Program Information
Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) for Stereotactic Body Radiation Therapy (SBRT) in Early Stage Lung Cancer
I Ahmad1 , R Yah2 , K Quinn1 , A Seebach1 , H Wang1*, (1) OSF Saint Anthony Medical Center, Rockford, IL, (2) University of Illinois College of Medicine at Rockford, Rockford, IL
Presentations
SU-E-T-338 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: This study evaluates the dosimetric differences using volumetric modulated arc therapy (VMAT) in patients previously treated with intensity modulated radiation therapy IMRT for stereotactic body radiotherapy (SBRT) in early stage lung cancer.
Methods: We evaluated 9 consecutive medically inoperable lung cancer patients at the start of the SBRT program who were treated with IMRT from November 2010 to October 2011. These patients were treated using 6 MV energy. The 9 cases were then re-planned with VMAT performed with arc therapy using 6 MV flattening filter free (FFF) energy with the same organs at risk (OARS) constraints. Data collected for the treatment plans included target coverage, beam on time, dose to OARS and gamma pass rate.
Results: Five patients were T1N0 and four patients were T2N0 with all tumors less than 5 cm. The average GTV was 13.02 cm3 (0.83-40.87) and average PTV was 44.65 cm3 (14.06-118.08). The IMRT plans had a mean of 7.2 angles (6-9) and 5.4 minutes (3.6-11.1) per plan. The VMAT plans had a mean of 2.8 arcs (2-3) and 4.0 minutes (2.2-6.0) per plan. VMAT had slightly more target coverage than IMRT with average increase in D95 of 2.68% (1.24-5.73) and D99 of 3.65% (0.88-8.77). VMAT produced lower doses to all OARs. The largest reductions were in maximum doses to the spinal cord with an average reduction of 24.1%, esophagus with an average reduction of 22.1%, and lung with an average reduction in the V20 of 16.3% The mean gamma pass rate was 99.8% (99.2-100) at 3 mm and 3% for VMAT with comparable values for IMRT.
Conclusion: These findings suggest that using VMAT for SBRT in early stage lung cancer is superior to IMRT in terms of dose coverage, OAR dose and a lower treatment delivery time with a similar gamma pass rate.
Contact Email: