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Radiat Oncol. 2012 Dec 18;7:218. doi: 10.1186/1748-717X-7-218.

Investigation of the change in marker geometry during respiration motion: a preliminary study for dynamic-multi-leaf real-time tumor tracking.

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  • 1Graduate School of Health Sciences, Hokkaido University, Sapporo, Japan.

Abstract

BACKGROUND:

The use of stereotactic body radiotherapy (SBRT) is rapidly increasing. Presently, the most accurate method uses fiducial markers implanted near the tumor. A shortcoming of this method is that the beams turn off during the majority of the respiratory cycle, resulting in a prolonged treatment time. Recent advances in collimation technology have enabled continuous irradiation to a moving tumor. However, the lung is a dynamic organ characterized by inhalation exhalation cycles, during which marker/tumor geometry may change (i.e., misalignment), resulting in under-dosing to the tumor.

FINDINGS:

Eight patients with lung cancer who were candidates for stereotactic radiotherapy were examined with 4D high-resolution CT. As a marker surrogate, virtual bronchoscopy using the pulmonary artery (VBPA) was conducted. To detect possible marker/tumor misalignment during the respiration cycle, the distance between the peripheral bronchus, where a marker could be implanted, and the center of gravity of a tumor were calculated for each respiratory phase. When the respiration cycle was divided into 10 phases, the median value was significantly larger for the 30%-70% respiratory phases compared to that for the 10% respiratory phase (P<0.05, Mann-Whitney U-test).

CONCLUSIONS:

These results demonstrate that physiological aspect must be considered when continuous tumor tracking is applied to a moving tumor. To minimize an "additional" internal target volume (ITV) margin, a marker should be placed approximately 2.5 cm from the tumor.

PMID:
23249681
[PubMed - indexed for MEDLINE]
PMCID:
PMC3552716
Free PMC Article
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