肝细胞癌放疗安全性指标探索：一项真实世界研究（英文）

Exploration of safety indicators for radiotherapy in hepatocellular carcinoma: A real-world study

摘要

目的 肝细胞癌(hepatocellular carcinoma，HCC)是原发性肝癌中最常见的病理类型，其发病率和病死率均较高。体外放射治疗(external beam radiation therapy，EBRT)是HCC患者常用的局部治疗手段之一，可用于不同分期HCC患者的治疗。在精准放疗时代，针对HCC放疗的安全性，目前尚缺乏统一的评估指标。癌旁正常肝组织在经高剂量放射线照射后，可能失去正常肝功能。本研究将剩余功能性肝体积(remnant functional liver volume，RFLV)定义为经一定剂量照射后仍有正常功能的肝组织体积，接受x剂量单位照射后仍有功能的剩余肝体积(residual remnant functional liver volume after x Gy irradiation，rRFLV_x)定义为接受小于一定照射剂量(x Gy)的肝绝对体积，并基于真实世界数据探索rRFLV_x作为放疗安全性剂量指标的性能，同时探索EBRT用于HCC的安全性及疗效。 方法 前瞻性收集并选取2015年至2023年期间就诊于中南大学湘雅三医院的肝病灶接受立体定向放射治疗(stereotactic body radiotherapy，SBRT)或调强放射治疗(intensity-modulated radiation therapy，IMRT)的HCC患者113例，其中SBRT治疗组35例，IMRT治疗组78例。统计放射性肝病(radiation-induced liver diseases，RILDs)的发生情况，并采用二元逻辑回归Hosmer-Lemeshow检验分析与RILDs发生可能相关的剂量学参数，主要包括平均肝脏剂量(mean liver dose，MLD)、剩余肝脏体积(remnant liver volume，RLV)、标准肝体积(standard liver volume，SLV)及rRFLV_x等。同时观察放疗相关肝炎病毒再激活及其他放疗相关毒性。采用无进展生存期(progression-free survival，PFS)和总生存期(overall survival，OS)评估分析EBRT治疗HCC的疗效。 结果 纳入分析的113例HCC患者中，共12例患者诊断为RILDs，其中IMRT治疗组11例，SBRT治疗组仅1例。二元逻辑回归Hosmer-Lemeshow检验结果提示rRFLV₂₅、rRFLV₂₀、rRFLV₁₅、rRFLV₂₅/SLV、rRFLV₂₀/SLV及rRFLV₁₅/SLV与IMRT治疗组HCC患者RILDs的发生显著相关(均P<0.05)，而MLD及RLV与RILDs的发生无相关性(P=0.88)。1例未规律抗肝炎病毒治疗的患者被诊断为放疗相关HBV临床再激活，还有1例患者被诊断为免疫治疗相关HBV临床再激活。IMRT治疗组和SBRT治疗组患者中位PFS分别为5.6个月和16.4个月，最佳局控率分别为98.6%和100.0%。IMRT治疗组与SBRT治疗组患者中位OS分别为12.2个月和33.5个月。IMRT治疗组患者6个月、1年和2年OS率分别为77.1%、52.6%和18.6%。SBRT治疗组患者1年、2年、3年、4年和5年OS率分别为86.1%、61.7%、39.2%、25.7%和18.3%。 结论 EBRT用于治疗不同阶段HCC患者是安全且有效的。相较于MLD及RLV，rRFLV_x及rRFLV_x/SLV用于评估IMRT治疗后RILDs的发生可能更可靠。对于有肝炎史的患者，在放疗期间同步予以抗病毒治疗是相对安全的，但需要密切监测患者血清病毒载量。对于放疗联合靶向及免疫治疗的疗效及安全性，需要进一步研究探索。

Abstract

Objective Hepatocellular carcinoma (HCC) is the most common pathological subtype of primary liver cancer and is associated with high incidence and mortality. External beam radiation therapy (EBRT) is a widely used local treatment modality for HCC across different disease stages. In the era of precision radiotherapy, standardized safety evaluation indicators for HCC radiotherapy remain lacking. Normal liver tissue surrounding the tumor may lose hepatic function after high-dose irradiation. In this study, remnant functional liver volume (RFLV) was defined as the volume of liver tissue that retains normal function after irradiation, and the residual remnant functional liver volume after x Gy irradiation (rRFLV_x) was defined as the absolute liver volume receiving less than a given dose threshold (x Gy), and plans to explore the performance of rRFLV_x as a radiotherapy safety dose indicator based on real-world data, as well as to explore the safety and efficacy of EBRT in HCC. Methods A total of 113 HCC patients who received stereotactic body radiotherapy (a SBRT group, n=35) or intensity-modulated radiation therapy (a IMRT group, n=78) for liver lesions at the Third Xiangya Hospital of Central South University between 2015 and 2023 were prospectively collected and selected. The occurrence of radiation-induced liver diseases (RILDs) was recorded. Dosimetric parameters potentially associated with RILDs were analyzed using binary logistic regression with Hosmer-Lemeshow test, mainly including mean liver dose (MLD), remnant liver volume (RLV), standard liver volume (SLV), and rRFLV_x. Radiotherapy-related hepatitis virus reactivation and other radiotherapy-related toxicities were also observed. Progression-free survival (PFS) and overall survival (OS) were used to evaluate the efficacy of EBRT in HCC. Results Among the 113 HCC patients, 12 were diagnosed with RILDs, including 11 in the IMRT group and only 1 in the SBRT group. Binary logistic regression with Hosmer-Lemeshow test results suggested that rRFLV₂₅, rRFLV₂₀, rRFLV₁₅, rRFLV₂₅/SLV, rRFLV₂₀/SLV, and rRFLV₁₅/SLV were significantly associated with the occurrence of RILDs in HCC patients in the IMRT group (all P<0.05), while MLD and RLV were not associated with the occurrence of RILDs (P=0.88). One patient without regular anti-hepatitis viral treatment was diagnosed with radiotherapy-related HBV clinical reactivation, and one patient was diagnosed with immunotherapy-related HBV clinical reactivation. The median PFS was 5.6 months in the IMRT group and 16.4 months in the SBRT group, and the best local control rates were 98.6% and 100.0%, respectively. The median OS was 12.2 months in the IMRT group and 33.5 months in the SBRT group. The 6-month, 1-year, and 2-year OS rates in the IMRT group were 77.1%, 52.6%, and 18.6%, respectively. The 1-year, 2-year, 3-year, 4-year, and 5-year OS rates in the SBRT group were 86.1%, 61.7%, 39.2%, 25.7%, and 18.3%, respectively. Conclusion EBRT is safe and effective for HCC patients at different stages. Compared with MLD and RLV, rRFLV_x and rRFLV_x/SLV may be more reliable for evaluating the occurrence of RILDs after IMRT treatment. For patients with hepatitis background, concurrent antiviral therapy during radiotherapy is relatively safe, but serum viral load should be closely monitored. Further research is needed to explore the efficacy and safety of radiotherapy combined with targeted and immunotherapy.

Graphical abstract

关键词

肝细胞癌 / 放射治疗 / 安全性 / 真实世界研究 / 剩余功能性肝体积

Key words

hepatocellular carcinoma / radiotherapy / safety / real-world study / remnant functional liver volume

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the second leading cause of cancer-related death^[1-2]. More than 80% of HCCs develop in fibrotic or cirrhotic livers, which are mainly caused by viral infections, i.e., hepatitis B virus (HBV) and hepatitis C virus (HCV)^[3]. Since patients with cirrhosis are usually accompanied by varying degrees of liver insufficiency, it is necessary to minimize the damage to normal liver tissue in the treatment of HCC^[4-5].

External beam radiation therapy (EBRT) is a flexible local treatment, allowing for treatment in a broad range of indications, including large tumors, multifocal disease, the presence of tumor vascular invasion, as a bridge therapy to liver transplantation, and as postoperative treatment for patients with positive margins or narrow margins^[6-13]. However, radiotherapy may cause varying degrees of liver insufficiency and even hepatic decompensation, especially in patients with advanced cirrhosis^[14]. The mean normal liver volume (NLV) and the mean liver dose (MLD) were often used as reference indicators when formulating radiotherapy plans^[15-16]. However, in the era of precision radiotherapy, the concept of MLD may not be accurate. Similarly, using NLV as an indicator, which is defined as liver volume minus tumor volume, roughly assumes that other liver tissues, except tumors, still have normal functionality after irradiation. Studies^[17-18] have confirmed through pathology that liver tissue in high-dose areas and relatively high-dose areas after radiotherapy showed liquefaction necrosis and vascular damage, respectively. These necrotic and damaged liver tissues and tumor tissues do not have normal liver functions. NLV overestimates the size of the ‘normal’ liver volume, which may lead to an underestimation of toxicity after radiotherapy. Therefore, this study attempts to propose the concept of remnant functional liver volume (RFLV). The remnant functional liver volume receiving less than x Gy of irradiation (rRFLV_x) was defined as the absolute liver volume receiving less than a certain irradiation dose (x Gy). This part of the liver below x Gy still has normal functions after irradiation, so it may be relatively safe to perform radiotherapy when this volume requirement is met. In fact, due to individual differences, the minimum required functional liver volume may vary among liver cancer patients. For instance, male and female patients, as well as obese and underweight patients, may theoretically require different minimum functional liver volumes. Standard liver volume (SLV) refers to the liver volume in a normal individual, usually estimated based on factors such as height, weight, and body surface area^{[17, 19-20]}. Standardizing each patient’s residual rRFLV using SLV before performing statistical analysis may help to stabilize the results^[21].

Moreover, international guidelines have endorsed targeted immunocombination therapy as the new standard of first-line treatment for advanced HCC^[22-23]. However, the efficacy and safety of targeted immunocombination combined with EBRT require further exploration^[24].

This study aims to analyze the efficacy and toxicity of HCC patients who received EBRT in an actual clinical setting, and initially explore the feasibility of the idea of rRFLV.

1 Subjects and methods

1.1 Ethics statement

This study was conducted according to the ethics guidelines in the Declaration of Helsinki. This is to certify that the research design and methods follow the requirements of related regulations and procedures as well as the ethical principles. The co-authors had access to the study data and reviewed and approved the final manuscript. The Institutional Review Board has approved the research to be conducted (registration number: 2018-S223).

1.2 Patients

Between March 2015 and July 2023, HCC patients who would receive intensity-modulated radiation therapy (IMRT) or stereotactic body radiotherapy (SBRT) for liver lesions in the Third Xiangya Hospital of Central South University were prospectively enrolled. Patients have given informed consent and signed the consent form. A total of 120 patients were followed up. Inclusion criteria: 1) Meeting the diagnosis criteria of HCC; 2) Child-Pugh score class A or B without encephalopathy; 3) age between 18-85 years old. Exclusion criteria: 1) History of upper abdominal radiotherapy or liver transplantation; 2) failed to complete radiotherapy as scheduled; 3) previous cancer treatment-related toxicities that did not return to baseline or grade 0-1 (except for hair loss and peripheral neuropathy). Finally, a total of 113 patients were included in the analysis.

1.3 Treatment administration and outcome measures

The flowchart of the study is shown in Figure 1.

1.3.1 Liver topical treatment

Patients were immobilized in a supine position, free quiet breathing, by a thermoplastic body mask fixation system (Klarity, Guangzhou, China), with their arms overhead, simulating a high-resolution thin slice (1.2 mm) CT scans. Immediately after the start of the loversol injection, CT imaging was performed during arterial dominant (20-30 seconds), portal venous (55-65 seconds), and delayed (120-130 seconds) phases. Before formulating a radiotherapy plan, we used a simulation calibration machine to measure the maximum movement distance (D) of the lower lung boundary during the patient’s respiratory movement when taking deep breaths. The target volumes and organs at risk (OAR) were contoured using the Eclipse version 11.0 (Varian, USA) treatment planning system. The radiotherapy plan was contoured by the same irradiation oncologist specializing in radiation treatment of liver carcinoma with more than 15 years of radiotherapy experience. Patients were treated with a TrueBeam Linear Accelerator (Varian, USA). The gross tumor volume (GTV) was determined as the tumor volume that showed enhancement in the arterial phase of dynamic CT and magnetic resonance imaging (MRI), including macrovascular invasion (MVI). For patients with postoperative narrow surgical margins, the GTV tumor bed (GTVtb) was expanded 1 cm from the surgical margin. A 5.0 mm three-dimensional expansion was applied to the GTV to create the clinical tumor volume (CTV). The planning target volume (PTV) was a three-dimensional extension of 5 mm on CTV. In addition, a 1/2 D extension distance was added in the direction of the head and feet. The prescription dose of SBRT was 40.0-48.0 Gy in 5-6 fractions (7.0 or 8.0 Gy per fraction) for the planning target volume, and the prescription dose of IMRT was 39.0-60.0 Gy in 15-28 fractions (1.8-3.0 Gy per fraction).

1.3.2 Systemic therapy

Including systemic chemotherapy, immune checkpoint inhibitor (ICI), tyrosine kinase inhibitor (TKI), and supportive care.

1.3.3 Data collection

Created a standardized data form to collect all relevant information from the beginning of follow-up. Including: Clinical characteristics; laboratory variables such as alpha-fetoprotein (AFP), alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase (ALP), Child-Pugh class^[25], the China Liver Cancer (CNLC) staging^[26], and the Barcelona Clinic Liver Cancer (BCLC) staging^[27]; details of treatment and follow-up.

1.3.4 Efficacy evaluation

Patients undergo imaging review 1 month after radiotherapy and every 3 months thereafter. Radiologic responses were defined using the mRECIST version 1.1 guidelines^[28]. The treatment response was classified as complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD). The progression-free survival (PFS) was defined as the time from initiation of radiotherapy to intrahepatic or systemic PD. The overall survival (OS) was defined as the time from radiotherapy to death or loss to follow-up. The local control (LC) was defined as a lack of progression within the liver radiation field.

1.3.5 Toxicity assessment

Assess radiation-induced liver diseases (RILDs) based on follow-up data from the start to 3 months after radiotherapy. RILDs were manifested as: 1) Elevation of ALP level to at least twice the upper limit of normal (ULN); 2) elevation of transaminases to at least 5 times the ULN or pretreatment level; 3) a worsening of Child-Pugh score by 2 points. Diagnosis of RILDs must exclude tumor progression, viral, or drug-induced liver function damage^[29].

HBV reactivation is classified into virological reactivation and clinical reactivation. The virological reactivation: In HBsAg-positive patients, HBV-DNA levels increase by ≥10-fold from baseline, or change from undetectable (<10 U/mL) to detectable (>10 U/mL). In HBsAg-negative/anti-HBc-positive patients (occult infection), HBV-DNA becomes detectable (>10 U/mL). The clinical reactivation is defined as virological reactivation accompanied by an elevation of ALT to more than 3 times the upper limit of normal or baseline levels, and may be associated with jaundice, hepatic decompensation, or symptoms of acute hepatitis.

Other treatment-related toxicities were classified according to the CTCAE version 5.0^[30].

1.3.6 Dosimetric parameters

The remnant liver volume (RLV) was defined as the liver volume minus tumor volume. The D_mean was the average dose received by the liver that was not involved by the tumor. A schematic diagram of RLV and rRFLV is shown in Figure 2. The SLV was calculated with the Chengdu formula^[20]:

SLV=\mathrm{11.5}\times \mathrm{b}\mathrm{o}\mathrm{d}\mathrm{y}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}+\mathrm{334.0}.

1.4 Statistical analysis

The statistical analysis was performed using SPSS 23.0 software.Categorical variables were presented as counts and percentages, while continuous variables were presented as medians and ranges. The Kaplan-Meier method was used to construct survival curves and determine the median OS and PFS. Survival rate comparisons between groups were performed using the Log-rank test. Comparisons between patients with RILDs and without RILDs for dosimetric parameters were conducted by binary logistic regression analysis Hosmer-Lemeshow test^[31], it should be explained that the result of the Hosmer-Lemeshow test was different from the conventional statistical analysis, when the test statistics do not reach the significant level (P>0.05), it means that the adaptability of the overall model is good, and if the P<0.05 reaches the significant level, it means that the adaptability of the regression model is not ideal.To evaluate the discrimination ability of the Logistic regression model, a receiver operating characteristic (ROC) curve was plotted, and the area under the curve (AUC) was calculated. It is considered statistically significant when P<0.05.

2 Results

2.1 Baseline characteristics of patients

The baseline data of the enrolled patients are shown in Table 1. Patients were predominantly male (n=96, 84.96%). The HBV was the most common etiology (n=98, 86.73%) of chronic liver disease, among them, 37 patients had HBV-DNA≥2 000 U/mL before radiotherapy. In addition, 5 patients had HCV, 3 of them had HCV-RNA>25 U/mL before treatment, and they were supplemented with anti-HCV therapy before starting radiotherapy. Most of the patients (n=101, 89.38%) had a baseline Child-Pugh class of A.

SBRT was more commonly used for radical radiotherapy in patients, while IMRT is used in some patients with a large number of lesions, larger tumor sizes, and proximity of the lesions to the hollow organs. As a result, the majority of patients who received SBRT had CNLC stage Ⅰ-Ⅱ (27/35), while most patients in the IMRT group had CNLC stage Ⅲ (62/78). The median GTV size of patients in the SBRT group and the IMRT group was 32.89 cm³ and 317.74 cm³, respectively. And the median NLV of patients in the SBRT group and the IMRT group was 1 219.70 (824.56-1 972.23) cm³ and 1 131.08 (629.10-2 010.87) cm³, respectively. In the IMRT group, 3 patients (3.85%) had RLV<700 cm³, and all patients in the SBRT group had RLV>800 cm³. In the IMRT group, there were 18 patients (23.08%) with MLD>24 Gy. In the SBRT group, there were 11 (31.43%) and 6 (17.14%) patients with MLD>15 Gy and >18 Gy, respectively. Dosimetry data for patients treated with IMRT and SBRT are shown in Table 2.

2.2 Exploration of rRFLV_x

In the SBRT group, one patient was diagnosed with RILDs. The MLD of this patient was 11.66 Gy and the RLV was 1 273.78 cm³. In the IMRT group, 11 patients were diagnosed with RILDs. The baseline Child-Pugh scores of these 11 patients were grade A (n=10) and grade B7 (n=1). It was worth mentioning that only 1 out of 3 patients with RLV<700 cm³ and only 2 out of 18 patients with MLD>24 Gy developed RILDs in the IMRT group.

Binary logistic regression analysis Hosmer-Lemeshow test was further performed on factors that may affect the occurrence of RILDs in the IMRT group. The results showed that the rRFLV₂₅, rRFLV₂₀, rRFLV₁₅, rRFLV₂₅/SLV, rRFLV₂₀/SLV, and rRFLV₁₅/SLV were statistically significant in analysis (all P<0.05), while the rRFLV₃₀, rRFLV₃₀/SLV, RLV, and MLD were not statistically significant. The P-value of the Hosmer-Lemeshow test reaches 0.88, as shown in Table 3.

The calculated AUC value was 0.712 (Figure 3A). The calibration curve is shown in Figure 3B.

In addition, 6 patients also had an elevated Child-Pugh score or aminotransferase within 3 months after the end of EBRT (Table 4), which was considered to be related to drug therapy or disease progression.

2.3 Hepatitis virus reactivation

2.3.1 HBV reactivation

Before radiotherapy, 39 patients had serum HBV-DNA load>10 U/mL, of which 26 patients had> 2 000 U/mL. The vast majority of patients with serum HBV-DNA load>10 U/mL were combined with antiviral therapy. After radiotherapy, 24 patients had serum HBV-DNA load>10 U/mL, of which only 2 patients had>2 000 U/mL (Figure 4).

Two (3.51%) patients were diagnosed with HBV clinical reactivation, one was considered to be related to radiotherapy. This patient with HBV-DNA=3.96×10² U/mL before IMRT, without anti-HBV drugs. One month after radiotherapy, the patient’s transaminase was>7×ULN, and the serum HBV-DNA load increased to 6.8×10⁵ U/mL, which was evaluated as HBV reactivation (grade 3). Intravenous drugs were used to protect the liver, and entecavir was used for treatment. The serum HBV-DNA load dropped to 34.9 U/mL in 2 months, and transaminase returned to normal. Another patient who received IMRT had a baseline serum HBV-DNA load of 7.7×10⁵ U/mL, treated with entecavir. At the end of the IMRT, the serum HBV-DNA load was <10 U/mL. ICI was used after radiotherapy. One month later, the serum HBV-DNA load increased to 1.8×10² U/mL, accompanied by elevated transaminases (>3×ULN). This patient was considered a reactivation of HBV (grade 2) and was related to immunotherapy.

2.3.2 HCV reactivation

Among the 5 patients, 3 patients had serial HCV-RNA load >1×10⁶ U/mL before radiotherapy. Anti-hepatitis C drugs were used during and after radiotherapy. After treatment, 2 cases with serial HCV-RNA loads <25 U/mL, and 1 case with 9.7×10 U/mL. Two patients had serum HCV-RNA loads <25 U/mL before and after radiotherapy.

2.4 Other toxicities

No other grade 3 or higher radiation-related toxicities occurred in the SBRT group. In the IMRT group, 8 patients were diagnosed with upper gastrointestinal ulcer (grade 2). Other major toxicities included bone marrow suppression (n=2, grade 3), biliary tract infection (n=1, grade 2), and radiation pneumonitis (n=1, grade 3).

2.5 Efficacy analysis

2.5.1 PFS and OS

The median PFS for the IMRT group and the SBRT group were 5.6 (1.4-44.6) months and 16.4 (1.0-52.3) months, respectively. The 6- and 12-month actuarial PFS rates in the IMRT group were 46.41% and 20.60%, respectively. The 1-, 2-, and 3-year PFS rates in the SBRT group were 55.26%, 34.53%, and 25.90%, respectively. The median follow-up time for the IMRT group and the SBRT group was 11.4 (1.6-63.0) months and 27.1 (1.6-67.6) months, respectively (Figure 5A).

OS was achieved in 64 (82.05%) patients in the IMRT group and 20 (57.14%) patients in the SBRT group. The median OS of the IMRT and SBRT groups was 12.2 and 33.5 months, respectively. The 6-, 12-, and 24-month actuarial OS rates were 77.14%, 52.58%, and 18.64% in the IMRT group, respectively. The 1-, 2-, 3-, 4-, and 5-year actuarial OS rates were 86.05%, 61.65%, 39.19%, 25.71%, and 18.29% in the SBRT group, respectively (Figure 5B).

In the IMRT group: The median PFS for CNLC stage I-II and stage III were 11.3 and 4.4 months, respectively (Figure 5C); the median OS of CNLC stage I-II and stage III were 24.8 and 11.7 months, respectively (Figure 5D).

In the SBRT group: The median PFS for CNLC stage I, II, and III were 17.2, 11.3, and 48.1 months, respectively (Figure 5E); the median OS of CNLC stage I, II, and III were 42.0, 14.9, and 33.5 months, respectively (Figure 5F).

2.5.2 Treatment response

In the IMRT group, 51 patients were evaluated as PD. The reasons included: Intrahepatic recurrence outside radiation field (n=30), extrahepatic progression (n=17), simultaneous occurrence of intrahepatic outside radiation field and extrahepatic progression (n=3), and recurrence within radiation field (n=1). In the SBRT group, 19 patients developed PD, mainly due to simple intrahepatic recurrence outside the radiation field (n=15) or simultaneous distant metastasis (n=4).

Evaluation of the best response within the radiation field at 3 months after radiotherapy (the second radiographic review). In the IMRT group, 5 (7.04%) patients achieved CR, 64 (90.14%) patients achieved PR, 1 (1.41%) patient achieved SD, and 1 (1.41%) patient achieved PD. And in the SBRT group, 19 (54.29%) patients achieved CR, 15 (42.86%) patients achieved PR, and 1 (2.85%) patient achieved SD. The LC rate of the IMRT group and the SBRT group was 98.61% and 100.00%, respectively.

2.6 Systemic treatment and radiotherapy

For patients who received radiotherapy between 2015 to 2018 (n=44), most patients did not receive systemic treatment (n=32). Since 2019, the number of patients receiving TKI and ICI has gradually increased. And from 2021, TKI+ICI treatment became the main means of systemic treatment. Analysis showed that whether or not receiving TKI/ICI/TKI+ICI has no statistical significance on PFS and OS in the IMRT group and the SBRT group (Figure 6A).

The median PFS for patients with and without TKI/ICI/TKI+ICI was 9.3 and 14.1 months in the IMRT group, and was 16.4 and 17.2 months in the SBRT group, respectively (Figure 6B and 6C).

The median OS for patients with and without TKI/ICI/TKI+ICI was 10.3 and 13.7 months in the IMRT group, and was 33.5 and 34.1 months in the SBRT group, respectively (Figure 6D and 6E).

3 Discussion

EBRT is a common local treatment method for HCC patients at different stages and conditions^{[6, 9, 11]}. This study prospectively records the information of HCC patients who received EBRT for liver lesions from 2015 to 2023, and proposes that, in the era of precision radiotherapy, RFLV could be used as an indicator of the safety of IMRT for HCC by referring to the standards for surgical liver resection. However, in HCC patients treated with SBRT, the reference significance of RFLV for radiotherapy safety needs to be further studied.

Lyman-Kutcher-Burman normal tissue complication probability (NTCP) models were often used to calculate the probability of RILDs in previous literature. And the effective volume (Veff) was usually calculated by dose-volume histogram (DVH) and biological effective dose (BED)^{[15, 32]}. However, obtaining the results through complex calculations may be relatively cumbersome, and it is primarily used to guide the evaluation of dose fractionation rather than how much safe functional volume to retain. In addition, with the development of imaging technology, some specific techniques, such as hepatobiliary scintigraphy or Gd-EOB-DTPA-enhanced hepatic MRI, can also assess the functional liver reserve^[33-34]. However, the liver’s uptake of tracers or contrast agents may be affected by albumin or bilirubin levels, which may affect the evaluation of the functional liver reserve^[34].

The guidelines of the Chinese Society of Clinical Oncology (CSCO) and the American Society for Radiation Oncology (ASTRO) used NLV and MLD as reference indicators for the safety of EBRT for HCC^{[11, 35]}. In this study, though the MLD exceeded those recommended in the literature, only 2 patients developed non-classical RILD, and no other adverse events were observed. Previous studies have confirmed through pathology that radiation damage in liver tissue after receiving radiotherapy shows a zonal pattern: at the center of the radiation target was liquefaction necrosis, the second zone consisted of damaged, but non-necrotic, liver tissue. Finally, normal or near normal histologic liver architecture surrounded the region of liver damage^[17]. Therefore, functional liver volume may be more suitable than NLV for assessing the safety of RT. The biological rationale for rRFLV_x is rooted in hepatic functional heterogeneity and the gradient relationship between radiation dose and functional loss. Unlike pure dose or volume parameters, rRFLV_x innovatively integrates functional hepatic reserve with dose-volume effects, creating a composite metric that aligns with the clinical goal of “functional unit preservation”—maintaining sufficient functional hepatocytes for vital metabolic processes. From a translational perspective, rRFLV_x can be seamlessly integrated into existing radiotherapy planning systems: after accurate dose calculation, three-dimensional dose distributions are used to automatically contour rRFLV_x parameters, ultimately generating a functional preservation report during plan evaluation. Future research will explore more precise rRFLV thresholds through focal liver reaction (FLR), a specific post-radiation hepatic injury manifestation, enabling individualized, dynamic, and precise safety assessment for liver radiotherapy. Some studies^[15-16] have recommended that >700 cm³ of normal liver <15 Gy to ensure the safety of radiotherapy. But in fact, many Chinese HCC patients have an RLV <700 cm³ because of their concomitant hepatitis cirrhosis. Referring to this criterion, a significant proportion of HCC patients who may benefit from EBRT will be excluded. In fact, some of the patients in this study had NLV<700 cm³ and did not have RILD after EBRT.

Experiences gained from conventional liver resection have indicated that after an extended hepatectomy involving 70%-75% of the liver, the liver can still function well in non-cirrhotic patients^[36]. Analogous to the concept of surgery, we believe that in radiotherapy for HCC, when the RFLV/SLV meets a certain ratio, the patient’s normal liver function can be maintained without causing the occurrence of RILDs. The rationale for exploring rRFLV thresholds at 15-30 Gy increments stems from established clinical guidelines and histopathological evidence. Current SBRT guidelines for HCC recommend limiting the MLD ≤15 Gy in Child-Pugh A patients, representing a validated tolerance threshold. Additionally, a retrospective histopathological study^[17] demonstrated that liver regions receiving 30 Gy exhibited liquefactive necrosis and fibrosis with complete loss of functional hepatocytes. Through binary logistic regression analysis Hosmer-Lemeshow test, we found that rRFLV₂₅, rRFLV₂₀, rRFLV_15, and their respective ratios to SLV were statistically significant in the IMRT group. The SLV calculated from weight and height effectively minimizes the impact of body size differences on the original liver volume, thereby reducing the interference of this factor on the results. However, this method still has certain limitations: SLV is estimated based on the average values of normal individuals and does not account for potential liver lesions or functional changes in liver cancer patients. It is noteworthy that the odds ratio (OR) for the rRFLV₂₀ level was abnormally high [OR=566.69, 95% confidence interval (CI) 3.55 to 90 454.01], with an extremely wide CI, suggesting potential data sparsity or complete segregation at this level. The HL test P=0.88 only reflects good overall model calibration but cannot identify segregation at specific covariate levels. We analyzed that the possible reason why rRFLV₃₀ has no significant impact on whether RILDs occur is that liver tissue of 30 Gy and above may lose normal liver function after radiation exposure. A notable limitation of our study is the small SBRT subgroup (n=35) with only a single RILD event, which precluded robust statistical evaluation of rRFLV’s predictive value in this setting. However, under what irradiation dose liver cells can maintain normal function, and how much liver volume is required below this dose to maintain normal liver function in HCC patients, we will further explore these 2 questions through radiomics and deep learning methods in subsequent studies.

For patients with liver-confined or advanced HCC, the IMRT or SBRT could be considered, with choice of regimen based on tumor location, underlying liver function, and available technology^[11]. Many studies^[37-39] have confirmed that SBRT exhibits excellent LC and OS. IMRT was generally considered an incurable treatment modality for HCC patients in the past. HCC was relatively sensitive to RT. As found in this study and other previous literature^[40-42], the IMRT could also achieve a considerable LC rate.

While targeted therapy and immunotherapy remain the cornerstone of systemic treatment for advanced HCC with well-established efficacy—and their combination with locoregional therapies has shown improved outcomes, particularly in patients with portal vein tumor thrombosis—our study unexpectedly did not demonstrate significant survival benefits (OS or PFS) when these agents were combined with EBRT^{[24, 41]}. This negative finding warrants cautious interpretation in light of several layers of complexity. Firstly, selection bias inherent to real-world clinical practice may have contributed: patients with more advanced disease or a heavier tumor burden are more likely to receive systemic therapy, potentially diluting survival advantages. Secondly, most of our cohort had main portal vein invasion—a high-risk population routinely excluded from clinical trials—introducing additional confounding. Moreover, the interaction between EBRT and systemic therapies is not a simple additive process. External radiotherapy can modulate the tumor immune microenvironment, involving mechanisms such as the abscopal effect, immune-related reprogramming of the tumor microenvironment, and dose-fractionation―dependent immunomodulatory effects, all of which may influence treatment response in unpredictable ways^[24]. These multifaceted biological interactions further complicate interpretation of the observed outcomes. Taken together, these observations highlight the need for prospective validation using well-controlled study designs or methods such as propensity score matching to clarify the true therapeutic benefit of combining EBRT with targeted or immunotherapy.

It has often been reported that the reactivation of HBV is a well-recognized complication in infected HCC patients who undergo medical treatment. But convincing data that support routine use of preventive therapy against virus reactivation in EBRT for HCC are lacking. A multicenter study enrolled 133 HCC patients who were treated with SBRT or IMRT. Antiviral therapy was administered in the HCC patients who had an ALT>UNL and detectable levels of HBV-DNA. The HBV-DNA reactivation occurred in 17 (12.7%) patients after RT, antiviral group showed a lower incidence of HBV reactivation compared to the non-antiviral group (P<0.001)^[43]. In this study, only 1 patient (without antiviral therapy) experienced radiation-related HBV reactivation. These results suggest that RT may increase the risk of HBV reactivation, and preventive antiviral treatment can reduce this risk.

This study has several limitations. Firstly, as a single-center retrospective analysis, the sample size was limited with only 12 RILDs events, resulting in severely insufficient events per variable and risks of selection and information biases. Secondly, the SBRT subgroup comprised only 35 cases with a single RILDs event, precluding statistical evaluation of rRFLV’s predictive utility in this modality. Thirdly, while the RFLV dose thresholds (15-30 Gy) were based on guideline recommendations and histopathological evidence, the rationale for not systematically exploring other thresholds (e.g., 10 Gy or 35 Gy) was insufficiently elaborated. Fourthly, HBV reactivation analysis reported only incidence rates without multivariate assessment of viral load, Child-Pugh classification, and radiation dose associations. Fifthly, the targeted/immunotherapy benefit analysis was confounded by selection bias—advanced-stage patients were preferentially selected for systemic therapy, potentially diluting efficacy advantages; thus, negative results require cautious interpretation and do not imply treatment inefficacy. Sixthly, the aberrant Exp(B) value for rRFLV₂₀ (566.69) in Table 3 stemmed from complete separation due to small sample size rather than a true effect. Seventhly, conclusions regarding EBRT combined with targeted/immunotherapy warrant broader consideration: The radiotherapy-immunotherapy interaction is complex, and factors such as sequencing, dose fractionation, and PD-L1 expression may influence efficacy—unoptimized in this study, these findings should not be considered definitive. Eighth, although rRFLV represents an innovative concept, discussion of its biological plausibility (the interaction between functional hepatic reserve and dose-volume parameters) and clinical translation pathways lacks depth. In summary, this work constitutes preliminary exploration; conclusions require validation in prospective, multicenter large cohorts with refined designs incorporating equivalent dose in 2‑Gy fractions (EQD₂) standardization and stratification by hepatic function to establish clinically actionable rRFLV thresholds.

In conclusion, this real-world study demonstrated that EBRT for HCC is safe and effective. Compared with MLD, RFLV, and RFLV/SLV may be more reliable in assessing the safety of IMRT. For patients with a background of hepatitis, it is safe to give radiotherapy concurrently with antiviral therapy. The effectiveness and safety of radiotherapy combined with target and immune therapy deserve further exploration.

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基金资助

the National Natural Science Foundation(81872473)

the Chen Xiaoping Foundation for the Development of Science and Technology of Hubei Province(CXPJJH12000001-2020216)

the Wu Jieping Medical Foundation(320.6750.19094-30)

RIGHTS & PERMISSIONS

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