This article has Open Peer Review reports available.
Long-term effect of stereotactic body radiation therapy for primary hepatocellular carcinoma ineligible for local ablation therapy or surgical resection. Stereotactic radiotherapy for liver cancer
- Jung Hyun Kwon†1,
- Si Hyun Bae†1Email author,
- Ji Yoon Kim†2,
- Byung Ock Choi†2,
- Hong Seok Jang†2,
- Jeong Won Jang†1,
- Jong Young Choi†1,
- Seung Kew Yoon†1 and
- Kyu Won Chung†1
© Kwon et al; licensee BioMed Central Ltd. 2010
Received: 5 March 2010
Accepted: 3 September 2010
Published: 3 September 2010
We evaluated the long-term effect of stereotactic body radiation therapy (SBRT) for primary small hepatocellular carcinoma (HCC) ineligible for local therapy or surgery.
Forty-two HCC patients with tumors ≤ 100 cc and ineligible for local ablation therapy or surgical resection were treated with SBRT: 30-39 Gy with a prescription isodose range of 70-85% (median 80%) was delivered daily in three fractions. Median tumor volume was 15.4 cc (3.0-81.8) and median follow-up duration 28.7 months (8.4-49.1).
Complete response (CR) for the in-field lesion was initially achieved in 59.6% and partial response (PR) in 26.2% of patients. Hepatic out-of-field progression occurred in 18 patients (42.9%) and distant metastasis developed in 12 (28.6%) patients. Overall in-field CR and overall CR were achieved in 59.6% and 33.3%, respectively. Overall 1-year and 3-year survival rates were 92.9% and 58.6%, respectively. In-field progression-free survival at 1 and 3 years was 72.0% and 67.5%, respectively. Patients with smaller tumor had better in-field progression-free survival and overall survival rates (<32 cc vs. ≥32 cc, P < 0.05). No major toxicity was encountered but one patient died with extrahepatic metastasis and radiation-induced hepatic failure.
SBRT is a promising noninvasive-treatment for small HCC that is ineligible for local treatment or surgical resection.
Hepatocellular carcinoma (HCC) is one of the most common malignant diseases [1–3]. Of the current therapeutic approaches for HCC, surgical resection and liver transplantation are used with curative intent for patients with small HCC . However, the majority of HCC patients are ineligible for surgery because most have a cirrhotic liver with poor liver function or tumors are located in the central segments. Several modalities including radiofrequency ablation (RFA) and percutaneous ethanol injection (PEI) have been used to treat small HCC, but the optimal treatment remains controversial particularly for cases of small HCC ineligible for curative therapy.
Cyberknife (Accuracy Inc., Sunnyvale, CA) is a new stereotactic body radiation therapy (SBRT) that delivers a high dose of radiation in a short time to well-defined tumor sites. Cyberknife has been extended to extracranial SBRT applications [5–7] since it was invented for the treatment of intracranial lesions . However, to date few studies have reported SBRT including Cyberknife for the treatment of intrahepatic tumors, especially primary HCC [9–14]. In our previous report , the overall response rate of non-resectable small HCC and portal vein tumor thrombosis (PVTT) in advanced HCC was 71.9% for a median follow-up of 10.5 months. This report expands our experience further, and discusses the long-term effect in primary HCC of Cyberknife SBRT that was limited to targeting parenchymal lesions ineligible for local ablation therapy or surgical resection.
Stereotactic body radiation therapy
SBRT was performed using a Cyberknife (Accuracy Inc.) image-guided radiosurgery system. To obtain radiographic landmarks, we percutaneously implanted four 3 × 1 mm gold seeds under ultrasonographic guidance in liver parenchyma near the tumor targets. On the following day, patients were vacuum immobilized in the supine position, and computed tomographic (CT) images were taken in spiral mode with a 2 mm slice thickness at maximum expiration. We used breath-holding techniques during Cyberknife treatment as described in our previous protocol .
Dose limitation to normal tissues
The liver, esophagus, stomach, duodenum, intestine, kidneys, and spinal cord were contoured during the planning process and dose-volume histograms (DVH) were used to ensure that normal tissue tolerances were not exceeded. We limited the dose to normal tissues as in our previous protocol .
We evaluated V20 as a predictor for liver damage accrued from the SBRT in our study: in the α/β ratio of 3, 30-35 Gy with conventional fractionation is equivalent to a dose of 3 × 6 Gy (total, 18 Gy) to the whole liver. The V20 was limited so as not to exceed 50% of the functional whole liver tissue.
Stomach, duodenum and intestine
Because of the lack of clinical data on the effect of very high fractional doses exceeding 8 Gy, a dose of 7 Gy was chosen based on the experience in brachytherapy. Therefore, the maximum dose to the stomach, duodenum and intestine was limited to below 7 Gy per fraction (total, 21 Gy).
In this study, at least two-thirds of the right kidney was limited to receiving a dose of less than 5 Gy per fraction (total, 15 Gy). With an α/β ratio of 3, 23 Gy with conventional fractionation is equivalent to a dose of 3 × 5 Gy (total 15 Gy).
The maximum dose to the spinal cord was limited to below 7 Gy per fraction from the linear-quadratic formula of Withers et al. For an α/β ratio of 3, 42 Gy with conventional fractionation is equivalent to a dose of 3 × 7 Gy (total, 21 Gy)
Assessment of response and toxicity
Patients underwent dynamic CT scans 1 month after completion of SBRT, and then tumor response was checked at 2-3 month intervals. Treatment response and local recurrence were evaluated using follow-up dynamic CT scans and serum alpha-fetoprotein (AFP). MRI scans and/or Positron emission tomography (PET) CT scans were used to discriminate the vague lesion or response and evaluate overall response in some cases. In patients who experienced local recurrence or intrahepatic metastasis after Cyberknife treatment, transarterial chemoembolization (TACE), local ablation therapies, or liver transplantation were recommended.
In-field and overall tumor responses were defined principally according to the amended Response Evaluation Criteria in Solid Tumors (RECIST) criteria , taking into account tumor necrosis recognized by non-enhanced areas. An in-field response was defined as target lesion response within the irradiated field. Complete response (CR) was defined as the disappearance of any intratumoral arterial enhancement in all target lesions. Partial response (PR) was defined as at least a 30% decrease in the sum of the diameters of viable (contrast enhancement in the arterial phase) target lesions, taking as a reference the baseline sum of the diameters of target lesions. Progressive disease (PD) was defined as at least 20% increase in the sum of the diameters of viable (enhancing) target lesions or the appearance of a new lesion, and stable disease (SD) was defined as a tumor status that did not meet the above three response criteria. Initial in-field response was evaluated by determining the maximum reduction rate within 12 months following Cyberknife treatment. In-field progression was defined as any progression of the target lesion within the irradiated field after initial response to Cyberknife treatment. In-field progression-free survival was calculated from the date of initial response to the date of in-field progression. Overall in-field response was defined as target lesion response at the end of follow-up or the date of death. Overall response was defined as the whole body response considering hepatic out-of-field progression and extrahepatic metastasis in addition to the hepatic in-field response at the end of follow-up or the date of death.
Serum AFP response was also evaluated in patients with a serum AFP level greater than normal before Cyberknife treatment. Based on percentage changes versus baseline levels, AFP responses were categorized as CR (AFP normalization), PR (an AFP reduction of ≥ 50%), PD (an AFP increase of ≥ 25%), and SD (an AFP change that did not meet the above three response criteria) .
Toxicities were assessed using the Radiation Therapy Oncology Group (RTOG) guidelines [20, 21]. Acute toxicity was assessed weekly until 90 days post-treatment. Late toxicity was defined as a toxicity occurring at > 90 days post treatment. For both acute and late toxicities, grade 3-4 indicates major toxicity.
Data are expressed as mean ± SDs, medians (ranges), or rate. Statistical analyses were performed using SPSS version 14.0 for Windows (SPSS Inc., Chicago, IL). Patient survival was calculated from the date of Cyberknife treatment until the date of death or last follow-up. Cumulative survival rates were estimated using the Kaplan-Meier method. The factors affecting the survival rate were identified on univariate and multivariate analysis using Cox's proportional hazard model.
Basal characteristics of patients
N = 42
Overall median follow up period (months, range)
Age (years, mean ± SD)
60.1 ± 10.9
Cause of HCC (HBV/HCV/Alcohol/Others)
ECOG performance (0/1)
Child-Pugh classification (A/B/C)
AJCC stage (I/II/IIIa/IV)
Median tumor volume (cc, range)
Tumor number (solitary/multifocal)
Initial median AFP (ng/dl, range)
TACE combined with locoregional therapies
16 (PEI 13, RFA 3)
TACE combined with surgical resection
Tumor and AFP response
Tumor and AFP response
Overall In-field response
Initial response → Progression
After Cyberknife treatment, 25 patients (59.5%) who experienced local recurrence or intrahepatic metastasis underwent salvage therapy such as TACE and/or local therapy or liver transplantation.
Serum AFP response was assessed in the 22 evaluable patients with an increased AFP level at baseline (Table 2). Overall, 10 (45.5%) and four (18.2%) of these patients achieved CR or PR for AFP, respectively. In the follow-up period, 4 of the 22 patients achieving overall CR maintained CR for AFP. Of the 18 of the 22 patients having overall PD, seven showed CR, two PR, one SD and eight PD for AFP. The seven patients with overall PD who showed CR for AFP did not develop extrahepatic metastasis, but developed in-field or hepatic out-of-field progression. However, there was no significance between other patterns of final AFP response and tumor progression type.
Factors identified on univariate and multivariate analysis as influencing the survival
Hazard ratio (95% Confidence Interval)
Initial In-field response
Hepatic out-field recurrence
Initial tumor volume 32 cc (< vs. ≥)
Child-Pugh classification score
Adverse events related to treatment
Adverse events related to treatment
Elevated liver enzyme
Elevated bilirubin and alkaline phosphatase
Other (target error)
The results of this study show excellent in-field responses to Cyberknife SBRT in HCC within tumors < 100 cc in volume that are ineligible for local ablation therapies or surgical resection. Furthermore, all patients that initially achieved CR for in-field lesions experienced no in-field progression during the follow-up period.
Surgical resection is best indicated for patients with a single tumor and well-preserved liver function, and such patients may achieve a 5-year survival rate of 60-70% [22, 23]. In the present study, the 3-year survival rate for Cyberknife SBRT was 58.6%, which was slightly lower than for surgical resection. In view of the large proportion of multifocal tumors in our study population and the difficult tumor sites for operation, we find this survival rate acceptable [4, 24]. Other local treatment methods, especially RFA, are emerging as alternative curative options for patients unsuitable for surgery or liver transplantation . Complete tumor necrosis by RFA was pathologically shown by 83% of tumors < 3 cm , but proximity of lesions to the gall bladder or main vessels, a sub-diaphragmatic location, or the presence of a non-echogenic lesion present major problems for the use of RFA . Although radiotherapy alone or in combination with TACE has become a potential treatment option for advanced HCC, it is not considered as first-line treatment for small HCC [27, 28]. Doses of 30-35 Gy with conventional fractionation are often considered to be the limit of liver tolerance. However, the role of radiotherapy for the treatment of small HCC or portal vein thrombosis has recently been emphasized in the context of the development of SBRT. This is because the radiation dose delivered by SBRT rapidly falls off at the periphery of target lesions, which enables the accurate delivery of high doses of radiation to a specified lesion with hypofractionation as opposed to traditional protracted treatment courses over several weeks. We did not intend to compare RFA/surgical resection and SBRT in small HCC, but we suggest that SBRT is an alternative option in case of ineligible for the former treatment.
Hypofractionated radiotherapy trials on primary and metastatic hepatic tumors
Lesions (HCC/CCC/Metastatic tumor)
Treatment (prescription dose/fractionated frequency/isodose)
Median follow-up months (range)
Local control rate *
Median tumor volume cc (range)
Takeda  2008
100% at 1 year, 94% at 2 year
100% at 2 year
TSE  2008
36 (24-54) gy/6/NA
65% at 1 year (CR 5%, PR 44%, SD 42%)
51% at 1 year (HCC 48% at 1 year)
No SE 5 patients (12%); grade 3 (liver)
33 (30-39) gy/3/80%
72.0, 67.5% at 1 and 2, 3 and 4 year (CR 60%, PR 26%, SD 14%)
92.9/77.3/58.6/58.6% at 1, 2, 3, 4 year
1 patient (2%); grade 4 (liver)
The use of Cyberknife SBRT as a method for hypofractionated SBRT to treat primary HCC is an important aspect of our study. A phase I dose escalation trial of Cyberknife SBRT in liver tumors was published in abstract form in the American Society of Clinical Oncology (ASCO) in 2006 and 2007 [13, 14] and our preliminary findings were reported in 2008 . The 2006 ASCO report of 12 unresectable primary or metastatic liver tumors with a mean volume of 27.1 cc and a median follow-up of 6 months demonstrated an interval decrease in size for six lesions and stable disease for three lesions. According to the ASCO 2007 report, Cyberknife SBRT-treated primary liver or metastatic tumors achieved 24% CR and 40% PR over a median follow-up of 7 months. These outcomes are better than those mentioned in prior reports for other hypofractionated SBRT using the conventional LINAC. In our previous study , CR and PR for the small HCC group that was not the PVTT target group were 26.1% and 56.3%, respectively. Our study shows better responses (CR 59.6% and PR 25.5%) than the ASCO reports [13, 14], although we analyzed only primary HCCs of ≤ 100 cc. The advantage of the present study is that Cyberknife SBRT was used to treat a large number of primary HCC and patients were followed over a relatively long follow-up period.
At the time we began the use of Cyberknife for HCC, there was no report identifying the safe dose. In terms of toxicity, the present study shows that Cyberknife SBRT is feasible and safe in primary HCC, which is consistent with the findings of a previous phase I study [13, 14] and our previous study . One of our patients died as a result of radiation-induced hepatic failure 20 months after Cyberknife treatment, but he also experienced combined tumor progression and metastasis. Takeda et al. and Tse et al. also reported no serious SBRT-related toxicities [9, 11]. A targeting error suggests the importance of tumor location, particularly in the hepatic angle or near the beating heart, and of control breath holding. We contoured the liver, stomach, duodenum, intestine, kidney, and spinal cords during the planning process and used DVH to ensure that normal tissue tolerances were not exceeded. We plan to escalate the total dose 42-45 Gy in three fractionation in case of favorable tumor sites, taking into consideration the limitation dose to normal tissues.
In the present study, excellent in-field responses were obtained for Cyberknife SBRT in HCC. Notably, all patients who initially achieved CR for in-field lesions maintained in-field CR during the follow-up period (median 28.7 months). Furthermore, this study shows that Cyberknife SBRT is a feasible, effective treatment for primary HCC, and suggests that Cyberknife SBRT be considered a promising noninvasive modality when small HCC of < 32 cc is inappropriate for surgical resection or ablation therapy. Further study is required to define the effects of administered radiation dose and fractionation, and to determine toxicities in selected patients with small HCC.
- El-Serag HB: Hepatocellular carcinoma: recent trends in the United States. Gastroenterology. 2004, 127 (suppl 1): S27-S34. 10.1053/j.gastro.2004.09.013.View ArticlePubMedGoogle Scholar
- Yang L, Parkin DM, Ferlay J, Li L, Chen Y: Estimates of cancer incidence in China for 2000 and projections for 2005. Cancer Epidemiol Biomarkers Prev. 2005, 14: 243-250. 10.1158/1055-9965.EPI-04-0680.View ArticlePubMedGoogle Scholar
- Dyer Z, Peltekian K, van Zanten SV: Review article: the changing epidemiology of hepatocellular carcinoma in Canada. Aliment Pharmacol Ther. 2005, 22: 17-22. 10.1111/j.1365-2036.2005.02504.x.View ArticlePubMedGoogle Scholar
- Llovet JM, Burroughs A, Bruix J: Hepatocellular carcinoma. Lancet. 2003, 362: 1907-1917. 10.1016/S0140-6736(03)14964-1.View ArticlePubMedGoogle Scholar
- Cupp JS, Koong AC, Fisher GA, Norton JA, Goodman KA: Tissue effects after stereotactic body radiotherapy using cyberknife for patients with abdominal malignancies. Clin Oncol. 2008, 20: 69-75. 10.1016/j.clon.2007.08.009.View ArticleGoogle Scholar
- Hara W, Soltys SG, Gibbs IC: CyberKnife robotic radiosurgery system for tumor treatment. Expert Rev Anticancer Ther. 2007, 7: 1507-1515. 10.1586/14737126.96.36.1997.View ArticlePubMedGoogle Scholar
- Schellenberg D, Goodman KA, Lee F, Chang S, Kuo T, Ford JM, Fisher GA, Quon A, Desser TS, Norton J, et al: Gemcitabine chemotherapy and single-fraction stereotactic body radiotherapy for locally advanced pancreatic cancer. Int J Radiat Oncol Biol Phys. 2008, 72: 678-686. 10.1016/j.ijrobp.2008.01.051.View ArticlePubMedGoogle Scholar
- Adler JR, Chang SD, Murphy MJ, Doty J, Geis P, Hancock SL: The Cyberknife: a frameless robotic system for radiosurgery. Stereotact Funct Neurosurg. 1997, 69: 124-128. 10.1159/000099863.View ArticlePubMedGoogle Scholar
- Takeda A, Takahashi M, Kunieda E, Takeda T, Sanuki N, Koike Y, Atsukawa K, Ohashi T, Saito H, Shigematsu N, et al: Hypofractionated stereotactic radiotherapy with and without transarterial chemoembolization for small hepatocellular carcinoma not eligible for other ablation therapies: Preliminary results for efficacy and toxicity. Hepatol Res. 2008, 38: 60-69. 10.1111/j.1872-034X.2007.00084.x.View ArticlePubMedGoogle Scholar
- Mendez Romero A, Wunderink W, Hussain SM, De Pooter JA, Heijmen BJ, Nowak PC, Nuyttens JJ, Brandwijk RP, Verhoef C, Ijzermans JN, et al: Stereotactic body radiation therapy for primary and metastatic liver tumors: A single institution phase I-II study. Acta Oncol. 2006, 45: 831-837. 10.1080/02841860600897934.View ArticlePubMedGoogle Scholar
- Tse RV, Hawkins M, Lockwood G, Kim JJ, Cummings B, Knox J, Sherman M, Dawson LA: Phase I study of individualized stereotactic body radiotherapy for hepatocellular carcinoma and intrahepatic cholangiocarcinoma. J Clin Oncol. 2008, 26: 657-664. 10.1200/JCO.2007.14.3529.View ArticlePubMedGoogle Scholar
- Choi BO, Choi IB, Jang HS, Kang YN, Jang JS, Bae SH, Yoon SK, Chai GY, Kang KM: Stereotactic body radiation therapy with or without transarterial chemoembolization for patients with primary hepatocellular carcinoma: preliminary analysis. BMC Cancer. 2008, 8: 351-10.1186/1471-2407-8-351.View ArticlePubMedPubMed CentralGoogle Scholar
- Goodman KA LY, Yang G, Gibbs I, Fisher G, Loo BW, Nguyen M, Koong AC: Phase I dose escalation study of stereotactic radiosurgery for liver malignancies (poster presentation). Proceeding of the ASCO. 2006, (suppl; abstr 172), Gastrointestinal Cancer Symposium. San Francisco, CA, USA, 26-28 January 2006Google Scholar
- Anderson EM KA, Yang G, Gibbs IC, Fisher GA, Goodman KA: Phase I dose escalation study of stereotactic radiosurgery for liver malignancies (poster presentation). Proceeding of the ASCO. 2007, (suppl; abstr 171), Gastrointestinal Cnacer Symposium. Orlando, Florida, USA, 19-21 January 2007Google Scholar
- Wulf J, Hadinger U, Oppitz U, Thiele W, Ness-Dourdoumas R, Flentje M: Stereotactic radiotherapy of targets in the lung and liver. Strahlenther. Onkol. 2001, 177: 645-655.Google Scholar
- Wulf J, Guckenberger M, Haedinger U, Oppitz U, Mueller G, Baier K, Flentje M: Stereotactic radiotherapy of primary liver cancer and hepatic metastases. Acta Oncol. 2006, 45: 838-847. 10.1080/02841860600904821.View ArticlePubMedGoogle Scholar
- Herfarth KK, Debus J, Lohr F, Bahner ML, Rhein B, Fritz P, Hoss A, Schlegel W, Wannenmacher MF: Stereotactic single-dose radiation therapy of liver tumors: results of a phase I/II trial. J Clin Oncol. 2001, 19: 164-170.PubMedGoogle Scholar
- Llovet JM, Di Bisceglie AM, Bruix J, Kramer BS, Lencioni R, Zhu AX, Sherman M, Schwartz M, Lotze M, Talwalkar J: Design and endpoints of clinical trials in hepatocellular carcinoma. J Natl Cancer Inst. 2008, 100: 698-711. 10.1093/jnci/djn134.View ArticlePubMedGoogle Scholar
- Jang JW, Kay CS, You CR, Kim CW, Bae SH, Choi JY, Yoon SK, Han CW, Jung HS, Choi IB: Simultaneous Multitarget Irradiation Using Helical Tomotherapy for Advanced Hepatocellular Carcinoma with Multiple Extrahepatic Metastases. Int J Radiat Oncol Biol Phys. 2009, 74: 412-418. 10.1016/j.ijrobp.2008.08.034.View ArticlePubMedGoogle Scholar
- Trotti A, Byhardt R, Stetz J, Gwede C, Corn B, Fu K, Gunderson L, McCormick B, Morrisintegral M, Rich T: Common toxicity criteria: version 2.0. an improved reference for grading the acute effects of cancer treatment: impact on radiotherapy. Int J Radiat Oncol Biol Phys. 2000, 47: 13-47. 10.1016/S0360-3016(99)00559-3.View ArticlePubMedGoogle Scholar
- Cox JD, Stetz J, Pajak TF: Toxicity criteria of the Radiation Therapy Oncology Group (RTOG) and the European Organization for Research and Treatment of Cancer (EORTC). Int J Radiat Oncol Biol Phys. 1995, 31: 1341-1346. 10.1016/0360-3016(95)00060-C.View ArticlePubMedGoogle Scholar
- Bruix J, Boix L, Sala M, Llovet JM: Focus on hepatocellular carcinoma. Cancer Cell. 2004, 5: 215-219. 10.1016/S1535-6108(04)00058-3.View ArticlePubMedGoogle Scholar
- Bruix J, Sherman M: Management of hepatocellular carcinoma. Hepatology. 2005, 42: 1208-1236. 10.1002/hep.20933.View ArticlePubMedGoogle Scholar
- Llovet JM, Beaugrand M: Hepatocellular carcinoma: present status and future prospects. J Hepatol. 2003, 38 (suppl 1): S136-S149. 10.1016/S0168-8278(02)00432-4.View ArticlePubMedGoogle Scholar
- Lu DS, Yu NC, Raman SS, Limanond P, Lassman C, Murray K, Tong MJ, Amado RG, Busuttil RW: Radiofrequency ablation of hepatocellular carcinoma: treatment success as defined by histologic examination of the explanted liver. Radiology. 2005, 234: 954-960. 10.1148/radiol.2343040153.View ArticlePubMedGoogle Scholar
- Decadt B, Siriwardena AK: Radiofrequency ablation of liver tumours: systematic review. Lancet Oncol. 2004, 5: 550-560. 10.1016/S1470-2045(04)01567-0.View ArticlePubMedGoogle Scholar
- Seong J, Park HC, Han KH, Lee DY, Lee JT, Chon CY, Moon YM, Suh CO: Local radiotherapy for unresectable hepatocellular carcinoma patients who failed with transcatheter arterial chemoembolization. Int J Radiat Oncol Biol Phys. 2000, 47: 1331-1335. 10.1016/S0360-3016(00)00519-8.View ArticlePubMedGoogle Scholar
- Seong J, Keum KC, Han KH, Lee DY, Lee JT, Chon CY, Moon YM, Suh CO, Kim GE: Combined transcatheter arterial chemoembolization and local radiotherapy of unresectable hepatocellular carcinoma. Int J Radiat Oncol Biol Phys. 1999, 43: 393-397. 10.1016/S0360-3016(98)00415-5.View ArticlePubMedGoogle Scholar
- Blomgren H, Lax I, Näslund I, Svanstrom R: Stereotactic high dose fraction radiation therapy of extracranial tumors using an accelerator. Clinical experience of the first thirty-one patients. Acta Oncol. 1995, 34: 861-870. 10.3109/02841869509127197.View ArticlePubMedGoogle Scholar
- Blomgren H, Lax I, Göranson H, Kræpelien T, Nilsson B, Näslund I, Svanström R, Tilikidis A: Radiosurgery for tumors in the body: Clinical experience using a new method. J Radiosurgery. 1998, 1: 63-74. 10.1023/B:JORA.0000010880.40483.c4.View ArticleGoogle Scholar
- Schefter TE, Kavanagh BD, Timmerman RD, Cardenes HR, Baron A, Gaspar LE: A phase I trial of stereotactic body radiation therapy (SBRT) for liver metastases. Int J Radiat Oncol Biol Phys. 2005, 62: 1371-1378. 10.1016/j.ijrobp.2005.01.002.View ArticlePubMedGoogle Scholar
- Wada H, Takai Y, Nemoto K, Yamada S: Univariate analysis of factors correlated with tumor control probability of three-dimensional conformal hypofractionated high-dose radiotherapy for small pulmonary or hepatic tumors. Int J Radiat Oncol Biol Phys. 2004, 58: 1114-1120. 10.1016/j.ijrobp.2003.08.012.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2407/10/475/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.