Impact of Clinical Factors and RT-induced Lymphopenia on Risk of Disease Recurrence
Sixteen of 54 (30%) patients developed a recurrence at an average of 30.2 months after diagnosis. As expected, patients with M+ disease had a significantly increased risk of disease recurrence (log-rank p=0.0004; Cox p=0.001). Table 2 demonstrates the impact of clinical factors and RT-induced lymphopenia on the risk of disease recurrence. There was a higher risk of disease recurrence (lower RFS) in patients with grade 3 or lymphopenia during weeks 4 (log-rank p=0.015; Cox p=0.03) and 5 (log-rank p=0.0009; Cox p=0.004) of RT (Fig. 3 ). When considering the RFS of patients with ALC above or below the median during weeks 4 and 5 of RT, there was a significant difference during week 5 (log-rank p=0.0026; Cox p=0.002) (Fig. 4B ) but not during week 4 (log-rank p=0.123; Cox p=0.22) (Fig. 4A ). These results all held true when adjusted for risk group (Table 2 ). No correlation was found between risk of tumor recurrence and early lymphopenia (RT weeks 0-3) either when measured as CTCAE grade or as median ALC. Additionally, there was not a statistically significant difference between RFS in patients treated with proton compared to photon RT (Cox p=0.09) (Supplemental Fig. 1 ) or based on sex (Cox p=0.810).