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Positioning Accuracy for SBRT Lung Patients Determined by Post-Treatment Cone-Beam CT Imaging

T Reynolds1 , M Ozer1*, (1) MN Oncology, St Paul, MN


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Stereotactic body radiation therapy (SBRT) is the accurate delivery of a high dose of radiation to an extracranial target within the body in 2-5 fractions, while sparing the surrounding normal tissue. Since few high-dose ablative fractions are delivered to a target volume (TV) with small margins, the penalties of a geometric miss are severe. This work presents the results of the post treatment (PT) delivery set-up data collected using LINAC IX cone-beam CT (CBCT) imaging with 3D-couch for SBRT patients and compares the PT CBCT 3D-shift magnitudes with the target margins.

Methods: A total of sixty-one lung cancer patients who underwent SBRT were considered for this study. All patients were positioned in a flat and reproducible position: supine with both arms above their head, immobilized by vacuum bag. 4DCT images were acquired at simulation to create the internal TV (ITV). The plans were created using Eclipse V13.7 to deliver 4800–7000 cGy in 3-10 fractions. PT CBCT images were acquired at initial treatment and matched to the planning CT scan using manual fusion option. PT CBCT shift magnitude was calculated for each patient and compared with the ITV-PTV margin.

Results: In total, 56% of the patient did not require any PT shifts. The maximum shift in one axis was 4 mm and was observed in 2 patients (3%). The remaining 26%, 8% and 7% patients had maximum shifts of 1 mm, 2 mm and 3 mm, respectively. The average 3D-shift magnitude of PT CBCT (±standard deviation) was 0.91±1.25 mm, ranging from 0 to 5 mm, which was significantly lower than average ITV-PTV margin of 5.41±1.02 mm, ranging from 3 to 8 mm.

Conclusion: This study demonstrates PT CBCT corrections for SBRT lung patient. 5 mm ITV-PTV margin was adequate to address the intrafraction motion of TV for SBRT lung patients.


Lung, Localization, Linear Accelerator


TH- External beam- photons: extracranial stereotactic/SBRT

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