2330 - Comparative Study of HEDOS and EDIC for Predicting 2-Year Survival in Locally Advanced NSCLC Patients Undergoing Radiotherapy

Purpose/Objective(s): Lymphopenia is a recognized adverse effect of radiotherapy (RT) in non-small cell lung cancer (NSCLC) patients, potentially impacting survival [1,2]. This study aimed to quantify the radiation dose received by circulating immune cells during RT using EDIC [3] and HEDOS [4], and to evaluate their relationship with 2-year Overall Survival (OS2).

Materials/Methods: This multicenter retrospective study included 312 locally advanced stage III NSCLC patients treated with curative RT alone (6%) or in combination with chemotherapy (CH) (24% sequential and 51% concomitant CHRT) and immunotherapy (33%). Patients received Tomotherapy (24%) and VMAT (53%) between 2010 and 2022, with prescription doses ranging between 55 Gy and 66 Gy. The cohort was composed of 57% stage IIIA and 43% stage IIIB patients. An automated contouring system was used for thoracic structures. We calculated EDIC using the mean dose to the heart, lungs, and integral body dose. The DVH of circulating blood (bDVH) in HEDOS was based on aorta, pulmonary artery, right and left heart, superior and inferior vena cava, lungs, bronchus, liver, pancreas, esophagus and stomach, and tumor DVHs. We compared both methods in terms of their association with 2-year OS, aiming also to validate literature-based findings on EDIC [2].

Results: With a median follow-up of 27 months, the 2-year overall survival (OS) rate was 42.6%. The median EDIC value was 3.55 Gy (range: 2.9–4.5 Gy), while the median HEDOS mean dose was 3.56 Gy (range: 2.9–4.4 Gy). We developed a dose-response model based on EDIC and validated the NTCP model proposed in [3]. Table 1 reports the statistical parameters for both models. Consistent with previous studies [3], we identified two distinct regions where a 1 Gy increase in EDIC had different impacts on survival. Specifically:

• For patients with EDIC < 5 Gy (including 69% of patients with PTV(T+N)<400 cc and 62% with stage IIIA disease), the risk increase was 4.6%/Gy.
• For patients with EDIC > 5 Gy (including 31% of patients with PTV(T+N)<400 cc and 62% with stage IIIB disease), the risk increase was significantly higher at 13.8%/Gy.

Additionally, bDVH analysis did not identify any significant dose-related variables distinguishing survivors from non-survivors.

Conclusion: Although HEDOS should provide a more accurate estimation of the dose to lymphocytes, our results align with previous literature findings identifying dose-response relationship for EDIC and overall survival.

Abstract 2330 - Table 1