The Effect of Respiratory on Dose Distributions in Radiotherapy of Lung Cancer: A Phantom Study

Abstract

Internal organ motions are one of the most significant obstacles for radiotherapy, especially in the case of motions caused by respiratory during the lung irradiation. There is no any consensus about the margin limit given for the target volume (Clinical Target Volume-CTV, Planning Target Volume- PTV etc.), especially for tumors located moving organs such as lung. Besides, as far as we know, there is no any systematic phantom study showed the effects of respiratory motions on radiotherapy doses depending on PTV margins in the literature. In present study, our aim was to determine the success degree of enlarging the PTV margins on radiotherapy doses during the moving organ irradiations. The study was performed by using GaF-Chromic EBT films placed to a thorax phantom. A cylindrical part within the phantom can move on through craniocaudal direction with a range of 3 cm with 5 sec. period during the irradiation. From the profiles which were obtained from 3 cm moving situations for 3D-Conformal Radiotherapy (3D-CRT), Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc
Therapy (VMAT) with narrow margins, it was observed that PTV cannot get adequate dose. The irradiation was better for CTV with larger margins but there was still inhomogeneity for PTV. As a consequence, enlarging the margins alone is not a sufficient method against the negative effects of organ motions on the radiotherapy doses.

Keywords

• Radiotherapy,lung movement,respiratory

Akciğer Kanseri Radyoterapisinde Solunumun Doz Dağılımlarına Etkisi: Bir Fantom Çalışması

Abstract

Organ hareketleri, özellikle akciğer ışınlamaları sırasında nefes alıp vermeden kaynaklanan hareketler, radyoterapi için en önemli zorluklardandır. Özellikle akciğer gibi hareketli organlarda bulunan tümörler için hedef hacme (Clinical Target Volume-CTV, Planning Target Volume- PTV) verilecek marj sınırı hakkında herhangi bir fikir birliği yoktur. Bunun yanında, literatürde solunum hareketlerinin PTV marjlarına bağlı olarak radyoterapi dozlarına etkisini gösteren sistematik bir fontom çalışması bulunmamaktadır. Bu çalışmada amaç, PTV marjlarının genişlemesinin, organ hareketlerinin radyoterapi dozlarına etkileri üzerindeki başarısını ölçmektir. Çalışma GaF-Chromic EBT filmlerin bir göğüs kafesi fantomuna yerleştirilmesiyle gerçekleştirilmiştir. Fantom içerisindeki bir silindirik bölüm ışınlama sırasında 5 saniyelik periyotlarla, 3 cm genlikle ayak-baş doğrultusunda hareket etmektedir. 3 cm genlikli hareketin olduğu durum için alınan profillerden 3 Boyutlu Konformal Radyoterapi (3D-CRT), Yoğunluk Ayarlı Radyoterapi (IMRT), Yoğunluk Ayarlı Arc Tedavi (VMAT) planları dar marjlar için incelendiğinde, PTV’nin yeterli doz alamadığı gözlemlenmiştir. Işınlama CTV için daha geniş marjlarda iyileşmekte, ancak PTV için inhomojenite devam etmektedir. Sonuç olarak, marjların genişletilmesinin organ hareketlerinin radyoterapi dozları üzerindeki olumsuz etkileri için tek başına yeterli olmadığı gözlemlenmiştir. 

Keywords

• Radyoterapi,akciğer hareketi,solunum

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