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 (Î¸Â°, Î¦Â°, Î¨Â°) 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 meanÂ±SD shifts in lateral, longitudinal, vertical, roll, pitch, yaw directions were -1.9Â±6.8mm, 1.3Â±5.7mm, -0.4Â±4.1mm, 0.9Â±1.23Â°, -0.5Â±1.35Â°, and 0.64Â±1.28Â° respectively. Same values for Exactrack were 0.3Â±5.4mm, 1.4Â±4.5mm, -1.0Â±4.2Â°, 0.3Â±1.3, 0.1Â±1.5Â°, and 0.63Â±1.4Â°. PostTPC residual shifts were -0.5Â±1.6mm, -0.3Â±1.5mm, -0.5Â±1.6mm, 0.15Â±0.43Â°, 0.11Â±1.1Â°, and 0.2Â±0.8Â° for CBCT; residual-intrafraction shift for Exactrack were -0.04Â±0.2mm, 0.1Â±0.3mm, -0.1Â±0.4mm, 0.17Â±1.05Â°, 0.08Â±1.31Â°, and -0.05Â±0.65Â° 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.
Not Applicable / None Entered.