Effect of Deep Inspiration Breath Hold on Normal Tissue Sparing With Intensity Modulated Radiation Therapy Versus Proton Therapy for Mediastinal Lymphoma.PURPOSE
 Intensity modulated radiation therapy delivered with deep-inspiration breath hold (IMRT-BH) provides favorable normal tissue dosimetric profiles when treating patients with mediastinal lymphoma.  However, it is unclear if IMRT-BH plans are comparable to free breathing (FB) proton plans.  We performed a retrospective, comparative dosimetric study between IMRT-BH and FB passive scatter proton therapy (P-FB) or intensity modulated proton therapy (IMPT-FB).  Hypothesizing that BH would provide superior normal tissue sparing when added to proton therapy, we also compared plans to passive scatter BH (P-BH).


 For 15 patients who received involved-site RT with "butterfly" IMRT-BH, 3 additional proton plans (P-FB, IMPT-FB, P-BH) were optimized to deliver 30.6 Gy/Gy relative biological effectiveness.  Dosimetric variables (mean dose, V30, V25, V15, and V5) for organs at risk (OARs) were calculated and compared using nonparametric Wilcoxon signed-rank tests.


 Of 57 studied OAR parameters, IMRT-BH plans were comparable in 37 (65%) parameters with P-FB plans, 32 (56%) of IMPT-FB parameters, and 30 (53%) of P-BH parameters.  Mean doses and V5 of the total lung and heart were the highest with IMRT-BH; however, IMRT-BH resulted in comparable coronary and superior lung V30 relative to proton plans.  The addition of BH with proton therapy resulted in the greatest lung sparing, with mean lung dose reductions of 11% to 38%.


 CONCLUSIONS
 The use of BH with IMRT reduces the disparity in OAR doses with equivalence achieved in nearly two-thirds of OAR metrics compared with P-FB and 50% compared with IMPT-BH.  Because each modality exhibited unique benefits, personalization of modality selection is recommended. 
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