Program Information
Single Isocenter Volumetric Modulated Arc Therapy (VMAT) With Or Without Field Overlap in the Treatment of Left Sided Breast and Regional Lymphatic Tissue: Impact On Surrounding OAR Doses
O Algan , S Hossain*, G Lee , S Ahmad , University of Oklahoma Health Sciences Center, Oklahoma City, OK
Presentations
SU-E-T-701 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To investigate the impact of field overlap on dosimetric outcomes for patients receiving radiation therapy to the whole breast as well as the supraclavicular and internal mammary nodal regions.
Methods:Seven patients with left sided breast cancer were evaluated on this IRB approved study. Four 200° partial arcs were used to optimize single isocenter VMAT plans using 2 different techniques: Technique 1 utilized treatment plans with no field overlap (NFOL) and 30 or 330 degree collimation. Technique 2 utilized 2cm field overlap (FOL) and 30 degree collimation. A single physician contoured all PTV and contralateral breast volumes. The same PTV and OAR volumes were used for both treatment planning techniques. The prescription dose was 46Gy delivered in 23 fractions with a minimum of 95% of the volume receiving 95% of the dose. A two-sided paired t-test was used to compare evaluated dosimetric parameters.
Results:The mean PTV volume was 923cc (range 589-1218cc). In general, use of FOL resulted in a reduction (though not statistically significant, unless otherwise stated) in OAR dosimetric parameters when compared to NFOL. For left lung, mean dose was 14.3 vs. 13.6Gy, the V20Gy was 23.4% vs. 20.8%, and V30Gy was 10.8% vs. 7.1% (p < 0.01), for NFOL and FOL, respectively. Similarly, for total lung, mean dose was 9.2 vs. 8.8Gy, V20Gy was 11.2% vs. 9.9%, and V30Gy was 5.1 vs. 3.4% (p < 0.01), for heart, mean dose was 4.9 vs. 4.6Gy, V5Gy was 29.7 vs. 27.9%, and the V10Gy was 4.7 vs. 4.0%. Right breast was least impacted with the use of FOL: mean dose 2.6Gy vs. 2.6Gy, D2% of 9.0Gy vs. 9.4Gy (p = 0.5).
Conclusion:Use of a 2cm FOL with VMAT treatment plans resulted in reduced doses to the lung and heart with minimal increase in right breast dose.
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