3488 - Clinical Considerations of Splenic Dose Constraints to Mitigate Radiation-Induced Lymphopenia
Presenter(s)
Y. Ma1,2, J. Qian1,2, and L. Zhang1,2; 1Center of PRaG therapy, The Second Affiliated Hospital of Soochow University, Suzhou, China, 2Center for Cancer Diagnosis and Treatment, The Second Af?liated Hospital of Soochow University, Suzhou, China
Purpose/Objective(s): There is no consensus on the spleen dose-volume threshold for lymphopenia. Our previous results showed a correlation between them, but the threshold has not been determined. Therefore, we investigated the dynamics of lymphocyte depletion and recovery during and after radiotherapy (RT), identified the spleen dose threshold, and examined how these factors affect the prognosis of patients.
Materials/Methods: Absolute lymphocyte counts (ALC) of gastric cancer patients were obtained before, during, and 120 days after RT. Grade 4 (G4) lymphopenia was defined as an ALC nadir < 0.2 × 109/L. The status of lymphocyte recovery was estimated by lymphocyte recovery index (LRI). LRI < cut-off was regarded as insufficient recovery. Splenic dosimetric parameters were collected to identify their impacts on predicting G4 lymphopenia by logistic analysis. Cox analysis was conducted to evaluate the prognostic significance of lymphocyte decline and recovery status.
Results: 159 patients were enrolled. The median of ALC (× 109/L) at baseline and week1-6 during RT was 1.4, 0.8, 0.5, 0.4, 0.3, 0.25 and 0.2 respectively. The median of ALC decreased by 85.71% after RT. The incidence of G4 and G1-3 lymphopenia was 30.2% and 69.8%. There were 12.6% of patients whose ALC had recovered at 120 days after RT, while the remaining 87.4% were still accompanied by varying degrees of lymphopenia. Cox multivariable analysis revealed that pTNM stage and LRI were independent prognostic factor for overall survival (OS), pTNM stage and ?ALC were independent prognostic factor for disease free survival (DFS). Splenic Dmean and V5 were related to G4 lymphopenia and eventually V5 affected prognosis. Constraining the spleen V5 to < 180.6cm3 and < 272.2cm3 may potentially reduce the incidence of G4 lymphopenia and further decrease the risk of death by 60.9%.
Conclusion: Lymphocyte decline and insufficient recovery during and after RT induced the worse prognosis for patients. Therefore, attention should be paid not only to preventing lymphocyte depletion during RT but also to improving lymphocyte recovery after RT. Constraining the spleen V5 is a key approach.