Radiation and Cancer Physics

PD 12 - Physics 6 - Poster Discussion - Adaptive Planning/Delivery and Motion

1099 - Intrafraction Residual Error of Image-Guided Dibh Liver-SBRT: An Estimation By Ultrasound-Based Tracking Correlated With Diaphragm Position in CBCT

Tuesday, October 23
2:45 PM - 2:51 PM
Location: Room 217 C/D

Intrafraction Residual Error of Image-Guided Dibh Liver-SBRT: An Estimation By Ultrasound-Based Tracking Correlated With Diaphragm Position in CBCT
L. Vogel1, D. S. K. Sihono1, C. Weiß2, F. Lohr3, F. Stieler1, H. Wertz1, S. von Swietochowski1, A. O. Simeonova-Chergou1, F. Wenz1, M. Blessing1, and J. Boda-Heggemann1; 1Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany, 2Department of Clinical Statistics, Biomathematics, Information Processing, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany, 3Struttura Complessa di Radioterapia, Dipartimento die Oncologia, Az. Ospedaliero-Universitaria di Modena, Modena, Italy

Purpose/Objective(s): Craniocaudal motion during image-guided abdominal SBRT can be reduced by computer-controlled deep-inspiratory-breath-hold (DIBH). However, a residual error can occur in the DIBH-phases which can only be detected with intrafractional real-time-monitoring. We assessed the residual error of DIBH and compared residual motion of tracking-target structures during DIBH detected by ultrasound (US). US data were compared with residual motion of the diaphragm-dome (DD) detected in the kV-CBCT-projections.

Materials/Methods: During SBRT in DIBH, intrafractional US-based tracking was performed with an experimental US-system simultaneously to BH-only-kV-CBCT acquisition. A total of 706 breathholds during SBRT-treatments of metastatic lesions (liver, spleen, adrenal) of various primaries were registered in 13 patients. Residual motion of the tracking target was documented with US during each breath-hold. Motion of the DD was determined by comparison to a scan of a static reference phantom taking the individual geometrical setting at a given projection angle into account. Residual motion data detected by US was correlated to that of the diaphragm (kV-CBCT-projection).

Results: US-based tracking could be performed in all cases and was well tolerated by all patients. Additional time for daily US-based setup required 8+/-4min. 385 DIBHs of 706 could be analysed. In 59% of all DIBHs, residual motion was below 2mm. In 36%, residual motion of 2-5mm and in 4% of 5-8mm was observed. Only 1% of all DIBHs and 0.16% of all datapoints revealed a residual error of >8mm during DIBH. For DIBHs with a residual motion over 2mm, 137 of 156 CBCT-to-US curves had a paralell residual motion and showed a statistical correlation.

Conclusion: Soft-tissue tracking with ultrasound is a fast real-time method without additional radiation exposure. Computer-controlled-DIBH has a residual error of <5mm in >95% which is in line with the published intrafractional DIBH-precision. Ultrasound is a necessary technique to avoid larger intrafractional deviations reliably by stopping the beam at an US-defined threshold.
Table 1. DIBH analysed by magnitude of residual error and % of correlating data. *No correlation analysis for DIBHs with a residual error of <2mm
Residual motion during breath-hold Breath-hold (n) US vs. DD PCC >=0.5 US vs. DD PCC <0.5
<2mm 229 (59%) -* -*
2-5mm 137 (36%) 124 (91%) 13 (9%)
5-8mm 15 (4%) 12 (80%) 3 (20%)
>8mm 4 (1%) 2 (50%) 2 (50%)

Author Disclosure: L. Vogel: None. D. Sihono: None. F. Lohr: Honoraria; Elekta AB. F. Stieler: Honoraria; Elekta AB. H. Wertz: Honoraria; Elekta AB. S. von Swietochowski: None. A.O. Simeonova-Chergou: None. F. Wenz: Research Grant; Zeiss, Elekta AB. Honoraria; Elekta AB, Zeiss. M. Blessing: Research Grant; German Government. J. Boda-Heggemann: Honoraria; Elekta AB.

Lena Vogel, BS

Disclosure:
No relationships to disclose.

Presentation(s):

Send Email for Lena Vogel


Assets

1099 - Intrafraction Residual Error of Image-Guided Dibh Liver-SBRT: An Estimation By Ultrasound-Based Tracking Correlated With Diaphragm Position in CBCT



Attendees who have favorited this

Please enter your access key

The asset you are trying to access is locked. Please enter your access key to unlock.

Send Email for Intrafraction Residual Error of Image-Guided Dibh Liver-SBRT: An Estimation By Ultrasound-Based Tracking Correlated With Diaphragm Position in CBCT