Dosimetric impact of different CT datasets for stereotactic treatment planning using 3D conformal radiotherapy or volumetric modulated arc therapy

Markus Oechsner,Stephanie Elisabeth Combs,Leonhard Odersky,Jan Jakob Wilkens,Johannes Berndt,Marciana Nona Duma

doi:10.1186/s13014-015-0557-7

Abstract

BackgroundThe purpose of this study was to assess the impact on dose to the planning target volume (PTV) and organs at risk (OAR) by using four differently generated CT datasets for dose calculation in stereotactic body radiotherapy (SBRT) of lung and liver tumors. Additionally, dose differences between 3D conformal radiotherapy and volumetric modulated arc therapy (VMAT) plans calculated on these CT datasets were determined.MethodsTwenty SBRT patients, ten lung cases and ten liver cases, were retrospectively selected for this study. Treatment plans were optimized on average intensity projection (AIP) CTs using 3D conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT). Afterwards, the plans were copied to the planning CTs (PCT), maximum intensity projection (MIP) and mid-ventilation (MidV) CT datasets and dose was recalculated keeping all beam parameters and monitor units unchanged. Ipsilateral lung and liver volumes and dosimetric parameters for PTV (Dmean, D2, D98, D95), ipsilateral lung and liver (Dmean, V30, V20, V10) were determined and statistically analysed using Wilcoxon test.ResultsSignificant but small mean differences were found for PTV dose between the CTs (lung SBRT: ≤2.5 %; liver SBRT: ≤1.6 %). MIPs achieved the smallest lung and the largest liver volumes. OAR mean doses in MIP plans were distinctly smaller than in the other CT datasets. Furthermore, overlapping of tumors with the diaphragm results in underestimated ipsilateral lung dose in MIP plans. Best agreement was found between AIP and MidV (lung SBRT). Overall, differences in liver SBRT were smaller than in lung SBRT and VMAT plans achieved slightly smaller differences than 3D-CRT plans.ConclusionsOnly small differences were found for PTV parameters between the four CT datasets. Larger differences occurred for the doses to organs at risk (ipsilateral lung, liver) especially for MIP plans. No relevant differences were observed between 3D-CRT or VMAT plans. MIP CTs are not appropriate for OAR dose assessment. PCT, AIP and MidV resulted in similar doses. If a 4DCT is acquired PCT can be omitted using AIP or MidV for treatment planning.

Highlights

Stereotactic body radiotherapy (SBRT) is well established in the treatment of tumors and metastases of lung and liver [1,2,3,4]
Relative differences of doses over all patients for the planning target volume (PTV) are depicted in Table 1 and Table 2
For the lung stereotactic body radiotherapy (SBRT) the largest mean difference was found for 3D conformal radiotherapy (3D-CRT) plans and parameter D95 (MIP vs. planning computer tomography (CT) (PCT): 2.5 ± 1.8 %)

Summary

Introduction

Stereotactic body radiotherapy (SBRT) is well established in the treatment of tumors and metastases of lung and liver [1,2,3,4]. Movement of the tumor can be assessed by four-dimensional computer tomography (4DCT) Using this motion information different approaches have been proposed to generate the planning target volume (PTV). Maximum intensity projection (MIP) or average intensity projection (AIP) CT datasets can be calculated from the 4DCT to delineate the tumor [9,10,11] Another group suggested the generation of a mid-ventilation CT dataset (MidV) for target definition and treatment planning [12]. The purpose of this study was to assess the impact on dose to the planning target volume (PTV) and organs at risk (OAR) by using four differently generated CT datasets for dose calculation in stereotactic body radiotherapy (SBRT) of lung and liver tumors. Dose differences between 3D conformal radiotherapy and volumetric modulated arc therapy (VMAT) plans calculated on these CT datasets were determined

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