Validation of an elastic registration technique to estimate anatomical lung modification in Non-Small-Cell Lung Cancer Tomotherapy

Elena Faggiano,Cristina Ciavarro,Italo Dell'Oca,Giovanna Rizzo,Riccardo Calandrino,Diego Persano,Giovanni M Cattaneo

doi:10.1186/1748-717x-6-31

Abstract

BackgroundThe study of lung parenchyma anatomical modification is useful to estimate dose discrepancies during the radiation treatment of Non-Small-Cell Lung Cancer (NSCLC) patients. We propose and validate a method, based on free-form deformation and mutual information, to elastically register planning kVCT with daily MVCT images, to estimate lung parenchyma modification during Tomotherapy.MethodsWe analyzed 15 registrations between the planning kVCT and 3 MVCT images for each of the 5 NSCLC patients. Image registration accuracy was evaluated by visual inspection and, quantitatively, by Correlation Coefficients (CC) and Target Registration Errors (TRE). Finally, a lung volume correspondence analysis was performed to specifically evaluate registration accuracy in lungs.ResultsResults showed that elastic registration was always satisfactory, both qualitatively and quantitatively: TRE after elastic registration (average value of 3.6 mm) remained comparable and often smaller than voxel resolution. Lung volume variations were well estimated by elastic registration (average volume and centroid errors of 1.78% and 0.87 mm, respectively).ConclusionsOur results demonstrate that this method is able to estimate lung deformations in thorax MVCT, with an accuracy within 3.6 mm comparable or smaller than the voxel dimension of the kVCT and MVCT images. It could be used to estimate lung parenchyma dose variations in thoracic Tomotherapy.

Highlights

The study of lung parenchyma anatomical modification is useful to estimate dose discrepancies during the radiation treatment of Non-Small-Cell Lung Cancer (NSCLC) patients
Registration between the planning kVCT and 3 daily megavoltage CT scans (MVCT) images of each patient was analyzed for a total of 15 studies; we considered one MVCT scan at the beginning of treatment, one in the middle and one at the end, in order to account for different stages of anatomical deformation induced by Helical Tomotherapy (HT) treatment
All patients presented anatomical changes during the course of therapy as shown by Target Registration Errors (TRE) values and lung volume correspondence indices calculated after the sole rigid registration (Table 2, 3 and 4)

Summary

Introduction

The study of lung parenchyma anatomical modification is useful to estimate dose discrepancies during the radiation treatment of Non-Small-Cell Lung Cancer (NSCLC) patients. We propose and validate a method, based on free-form deformation and mutual information, to elastically register planning kVCT with daily MVCT images, to estimate lung parenchyma modification during Tomotherapy. MVCT images are primarily used for patient setup verification [2]. To analyze and study the anatomical changes of lung parenchyma due to radiation therapy, and to calculate the corresponding accumulated dose, rigid registration methods are not sufficient; the introduction of deformable registration methods has been fundamental [6]. A different registration procedure consisting in a multiple preprocessing step and a two-step optical flow deformable registration method was proposed to register abdominal MVCT and kVCT images [10]

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