A planning study conducted by a group of collective researchers in Europe. For six left sided breast cancer patients, treatment plans were made using non-coplanar volumetric modulated arc photon therapy (VMAT) or pencil beam scanning intensity modulated proton therapy (IMPT) to compare supine (S) and prone-crawl (P) position for irradiaiton to whole breast (WB) and loco-regional lymph node regions, including the internal mammary chain (LN_IM). This study reported that the average mean heart doses for S or P VMAT were 5.6 or 4.3 Gy, and 1.02 or 1.08 GyRBE for IMPT (p < 0.001 for IMPT versus VMAT).

The average mean lung doses for S or P VMAT were 5.91 or 2.90 Gy and 1.56 or 1.09 GyRBE for IMPT. In high-risk patients, average (range) thirty-year mortality rates from radiotherapy-related cardiac injury and lung cancer were estimated at 6.8% or 3.8% for S or P VMAT, and 1.6% or 1.2% for S or P IMPT, respectively. This study indicated that radiation-related mortality risk could outweigh the ~8% disease-specific survival benefit of WB + LN_IM radiotherapy for S VMAT but not P VMAT. IMPT carries the lowest radiation-related mortality risks.