Program Information

Quantification of Dosimetric Accuracy of Respiratory Gated Stereotactic Body Radiation Therapy

Rajesh Thiyagarajan¹*, N Arunai Nambiraj² , Sujit Nath Sinha³ , Ashokkumar Sigamani² , Girigesh Yadav⁴ , Kothanda Raman⁴ , S Vikraman¹ , S Maragathaveni¹ , N Dhivya¹ , Tejinder Kataria¹ ,(1) Medanta The Medicity, Gurgaon, Haryana, (2) VIT University, Vellore, Tamil Nadu, (3) Nayati Healathcare and Research Pvt Ltd, Mathura, Uttar pradesh, (4) Rajiv Gandhi Cancer Institute & Research Centre, Gurgaon, Haryana,

Presentations

SU-E-T-651 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:
To quantify the dosimetric accuracy of respiratory gated stereotactic body radiation therapy delivery using dynamic thorax phantom.

Methods:
Three patients with mobile target (2 lung, 1liver) were chosen. Retrospective 4DCT image sets were acquired for using Varian RPM system. An in-house MATLAB program was designed for MIP, MinIP and AvgIP generation. ITV was contoured on MIP image set for lung patients and on MinIP for liver patient. Dynamic IMRT plans were generated on selected phase bin image set in Eclipse (v10.0) planning system. CIRS dynamic thorax phantom was used to perform the dosimetric quality assurance. Patient breathing pattern file from RPM system was converted to phantom compatible file by an in-house MATLAB program. This respiratory pattern fed to the CIRS dynamic thorax phantom. 4DCT image set was acquired for this phantom using patient breathing pattern. Verification plans were generated using patient gating window and delivered on the phantom. Measurements were carried out using with ion chamber and EBT2 film. Exposed films were analyzed and evaluated in FilmQA software.

Results:
The stability of gated output in comparison with un-gated output was within 0.5%. The Ion chamber measured and TPS calculated dose compared for all the patients. The difference observed was 0.45%, -0.52% and -0.54 for Patient 1, Patient2 and Patient 3 respectively.Gamma value evaluated from EBT film shows pass rates from 92.41% to 99.93% for 3% dose difference and 3mm distance to agreement criteria.

Conclusion:
Dosimetric accuracy of respiratory gated SBRT delivery for lung and liver was dosimetrically acceptable. The Ion chamber measured dose was within 0.203±0.5659% of the expected dose. Gamma pass rates were within 96.63±3.84% of the expected dose.

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