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Home > 학회활동 > 국제학술지 |
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작성일 : 10-10-29 17:21
| 저 자 |
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Jeong-Woo Lee et al |
| 제 목 |
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Discrepancy of Intensity Modulation Radiation Therapy Dose Delivery due to the Dose-Dynamic Multi-Leaf Collimator Gravity E ect |
| 학회지명 |
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Journal of the Korean Physical Society |
| 권 호 |
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53 |
| 페이지 |
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3436-3443 |
| 년,월 |
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2008-12-1 |
| 링 크 |
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| Abstract |
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The aim of the present study was to investigate the multi-leaf collimator (MLC) gravity e ect
on intensity modulated radiation therapy (IMRT) dose-dynamic delivery at di erent gantry angles.
The non-uniform
uence for IMRT was generated by means of dose-dynamic MLC (DMLC) perfor-
mances, which were multiple static segments (MSS) or fully dynamic sliding window (SW) delivery
methods at di erent gantry angles. SW delivery is quite similar to MSS with regard to MLC sliding
pattern through the X1 to X2 jaw direction, except that it is irradiated during DMLC movement.
To determine how the DMLC gravity a ects the IMRT dose
uence, we mounted a two-dimensional
ion chamber matrix (MatriXX, Scanditronix-Wellhofer, Schwarzenbruck, Germany) to a linear ac-
celerator (CL 21EX, Varian, Palo Alto, CA, USA). Individual IMRT dose-dynamic segments were
applied by using MSS and SW for 6-MV photon beams at ve di erent gantry angles: 0 (neu-
tral gravity), 45 (semi-along gravity), 90 (vertical-along gravity), 315 (semi-against gravity) and
270 (against gravity). To test the correlation of leaf speed and gravity, we delivered half monitor
units (MUs) for planned doses for absolute dose comparison. Strict
-index (dose di erence: 2 %;
distance to agreement: 2 mm) histograms were used for quantitative analyses of the discrepancy.
The dose distribution by MSS under neutral gravity (gantry 0) with 137 MUs at a prescribed
dose (45 cGy) point, which was in the low gradient area, was used as a reference for the other
results. The
-index histograms showed an increased tendency of the dose discrepancy toward the
gravity-along direction rather than toward the gravity-against direction. The acceptable propor-
tional ranges below 1 of the
-index were 96.2 { 99.6 % (mean: 97.6 %), 92.6 { 93.5 % (mean: 93.0
%), 90.4 { 92.6 % (mean: 91.3 %), 94.6 { 98.0 % (mean: 96.4 %) and 92.9 { 96.8 % (mean: 95.0
%) for neutral, semi-along, vertical-along, semi-against and vertical-against gravity of the positions
of MLC segments, respectively. we noted that MSS deliveries were more stable than were the SW
deliveries (unacceptable
-index range 1.0 { 2.0: mean 3.6 % for MSS and 5.4 % for SW). For the
dose measurement on the prescribed dose point, all measurements showed a good agreement within
an average of 2 %. Our experiment conclusively demonstrated that the DMLC gravity a ects the IMRT dose distribution. The e ect may impact more severely in the gravity along direction and
SW while the leaf speed is not in
uenced so much. |
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