Elsevier

Medical Dosimetry

Volume 36, Issue 2, Summer 2011, Pages 213-218
Medical Dosimetry

Dosimetric Analysis of Respiratory-Gated Radiotherapy for Hepatocellular Carcinoma

https://doi.org/10.1016/j.meddos.2010.03.006Get rights and content

Abstract

The purpose of this study was to define individualized internal target volume (ITV) for hepatocellular carcinoma (HCC) using 4D computed tomography (4DCT), and to determine the geometric and dosimetric benefits of respiratory gating. Gross tumor volumes (GTVs) were contoured on 10 respiratory phases of 4DCT images for 12 patients with HCC. Three treatment plans were prepared using different planning target volumes (PTVs): (1) PTV3D, derived from a single helical clinical target volume (CTV) plus conventional margins; (2) PTV10 phases, derived from ITV10 phases, which encompassed all 10 CTVs plus an isotropic margin of 0.8 cm; (3) PTVgating, derived from ITVgating, which encompassed three CTVs within gating-window at end-expiration plus an isotropic margin of 0.8 cm. The PTV3D was the largest volume for all patients. The ITV-based plans and gating plans spared more normal tissues than 3D plans, especially the liver. Without increasing normal tissue complication probability of the 3D plans, the ITV-based plans allowed for increasing the calculated dose from 50.8 Gy to 54.7 Gy on average, and the gating plans could further escalate the dose to 58.5 Gy. Compared with ITV-based plans, the dosimetric gains with gating plan strongly correlated with GTV mobility in the craniocaudal direction. The ITV-based plans can ensure target coverage with less irradiation of normal tissues compared with 3D plans. Respiratory-gated radiotherapy can further reduce the target volumes to spare more surrounding tissues and allow dose escalation, especally for patients with tumor mobility >1 cm.

Introduction

One of the main difficulties in accurate targeting of liver tumor is respiration-induced internal target motion, which contributes to uncertainty in both imaging, treatment planning, and delivery of radiotherapy.1 Compared with conventional helical computed tomography (CT), the technology of 4D computed tomography (4DCT) is a potential strategy to reduce respiratory motion effects.2 4DCT permits individualized assessment of tumor mobility and generates internal target volume (ITV), which could substantially reduce the planning target volume (PTV) while safely covering the target.3, 4, 5 The 4DCT technique can also allow planning of respiration-gated radiotherapy (RGRT), which enables smaller target volumes to be used because irradiation is limited to chosen phases of the breathing cycle.6, 7 Both methods have the potential to reduce normal tissue irradiation while providing effective tumor dose coverage. Recently, many studies on the use of 4DCT data for treatment of lung cancer have been reported; however, there are few reports on liver cancer. The purpose of this study is to determine the geometric and dosimetric benefits of respiratory gating on hepatocellular carcinoma (HCC).

Section snippets

Patient characteristics

The 4DCT scans of 12 patients with HCC who were treated with conventionally fractionated conformal radiotherapy (CRT) were retrospectively analyzed. Patient and tumor characteristics are listed in Table 1.

4DCT data acquisition

The patients were immobilized with vacuum bags in the supine position, with the arms raised above the head during simulation. The 4DCT scanning was performed during uncoached, quiet breathing on a 16-slice positron emission tomography (PET)/CT (GE Medical Systems, Waukesha, WI). A respiratory

Volumetric comparison

Table 2 presents the volumes of different ITVs and PTVs. The PTV10 phases was 87.4 ± 29.8 cc less than PTV3D (p < 0.01), and PTVgating was 54.4 ± 29.6 cc less than PTV10 phases (p < 0.01). PTV3D was the significantly largest volume for all patients; nevertheless, patient specifics differed. As shown in the study, the PTV10 phases was smaller than PTV3D in 3 orthogonal planes for 7 patients (Fig. 1), but it exceeded the latter in some slices for the other 5 patients.

Dosimetric comparison for OARs

The dosimetric comparison for

Discussion

Tumor motion is typically included in radiotherapy treatment planning of thoracic and abdominal tumors. It has been reported that the use of standard population-based margins to account for mobility is inferior to the use of individualized margins.13 Theoretically, using 4DCT images to determine individualized ITV should be an ideal way to account for organ motion, and several studies have already been published in the literature. This conclusion is confirmed by our data. Compared with 3D

Conclusions

Our analysis indicates that the ITV-based plans can ensure target coverage with less irradiation of normal tissues compared with conventional 3D plans for liver radiotherapy. Respiratory-gated radiotherapy can further reduce the target volumes to spare more surrounding tissues and allow dose escalation, especally for patients with tumor mobility >1 cm in the CC direction.

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    • Cited by (0)

    Mian Xi and Li Zhang contributed equally to this study.

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