Association of Fiducial Marker Position with TargetVolume in Stereotactic Lung Irradiation: A Cross-Sectional Study
H Akasaka1*, K Mizonobe1, Y Oki1, K Uehara1, S Tamura2, Y Munetomo2, A Harada1, M Nakayama3, H Kawaguchi4, H Mayahara1, (1) Division of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, JP, (2) Division of Radiological Technology, Kobe Minimally Invasive Cancer Center, Kobe, JP, (3) Division of Radiation Therapy, Kita-Harima Medical Center, Kobe, JP, (4) Department of Radiology, Kobe Minimally Invasive Cancer Center, Kobe, JP
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PO-GePV-T-392 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: CyberKnife is the most advanced form of stereotactic body radiotherapy (SBRT) and uses a robotic arm to deliver highly focused beams of radiation. Before lung tumors undergo treatment with SBRT, the internal target volume (ITV) is created based on fiducial marker fusion using four-dimensional computed tomography (CT) images. It is important to minimize the ITV to reduce undesirable irradiation to normal lung tissues and side effects after SBRT. However, the ITV may increase if there is a change in the positional relationship between the fiducial marker and tumor. In this study, the relationship between the fiducial marker position and ITV was investigated to minimize the target volume for escape the unnecessary irradiation of normal lung tissue.
Methods: Between April 2015 and September 2021, 230 lung cancer patients who received a fiducial marker for SBRT were retrospectively reviewed. The distance of the fiducial marker to the gross tumor volume (GTV) in the expiratory (dex) and inspiratory (d¬in) CT, and the value of ITV/GTVex were investigated.
Results: There was no significant difference in ddiff and ITV/GTVex between the lower, upper and middle lobes for dex <10 mm. On the other hand, the ddiff and ITV/GTVex value was larger for lower lobe than for upper lobe for dex ≥10 mm (p<0.05). Furthermore, for all lung regions, the ddiff and ITV/GTVex value were larger for dex ≥10 mm than for dex <10 mm (p<0.05).
Conclusion: The ITV increased significantly when dex was ≥10 mm for all lung regions, and the ITV increase tended to be greater in the lower lung lobe. These findings can be useful for physicians, radiation technologists, and medical physicists to decrease the possibility of adverse events after SBRT.
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