Comparison of Different Strategies to Use Four-Dimensional Computed Tomography in Treatment Planning for Lung Cancer Patients
Received 9 August 2007; received in revised form 3 October 2007; accepted 9 November 2007.
Purpose
To discuss planning target volumes (PTVs) based on internal target volume (PTVITV), exhale-gated radiotherapy (PTVGating), and a new proposed midposition (PTVMidP; time-weighted mean tumor position) and compare them with the conventional free-breathing CT scan PTV (PTVConv).
Methods and Materials
Respiratory motion induces systematic and random geometric uncertainties. Their contribution to the clinical target volume (CTV)-to-PTV margins differs for each PTV approach. The uncertainty margins were calculated using a dose–probability-based margin recipe (based on patient statistics). Tumor motion in four-dimensional CT scans was determined using a local rigid registration of the tumor. Geometric uncertainties for interfractional setup errors and tumor baseline variation were included. For PTVGating, the residual motion within a 30% gating (time) window was determined. The concepts were evaluated in terms of required CTV-to-PTV margin and PTV volume for 45 patients.
Results
Over the patient group, the PTVITV was on average larger (+6%) and the PTVGating and PTVMidP smaller (−10%) than the PTVConv using an off-line (bony anatomy) setup correction protocol. With an on-line (soft tissue) protocol the differences in PTV compared with PTVConv were +33%, −4%, and 0, respectively.
Conclusions
The internal target volume method resulted in a significantly larger PTV than conventional CT scanning. The exhale-gated and mid-position approaches were comparable in terms of PTV. However, mid-position (or mid-ventilation) is easier to use in the clinic because it only affects the planning part of treatment and not the delivery.
Department of Radiation Oncology, The Netherlands Cancer Institute – Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands
Reprint requests to: Eugène M. F. Damen, Ph.D., Department of Radiation Oncology, The Netherlands Cancer Institute – Antoni van Leeuwenhoek Hospital, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands. Tel: (+31) 20-5121759; Fax: (+31) 20-6691101
Supported by a grant from the Dutch Cancer Society (NKI 03-2943).
Presented in part at the 2006 (Leipzig, Germany) and 2007 (Barcelona, Spain) Annual Meetings of the European Society for Therapeutic Radiology and Oncology (ESTRO).
Conflict of interest: J.-J. Sonke is partly sponsored by Elekta Oncology Systems.
ABSTRACT