Minimizing Long-Term Toxicities for Patients with Primary Mediastinal B-Cell Lymphoma Undergoing Modern Radiotherapy: Results from a Monocentric Biophysical Risk Evaluation

<b>Introduction:</b> Primary mediastinal B-cell lymphoma (PMBCL) is a rare form of aggressive B-cell lymphoma with a predominant onset in young patients. The minimization of potential (late) side effects is of cardinal interest for these patients. An anticipation of the individual risk profile is desirable to counsel the patient on the putative impact of radiotherapy (RT). <b>Methods:</b> RT plans for a cohort of 25 patients with PMBCL were prospectively designed. One plan with two parallel- opposing fields (APPA) and another with volume-modulated arc therapy (VMAT) technique with 40 Gy in 2 Gy fractions each. Normal The normal tissue complication probability (NTCP) was calculated using the Lyman--Kutcher--Burman model for heart, lung and oesophageal toxicity. <b>Results:</b> APPA planning resulted in lower median doses (Dmedian) for the heart and lungs, whereas all other dose metrics for heart, lungs and esophagus were lower in VMAT planning. A significant difference in the mean NTCPs when comparing the APPA to VMAT plans was seen for increased cardiac mortality, pneumonitis and esophagitis. PTV size correlated with increased cardiac mortality and esophagitis in both plan variations and with pneumonitis for VMAT plans. Dmean, Dmedian, and V20Gy correlated with the risk for pneumonitis, and Dmean, Dmedian, and V1% with the risk for esophagitis in both variants. <b>Conclusions:</b> We showed decreased risk of different NTCPs for VMAT and APPA planning for thoracic toxicities. The use of an IMRT technique like VMAT showed advantages for several DVH metrics in organs at risk and should therefore be recommended for radiation treatment of PMBCL.