Inclusion Criteria:

1. Age ≥ 18 years old;
2. Pathologically confirmed thoracic solid malignant tumors;
3. Local recurrence or failure of prior standard therapies (including surgery, radiotherapy, systemic therapy, etc.), deemed unsuitable for or lacking standard treatment options following Multidisciplinary Team (MDT) evaluation, and planned to receive heavy-ion radiotherapy；
4. Maximum diameter of the target lesion ≥ 4.5 cm;
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2;
6. Life expectancy ≥ 6 months;
7. Signed informed consent.

Exclusion Criteria:

1. Tumors adjacent to critical organs at risk (OARs) where dose constraints cannot be met through plan optimization;
2. Prior radiotherapy to the intended treatment area, where re-irradiation would fail to meet normal tissue dose constraints;
3. Presence of recognized standard treatment options for which the patient is eligible (e.g., radical surgery, concurrent chemoradiotherapy, or standard systemic therapy);
4. Primary hematologic malignancies;
5. Uncontrolled severe comorbidities, including active infections, unstable cardiovascular or cerebrovascular diseases, and severe hepatic or renal insufficiency;
6. Other diseases deemed by the investigator to compromise patient safety;
7. Psychiatric disorders or cognitive impairment that would prevent cooperation with treatment;
8. Pregnancy or lactation.