Comparison of butterfly volumetric modulated arc therapy to full arc with or without deep inspiration breath hold for the treatment of mediastinal lymphoma.

Purpose: Radiotherapy is an effective treatment for mediastinal lymphoma but induces late effects including cardiac toxicity and secondary breast and lung cancer. Therefore reducing the dose to these organs is vital. We compared full arc volumetric modulated arc therapy (F-VMAT) against limited angle 'Butterfly' VMAT (B-VMAT) on free breathing (FB) and deep inspiration breath-hold (DIBH) computed tomography scans. The aim was to assess the benefits of B-VMAT over F-VMAT and to establish if the addition of DIBH results is a cumulative benefit.

Materials And Methods: F-VMAT and B-VMAT plans were calculated for 20 consecutive patients (15 females) with mediastinal lymphoma on both FB and DIBH scans. The planning target volume V was kept comparable between all plans while reducing organ doses as much as possible.

Results: B-VMAT significantly reduced low lung doses (V), while F-VMAT was better for higher lung doses (V). DIBH further improved lung doses for both types of plans. DIBH B-VMAT produced the lowest mean lung dose. With FB, heart doses were slightly higher for B-VMAT but the maximum difference was small (0.8% for V) and only statistically significant for V. The mean heart dose increased by only 0.1 Gy. The addition of DIBH however significantly reduced heart doses. While DIBH F-VMAT had the lowest heart doses, the difference was small compared with DIBH B-VMAT. B-VMAT significantly reduced breast V while DIBH reduced the V.

Conclusion: B-VMAT and DIBH are both effective in reducing organ doses and the dosimetric benefit is additive for some parameters and complementary for others.