Plasma contains a variety of metabolites, among which sphingolipids, including ceramide, sphingosine, and sphingosine-1-phosphate, serve as important intracellular second messengers and are involved in various cellular signaling pathways, such as apoptosis. We hypothesize that plasma sphingolipid levels may be associated with the efficacy of radiotherapy for liver cancer. This study will utilize LC-MS/MS technology for qualitative and quantitative analysis of plasma sphingolipids in liver cancer patients undergoing radiotherapy. Clinical data related to patient prognosis will also be collected to investigate the correlation between plasma sphingolipid levels and the therapeutic efficacy of liver cancer radiotherapy. The aim is to establish the clinical diagnostic significance of plasma sphingolipid levels in predicting the efficacy of liver cancer radiotherapy, providing new insights to enhance the effectiveness of radiotherapy in liver cancer treatment.

Liver cancer is one of the most common malignant tumors worldwide, posing a significant challenge to public health. Radiotherapy plays a crucial role in controlling local recurrence and metastasis in hepatocellular carcinoma (HCC) and improving patient survival. Advanced radiotherapy techniques such as Intensity-Modulated Radiation Therapy (IMRT) and Stereotactic Body Radiation Therapy (SBRT) have enhanced tumor dose precision, increasing local control rates while minimizing radiation-induced side effects. However, current methods for assessing radiotherapy efficacy, including CT, MRI, and PET-CT, require extended post-treatment observation periods, delaying clinical decision-making. Additionally, radiotherapy can lead to radiation-induced liver disease (RILD) and other adverse effects such as radiation enteritis and bone marrow suppression. Therefore, identifying early predictive biomarkers for radiotherapy response and toxicity is critical for optimizing treatment strategies.

Sphingolipids, including ceramide (CER), sphingosine (SPH), and sphingosine-1-phosphate (S1P), are essential cellular signaling molecules involved in apoptosis, proliferation, and inflammation. Studies have shown that radiotherapy influences sphingolipid metabolism by altering enzyme activity, thereby affecting the balance of CER, SPH, and S1P-key regulators of tumor cell apoptosis. With advancements in lipidomics, the role of sphingolipid metabolism in radiation sensitivity has become an area of growing interest. Sphingolipid levels have been correlated with radiotherapy sensitivity in various cancers, making them potential prognostic biomarkers and therapeutic targets.

This study is designed as a single-center, prospective observational study with a two-year follow-up period, enrolling 260 primary liver cancer patients receiving radiotherapy. Plasma samples will be collected before, during, and after radiotherapy for qualitative and quantitative analysis of sphingolipid metabolites using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). Clinical imaging and laboratory data related to treatment response and adverse events will also be collected. Patients will be classified according to the mRECIST 1.1 criteria into complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD) groups for further correlation analysis.

The primary objective is to investigate the relationship between plasma sphingolipid levels and radiotherapy efficacy by analyzing overall survival (OS), objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), disease-free survival (DFS), and time to progression (TTP). The secondary objective is to explore the association between sphingolipid levels and radiation-induced toxicity, including RILD, radiation enteritis, and bone marrow suppression, to assess their potential as predictive biomarkers for treatment-related complications.

Patients will be followed at 1, 2, 6, 12, 18, 24, 36, and 48 months post-radiotherapy. The study does not involve any interventional treatment beyond standard clinical care, and patient management decisions will remain at the discretion of treating physicians. This research aims to provide new insights into the clinical significance of sphingolipid metabolism in predicting radiotherapy outcomes and toxicity in liver cancer, potentially improving personalized radiotherapy strategies.

Inclusion Criteria:

• Patients voluntarily signed the informed consent form.
• Aged between 18 and 80 years.
• Clinically diagnosed with primary liver cancer according to the latest treatment guidelines.
• Determined by the treating physician to require radiotherapy.
• Expected survival time of more than 3 months.

Exclusion Criteria:

• Patients who discontinued radiotherapy or did not complete the planned treatment.
• Presence of malignancies from other origins.
• Severe metabolic diseases such as uncontrolled diabetes, significant obesity, or fatty liver disease.
• Uncontrolled comorbidities, such as severe cardiovascular or pulmonary diseases, that may affect treatment or study outcomes.

This study will enroll adult patients aged 18 to 80 years who have been clinically diagnosed with primary liver cancer according to the latest treatment guidelines. Eligible participants must be determined by their treating physicians to require radiotherapy and have an expected survival time of more than three months. Patients with malignancies of other origins, severe uncontrolled metabolic disorders, or comorbidities that could interfere with treatment outcomes will be excluded.

Due to ethical and privacy concerns, the individual participant data (IPD) will not be shared. All data will be anonymized and stored securely to protect participants' privacy, as per institutional guidelines. Sharing IPD may pose a risk of re-identification or misuse of personal information, which could potentially violate the confidentiality agreement with the participants. Therefore, the data will remain confidential and only be used for the specific purposes outlined in the study protocol.