After an analysis of the dose linearity and spatial resolution of this 2D array (I'mRT MatriXX), the signal sampling time of 200 ms was selected for data acquisition. Multiple-sequence acquisitions at the nearest 4 positions with the shift of half of the distance between the centers of two adjacent ion chambers increase the spatial resolution up to four times when used with this I'mRT MatriXX. IMRT verification of head-and-neck case, which requires a large area for dosimetric verification, can be done with limited size of 24x24 cm(2), depending on the user requirements. It is found that the convolution method can also be used to improve the IMRT dose verification with the same parameters of the passing criteria significantly, viz., up to 99.87% agreement, by smoothening the treatment planning system profile.

No MeSH data available.


Lateral response profiles (dose profiles) of single ion chamber for different sampling times at different positions of 2-mm slit width of multileaves collimator (MLC).
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Figure 0003: Lateral response profiles (dose profiles) of single ion chamber for different sampling times at different positions of 2-mm slit width of multileaves collimator (MLC).

Mentions: The lateral response of a single ion chamber for different sampling times is shown in Figure 3. A prominent peak appearing in this figure can be utilized for the improvement of resolution of 2D arrays ion chamber matrix. The radiation dose delivered on the 2D ion chamber arrays with beam-sweeping fields of 2 mm MLC slit opening produces the changes in the relative response of a single ion chamber due to the different positions of MLC slit. The variation of relative response was characterized by standard deviations of 0.356, 0.354, 0.354, 0.353 and 0.347, respectively, for the different signal sampling times of 100, 150, 200, 250 and 300 ms. The maximum SD of 0.356 was found for sampling time of 100 ms while with minimum standard deviation of 0.347 for the sampling time of 300 ms. The variations of relative response were approximately equal for all the sampling times but were larger for smaller sampling times. The spatial spread, that is, full width at half maximum value (FWHM) of signal response, of each sample is also the same for all the signal samples times except a small difference at the peak, which is flattened in case of small sampling time and sharp for larger sampling time, as shown in Figure 3. We have used Fourier transformation technique to determine the differences between these peaks. The Fourier transformations of lateral response profiles are shown in terms of spatial frequency (mm−1) and amplitude (cGy) of Fourier signal [Figure 4]. The first zeros of each Fourier signal for different signal sampling times of 100, 150, 200, 250 and 300 ms were found at spatial frequency of 0.168, 0.163, 0.171, 0.154 and 0.163 mm−1, respectively [Table 1]. These differences could not be visualized with a simple Cartesian coordinate and dose response peaks of lateral response profiles. The first zero spatial frequency of 200 ms sampling time produced the largest spatial frequency (0.171 mm−1). The largest spatial frequency of first zero corresponds to better spatial resolution according to Fourier transformation. This shows that the sampling time of 200 ms provides better spatial resolution, though this 2D array ion chamber works with zero dead time of signal sampling. Poppe et al.[45] reported that the lateral response of PTW 2D-Array, 10024 version of PTW Freiburg, Germany, was a trapezium of 5 mm top and 9 mm base. We found that the first zero of this lateral function was found at almost the same spatial frequency of 0.144 mm−1 as reported by Poppe et al.[45]


Improvement of I'mRT MatriXX in terms of spatial resolution and large area acquisition for patient-specific intensity-modulated radiotherapy verification.

Oinam AS, Singh L, Sharma SC, Goswami P - J Med Phys (2009)

Lateral response profiles (dose profiles) of single ion chamber for different sampling times at different positions of 2-mm slit width of multileaves collimator (MLC).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2807681&req=5

Figure 0003: Lateral response profiles (dose profiles) of single ion chamber for different sampling times at different positions of 2-mm slit width of multileaves collimator (MLC).
Mentions: The lateral response of a single ion chamber for different sampling times is shown in Figure 3. A prominent peak appearing in this figure can be utilized for the improvement of resolution of 2D arrays ion chamber matrix. The radiation dose delivered on the 2D ion chamber arrays with beam-sweeping fields of 2 mm MLC slit opening produces the changes in the relative response of a single ion chamber due to the different positions of MLC slit. The variation of relative response was characterized by standard deviations of 0.356, 0.354, 0.354, 0.353 and 0.347, respectively, for the different signal sampling times of 100, 150, 200, 250 and 300 ms. The maximum SD of 0.356 was found for sampling time of 100 ms while with minimum standard deviation of 0.347 for the sampling time of 300 ms. The variations of relative response were approximately equal for all the sampling times but were larger for smaller sampling times. The spatial spread, that is, full width at half maximum value (FWHM) of signal response, of each sample is also the same for all the signal samples times except a small difference at the peak, which is flattened in case of small sampling time and sharp for larger sampling time, as shown in Figure 3. We have used Fourier transformation technique to determine the differences between these peaks. The Fourier transformations of lateral response profiles are shown in terms of spatial frequency (mm−1) and amplitude (cGy) of Fourier signal [Figure 4]. The first zeros of each Fourier signal for different signal sampling times of 100, 150, 200, 250 and 300 ms were found at spatial frequency of 0.168, 0.163, 0.171, 0.154 and 0.163 mm−1, respectively [Table 1]. These differences could not be visualized with a simple Cartesian coordinate and dose response peaks of lateral response profiles. The first zero spatial frequency of 200 ms sampling time produced the largest spatial frequency (0.171 mm−1). The largest spatial frequency of first zero corresponds to better spatial resolution according to Fourier transformation. This shows that the sampling time of 200 ms provides better spatial resolution, though this 2D array ion chamber works with zero dead time of signal sampling. Poppe et al.[45] reported that the lateral response of PTW 2D-Array, 10024 version of PTW Freiburg, Germany, was a trapezium of 5 mm top and 9 mm base. We found that the first zero of this lateral function was found at almost the same spatial frequency of 0.144 mm−1 as reported by Poppe et al.[45]

Bottom Line: After an analysis of the dose linearity and spatial resolution of this 2D array (I'mRT MatriXX), the signal sampling time of 200 ms was selected for data acquisition.Multiple-sequence acquisitions at the nearest 4 positions with the shift of half of the distance between the centers of two adjacent ion chambers increase the spatial resolution up to four times when used with this I'mRT MatriXX.It is found that the convolution method can also be used to improve the IMRT dose verification with the same parameters of the passing criteria significantly, viz., up to 99.87% agreement, by smoothening the treatment planning system profile.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, PGIMER, Chandigarh, India.

ABSTRACT
2D array of ionization chambers can be used for both absolute and relative dose verification of patient-specific intensity-modulated radiotherapy (IMRT) quality assurance. After an analysis of the dose linearity and spatial resolution of this 2D array (I'mRT MatriXX), the signal sampling time of 200 ms was selected for data acquisition. Multiple-sequence acquisitions at the nearest 4 positions with the shift of half of the distance between the centers of two adjacent ion chambers increase the spatial resolution up to four times when used with this I'mRT MatriXX. IMRT verification of head-and-neck case, which requires a large area for dosimetric verification, can be done with limited size of 24x24 cm(2), depending on the user requirements. It is found that the convolution method can also be used to improve the IMRT dose verification with the same parameters of the passing criteria significantly, viz., up to 99.87% agreement, by smoothening the treatment planning system profile.

No MeSH data available.