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Effect of Exactrac 6D Correction On Dose for SRT Patients with IR Body Markers

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B Durga Prasad

B Durga Prasad1*, A Yarramma2, P Reddy3, K Krishna Murthy4, R Reddy5, A Ananda Giri Babu6, K Karunakaran7, S Lingampally8, (1) Krishna Institute Of Medical Sciences, Secunderabad, Andhra Pradesh, (2) Jawaharlal Nehru Technological University, Hyderabad, ,(3) Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh, (4) Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh, (5) Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh, (6) Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh, (7) ,,,(8) Krishna Institute of Medical Sciences, Secunderabad, Andhra Pradesh

SU-E-J-51 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To study the 6D correction efficacy on dose to the target due to infrared(IR) body marker localization for stereotactic radiotherapy(SRT) patients

Methods:
Commercially available laboratory skull phantom, made of plastic is used in this study.It is filled with physiotherapy wax and a provision is made to insert CC13 ion-chamber(0.13cc). The dose at a point in skull phantom is measured by CC13 ion-chamber.An ordinary thermoplastic mould is prepared for skull phantom and 5 infrared body markers are placed at different places for localization as shown in figA. CT scan of the phantom is obtained using Siemens PET-CT scanner with and without ion-chamber. Treatment Planning is done on images which is without ion chamber .In the absence of ion chamber to fill the cavity a wax insert is inserted during the CT scan. 3mm slice thickness are obtained and imported to Eclipse treatment planning system(TPS) for contouring and planning.
Treatment plans of 3D CRT/IMRT are planned in Eclipse on skull phantom images with isocenter placed at the chamber sensitive volume.The plan is exported to Exactrac imaging system for localization and verification. After setup of skull phantom imaging is done with exactrac stereoscopic imaging system and the 6D shifts(Vertical,logitudenal,lateral,yaw,pitch,roll) are applied. The focus to skin distance(FSD) is noted-Table1.The radiation dose is delivered in Varian Novalis Tx.The charge collected /dose in CC13 ion chamber is noted from the DOSE1 electrometer-Table2.The planned FSD and dose are noted from TPS.

Results:
The mean difference between planned and measured FSD and Dose are 0.55cm and 2.7% respectively. The mean SD of FSD and Dose are 0.383 and 1.58% respectively.

Conclusion:
Even though Exactrac-6D couch shifts introduce change in FSD by 1-1.5cm the dose difference is within the range of 3% and is reasonable to treat frame less SRT treatments with IR body markers with ordinary mask.



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