3020 - Timing and Predictors of Grade 3 Lymphopenia in Lung Cancer Patients Undergoing Proton Chemoradiotherapy

05:00pm - 06:00pm PT

Hall F

Screen: 1

POSTER

Presenter(s)

Sreenija Yarlagadda, MD - Miami Cancer Institute, Miami, FL

E. Y. Y. Akdemir¹, R. Kotecha^1,2, S. Gurdikyan¹, R. Herrera¹, Z. Fellows¹, A. Gutierrez^1,3, A. Wroe^1,4, F. Albrecht⁵, M. P. Mehta^1,4, R. H. Press¹, and S. Yarlagadda¹; ¹Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, ²Miami Cancer Institute, Baptist Health South Florida, Miami, FL, ³Florida International University, Herbert Wertheim College of Medicine, Miami, FL, ⁴Herbert Wertheim College of Medicine, Florida International University, Miami, FL, ⁵Department of Medical Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL

Purpose/Objective(s):

Treatment-induced lymphopenia is a significant concern for lung cancer patients, especially so as immune checkpoint therapy (ICT) become standard of care. Proton therapy (PT) limits total integral dose to circulating blood volume compared to conventional radiotherapy and may be associated with less hematologic toxicity. This study aimed to investigate the prevalence, timing and associated variables for grade 3 lymphopenia (G3L), in lung cancer patients receiving definitive proton chemoradiotherapy (PT-CRT).

Materials/Methods:

We performed a single-institution retrospective analysis of locally advanced or recurrent lung cancer patients to evaluate the timing of and factors related to decline in absolute lymphocyte counts (ALCs) during PT-CRT. All patients were treated with conventionally fractionated PT-CRT. Lymphopenia was graded using CTCAE version 5.0. We analyzed the time to G3L and its association with patient related (age, sex, smoking history, pre-treatment ALC), disease-related (histology, time from initial diagnosis), and treatment-related (use of induction chemotherapy [ICT], type of concurrent CT) factors, with a specific emphasis of dosimetric variables (planning target volume [PTV], mean lung dose [MLD]). Additionally, EDIC (effective radiation dose to the immune cells) was calculated and integrated into the analysis of end-of-treatment (EOT) G3L. Factors related to EOT G3L were evaluated in univariate analysis, while time-to-event analyses was conducted for G3L occurring during treatment (DT) using Kaplan-Meier estimates and Cox regression models

Results:

47 patients (51.1% Hispanic) with a median age of 76 years (range, 54-88) and most frequently with adenocarcinoma histology (55.3%) were evaluated. The median target volume was 292.3 cc (range, 17.8-887.2 cc). Paclitaxel/carboplatin (80.9%) was the most common concurrent chemotherapy and 46.8% of patients received at least one cycle of ICT preceding CRT. A median dose of 60 GyE (range, 60-70 GyE) was delivered in 30 fractions (range, 30-35). Median time to G3L was of 31 days (range, 6-41 days). In cox regression model, only PTV was associated with shorter time to G3L, p<0.013. At the EOT, 31.9% of patients (n=15/47) had G3L. Median EDIC was 2.7 Gy (range, 0.5-4.9 Gy). Among the factors analyzed, only EDIC and PTV were significantly associated with G3L. Notably, EDIC demonstrated a stronger association (p=0.003) compared to PTV (p=0.005) in univariate analysis.

Conclusion:

This study reveals that treatment-induced lymphopenia is prevalent among elderly lung cancer patients undergoing definitive PT-CRT. Based on findings, larger PTV significantly shorten the time to G3L DT. EDIC emerges as the most significant predictor for G3L even more important than PTV, suggesting a more intricate relationship between radiation dose and immune cell dynamics within the body, and could be a variable that could be modulated during the treatment planning process to decrease anticipated lymphopenia rates.