Tumor Localization Using Cone-Beam CT Reduces Setup Margins in Conventionally Fractionated Radiotherapy for Lung Tumors
Received 2 June 2008; received in revised form 15 August 2008; accepted 26 September 2008. published online 22 April 2009.
Purpose
To determine whether setup margins can be reduced using cone-beam computed tomography (CBCT) to localize tumor in conventionally fractionated radiotherapy for lung tumors.
Methods and Materials
A total of 22 lung cancer patients were treated with curative intent with conventionally fractionated radiotherapy using daily image guidance with CBCT. Of these, 13 lung cancer patients had sufficient CBCT scans for analysis (389 CBCT scans). The patients underwent treatment simulation in the BodyFix immobilization system using four-dimensional CT to account for respiratory motion. Daily alignment was first done according to skin tattoos, followed by CBCT. All 389 CBCT scans were retrospectively registered to the planning CT scans using automated soft-tissue and bony registration; the resulting couch shifts in three dimensions were recorded.
Results
The daily alignment to skin tattoos with no image guidance resulted in systematic (Σ) and random (σ) errors of 3.2–5.6 mm and 2.0–3.5 mm, respectively. The margin required to account for the setup error introduced by aligning to skin tattoos with no image guidance was approximately 1–1.6 cm. The difference in the couch shifts obtained from the bone and soft-tissue registration resulted in systematic (Σ) and random (σ) errors of 1.5–4.1 mm and 1.8–5.3 mm, respectively. The margin required to account for the setup error introduced using bony anatomy as a surrogate for the target, instead of localizing the target itself, was 0.5–1.4 cm.
Conclusion
Using daily CBCT soft-tissue registration to localize the tumor in conventionally fractionated radiotherapy reduced the required setup margin by up to approximately 1.5 cm compared with both no image guidance and image guidance using bony anatomy as a surrogate for the target.
∗Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL
Reprint requests to: Kenneth Olivier, M.D., Department of Radiation Oncology, Mayo Clinic, Charlton Building, Desk R, 200 First St. S.W., Rochester, MN 55905. Tel: (507) 284-2511.
Conflict of interest: the authors' department received a grant from Elekta that pays 20% of A. Chvetsov's salary.
ABSTRACT