Biological effects of the intra-fraction
organ motion in the intensity modulation delivery of the liver tumor
1Hsiang-Chi
Kuo, 2Wen Shan Liu, 1Keh-Shih Chuang, 3Andrew Wu
1Department of Nuclear Science, National Tsing-Hua University, HsinChu, Taiwan;
2Radiation Oncology Department, Chung-Shan Medical University
Hospital, Taichung, Taiwan; 3Department of
Radiologic Sciences, Thomas Jefferson University,
Philadelphia, PA, USA
Fluence changes caused by organ motion were calculated
using Chui¡¯s convolution algorithm. This study was limited to fluence changes
associated with superior-inferior organ motion perpendicular to the moving MLC.
An effective fluence concept was used for forward dose calculations to study
the effects of distorted fluence map on dose plans. 108 effective fluence maps
created from 16 IMRT plans for eight liver patients incorporated their specific
motion patterns were calculated. The
effective fluence was then used for forward dose calculation. The effects of respiratory
motion on the IMRT plan created from DMLC were then evaluated with dose
distribution, DVH, dose uniformity, EUD, effective volume and NTCP. The results
of these studies indicate that the motion effect (average motion range 1.5cm)
appears to reduce the mean dose of the PTV by 3.6%. The value shows a decrease
of 0.6% if gated technique were applied such that the average motion range is
0.75cm. Since the respiratory motion seems to reduce a relatively large dose to
a relatively small volume, the EUD analysis indicates that the motion effect
will reduce the EUD of the PTV by 18.3% without gated technique as compared to
3.4% with gated technique. When the normal liver is considered as parallel
organ, the respiratory motion has little effect on the mean dose, EUD, NTCP of
the normal liver. This composite dose distribution analysis concludes that the
respiratory motion has severe effect on IMRT plan if the motion range is large.
Appropriate means should be taken to keep the motion range below 0.8cm to avoid
the unacceptable cold area within the PTV.
Corresponding
author: Andrew Wu, PhD, Department of Radiologic
Sciences,
Phila., PA 19107, USA, Tel. 215-503-2559,
Fax. 215-503-1031, E-mail: Andrew.wu@jefferson.edu