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Rotation Corrected Setup Margin Calculation for Stereotactic Body Radiation Therapy in Dual Imaging Environment

B Sarkar1*,T Ganesh2 ,A Manikandan 3 ,S Krishnankutty4 , L Chitral5 , A Munshi6 , BK Mohanti7 , (1) AMRI Cancer Centre, Kolkata, ,(2)Apollo protan centre ,Chennai, ,(3) Manipal Hospitals, Gurugram, ,(4) Manipal Hospitals, New Delhi, ,(5) Manipal Hospitals Dwarka, New Delhi, DL, (6) Manipal Hospitals, New Delhi, ,(7) Manipal Hospitals, New Delhi,


(Tuesday, 7/16/2019) 9:00 AM - 10:00 AM

Room: Pins Room | Hall 2

Purpose: Aim of this article is to demonstrate a mathematically rigorous technique to calculate the rotational positional error corrected linear setup margin for lung stereotactic body radiotherapy .

Methods: Total of 22 medically inoperable lung cancer patients, having tumour diameter less than 5 cm was considered in this study. Two on-board imaging systems were used, 4DCBCT (primary) and stereoscopic Exactrack (secondary). Pre-table position correction (PreTPC) both CBCT and Exactrck images were acquired and patient position was corrected using a 6-dimensional motion enable robotic couch on basis of primary imaging. Post table position correction (PostTPC) another 4DCBCT + Excatrack images were acquired to get the residual shift. Further a series of Excactrack images were acquired to identify the intrafraction positional error. Rotational positional errors (θ°, Φ°, Ψ°) were reduced in-terms of equivalent translational vectors (X, Y, Z) and further the margins for PreTPC and PostTPC were calculated for imaging systems.

Results: Total 82 sessions of 4DCBCT for PreTPC and PostTPC were analysed; 189 sessions of Exactrack images were analysed for PreTPC and residual-intrafraction setup margin. PreTPC CBCT mean±SD shifts in lateral, longitudinal, vertical, roll, pitch, yaw directions were -1.9±6.8mm, 1.3±5.7mm, -0.4±4.1mm, 0.9±1.23°, -0.5±1.35°, and 0.64±1.28° respectively. Same values for Exactrack were 0.3±5.4mm, 1.4±4.5mm, -1.0±4.2°, 0.3±1.3, 0.1±1.5°, and 0.63±1.4°. PostTPC residual shifts were -0.5±1.6mm, -0.3±1.5mm, -0.5±1.6mm, 0.15±0.43°, 0.11±1.1°, and 0.2±0.8° for CBCT; residual-intrafraction shift for Exactrack were -0.04±0.2mm, 0.1±0.3mm, -0.1±0.4mm, 0.17±1.05°, 0.08±1.31°, and -0.05±0.65° respectively. PostTPC linear margin in X,Y,Z directions without rotational correction were 5.0mm, 3.1mm, 4.4mm and with rotational correction 4.4mm, 2.8mm and 5.5mm. PostTPC Exactrack (residual + intrafraction) margins without rotational correction was 6.6mm, 9.6mm, 6.2mm and w/o rot was 6.3mm, 10.3mm and 6.2mm.

Conclusion: Present technique describe mathematically most rigorous strategy to calculate the setup margin in stereotactic body irradiation of lung by incorporating the rotational setup error.


Stereotactic Radiosurgery, Dual-energy Imaging, Setup Errors


Not Applicable / None Entered.

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