High-dose stereotactic body radiotherapy correlates increased local control and overall survival in patients with inoperable hepatocellular carcinoma
© Jang et al.; licensee BioMed Central Ltd. 2013
Received: 11 June 2013
Accepted: 23 October 2013
Published: 27 October 2013
Recent studies using stereotactic body radiotherapy (SBRT) for hepatocellular carcinoma (HCC) have reported high tumor response and local control. However, the optimal SBRT dose remains unknown, and it is still not clear whether a dose response relationship for local control (LC) and overall survival (OS) exist or not. We performed this study to determine whether a dose response relationship for LC and OS is observed in SBRT for inoperable HCC.
Between 2003 and 2011, 108 patients with HCC were treated with SBRT. All patients were unsuitable for surgery or local ablation and had incomplete response to transarterial chemoembolization. Eighty-two patients with a longest tumor diameter (LD) less than or equal to 7.0 cm who were treated with 3-fraction SBRT and were analyzed. This cohort comprised 74 Child-Turcotte-Pugh (CTP) class A patients and 8 CTP class B7 patients. The median LD was 3.0 cm (range, 1.0–7.0 cm), and the median dose was 51 Gy (range, 33–60 Gy).
LC and OS rates at 2 years after SBRT were 87% and 63%, respectively, with a median follow-up duration of 30 months for all patients. The 2-year LC/OS rates for patients treated with doses of > 54, 45–54, and < 45 Gy were 100/71, 78/64, and 64%/30%, respectively (p = .009/p < .001). Multivariate analysis revealed that the SBRT dose (p = .005) and Barcelona Clinic Liver Cancer stage (p = .015) were significant prognostic factors for OS. Correlation analysis revealed a positive linear relationship between the SBRT dose and LC (p = .006, R = .899)/OS (p = .002, R = .940) at 2 years. Based on the tumor-control probability model, a dose of 54.8 Gy provides 2-year LC with a 90% probability. Five patients experienced grade 3 or higher gastrointestinal toxicity, and 6 had deteriorating of CTP score by greater than or equal to 2 within 3 months of SBRT.
This study demonstrated a dose response relationship for LC and OS with SBRT for HCC. Higher LC rates resulting from an increased dose may translate into survival benefits for patients with HCC.
Liver cancer is the sixth most frequently diagnosed cancer worldwide, but the it was the second most frequent cause of cancer death in 2008 . The treatment of choice for hepatocellular carcinoma (HCC) is surgery, but less than 20% of patients are suitable for surgery [2–5]. For patients with inoperable HCC, radiofrequency ablation (RFA) and other ablative therapies achieve excellent local control (LC) for small tumors. However, not all patients are suitable for these local therapies because of a large tumor size, tumor location, unmanageable coagulopathy, or invisibility on ultrasonography [6–8]. For patients with HCC unsuitable for local ablative therapies, transarterial chemoembolization (TACE) had been widely used as the first line non-curative therapy . Radiotherapy (RT) has typically not been considered a frontline treatment for HCC due to the lower tolerance of the whole liver to RT . However, some recent studies reported favorable outcomes for three-dimensional conformal radiotherapy (3D-CRT) for HCC [11–14].
Stereotactic body radiotherapy (SBRT) is an external beam RT method used to very precisely deliver a high dose of radiation to an extracranial target within the body using either a single fraction or a small number of fractions . As the liver obeys the parallel architecture model of radiobiology, the risk of radiation-induced liver disease (RILD) is generally proportional to the mean dose of radiation delivered to normal liver tissue [16–18]. Several studies using SBRT for liver tumors have been performed, and these studies reported high tumor response and LC rates [19–24]. We previously reported our results from phase I and II trials of SBRT for HCC and observed high LC rates and low severe toxicity rates [25, 26]. Due to the small number of patients in each study, we were unable to determine the optimal dose for LC, or clarify a dose response relationship for local control and overall survival. In this study, we expanded our previous study to include more cases of SBRT for HCC and analyzed additional data to determine whether a dose response relationship for local control and overall survival is observed in SBRT for inoperable HCC.
Patient and tumor characteristics
No. of patients (%)
Hepatitis B virus
Hepatitis C virus
7 ( 9)
Diagnosis history at SBRT
Diagnose as recurrence
No. of previous TACE sessions
Portal vein tumor thrombosis
No. of tumor
Longest diameter (cm)
SBRT dose (Gy)
Stereotactic body radiotherapy
The SBRT technique used at our institution has been previously described [25, 26]. Briefly, patients were immobilized with a customized external vacuum-type (Vac-Loc; MedTec, Inc., Orange City, IA). Breathing-related tumor motion was minimized by abdominal compression using 4 belts . Gold fiducials (4 mm x 0.8 mm) or lipiodol deposits in the tumor were used to mark tumors for SBRT. Daily image guidance using orthogonal ×-ray imaging or on-board CT was used to relocalize the target lesion before treatment delivery. A CT image was taken with a slice thickness of 2 mm at 3 seconds per slice. These relatively slow CT images included the respiratory movement of the target; therefore, the tumor volume used for planning was larger than the gross tumor volume (GTV) and was referred to as the internal target volume (ITV) [28, 29]. The planning target volume (PTV) was defined as the ITV + 4 mm in the craniocaudal direction and the ITV + 2 mm in all other directions . SBRT doses were prescribed at an isodose line (70–80% of the maximum dose) that covered at least 97% of the PTV.
The SBRT doses were escalated from 33 Gy in 3 fractions to 60 Gy in 3 fractions in our previous study. The final prescribed doses were 60 Gy in 3 fractions, but the dosages were reduced by 0.5 or 1 Gy per fraction until normal tissue constraints were allowed. We adopted the normal tissue constraint that at least 700 ml of normal liver (entire liver minus the cumulative GTV) should not receive a total dose ≥ 15 (phase I) or ≥ 17 Gy (phase II). For the spinal cord, the maximum dose should not exceed 18 (phase I) or 22 Gy and 18 Gy to 0.25 ml or less of irradiated volume (phase II). For the esophagus the maximum dose should not exceed 24 Gy. In addition, although other normal tissue constraints were not considered, dosages to the kidneys, intestine, and stomach were restricted to the lowest level possible. SBRT was administered in a 3-fraction course over no more than 14 elapsed days.
Evaluation and statistical analysis
Treatment response was assessed using modified Response Evaluation Criteria in Solid Tumors . Toxicities were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.0. Classic RILD was defined as the presence of anicteric ascites and an at least twofold elevation in alkaline phosphatase relative levels to the pretreatment value in the absence of tumor progression . Non-classic RILD was defined as elevated transaminase levels (> 5× the upper limit of normal) or NCI-CTCAE grade 4 levels in patients with baseline levels more than 5 times the upper limit of normal range, within 3 months after the completion of SBRT, or deterioration of the CTP score by ≥ 2, in the absence of classic RILD . LC was defined as no tumor progression during follow-up and determined via post-SBRT radiographic studies. LC and overall survival (OS) rates (from the first date of SBRT treatment) were calculated using the Kaplan-Meier method and intergroup comparisons were performed using the log-rank test. All factors with p-value lower than or equal to 0.1 in univariate analysis were subjected to multivariate analysis using a Cox proportional hazards regression model with a forward, stepwise procedure to determine whether factors acted independently. All statistical analyses were performed using SPSS statistical software (version 12.0; SPSS, Inc., Chicago, IL, USA), and p-values < 0.05 were considered statistically significant.
Tumor control probability model
where D refers to the total dose, γ describes the slope of the curve, and D50 is the dose that achieves a TCP of 50% for the prescribed dose. D50 and γ were estimated by logit functions. The 95% confidence intervals (CIs) were found using the probability density function of normal distribution. The formula was implemented using MATLAB R2011b (The MathWorks Inc., Natick, MA).
Prognostic factors: univariate analysis
Diagnosis history at SBRT
Portal vein tumor thrombosis
Longest diameter (cm)
No. of previous TACE sessions
SBRT dose (Gy)
Published studies of RFA and high-dose SBRT group of the present study
Tumor size (cm)
Local control (%)
Overall survival (%)
Severe toxicity (%)
Shiina 2005 (7)
Bouza 2009 (8)
Waki 2010 (38)
Feng 2012 (39)
Shiina 2012 (6)
Median 2.0 Mean 2.5
Present study(> 54 Gy)
32 (Rec 53%)
Median 3.0 Mean 3.1
Bowel 3.1; Others 3.1
Tumor control probability
One patient (1%) experienced grade 3 hyperbilirubinemia, but this patient had pre-existing grade 1 hyperbilirubinemia. Two patients (2%) experienced grade 3 ascites that required paracentesis without evidence of disease progression and with normal alkaline phosphatase levels. No classic RILD was observed, but 6 patients (7%) experienced non-classic RILD (worsening of CTP score by ≥ 2 in all) within 3 months after SBRT. Excluding the patient with disease progression, 4 patients (5%) experienced non-classic RILD, and 3 of these patients were reversibly converted during long-term follow-up. One patient (1%) experienced grade 3 soft tissue toxicity in the right upper quadrant of the abdomen, and this patient had a large tumor (LD, 6.2 cm) near the skin. Five patients (6%) experienced grade 3 or 4 gastrointestinal (GI) toxicity as follows: gastroduodenal ulcer in 2 patients, colonic ulcer in 1 patient, and gastroduodenal perforation in 2 patients. Two patients with gastroduodenal perforation recovered after supportive care in one and primary repair in the other.
For optimal dose quantification, we adopted the logistic model. On the basis of the best-fitted TCP curve, doses of 54.8 Gy and 46.4 Gy produce 2-year LC with probabilities of 90% and 80%, respectively. These findings suggest that 54 Gy in 3 fractions is an acceptable dose to achieve LC for HCC lesions with LD ≤ 7.0 cm. However, the SBRT dose required to achieve the same LC rates may differ according to tumor size. We estimated the TCP curve after stratification by LD (≤ 5.0 cm vs. > 5.0 cm). For lesions with LD ≤ 5.0 cm or > 5.0 cm, the estimated SBRT doses to provide 2-year LC with a probability of 90% were 51.1 (95% CI, 47.7–54.5) and 61.2 Gy (95% CI, 58.4–64.0), respectively.
To date, no prospective randomized study has compared dose-fractionation regimens in SBRT for HCC. We suggested a SBRT dose of 54 Gy in 3 fractions by fitted TCP curve and survival analysis. In an Indiana University study, the prescribed doses were 48 Gy in 3 fractions for patients with CTP class A and 40 Gy in 5 fractions for those with CTP class B. In that study, the 2-year LC rate was 90% . In a Belgium study, the prescribed dose was 45 Gy in 3 fractions, and the 2-year LC rate was 95% . The results of these studies are comparable with those of the lesions that received higher doses in our study, despite use of slightly lower doses in the above mentioned studies. These observations may be attributable to the additional margin to the GTV. In the Indiana University study, CTV expansion was not performed, and the PTV was defined as GTV + 5–10 mm. In the Belgium study, the CTV was defined as the GTV + 10 mm in all directions the within liver and the PTV as CTV + 1.5 mm margin. In our institution, CTV expansion was not performed and the PTV was defined as GTV + 2–4 mm. In SBRT, the differences in the additional margin to the GTV affect dose-distribution. Even without a GTV expansion, the surrounding 0.5 cm may be adequately covered by the SBRT prescription. In fact, the total dose to cover the GTV may be similar among 3 institutions. When we reviewed our plan, PTVs with additional margins of 5–10 mm or 11 mm were adequately covered by isodose lines of 48 Gy and 45 Gy, respectively. Therefore, to compare the studies of SBRT for HCC, an additional margin and a prescribed isodose line should be considered. Comparisons using a dose covering the GTV or maximum dose may be suggested as appropriate methods. Furthermore, we think that consensus or standardization of the SBRT technique for HCC, such as defining of additional margin to GTV and prescribed isodose line, is needed.
Although it appears that the tumor response increases with increasing radiation doses, it is difficult to demonstrate a dose-relationship for OS because many complicated factors are involved in determining survival. This is especially true in HCC because most of patients have liver cirrhosis, and minimizing the deterioration of liver function induced by treatment is critical. Further, as many patients who experienced intrahepatic tumor recurrence after treatment exhibited a complete response, preserving liver function for further treatment is important for prolonging OS. In patients with HCC treated by 3D-CRT, RILD is a relatively common severe toxicity [11–14, 36]. However, classic RILD was not reported after SBRT and we also observed no classic RILD, perhaps due to the substantial difference in the normal liver dose distribution between 3D-CRT and SBRT [20–26]. On the other hand, we observed non-classic RILD in 6 patients (7%) within 3 months after SBRT. Excluding the patient with disease progression, 4 patients (5%) experienced non-classic RILD. Additionally, if late toxicity can influence survival, the fact that 75% of patients who experienced non-classic RILD without disease progression were reversibly converted during long-term follow-up duration is encouraging. Due to the high LC rate and little liver deterioration induced by treatment, in our study, the SBRT dose as a continuous variable was a prognostic factor for OS in multivariate analysis.
Overall 5 patients (6%) experienced grade 3 or 4 gastrointestinal toxicity. These patients had the lesion in close proximity (within 0–0.4 cm) to the GI tract and relatively high doses were delivered to the GI tract. The maximum doses to GI tract of these patients were 42, 45, 55, 55, and 60 Gy, respectively. Three patients had pre-SBRT gastroduodenal ulcer confirmed by esophagogastroduodenoscopy. We previously performed studies about severe gastroduodenal and intestinal toxicity after SBRT using 3 fractions for abdominopelvic malignancies and reported their results [37, 38]. In the study about gastroduodenal toxicity, we suggested that Dmax is a valuable predictor of severe gastroduodenal tocivity. A history of ulcer before SBRT should be carefully considered as a clinical predictor, especially in patients who receive a high dose to gastroduodenum . In the study about intestinal toxicity, we V25 is a valuable predictor of severe intestinal toxicity. And SBRT would be conducted with a treatment interval of at least 48 hours if possible .
LC and OS rates in SBRT for HCC patients with dose > 54 Gy were excellent and potentially equivalent to those treated by RFA [6–8, 39, 40] (Table 3). Of course, because of differences in baseline prognostic features between the patients, direct comparison between SBRT and RFA has been limited. In most RFA series, the patients had initial disease and received RFA as the first treatment. However, in this study, 53% of the patients had recurrent disease and all patients had an incomplete response to prior TACE. Irrespective of these potential unfavorable prognostic features, the outcomes were comparable with those of RFA. Toxicities were also tolerable in SBRT for HCC. On the basis of these observations, a phase II trial of high-dose SBRT for the patients with small-sized HCC (≤ 5.0 cm) is ongoing in Korea. Furthermore, we expect randomized trials comparing SBRT and RFA for HCC to follow.
This study had some limitations. First, this study was not a randomized trial, and therefore, patients were not controlled with respect to variable prognostic factors. Nevertheless, all patients met the inclusion criteria of prospective studies and received SBRT with consistent technique. Therefore, selection bias can be controlled to a considerable degree. Second, the TCP curve was estimated using the logistic model. This result may be regarded as hypothesis generating and should be validated with clinical data. Third, only a small number of large tumors were included, and it may be inaccurate to apply our results to large tumors. We believe that our results are more powerful and reliable for small tumors rather than large tumors. In separate prospective SBRT trial for large HCC, we expect implemental results for large-sized HCC.
In conclusion, this study demonstrated a dose response relationship for LC and OS with SBRT for HCC. Higher LC rates resulting from higher doses may improve survival benefit for HCC. High-dose SBRT may be as effective and safe a treatment modality as RFA, a major nonsurgical ablative modality. Based on the TCP model, a dose of 54.8 Gy produces 2-year LC with a probability of 90%. To validate our results and obtain definitive conclusions, prospective studies in larger populations will be needed in the future.
The study was supported by the National Nuclear R&D Program of the Ministry of Science, ICT and Future Planning, Republic of Korea.
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