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Combination of Volumetric Modulated Arc Therapy (VMAT) and Partially Wide Tangents (PWT) for Improved Sparing of the Ipsilateral Lung and Heart Compared to VMAT Or PWT Alone

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V Dumane

V Dumane1*, Y Lo2 , S Green3 , (1) THE MOUNT SINAI MEDICAL CENTER, New York, NY, (2) Mount Sinai Medical Center, New York, NY, (3) Mount Sinai Hospital, New York, New York


SU-I-GPD-T-386 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To show that a combination of VMAT and PWT can provide optimal target coverage while sparing the ipsilateral lung and heart while neither technique on its own is able to provide a clinically viable plan, with respect to the ability to meet the V20Gy constraint of the ipsilateral lung.

Methods: One left and one right-sided case requiring breast/chestwall and regional nodal irradiation (RNI) including the internal mammary nodes (IMNs) was first planned with PWT using 6MV or a combination of 6MV+16MV photons in Eclipse V 13.6. Each case was re-planned with VMAT alone using 6MV and then using a combination of VMAT for the superior and PWT for the inferior portion of the target volume without compromising coverage. The junction/isocenter was placed 1.5-2 cm superior to the heart.

Results: For the left-sided case, the ipsilateral lung V20Gy for the combined plan was 24.4%, while using PWT alone, it was 42.2%. The combined plan result was comparable to that of VMAT alone at 22.8%. However, the fomer was preferred to VMAT because of a lower mean heart dose (MHD) at 2.6Gy versus 7.9Gy with the latter. For the right-sided case, the ipsilateral lung V20Gy was 30% for both combined and VMAT plans. For PWT, it was 51.3%. However, since the MHD in the combined plan was 0.6Gy, it was preferred over the VMAT plan for which the MHD was raised to 5Gy. Coverage to the breast/chestwall and nodes was comparable in all plans.

Conclusion: When the ipsilateral lung V20Gy < 35% is unable to be met with 3D conformal planning, unlike VMAT alone, a combination of VMAT and 3D can help meet this constraint without increasing dose to other critical structures especially the heart.

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