ESTRO 2025 - Abstract Book

S1360

Clinical - Lung

ESTRO 2025

2521

Mini-Oral Omitting clinical target volume of primary tumor versus standard irradiation for LS-SCLC: preliminary report of a randomized, non-inferior trial Shuohan Zheng 1,2 , Qiwen Li 1,2 , Nan Bi 3 , Lin Cai 1,2 , Ming Chen 1,2 1 Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, China. 2 United Laboratory of Frontier Radiotherapy Technology of Sun Yat-sen University & Chinese Academy of Sciences Ion Medical Technology Co., Ltd, Sun Yat-sen University, Guangzhou, China. 3 Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Beijing, China Purpose/Objective: The margin of subclinical microscopic malignant lesions of small cell lung cancer is unclear. We found that a margin of only 1.4 mm could cover 95% of the microscopic disease extension in patients who received 2-cycle neoadjuvant chemotherapy in our previous study. We aimed to assess the feasibility of omitting the clinical target volume (CTV) in patients with limited-stage small cell lung cancer (LS-SCLC) after neoadjuvant chemotherapy. Material/Methods: This open-label, randomized, non-inferior trial was performed at 5 public hospitals in China. Chemotherapy consisted of 4-6 cycles of etoposide and cisplatin or carboplatin. After 2-4 cycles of etoposide and cisplatin or carboplatin, patients without disease progression were randomly assigned to receive thoracic radiotherapy to either omit CTV of the primary tumor or include CTV with a margin of 8mm as the study arm (PGTV group) or control (PCTV group). Elective nodal irradiation was omitted for both groups. Forty-five Gy/30 Fx/15 days or 45 Gy/15 Fx/15 days thoracic radiotherapy was administered concurrently with chemotherapy. Prophylactic cranial irradiation was administered to patients with complete remission or partial response. Survival outcomes and dosimetric characteristics of regions of interesting were compared. Results: Thirty-four and 38 patients were randomly assigned to the PGTV group and PCTV group, respectively. Four patients (11.8%) experienced local recurrence in the PGTV group (3 [8.8%] had in-field failures, 1 [3.0%] had marginal failures), while 5 patients (13.2%) experienced local recurrence in the PCTV group (all had in-field failures). The median local recurrence-free survival was similar in the PGTV group (13.4 months) and PCTV group (12.5 months) (P=0.83). The median progression-free survival was 13.4 months in the PGTV group, compared to 9.0 months in the PCTV group (P=0.29). Two patients (5.3%) in the PCTV group had grade 3 pneumonitis, which was not observed in the PGTV group. The medians of mean lung dose were 10.9 Gy in the PGTV group and 9.5 Gy in the PCTV group. The median of normal lung tissue receiving 20 Gy or more (V20 Gy) was 19.1% versus 18.3%, and the median of V30 Gy was 10.7% versus 12.1%. The medians of mean heart doses of the two groups were 8.7 Gy and 9.2 Gy, respectively. Conclusion: Compared with the implementation of CTV, omission of CTV did not increase local recurrence but might decrease radiotherapy toxicity. Further investigation is warranted.

Keywords: limited-stage small cell lung cancer