Partial Liver Irradiation Research Articles

Partial liver irradiation in rats induces the hypertrophy of nonirradiated liver lobes through hepatocyte proliferation†.

Irradiation of the liver induces a regenerative response in the nonirradiated part of the liver. It is unclear whether this leads to actual liver enlargement. The aim of this study was to evaluate the weight of compensatory hypertrophy that occurs in nonirradiated livers and to clarify the mechanism of hypertrophy from the viewpoint of hepatocyte proliferation. The anterior liver lobes (anterior lobes) were irradiated with 60Gy of X-rays (X60Gy) under opening laparotomy. Body weights and liver lobe weights were measured before and at 1, 4, 8 and 12weeks after irradiation, and serum and liver tissue samples were analyzed at each time point. The anterior lobes atrophied progressively, whereas the posterior liver lobes (posterior lobes) hypertrophied in the X-ray irradiated (X-irradiated) group. Although temporary liver damage was observed after irradiation, liver function did not decrease at any time point. Hepatocyte degeneration and loss were observed in the anterior lobes of the X-irradiated group, and significant fibrosis developed 8weeks postirradiation. Following irradiation, the proportion of Ki-67-positive cells in the anterior lobes decreased markedly in the early postirradiation period, whereas the proportion of positive cells in the posterior lobes increased, peaking at 4weeks postirradiation (P < 0.05). Increased tumor necrosis factor-α expression was observed only in the anterior liver lobes of the X-irradiated group at 1 and 4weeks postirradiation. Partial liver irradiation with X60Gy induced compensatory hypertrophy of nonirradiated liver lobes. This study suggests that liver hypertrophy after partial liver irradiation is caused by increased hepatocyte mitosis.

P0176 Dosimetric comparison of volumetric intensity-modulated arc (RapidArc) therapy, intensity-modulated radiotherapy, and 3D conformal radiotherapy for primary liver tumours

Background To compare the dosimetric outcomes of volumetric arc radiotherapy (RapidArc), intensity-modulated radiotherapy (IMRT), and 3D conformal radiotherapy (3DCRT) plans for primary liver tumours. Methods 7 patients with localised unresectable hepatocellular carcinoma were included in this study. CT simulation was done with voluntary deep inspiratory breath-holding after administering 80–90 mL of intravenous iodinated contrast. The mean tumour size was 5.6 cm (range 2.1–9.8) and two patients had multiple lesions (range 1–3). All patients were planned for partial liver irradiation for a total dose of 50–66 Gy in 2 Gy per fraction with conformal techniques. 3DCRT, IMRT, and RapidArc plans were generated using Eclipse planning system v.13 and dosimetric analysis was done to evaluate the plan quality and efficiency, including CI, HI, MU delivered, PTV D mean and D max . IMRT plans had 3–5 fields and RapidArc plans had 3–5 arcs. V 10 ,V 20 ,V 30 and V 40 of normal liver and D mean of organs at risk (OAR) and D max of spinal cord were also evaluated. Analysis was done using ANOVA and paired t -test with two tailed p Findings All the three techniques had comparable PTV coverage, dose homogeneity, and OAR sparing. IMRT and Rapid Arc had a significantly better conformity index than 3DCRT ( p = 0.03). The high dose areas within the normal liver; V 40 and V 30 were significantly lower in RapidArc and IMRT plans ( p = 0.03 and p = 0.04, respectively), although no significant differences were noted between IMRT and RapidArc. One patient could not attain the normal liver constraint V 33 Interpretation RapidArc and IMRT provide better normal liver sparing and conformity than 3DCRT. However, RapidArc was not better than IMRT for liver protection. Further large trials are required to clearly establish the benefits of IMRT and Rapid Arc techniques to treat primary liver tumours.

Liver Sinusoidal Endothelial Cell Transplantation Ameliorated Radiation-induced Liver Deformation And Sulfur Colloid SPECT Defect In Mouse Livers Following Partial Liver Irradiation

Purpose/Objective(s): To examine liver deformation and spatial liver function in a mouse model of radiation induced liver disease (RILD), using functional imaging with 99mTechnetium (99mTc) labeled Sulfur Colloid SPECT/CT. We further investigated whether liver sinusoidal endothelial cell (LSEC) transplantation can improve liver function and ameliorate deformation following image-guided stereotactic partial liver irradiation (HIR). Materials/Methods: DPPIV-deficient or C57Bl6 mice underwent a planning CBCT after gastrograffin gavage. Fifty Gy partial liver irradiation was delivered to the median lobe (ML) using the Small Animal Irradiator Platform (SARRP system) set at 220 kVP and 13.5 mA. Maximum bowel point dose was maintained under 20 Gy to prevent GI toxicity. SPECT/CT imaging was obtained using the Inveon Platform 20 mins after 99mTc Sulfur Colloid injection. Sulfur Colloid uptake was quantified in the irradiated and non-irradiated liver regions using planning CBCT isodose lines. For cell transplantation, DPPIV positive LSECs were isolated from C57Bl/6 mice and then injected intrasplenically to anesthetized congenic DPPIV-deficient mice 24 hours after HIR. The recipient mice were sacrificed 4 months post transplantation. Individual liver lobes were weighted separately and liver tissues were analyzed for engraftment and repopulation of transplanted cells using DPPIV histochemistry. Results: Partial liver irradiation to the ML resulted in a significant decrease in the ML weight from 35 4% of the liver weight to 25 3%, one to two months after irradiation. At 4 months, ML weight reached 16% of the whole liver. Sulfur colloid SPECT/CT imaging demonstrated decreased uptake in the irradiated liver regions by 20-25%, six weeks following HIR. One animal that received HIR, followed by mitotic stimulus with hepatocyte growth factor, showed virtually no uptake in the irradiated lobe with significant compensatory hypertrophy of the unirradiated liver one year after HIR. LSEC transplantation restored ML liver weight and by 4 months made up 37-40% of the liver weight while also restoring 99mTc sulfur colloid uptake in the irradiated lobe to baseline levels. DPPIV histochemistry confirmed near total replacement of the irradiated LSECs by the transplanted DPPIV positive cells. Conclusions: This data suggests that HIR resulted in a time-dependent decrease in the weight and functional uptake of 99mTc labeled sulfur colloid in the irradiated liver lobe. LSEC transplantation restored liver weight and improved liver function as demonstrated by 99mTc sulfur colloid SPECT/ CT imaging. Our data provide a rationale for investigating the use of 99mTc sulfur colloid SPECT/CT imaging to monitor patients at risk for developing RILD and LSEC transplantation to ameliorate against RILD. Author Disclosure: R. Kabarriti: None. H. Yaffe: None. W. Zhang: None. W.P. Koba: None. L. Liu: None. P. Asp: None. W.A. Tome: None. C. Guha: None.

Co-transplantation of Liver Sinusoidal Endothelial Cells Promotes Repopulation of Transplanted Hepatocytes Following Hepatic Irradiation

Preparative hepatic irradiation enhances engraftment of transplanted hepatocytes. In this study, we sought to investigate the effect of hepatic irradiation on liver sinusoidal endothelial cells (LSECs) and whether co-transplantation of LSECs with hepatocytes can promote the proliferation of transplanted hepatocytes. Male F344 rats received HIR (10, 25 and 50 Gy) using a 320 kVP Philips orthovoltage unit and were sacrificed at various time points from 0 to 1 week post-HIR. Liver tissues were analyzed by H&E, TUNEL apoptosis assay, and electron microscopy. In the transplantation studies, 5 x 105 DPPIV-positive LSEC’s and/or 5 x 105 DPPIV-positive hepatocytes isolated from C57Bl/6 mice were injected intrasplenically to anesthetized DPPIV-deficient mice twenty-four hours after partial liver irradiation using HIR (20 and 40 Gy). The recipient mice were then sacrificed 60 days post transplantation. There was a dose-dependent increase in the number of apoptotic LSECs, as early as 2 h post-HIR, which peaked at 6 h. Electron microscopy demonstrated significant LSEC dehiscence at 24 h. Co-transplantation of liver sinusoidal endothelial cells and hepatocytes resulted in a dose dependent repopulation of the transplanted cells in the irradiated lobes. Interestingly, transplanted hepatocyte colonies formed only next to newly repopulated LSECs and there were no isolated DPPIV positive hepatocyte colonies (>10 cells) in areas where there was no DPPIV positive liver sinusoidal endothelial proliferation. This data suggests a dose-dependent hepatic LSEC injury. Transplantation of LSECs not only replaced injured liver endothelial cells but also promoted repopulation of the newly transplanted hepatocytes. This is consistent with recent reports demonstrating that newly recruited liver sinusoidal endothelial cells played a crucial role in liver regeneration and restoration of liver mass following partial hepatectomy and toxic liver injury and provide a rationale for promoting LSEC recruitment from progenitor cells in the liver and bone marrow to ameliorate liver function after radiation injury.

Tolerance of Liver as a Predictor of Hepatic Dysfunction in Stereotactic Body Radiation Therapy

Purpose/Objective(s): In recent years, stereotactic body radiation therapy (SBRT) has been used to treat liver cancer and has resulted in good outcomes. However, the hepatic tolerance to small volume with hypofractionated high dose irradiation is unclear. Especially partial liver irradiation with high doses may render cirrhotic liver more susceptible to RT-induced liver injury than normal liver parenchyma. We investigated and analyzed the hepatic dysfunction associated with the dose distribution by MRI using the hepatocyte-targeted Gd-EOB-DTPAwhich has a similar feature to ICG (indocyanine green) for the liver function test. Materials/Methods: A total of 64 liver cancer patients were treated by SBRT. Of these patients, 54 were hepatocellular carcinoma (HCC) in liver cirrhosis, and 10 were metastatic cancer in normal liver. The median PTV volumes were 33.0cm3 (8.7-232.9) with HCC and 64.4cm3 (8.5-204.5) with liver metastases. The median prescribed dose delivered to the PTV was 44.0Gy (40.0-55.5) for HCC and 55.5Gy (48.0-65.0) for liver metastases, with median fraction size of 5.0Gy (4.0-15.0) and 5.5Gy (4.025.0), respectively. MRI was performed during 3-6 months after SBRT. MR-sequences were conducted with T1WI with GRE (LAVA; liver acquisition with volume acceleration) enhanced by Gd-EOB-DTPA which was injected twenty minutes before the image acquisition. All MRI data sets were merged with 3D-dosimetry data by using in-house DICOM-RT image fusion software which also indicated the border of hypointensity on T1WI (loss of hepatocyte function) and read the isodose line on the border. This boundary doses were corrected to biologically effective dose (BED) using the linear-quadratic (LQ) formulation assuming an a/b Z 2Gy for intercomparing over a wide variety of dose distribution around the border. Results: The registration error was negligible small after image fusion of the planning CT to the follow-up MRI so that the development of hepatocyte dysfunction was definitely validated in correlation to the isodose distribution. The BED2 provoking hepatic dysfunction was a median of 92Gy (70-179) in normal liver. However, in cirrhotic liver, it was significantly decreased to a median of 56Gy (30-228) which shows that the hypersensitivity to radiation lowered the threshold dose for hepatic dysfunction. Conclusions: The fundamental premise for liver SBRT is to preserve adequate liver function, therefore, pretreatment validation of the future liver remnant volume is critical. In this study, tolerance of liver was evaluated as a predictor of hepatic dysfunction in SBRT. The critical dose provoking hepatic dysfunction was estimated to be 56Gy (BED2) in cirrhotic liver which was about half of the dose with normal liver. Author Disclosure: R. Oh: None. H. Shiomi: None. Y. Imai: None. D. Tatsumi: None. N. Masai: None. T. Inoue: None.

Hepatocyte senescence induced by radiation and partial hepatectomy in rat liver

Purpose: Exposure to radiation primes the liver for extensive replacement of the resident parenchymal cells by transplanted hepatocytes. The mechanisms underlying this repopulation remain to be clarified. In these studies, we examined the possible occurrence of cell senescence in vivo following radiation-associated preconditioning of the host liver.Materials and methods: Fischer 344 rats underwent external-beam, computed-tomography-based partial liver irradiation. A single dose of 25 Gy was delivered to the right liver lobes (40% of liver mass). An additional group of animals received a 1/3 partial hepatectomy (removal of the left anterior lobe) four days after irradiation. Non-irradiated groups served as controls. All rats were sacrificed four weeks after the initial treatment.Results: The irradiated livers displayed several markers of cell senescence, including expression of senescence-associated-β-galactosidase (SA-β-gal), increase in cell size, and up-regulation of cyclin-dependent kinase inhibitors (CDK-I) p16 and p21. Furthermore, quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) analysis revealed activation of the senescence-associated secretory phenotype (SASP), including the cytokines interleukin 6 (IL6) and 1α (IL1α). The senescence-related changes were more prominent in rats undergoing partial hepatectomy (PH) following irradiation (IR).Conclusions: We conclude that priming with radiation for liver repopulation results in the induction of cell senescence and the up-regulation of a senescence-associated secretory phenotype. The latter can contribute to the extensive growth of transplanted cells in this system.

Tolerance of Cirrhotic Liver Comparing With Normal Liver to Stereotactic Body Radiation Therapy

Purpose/Objective(s): In recent years stereotactic body radiation therapy (SBRT) has been used to treat liver cancer and has resulted in good outcomes. However, the hepatic tolerance to small volume with hypofractionated high dose irradiation is unclear. Especially partial liver irradiation to high doses may render cirrhotic liver more susceptible to RT-induced liver injury than normal liver. We investigated and analyzed the hepatic radiation injury associated with the dose distribution by using MRI with hepatocyte-targeted Gd-EOB-DTPA. Materials/Methods: A total of 19 liver cancer patients were treated by SBRT. Of these patients, 13 were hepatocellular carcinoma (HCC) in liver cirrhosis, and 6 were metastatic cancer in normal liver. The median prescribed dose delivered to the PTV was 52 Gy (range, 40-56 Gy), with median fraction size of 9 Gy (range, 5-14 Gy) and in a median total irradiation time of 6 days (range, 4-12 days). MRI was performed during 3-6 months after SBRT. MR-sequences were conducted with T1WI with GRE (LAVA; liver acquisition with volume acceleration) enhanced by Gd-EOB-DTPA. All MRI data sets were merged with 3D-dosimetry data by using in-house DICOM-RT image fusion software. The reviewer indicated the border of hypointensity on T1WI (loss of hepatocyte function) and read the isodose line on the border. This boundary doses were corrected to biologically effective dose (BED) using the linear-quadratic (LQ) formulation assuming an a/ b Z 2 Gy for intercomparing over a wide variety of dose distribution around the border. Results: The registration errors were negligible small after image fusion of the planning CT to the follow-up MRI so that the development of hepatocyte dysfunction was definitely validated in correlation to the isodose distribution. The dose per fraction at the border of hepatocyte dysfunction was a median of 4 Gy (range, 2.4-8 Gy). This results indicated that the minimal BED provoking hepatocyte function loss was a median of 105 Gy (range, 70-137 Gy, using LQ formulation, a/b Z 2 Gy) in normal liver. However, in cirrhotic liver, it was significantly decreased to a median of 51 Gy (range, 30-70 Gy, using LQ formulation, a/b Z 2 Gy) so that the toxic effects lowered the threshold dose for hepatic dysfunction in liver cirrhosis. Conclusions: For liver SBRT, the fundamental premise is that to preserve adequate liver function, a minimum volume of normal liver must be spared from receiving a dose that might render it nonfunctional. In this study, the maximum dose allowed to this critical volume was estimated to be 16 Gy in four fractions (BED Z 50 Gy based on LQ conversion, a/b Z 2 Gy) in cirrhotic liver which was half of the BED for normal liver. Author Disclosure: R. Oh: None. H. Shiomi: None. Y. Imai: None. T. Igura: None. Y. Miyata: None. H. Nakamura: None. T. Inoue: None.

Salvage Treatment With Hypofractionated Radiotherapy in Patients With Recurrent Small Hepatocellular Carcinoma

To investigate the rates of tumor response and local control in patients with recurrent small hepatocellular carcinoma (HCC) treated with hypofractionated radiotherapy (RT) as a salvage treatment and to evaluate treatment-related toxicities. Between 2006 and 2009, a total of 20 patients with recurrent small HCC were treated with hypofractionated RT after the failure of previous treatment. The eligibility criteria for hypofractionated RT were as follows: 1) HCC less than 5 cm, 2) HCC not adjacent to critical organs, 3) HCC without portal vein tumor thrombosis, and 4) less than 15% of normal liver volume that would be irradiated with 50% of prescribed dose. The RT dose was 50 Gy in 10 fractions. The tumor response was determined by CT scans performed 3 months after the end of RT. The median follow-up period after RT was 22 months. The overall survival rates at 1and 2 years were 100% and 87.9%, respectively. Complete response (CR) was achieved in seven of 20 lesions (35%) evaluated by CT scans performed 3 months after the end of RT. In-field local control was achieved in 85% of patients. Fourteen patients (70%) developed intra-hepatic metastases. Six patients developed grade 1 nausea or anorexia during RT, and two patients had progression of ascites after RT. There was no grade 3 or greater treatment-related toxicities. The current study showed a favorable outcome with respect to hypofractionated RT for small HCC. Partial liver irradiation with 50 Gy in 10 fractions is considered tolerable without severe complications.

Hepatic proliferation after partial liver irradiation in Sprague–Dawley rats

The liver has powerful capability to proliferate in response to various injuries, but little is known as to liver proliferation after irradiation (IR) injury. This study investigated whether liver proliferation could be stimulated in low-dose irradiated liver by partial liver IR injury with high dose radiation. Sprague-Dawley rats were irradiated by 6-MV X-ray with single dose of 25Gy to the right-half liver, while the left-half liver was shielded (0.7Gy) or irradiated with single doses of 3.2, 5.6, and 8.0Gy, respectively. Hepatic proliferation in the shielded and low-dose irradiated left-half liver was evaluated by serum hepatic growth factor (HGF), proliferating cell nuclei antigen (PCNA), liver proliferation index (PI), hepatocyte mitosis index (MI). The observation time was 0day (before IR), 30, 60, 90, and 120days after IR. Our results showed that serum HGF and hepatocyte HGF mRNA increased after IR with HGF mRNA peak on day 30 in the shielded and low-dose irradiated left-half livers, and their values increased as the dose increased to the left-half liver. Liver PI and PCNA mRNA peaked on day 60 with stronger expressions in higher doses-irradiated livers. MI increased after IR, with the peak noted on day 60 in the shielded and on day 90 in the low-dose irradiated left-half livers. There was a 30day delay between MI peaks in the shielded and low-dose irradiated livers. In conclusion, 25Gy partial liver IR injury could stimulate the shielded liver and low-dose irradiated liver to proliferate. In the livers receiving a dose range of 3.2-8.0Gy, the proliferation was stronger in higher doses-irradiated liver than the low-dose irradiated. However, IR delayed hepatocyte mitosis.

Radiothérapie en conditions stéréotaxiques des métastases hépatiques

Liver metastases are frequently found in oncologic patients. Chemotherapy is the standard treatment in plurimetastatic patients, with the possibility to obtain a clear improvement of their prognosis. Local treatment (surgery, radiofrequency, cryotherapy, radiotherapy, etc.) could be proposed for oligometastatic patients, particularly for those with a good prognosis. Historically, radiation therapy has had a limited role in the treatment of liver metastases because of its toxicity when whole liver irradiation was delivered. Improvements in the knowledge of liver radiobiology and radiopathology as well as technical innovations in delivering radiation therapy are the basis of the modern partial liver irradiation concept. In this historical and therapeutic landscape, extracranial stereotactic radiation therapy is particularly interesting for the treatment of liver metastases. This review summarises published data on stereotactic radiotherapy for the treatment of liver metastases.

Hepatic Regeneration after Sublethal Partial Liver Irradiation in Cirrhotic Rats

Our previous animal study had demonstrated that partial liver irradiation (IR) could stimulate regeneration in the protected liver, which supported the measurements adopted in radiotherapy planning for hepatocellular carcinoma. The purpose of this present study is to investigate whether cirrhotic liver repopulation could be triggered by partial liver IR. The cirrhosis was induced by thioacetamide (TAA) in rats. After cirrhosis establishment, TAA was withdrawn. In Experiment 1, only right-half liver was irradiated with single doses of 5 Gy, 10 Gy and 15 Gy, respectively. In Experiment 2, right-half liver was irradiated to 15 Gy, and the left-half to 2.5 Gy, 5 Gy and 7.5 Gy, respectively. The regeneration endpoints, including liver index (LI); mitotic index (MI); liver proliferation index (LPI); PCNA-labeling index (PCNA-LI); serum HGF, VEGF, TGF-α and IL-6, were evaluated on 0 day, 30-day, 60-day, 90-day, 120-day and 150-day after IR. Serum and in situ TGF-β1 were also measured. In both experimental groups, the IR injuries were sublethal, inducing no more than 9% animal deaths. Upon TAA withdrawal, hepatic regeneration decelerated in the controls. In Experiment 1 except for LI, all other regeneration parameters were significantly higher than those in controls for both right-half and left-half livers. In Experiment 2 all regeneration parameters were also higher compared with those in controls for both half livers. Serum HGF and VEGF were increased compared with that of controls. Both unirradiated and low dose-irradiated cirrhotic liver were able to regenerate triggered by sublethal partial liver IR and higher doses and IR to both halves liver triggered a more enhanced regeneration.

A natural process of cirrhosis resolution and deceleration of liver regeneration after thioacetamide withdrawal in a rat model

Characteristics of thioacetamide (TAA)-induced liver cirrhosis in rat was observed for 120 days after TAA withdrawal as part of the radiobiological study of partial liver irradiation on TAA-induced cirrhotic rats. The natural process focused on cirrhosis and regeneration was recorded as a baseline condition for the interpretation of the outcome of the partial liver irradiation study. Cirrhosis in rats was successfully induced by drinking 0.03% TAA water orally for 29 weeks with a modeling rate of 96%. After establishment of the cirrhosis model, the rats were observed for 120 days upon TAA withdrawal to investigate the dynamic changes of cirrhosis and regeneration. The following characteristics were observed: (1) Histological changes; (2) Liver functions; (3) Cirrhosis: trichrome stain, quantification of hydroxyproline in hydrolysed liver tissue and TGF-β1; (4) Liver regeneration: liver index, hepatocyte mitotic index (MI), hepatocyte proliferation index (PI) by flow cytometry, PCNA labeling index (LI) by IHC and expression of PCNA mRNA; and (5) Growth factors: serum HGF, VEGF, TGF-α, and IL-6. After TAA withdrawal, gradual improvement in liver functions was noted with decreases of ALT, AST, and ALP, and increase of PA. The resolution of cirrhosis was evident by histological improvement with attenuation of collagen fiber and decrease of TGF-β1 IHC index, and also decrease of trichrome stain and hydroxyproline content. However, cirrhosis was still existed on 120 days after TAA withdrawal. Significant deceleration of liver regeneration was demonstrated with TAA withdrawal, evidenced by decrease of MI and PI, reduced expression of PCNA mRNA and PCNA LI. In conclusion, upon TAA withdrawal hepatic cirrhosis was continuously resolved, but persisted up to 120 days, and liver regeneration was significantly decelerated.

Highly Conformal Partial Liver Irradiation for Chemorefractory Unresectable Colorectal Liver Metastases

There is limited safety data regarding liver irradiation in patients that have been extensively pretreated for metastatic liver disease. The aim is to report toxicity and response data from a phase I study of partial liver irradiation using highly conformal radiotherapy (CRT) for unresectable colorectal liver metastases (CRLM) that have received all lines of therapy available. Eligible patients had unresectable or medically inoperable CRLM and received all standard therapies (chemotherapy, surgery, radiofrequency ablation), Childs score A and KPS > 60 and signed informed consent. CRT was delivered hypofractionated in 10 fractions over 2 weeks. Adaptive radiotherapy management was used with planning target volume being patient specific according to tumor motion characterized on 4DCT and cine MRI. Delivered dose was individualized according to volume of uninvolved liver irradiated to the prescribed dose in 3 dose bins: <30% = 40 Gy, 30-50% = 35 Gy, 50-70% = 30 Gy and to maintain the estimated risk of liver toxicity <5%. Six patients were entered in each dose bin. The primary endpoints were feasibility and toxicity, secondary local control, and survival. The toxicity was assessed using CTCAE v 3.0 scale: weekly during CRT, and at 1 month, then 3 monthly assessments also with imaging. Radiation induced liver disease (RILD) grade 4 within 12 weeks of radiation would have stopped recruitment. From Nov 2006 to March 2010, 18 patients were recruited and all completed CRT. Mean age 70 year (range, 44-85). Eight patients had metastatic disease at initial diagnosis. All patients had combination chemotherapy and or biological agents: median 2 lines (range, 1-4), 5 patients had hepatic resection and 7 also had radiofrequency ablation. The mean tumor volume was 85 cc (range, 3 cc to 395 cc). A total of 26 metastases were treated. The CRT tumor dose ranged from 30 Gy to 40 Gy (average 35 Gy. No grade 3/4/5 related acute toxicity was observed. No radiation-induced liver disease (RILD) was observed. Other toxicity within 3 months following CRT included grade 2: anemia (1), liver capsular pain (1), nausea (1) fatigue (2) and skin toxicity (1). Fifteen patients had at least 3 months of follow-up, in-field response assessed using CT at 3 months was: PR (6), MR/SD (5), PD (4). Median follow-up was 8.7 months (1.5 to 40 months). Median in field progression-free survival was 8.9 months. Median overall survival (OS) 17.7 months; 1 year OS 42% (95% CI 18-64%). On progression, 6 patients were re-challenged with chemotherapy. No late toxicities grades 3-5 were seen. In a heavily pretreated population with large liver burden disease this approach of individual dose CRT appears safe; with no additional toxicity observed in higher dose bin (40 Gy).

Hepatocyte regeneration after partial liver irradiation in rats

Liver has a strong potential for regeneration after physical, biological or chemical injury, but no data have been reported so far on liver regeneration in response to irradiation injury. The present experiment in rats was designed to clarify whether partial liver irradiation could induce and stimulate the unirradiated part of liver to regenerate. The left-half of rat liver was irradiated with a single dose of 25 Gy. Liver tissues from the irradiated and unirradiated liver, and blood sample were collected at different time points after irradiation. Radiation injury was evaluated by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, histopathologic features and trichrome stain. The hepatic regeneration was assessed by serum hepatic growth factor (HGF), mitotic index and proliferation cell nuclear antigen (PCNA) immunohistochemical stain. Expression of transforming growth factor-β1 (TGF-β1) by immunohistochemistry assay was also performed. Results showed that 25 Gy of single-dose irradiation produced severe hepatic injury in the irradiated liver, and the unirradiated liver had been stimulated to regenerate, demonstrated by significant increases of serum HGF 30 days after irradiation, and increase of mitotic index and the number of PCNA-positive hepatocytes 60 days after irradiation. TGF-β1 was strongly and uniformly expressed in the irradiated liver 90-day-post-irradiation, and it was also expressed slightly in unirradiated liver region. In summary, partial liver irradiation could stimulate the unirradiated liver to regenerate, and the role of TGF-β1 in hepatic injury and proliferation needs further investigation.

175: A New Paradigm for Tissue Regeneration: Preparative Irradiation for Cell-Based Therapies as an Alternative to Organ Transplantation

Orthotopic liver transplantation (OLT) is the only curative therapy for patients with terminal liver diseases. A significant number of patients fail to get OLT due to shortage of donor livers. Hepatocyte transplantation (HT) is being explored as a therapeutic alternative to OLT for the treatment of end-stage liver diseases. However, the number of cells that can be safely transplanted into the liver and the inability of the transplanted hepatocytes to proliferate in the host liver currently limit the clinical application of this procedure. We hypothesized that a preparative regimen of hepatic irradiation (HIR), in combination with hepatic mitotic stimuli, would suppress host hepatocellular proliferation and induce post-mitotic death, thus ”making room“ for transplanted, nonirradiated hepatocytes to proliferate preferentially and repopulate the irradiated host liver. C57Bl/6 mice received HIR (0-50 Gy) to the anterior liver lobes after exposing the liver by laparotomy and shielding the posterior liver lobes and other abdominal organs, followed by an injection of a recombinant adenoviral vector expressing human hepatocyte growth factor (Ad-HGF, 5-10 x 1010 particles). One day after HIR, the mice received intrasplenic HT with 0.8-1×106 primary hepatocytes, freshly isolated from congenic, beta-galactosidase-expressing transgenic (ROSA)26 C57Bl/6 mice. Control mice received Ad-HGF alone, or HIR + Ad-LacZ with HT. Animals were sacrificed at 7 days, 1, 2, 4 and 6 months after HT and the liver sections were examined for beta-galactosidase-expressing donor cells after histochemical and hematoxylin-eosin staining. Compared to unirradiated controls, HIR augmented the engraftment of transplanted hepatocytes, with an increase in the number of integrated donor hepatocytes into liver cords by 7 days (p<0.01). There was progressive repopulation of the irradiated anterior liver lobes by transplanted hepatocytes with near-total (80-95%) replacement of the host hepatocytes by the donor cells within 6 months. In contrast, the unirradiated posterior and caudate liver lobes exhibited occasional presence of beta-galactosidase-expressing donor hepatocytes, indicating engraftment without repopulation. H&E staining demonstrated normal liver architecture without any evidence of hepatic radiation injury. Liver function tests of the transplanted animals were normal. Preparative irradiation is routinely used for bone marrow transplantation, but we are the first to use HIR to facilitate the engraftment and host liver repopulation by donor cells after HT in rodent models. HIR significantly enhanced the integration of transplanted cells in the host liver. Furthermore, partial liver irradiation enabled selective repopulation of a liver lobe by the donor cells, thereby increasing the safety of our regimen. Clinically, preparative HIR could be safely administered using radiosurgery or 3-D conformal RT and combined with systemic administration of hepatic growth factors to facilitate HT for 1) the treatment of inherited liver diseases, 2) liver failure, 3) ex vivo hepatic gene therapy, 4) rescuing patients with liver cancer, following chemo-radiation therapy, and 5) expanding human hepatocytes in animal liver for generating animal models for human-specific infections.

Noninvasive evaluation of liver repopulation by transplanted hepatocytes using 31P MRS imaging in mice

Hepatocyte transplantation (HT) is being explored as a substitute for liver transplantation for the treatment of liver diseases. For the clinical application of HT, a preparative regimen that allows preferential proliferation of transplanted cells in the host liver and a noninvasive method to monitor donor cell engraftment, proliferation, and immune rejection would be useful. We describe an imaging method that employs the creatine kinase (CK) gene as a marker of donor hepatocytes. Creatine kinase is unique among marker genes, because it is normally expressed in brain and muscle tissues and is therefore not immunogenic. Preferential proliferation of transplanted CK-expressing hepatocytes was induced by preparative hepatic irradiation and expression of hepatocyte growth factor using a recombinant adenoviral vector. CK is normally not expressed in mouse liver and its expression by the donor cells led to the production of phosphocreatine in the host liver, permitting (31)P magnetic resonance spectroscopic imaging of liver repopulation by engrafted hepatocytes. In conclusion, this study combined a noninvasive imaging technique to assess donor hepatocyte proliferation with a preparative regimen of partial liver irradiation that allowed regional repopulation of the host liver. Our results provide groundwork for future development of clinical protocols for HT.

Radiotherapy of liver malignancies. From whole liver irradiation to stereotactic hypofractionated radiotherapy.

Until recently radiotherapy of hepatic malignancies has played a limited role due to the well-known limited radiotolerance of the liver. The aim of this paper is to review the available data on the risk of radiation-induced liver disease (RILD) and to define the modern role of radiotherapy in the management of patients with metastatic or primary liver malignancies. The advent of three-dimensional conformal treatment planning with dose-volume histogram analysis has made the study of partial liver irradiation possible. Limited portions of the liver may withstand high doses of radiation with minimal risk of RILD. Patients with solitary unresectable liver tumors may be treated with high-dose radiotherapy with curative intent. Recently, the feasibility of stereotactically guided treatment techniques with a single fraction or few treatment sessions has been explored in numerous institutions. The radiation tolerance of the whole liver found by several investigations is in the order of approximately 30 Gy, which seriously restricts its clinical application. The role of whole liver irradiation therefore appears of limited benefit in the palliation of patients with multiple liver metastases. The use of three-dimensional conformal techniques has made partial liver irradiation possible to doses in the 70-80 Gy range with conventional fractionation. At least two published series have reported improved local control and survival rates with dose escalation with three-dimensional conformal radiotherapy in patients with unresectable liver metastases. Similar outcomes have been recently reported with single dose (or hypofractionated) stereotactic radiotherapy both in metastatic and primary hepatic malignancies with minimal morbidity. Accurate target delineation and treatment reproducibility are the key to the success of this novel treatment approach, and specific treatment planning techniques and patient setup procedures must be developed to implement it. Stereotactic high-dose radiotherapy is technically feasible for the treatment of inoperable liver malignancies, with the potential of high local control and low morbidity. Definitive evidence on the clinical advantages of this technique over other more established treatments can only be gathered from well-designed clinical studies.

Partial volume rat lung irradiation: An evaluation of early DNA damage

1. To investigate early DNA damage induced in rat lung cells following single-dose, partial-volume irradiation (lung base and lung apex). 2. To determine the variation in DNA damage in different lung regions. 3. To investigate the possible mechanisms associated with early DNA damage after lung irradiation. The whole lung or the upper or lower half of the entire lung of Sprague-Dawley rats was exposed to 10 Gy 60Co gamma rays. The animals were sacrificed at various times up to 42 h after irradiation. A trypsin-digested lung cell suspension was prepared and cells that attached to slides in the initial 24-h period were then grown in the presence of culture medium with cytochalasin-B for a further 72 h. Radiation-induced DNA damage was quantified in the cells (primarily fibroblasts) from both irradiated and unirradiated lung regions by using a well-characterized micronucleus assay. When the lungs were removed at 16-18 h after whole-lung irradiation, about 0.85 micronuclei (MN) per binucleate cell (BNC) were observed in the lung cells of the irradiated animals, compared to 0.02 MN/BNC in the lung cells of the controls. When only the lung base was irradiated, the frequency of micronuclei was 0.85 MN/BNC compared to 0.43 MN/BNC observed in cells from the irradiated lung apex. Of particular interest was the finding that the unirradiated lung apex also showed a large frequency of micronuclei (0.43 MN/BNC) after the irradiation of the lung base, whereas the unirradiated lung base showed only a marginal (approximately 2-fold) increase relative to the spontaneous frequency following irradiation of the lung apex. The changes in the frequency of micronuclei varied with the time at which the lungs were removed from the rats for early times, but had stabilized by 18 h after irradiation. Normal (unirradiated) cells grown in filtered or unfiltered conditioned media obtained from irradiated cell cultures showed an insignificant marginal increase in the number of micronuclei relative to the spontaneous frequency. Lung cells obtained from the lung base or the lung apex of healthy controls and irradiated separately in vitro showed no regional differences in the induction of micronuclei. Cells from the lungs of rats injected with superoxide dismutase, within 1 h prior to irradiation of the lung base, and processed 16-18 h after irradiation showed a reduction in the number of MN in the shielded lung apex, indicating the possible involvement of oxygen radicals. These data indicate that cells in the lung base sustain more DNA damage than those in the lung apex when either region is irradiated; however, when the whole lung, is irradiated, the lung damage observed is similar in the two regions. Also, out-of-field effects are observed for the lung apex but not the lung base. Possible mechanisms include a clastogenic (chromosome damaging) factor produced in the plasma following irradiation and/or the production of oxygen radicals by activated lymphocytes/monocytes. The partial blocking of the DNA damage, observed in the unirradiated lung apex following irradiation of the lung base, by superoxide dismutase, suggests that oxygen radicals are involved in this out-of-field effect. These radicals are likely produced as a result of the induction of inflammatory cytokines, such as tumor necrosis factor (TNF) and interleukin-1 (IL-1) by the irradiation. The reason for the lack of an out-of-field effect in the lung base when the lung apex is irradiated is unknown, but may be due to the greater volume of lung irradiated in the lower lung field, because this is likely to affect the level of cytokines produced. Alternatively, it may reflect cytokines produced as a result of the partial liver irradiation that occurs with the lower lung field.

Potential benefits of eliminating planning target volume expansions for patient breathing in the treatment of liver tumors

To investigate potential benefits derived from reduction or elimination of planning target volume (PTV) margins associated with patient breathing through examination of hepatic tumors treated with conformal therapy. We reviewed the treatment plans of 50 patients who had previously received conformal partial organ liver irradiation for treatment of hepatic malignancies. PTVs for these plans included expansions (1-2 cm) for patient breathing. Data consisted of the three-dimensional dose distributions computed for the conformal plans generated for these volumes, and also for plans using identical beam arrangements but smaller block margins to treat planning target volumes that did not include the expansions for breathing. We calculated effective volumes (V(eff)) and normal tissue complication probabilities (NTCP) using dose-volume histograms for normal liver and analyzed changes in: V(eff), NTCP at the prescription dose, doses associated with selected NTCP levels, and tumor control probabilities (TCP) at these new dose levels. Elimination of the patient breathing components of the PTVs for these conformal treatments of liver tumors: (a) decreased the average V(eff) by 5%; (b) decreased the average predicted NTCP at the prescription (isocenter) dose used to treat the patients by 4.5%; (c) increased the average target volume (isocenter) dose associated with low (1-10%) predicted normal liver NTCP by 6-8 Gy, which corresponded to (d) a predicted average 6-7% increase in TCP for aggressive liver tumors. Plans with PTV expansions for breathing that occurred mostly within the liver showed greatest potential benefit. Elimination of the margin added to hepatic target volumes for patient ventilation could lead to clinically meaningful increases in dose without increasing the predicted frequency of complications.

Radiation tolerance of the liver in relation to the preserved functional capacity.

The radiation tolerance of the liver was investigated in 12 patients, 11 of them with liver cirrhosis, treated for hepatocellular carcinoma by partial liver irradiation with doses between 50 and 77 Gy. The tolerance was assessed by the complication probability (Lyman's model), which concerned the injured tissue itself, and by a prediction score used for postsurgical liver failure, which concerned the preserved functional capacity, assuming that the > or = 30 Gy volume was equivalent to the resected volume. The prediction score corresponded better with the observed risk of fatal liver failure than the complication probability. The liver volume after radiotherapy correlated largely with the untreated volume and the low-dose volume. Thus the preserved functional capacity gives a better expression of the radiation tolerance than direct measures of the extent of injured tissue.