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KMID : 1164220140260010011
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Journal of Korean Society for Radiotherapeutic Technology
2014 Volume.26 No. 1 p.11 ~ p.19
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Analysis of the major factors of influence on the conditions of the Intensity Modulated Radiation Therapy planning optimization in Head and Neck
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Kim Dae-Sup
Lee Woo-Seok
Yoon In-Ha
Back Geum-Mun
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Abstract
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Purpose : To derive the most appropriate factors by considering the effects of the major factors when applied to the
optimization algorithm, thereby aiding the effective designing of a ideal treatment plan.
Materials and Methods : The eclipse treatment planning system(Eclipse 10.0, Varian, USA) was used in this study. The PBC(Pencil Beam Convolution) algorithm was used for dose calculation, and the DVO (Dose Volume Optimizer 10.0.28)
Optimization algorithm was used for intensity modulated radiation therapy. The experimental group consists of patients
receiving intensity modulated radiation therapy for the head and neck cancer and dose prescription to two planned target
volume was 2.2 Gy and 2.0 Gy simultaneously. Treatment plan was done with inverse dose calculation methods utilizing 6 MV beam and 7 fields. The optimal algorithm parameter of the established plan was selected based on volume dosepriority(Constrain), dose fluence smooth value and the impact of the treatment plan was analyzed according to the variation of each factors. Volume dose-priority determines the reference conditions and the optimization process was carried out under the condition using same ratio, but different absolute values. We evaluated the surrounding normal organs of treatment volume according to the changing conditions of the absolute values of the volume dose-priority. Dose fluence smooth value was applied by simply changing the reference conditions (absolute value) and by changing the related volume dose- priority. The treatment plan was evaluated using Conformal Index, Paddick’s Conformal Index, Homogeneity Index and the average dose of each organs.
Results : When the volume dose-priority values were directly proportioned by changing the absolute values, the CI values were found to be different. However PCI was 1.299 ± 0.006 and HI was 1.095 ± 0.004 while D5%/D95% was 1.090 ± 1.011. The impact on the prescribed dose were similar. The average dose of parotid gland decreased to 67.4, 50.3, 51.2, 47.1 Gy when the absolute values of the volume dose-priority increased by 40,60,70,90. When the dose smooth strength from each
treatment plan was increased, PCI value increased to 1.338 ± 0.006.
Conclusion : The optimization algorithm was more influenced by the ratio of each condition than the absolute value of volume dose-priority. If the same ratio was maintained, similar treatment plan was established even if the absolute values were different. Volume dose-priority of the treatment volume should be more than 50% of the normal organ volume dose-priority in order to achieve a successful treatment plan. Dose fluence smooth value should increase or decrease proportional to the volume dosepriority. Volume dose-priority is not enough to satisfy the conditions when the absolute value are applied solely.
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KEYWORD
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Radiation Treatment Planning, Dose Optimization, Volume Dose Priority, Dose Fluence smooth
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