Dosimetric superiority of deep inspiration breath hold-proton beam therapy for cardiac metastasis.

The purpose of this case report is to compare the dosimetric disparities between photon radiotherapy and intensity-modulated proton therapy (IMPT) with or without deep inspiration breath hold (DIBH) for cardiac tumors. We present a case involving a 66-year-old female with cardiac metastasis from thymic carcinoma. A total dose of 50Gy/50Gy(RBE) in 25 fractions was administered to the cardiac metastases. Two simulation CT scans were obtained during free breath (FB) and DIBH. Dose distribution to target and organs at risk(OARs) was compared between intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) and IMPT. All of the 6 plans satisfied treatment planning goals. The coronary artery (CA) Dmean (mean dose) was 28.32 Gy for IMRT-DIBH, 42.66 Gy for IMRT-FB, 26.44 Gy for VMAT-DIBH, 40.85 Gy for VMAT-FB, 27.71 Gy for IMPT-DIBH, and 39.51 Gy for IMPT-FB. The heart V50 (volume receiving ≥50 Gy) was 3.90 Gy for IMRT-DIBH, 6.71 Gy for IMRT-FB, 4.80 Gy for VMAT-DIBH, 6.63 Gy for VMAT-FB, 0.99 Gy for IMPT-DIBH, and 6.67 Gy for IMPT-FB, respectively. DIBH resulted in dose reductions in all OARs, particularly the heart and CA, compared to FB in all 3 planning techniques (IMRT, VMAT, and IMPT). Similarly, compared with IMRT or VMAT, IMPT reduced radiation doses to most OARs, including the heart and CA, in both FB and DIBH. DIBH-IMPT demonstrated superior dose coverage and OARs sparing in this thymic carcinoma patient with cardiac metastasis. Given the anticipated reduction in toxicities, IMPT with DIBH is preferred for cardiac tumors. The potential for broader application of IMPT with DIBH in clinical practice is currently being evaluated, and further studies are needed.