Prog Med Phys.  2017 Dec;28(4):164-170. 10.14316/pmp.2017.28.4.164.

Dosimetric Analysis on the Effect of Target Motion in the Delivery of Conventional IMRT, RapidArc and Tomotherapy

• Song JY

• KMID: 2401378
• DOI: http://doi.org/10.14316/pmp.2017.28.4.164

Abstract

One of the methods to consider the effect of respiratory motion of a tumor target in radiotherapy is to establish a treatment plan with the internal target volume (ITV) created based on an accurate analysis of the target motion displacement. When this method is applied to intensity modulated radiotherapy (IMRT), it is expected to yield a different treatment dose distribution under the motion condition according to the IMRT method. In this study, we prepared ITV-based IMRT plans with conventional IMRT using fixed gantry angle beams, RapidArc using volumetric modulated arc therapy, and tomotherapy using helical therapy. Then, the variation in dose distribution caused by the target motion was analyzed by the dose measurement in the actual motion condition. A delivery quality assurance plan was prepared for the established IMRT plan and the dose distribution in the actual motion condition was measured and analyzed using a two-dimensional diode detector placed on a moving phantom capable of simulating breathing movements. The dose measurement was performed considering only a uniform target shape and motion in the superior-inferior (SI) direction. In this condition, it was confirmed that the error of the dose distribution due to the target motion is minimum in tomotherapy. This is thought to be due to the characteristic of tomotherapy that treats the target sequentially by dividing it into several slices. When the target shape is uniform and the main target motion direction is SI, it is considered that tomotherapy for the ITV-based IMRT method has a characteristic which can reduce the dose difference compared with the plan dose under the target motion condition.

Keyword

Internal target volume (ITV); RapidArc; TomoTherapy; Tumor motion; MapCHECK2

MeSH Terms

Clothing
Methods
Radiotherapy
Radiotherapy, Intensity-Modulated
Respiration

Figure

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  Fig. 1. Virtual tumor target and peripheral organs at risk for the preparation of IMRT plan.

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  Fig. 2 Phantom setup image for the dose measurement in the Novalis Tx.

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  Fig. 3 Phantom setup image for the dose measurement in the Tomotherapy.

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  Fig. 4 Example of the measured dose distribution and error analysis in the moving condition. (a) RapidArc, (b) FB-IMRT, (c) Tomotherapy.

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  Fig. 5 Graphs showing the effect of target motion according to the CTV increase due to CTV length increase. (a) Pass rate in 2 cm moving condition. (b) Pass rate in 4 cm moving condition.

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