Saudur Rahman BSc, Presenter: Nothing to Disclose

Tracy Sherertz Bray MD, Abstract Co-Author: Nothing to Disclose

John C. Roeske, Abstract Co-Author: Research grant, Varian Medical Systems, Inc

Suneel Nagda, Abstract Co-Author: Nothing to Disclose

Definitive radiotherapy for lung cancer patients depends on accurate daily setup to ensure coverage of the clinical target volume. Kilovoltage (kV)-based Image Guided Radiation Therapy (IGRT) allows the use of diagnostic quality X-ray images that highlight skeletal anatomy for improved daily patient alignment. The purpose of this study was to evaluate the changes in ipsilateral chest wall measurements during a course of definitive IGRT for lung cancer.

Thirty-two patients treated definitively with daily kV-based IGRT for lung cancer from 2009-2010 were identified; 30 were analyzable. The majority of patients had stage III NSCLC. Median dose was 64 Gy (45-70 Gy), and median fractions was 32 (23-37). Median setup margin i.e. planning target volume (PTV) was 0.5 cm. Setup digitally reconstructed radiographs (DRRs) and daily anterior-posterior (AP) and lateral kV images were analyzed for changes in ipsilateral chest wall anatomy. On AP images, the lateral dimension of the ipsilateral hemithorax was estimated by measuring the distance (in cm) from the spinous process to the lateral edge of the rib at the level of the isocenter (ISO), and at 3 cm above and below ISO. On lateral images, the AP dimension of the hemithorax was estimated by measuring the distance from the posterior edge of the vertebral body to the anterior edge of the sternum at ISO and 3cm above and below ISO. An average of the three measurements on each image was calculated and the absolute difference from DRR was calculated for each daily kV image.

On average, the change in the lateral dimensions of the hemithorax compared to DRR was 0.2 ± 0.1 cm, and in the AP dimension was 0.3 ± 0.2 cm for all patients. A difference greater than 0.5 cm in either the lateral or AP dimensions compared to the DRR was noted in 21 % of treatment fractions.

Patient setup for daily kV-based IGRT relies primarily on skeletal anatomy. While the mean differences in ipsilateral chest wall anatomy were within our PTV, in >20% of fractions the difference between DRR and kV was greater than the PTV. Depending on registration, a subset of patients may require soft tissue, rather than skeletal imaging to ensure adequate daily setup.

IGRT in the treatment of lung cancer patients may require the use of complementary imaging techniques such as soft tissue imaging.

Rahman, S, Bray, T, Roeske, J, Nagda, S, Changes in Chest Wall Anatomy in Lung Cancer Patients Treated with Daily kV-based Image-guided Radiotherapy.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11016990.html