ESTRO meets Asia 2024 - Abstract Book

S399

RTT – Treatment planning, OAR and target definitions

ESTRO meets Asia 2024

Center for Cancer Diagnosis and Treatment, The Second Affiliated Hospital of Soochow University, Suzhou, China

Purpose/Objective:

Lymphocytes, known for their high sensitivity to radiation, are vital for the body's anti-tumor mechanisms. Radiation-induced lymphopenia has been linked to worse prognosis across various cancer types. Despite being the largest secondary lymphoid organ, the spleen is not currently designated as an organ at risk in radiation therapy protocols. This study seeks to provide a reference for splenic dose-volume constraints in clinical radiotherapy practice.

Material/Methods:

To exclude the influence of tumor factors on the radiation dose to the spleen and given the spleen's anatomical proximity to the target area for gastric cancer radiotherapy, we selected patients with R0 gastrectomy who underwent adjuvant radiotherapy. A retrospective group of 96 individuals with locally advanced gastric cancer who had undergone postoperative chemoradiotherapy (CRT) between May 2010 and May 2017 was analyzed. Complete blood counts were collected before, during, and after CRT. We conducted a multiple stepwise regression analysis to establish a model for predicting the minimum absolute lymphocyte count (Min ALC) and to investigate potential associations between spleen dosimetric variables and Min ALC.

Results:

The median follow-up period was 60 months. The 5-year OS and DFS were 65.2% and 56.8%, respectively. The median values of pre-treatment ALC, Min ALC, and post-treatment ALC were 1.40 × 10 9 /L, 0.23 × 10 9 /L, and 0.28 × 10 9 /L. The median values of ALC decreased by 80% after postoperative CRT. Regression analysis confirmed that the primary tumor location, number of fractions, and spleen V5 were significant predictors of Min ALC during radiation therapy (R 2 = 0.298, F = 13.043; p < 0.001). Change in ALC (ΔALC) was identified as an independent predictor of both OS and DFS.

Conclusion:

Spleen V5 independently predicts Min ALC, and higher maximum dose of the spleen are linked to an elevated risk of severe lymphopenia. Additionally, ΔALC can function as a prognostic indicator for adjuvant radiotherapy in gastric cancer patients. Consequently, we propose limiting spleen V5 in the design of radiotherapy treatments.

Keywords: Dose limitation, Spleen radiation, Lymphopenia

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