Abdullah Rasheed, Presenter: Nothing to Disclose

Purpose/Objective(s): Lung cancer tumors exhibit motion during respiration, complicating the delivery of radiation therapy (RT). The abdominal compression plate (ACP) is thought to mitigate this clinical problem by controlling respiratory motion. This study intends to quantify the effect of ACP on respiratory-induced motion by evaluating volume and displacement changes of the heart, lungs, and tumor with and without ACP as demonstrated by 4DCT.Materials/Methods: Lung cancer patients (n=17) received 4DCT simulation scans (10 CTs from 0%-90% breathing phases) with and without ACP. Maximally tolerated diaphragmatic pressure was applied and tumor motion was visualized by fluoroscopy. The gross tumor volume (GTV), heart and lungs were contoured in treatment planning software for each of the 10 phases. Structures were exported for external algorithmic analysis. For each phase of the 4DCT with and without ACP, tumor and organ absolute centroid range of motion, 3D centroid displacement from the average, and volume were calculated. Parametric Student’s t-test comparing the motion and volume with and without ACP were conducted with significance set at p<0.05.Results: 9 patients (53%) had upper lobe tumors, 4 (24%) had middle lobe tumors and 4 (24%) had lower lobe tumors. Averaged across all patients, centroid range of motion for GTV, heart, and lungs without compression was 4.77 ± 4.75 mm, 5.92 ± 2.13 mm & 6.99 ± 2.79 mm, respectively and 4.80 ± 3.85 mm, 5.65 ± 1.99 mm & 5.99 ± 3.19 mm, with compression, respectively. With ACP use, GTV centroid displacement was reduced in 3 patients (17.6%; 3 upper lobe tumors) by a mean of 1.13 mm (p<0.01), increased in 5 patients (29.4%; 3 upper lobe tumors, 1 middle lobe, 1 lower lobe) by a mean of 0.87 mm (p<0.01), and not significantly changed in 9. Of the 8 patients with a significant change in GTV centroid displacement, on average, all exhibited increased mean GTV volume and decreased centroid displacement/mean volume of the heart & lungs.Conclusions: ACP efficacy is patient specific, with variation possibly attributable to preexisting factors such as COPD severity, chest wall elasticity, lung tumor location, or patient comfort. Tumor lobe location does not pre-determine compression efficacy. Patients should be simulated with and without ACP, regardless of tumor location, to grossly assess feasibility of ACP use. It appears that GTV motion is most important in determining whether a patient is suitable for compression. Of the 8 patients with a significant change in GTV motion (increased or decreased), on average, all experienced improved motion & volume control of the heart & lungs. Alternative motion control should be considered in patients who do not benefit from compression. In patients who clearly benefited, ACP may enhance tumor coverage while minimizing toxicity to surrounding organs. Larger scale studies are necessary to make definitive treatment recommendations.

Rasheed, A, The Effects of Abdominal Compression on the Motion and Volume of the GTV, Lungs and Heart in Lung Cancer Patients Using 4DCT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14044249.html