Proton beam therapy for hepatocellular carcinoma

Proton Beam Therapy and Photon-Based Magnetic Resonance Image-Guided Radiation Therapy: The Next Frontiers of Radiation Therapy for Hepatocellular Carcinoma

External beam radiation therapy (EBRT) has increasingly been utilized in the treatment of hepatocellular carcinoma (HCC) due to technological advances with positive clinical outcomes. Innovations in EBRT include improved image guidance, motion management, treatment planning, and highly conformal techniques such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT). Moreover, proton beam therapy (PBT) and magnetic resonance image-guided radiation therapy (MRgRT) have expanded the capabilities of EBRT. PBT offers the advantage of minimizing low- and moderate-dose radiation to the surrounding normal tissue, thereby preserving uninvolved liver and allowing for dose escalation. MRgRT provides the advantage of improved soft tissue delineation compared to computerized tomography (CT) guidance. Additionally, MRgRT with online adaptive therapy is particularly useful for addressing motion not otherwise managed and reducing high-dose radiation to the normal tissue such as the stomach and bowel. PBT and online adaptive MRgRT are emerging technological advancements in EBRT that may provide a significant clinical benefit for patients with HCC.

The Tumor Microenvironment of Hepatocellular Carcinoma: Untying an Intricate Immunological Network

HCC, the most prevalent form of primary liver cancer, is prototypically an inflammation-driven cancer developing after years of inflammatory insults. Consequently, the hepatic microenvironment is a site of complex immunological activities. Moreover, the tolerogenic nature of the liver can act as a barrier to anti-tumor immunity, fostering cancer progression and resistance to immunotherapies based on immune checkpoint inhibitors (ICB). In addition to being a site of primary carcinogenesis, many cancer types have high tropism for the liver, and patients diagnosed with liver metastasis have a dismal prognosis. Therefore, understanding the immunological networks characterizing the tumor microenvironment (TME) of HCC will deepen our understanding of liver immunity, and it will underpin the dominant mechanisms controlling both spontaneous and therapy-induced anti-tumor immune responses. Herein, we discuss the contributions of the cellular and molecular components of the liver immune contexture during HCC onset and progression by underscoring how the balance between antagonistic immune responses can recast the properties of the TME and the response to ICB.

Proton irradiation induced reactive oxygen species promote morphological and functional changes in HepG2 cells

The increased use of proton therapy has led to the need of better understanding the cellular mechanisms involved. The aim of this study was to investigate the effects induced by the accelerated proton beam in hepatocarcinoma cells. An existing facility in IFIN-HH, a 3 MV Tandetron™ accelerator, was used to irradiate HepG2 human hepatocarcinoma cells with doses between 0 and 3 Gy. Colony formation was used to assess the influence of radiation on cell long-term replication. Also, the changes induced at the mitochondrial level were shown by increased ROS and ATP levels as well as a decrease in the mitochondrial membrane potential. An increased dose has induced DNA damages and G₂/M cell cycle arrest which leads to caspase 3/7 mediated apoptosis and senescence induction. Finally, the morphological and ultrastructural changes were observed at the membrane level and the nucleus of the irradiated cells. Thus, proton irradiation induces both morphological and functional changes in HepG2 cells.

Clinical Management of Liver Cancer in India and Other Developing Nations: A Focus on Radiation Based Strategies

Hepatocellular carcinoma (HCC) is a global killer with preponderance in Asian and African countries. It poses a challenge for successful management in less affluent or developing nations like India, with large populations and limited infrastructures. This review aims to assess the available options and future directions for management of HCC applicable to such countries. While summarizing current and emerging clinical strategies for detection, staging and therapy of the disease, it highlights radioisotope- and radioactivity-based strategies as part of an overall program. Using the widely accepted Barcelona Clinic Liver Cancer (BCLC) staging system as a base, it evaluates the applicability of different therapeutic approaches and their synergistic combination(s) in the context of a patient-specific dynamic results-based strategy. It distills the conclusions of multiple HCC management-focused consensus recommendations to provide a picture of clinical strategies, especially radiation-related approaches. Additionally, it discusses the logistical and economic feasibility of these approaches in the context of the limitations of the burdened public health infrastructure in India (and like nations) and highlights possible strategies both at the clinical level and in terms of an administrative health policy on HCC to provide the maximum possible benefit to the widest swathe of the affected population.

Long-term clinical outcomes of patients receiving proton beam therapy for caudate lobe hepatocellular carcinoma

Hepatocellular carcinoma (HCC) located in the caudate lobe (caudate HCC) is rare; however, patients with this type of tumour have poorer prognoses than those with HCC in other segments. Despite many published reports on the clinical usefulness of proton beam therapy (PBT) for HCC, data on the clinical outcomes of patients undergoing PBT for caudate HCC remain scarce. Therefore, the present study aimed to investigate the outcomes of this group of patients. Thirty patients with caudate HCC who underwent definitive PBT between February 2002 and February 2014 were retrospectively analysed. The total irradiation doses ranged from 55 to 77 (median 72.6) Gy relative biological dose. The median follow-up period was 37.5 (range, 3.0-152.0) months. The overall survival (OS) rates at one, three and five years were 86.6%, 62.8% and 46.1%, respectively. According to univariate and multivariate analyses, Child-Pugh A (P < 0.01), having a single tumour (P = 0.02) and a low serum alpha-fetoprotein level (AFP; P < 0.01) were significant factors predicting longer survival. The local control (LC) rates at one, three and five years were 100%, 85.9% and 85.9%, respectively, while the corresponding progression-free survival (PFS) rates were 65%, 27.5% and 22%, respectively. No grade 3 or worse adverse events were observed. PBT is effective and safe for the treatment of caudate HCC, and should therefore be considered a feasible option for intervention in patients with this disease.

Comparison of the [18F]-FDG and [18F]-FLT PET Tracers in the Evaluation of the Preclinical Proton Therapy Response in Hepatocellular Carcinoma

PURPOSE

The main objective of the present study was to compare the 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]-FDG) and 3'-[¹⁸F]fluoro-3'-deoxythymidine ([¹⁸F]-FLT) PET imaging biomarkers for the longitudinal follow-up of small animal proton therapy studies in the context of hepatocellular carcinoma (HCC).

PROCEDURES

SK-HEP-1 cells were injected into NMRI nude mice to mimic human HCC. The behavior of [¹⁸F]-FDG and [¹⁸F]-FLT tumor uptake was evaluated after proton therapy procedures. The proton single-fraction doses were 5, 10, and 20 Gy, with a dose rate of 10 Gy/min. The experimental protocol consisted of 8 groups of 10 mice, each group experiencing a particular dose/radiotracer condition. A reference PET exam was performed on each mouse the day before the irradiation procedure, followed by PET exams every 3 days up to 16 days after irradiation.

RESULTS

[¹⁸F]-FDG uptake showed a linear dose-dependent increase in the first days after treatment (37%, p < 0.05), while [¹⁸F]-FLT uptake decreased in a dose-dependent manner (e.g., 21% for 5 Gy compared to 10 Gy, p = 1.1e-2). At the later time point, [¹⁸F]-FDG normalized activity showed an 85% decrease (p < 0.01) for both 10 and 20 Gy doses and no variation for 5 Gy. Conversely, a significant 61% (p = 0.002) increase was observed for [¹⁸F]-FLT normalized activity at 5 Gy and no variation for higher doses.

CONCLUSION

We showed that the use of the [¹⁸F]-FDG and [¹⁸F]-FLT radiolabeled molecules can provide useful and complementary information for longitudinal follow-up of small animal proton therapy studies in the context of HCC. [¹⁸F]-FDG PET imaging enables a treatment monitoring several days/weeks postirradiation. On the other hand, [¹⁸F]-FLT could represent a good candidate to monitor the treatment few days postirradiation, in the context of hypo-fractioned and close irradiation planning. This opens new perspectives in terms of treatment efficacy verification depending on the irradiation scheme.

The Potential Role of Intensity-Modulated Proton Therapy in Hepatic Carcinoma in Mitigating the Risk of Dose De-Escalation

PURPOSE

To investigate the role of intensity-modulated proton therapy (IMPT) for hepatocellular carcinoma (HCC) patients to be treated with stereotactic body radiation therapy (SBRT) in a risk-adapted dose prescription regimen.

METHODS

A cohort of 30 patients was retrospectively selected as "at-risk" of dose de-escalation due to the proximity of the target volumes to dose-limiting healthy structures. IMPT plans were compared to volumetric modulated arc therapy (VMAT) RapidArc (RA) plans. The maximum dose prescription foreseen was 75 Gy in 3 fractions. The dosimetric analysis was performed on several quantitative metrics on the target volumes and organs at risk to identify the relative improvement of IMPT over VMAT and to determine if IMPT could mitigate the need of dose reduction and quantify the consequent potential patient accrual rate for protons.

RESULTS

IMPT and VMAT plans resulted in equivalent target dose distributions: both could ensure the required coverage for CTV and PTV. Systematic and significant improvements were observed with IMPT for all organs at risk and metrics. An average gain of 9.0 ± 11.6, 8.5 ± 7.7, 5.9 ± 7.1, 4.2 ± 6.4, 8.9 ± 7.1, 6.7 ± 7.5 Gy was found in the near-to-maximum doses for the ribs, chest wall, heart, duodenum, stomach and bowel bag respectively. Twenty patients violated one or more binding constraints with RA, while only 2 with IMPT. For all these patients, some dose de-intensification would have been required to respect the constraints. For photons, the maximum allowed dose ranged from 15.0 to 20.63 Gy per fraction while for the 2 proton cases it would have been 18.75 or 20.63 Gy.

CONCLUSION

The results of this in-silico planning study suggests that IMPT might result in advantages compared to photon-based VMAT for HCC patients to be treated with ablative SBRT. In particular, the dosimetric characteristics of protons may avoid the need for dose de-escalation in a risk-adapted prescription regimen for those patients with lesions located in proximity of dose-limiting healthy structures. Depending on the selection thresholds, the number of patients eligible for treatment at the full dose can be significantly increased with protons.

LncRNA TRG-AS1 stimulates hepatocellular carcinoma progression by sponging miR-4500 to modulate BACH1

Background

T cell receptor gamma locus antisense RNA 1 (TRG-AS1) has been reported to involve in the progression of glioblastoma, however the role and its underlying molecular mechanism in hepatocellular carcinoma (HCC) remain unknown.

Methods

Quantitative real-time polymerase chain reaction (RT-qPCR) was applied to detect TRG-AS1 expression in HCC cells. Besides, the proliferation abilities of HCC cells were assessed by colony formation and EdU assays. The migratory and invasive abilities of HCC cells were examined by transwell assays. Imunofluorescence staining (IF) was used to analyze the epithelial–mesenchymal transitions (EMT). The interaction among TRG-AS1, miR-4500 and BTB domain and CNC homolog 1 (BACH1) were proofed by means of RIP and RNA pull down and luciferase reporter assays.

Results

TRG-AS1 was conspicuously overexpressed in HCC cells. TRG-AS1 silencing apparently suppressed HCC cell proliferation, migration, invasion and epithelial-mesenchymal transition (EMT). Mechanism exploration revealed that TRG-AS1 acted as a molecular sponge of miR-4500 to regulate BACH1. MiR-4500 silencing or BACH1 overexpression in BACH1-downregulated cells fully rescued cell proliferation migration, invasion and EMT progress.

Conclusion

TRG-AS1 regulates HCC progression by targeting miR-4500/BACH1 axis.

The role of a knowledge based dose-volume histogram predictive model in the optimisation of intensity-modulated proton plans for hepatocellular carcinoma patients : Training and validation of a novel commercial system

PURPOSE

To investigate the performance of a knowledge-based RapidPlan, for optimisation of intensity-modulated proton therapy (IMPT) plans applied to hepatocellular cancer (HCC) patients.

METHODS

A cohort of 65 patients was retrospectively selected: 50 were used to "train" the model, while the remaining 15 provided independent validation. The performance of the RapidPlan model was benchmarked against manual optimisation and was also compared to volumetric modulated arc therapy (RapidArc) photon plans. A subanalysis appraised the performance of the RapidPlan model applied to patients with lesions ≤300 cm³ or larger. Quantitative assessment was based on several metrics derived from the constraints of the NRG-GI003 clinical trial.

RESULTS

There was an equivalence between manual plans and RapidPlan-optimised IMPT plans, which outperformed the RapidArc plans. The planning dose-volume objectives were met on average for all structures except for D_0.5 cm3 ≤30 Gy in the bowels. Limiting the results to the class-solution proton plans (all values in Gy), the data for manual plans vs RapidPlan-based IMPT plans, respectively, showed the following: D_99% to the target of 47.5 ± 1.4 vs 47.2 ± 1.2; for organs at risk, the mean dose to the healthy liver was 6.7 ± 3.6 vs 6.7 ± 3.7; the mean dose to the kidneys was 0.2 ± 0.5 vs 0.1 ± 0.2; D_0.5 cm3 for the bowels was 33.4 ± 16.4 vs 30.2 ± 16.0; for the stomach was 17.9 ± 19.9 vs 14.9 ± 18.8; for the oesophagus was 17.9 ± 15.1 vs 14.9 ± 13.9; for the spinal cord was 0.5 ± 1.6 vs 0.2 ± 0.7. The model performed similarly for cases with small or large lesions.

CONCLUSION

A knowledge-based RapidPlan model was trained and validated for IMPT. The results demonstrate that RapidPlan can be trained adequately for IMPT in HCC. The quality of the RapidPlan-based plans is at least equivalent compared to what is achievable with manual planning. RapidPlan also confirmed the potential to optimise the quality of the proton therapy results, thus reducing the impact of operator planning skills on patient results.

Postoperative adjuvant treatment strategy for hepatocellular carcinoma with microvascular invasion: a non-randomized interventional clinical study

BACKGROUND

Microvascular invasion (MVI) is considered to be one of the important prognostic factors that affect postoperative recurrence in patients with hepatocellular carcinoma (HCC) with variable results across their treatment options. This study was carried out to investigate efficacy of postoperative adjuvant RT in HCC patients with MVI.

METHODS

This was single center, prospective study carried out in HCC patients with MVI, aged 35-72 years. All patients were non-randomly allocated to receive standard postoperative treatment of HBV/HCV and nutritional therapy or RT in addition to standard postoperative treatment (1:1). The primary endpoints assessed were relapse-free survival and overall survival. The prognostic factors associated with survival outcomes were also analyzed. The safety events were graded according to NCI-CTCAE v4.03 criteria.

RESULTS

Of the 115 patients eligible for study, 59 patients were included in analysis. Univariate analysis revealed that MVI classification (P = 0.009), post-operative treatment strategies (P = 0.009) were prognostic factors for worst RFS; tumor size (P = 0.011), MVI classification (P = 0.005) and post-operative treatment (P = 0.015) were associated for OS. The 1-, 2-, 3-year RFS rates were 86.2, 70.5 and 63.4% for patients in RT group, and 46.4, 36.1, and 36.1% in control group. For OS, corresponding rates were 96.6, 80.7, and 80.7% for patients in RT group and 79.7, 58.3, and 50.0% in control group. Subgroup classification of HCC patients according to low risk MVI showed significantly longer RFS (P = 0.035) and OS (P = 0.004) in RT group than control group, while for high risk MVI, RT depicted longer OS than control group with no significance (P = 0.106). Toxicities were usually observed in acute stage with no grade 4 toxicities.

CONCLUSION

Postoperative adjuvant RT following hepatectomy offers better RFS for HCC patients with MVI than with standard postoperative therapy. Also, it will be useful to control microscopic lesions in both M1 (low risk) and M2 (high risk) subgroups of HCC patients with MVI.

TRIAL REGISTRATION

Trial Registration number: ChiCTR1800017371 . Date of Registration: 2018-07-26. Registration Status: Retrospectively registered.

A Real-World Study of Prognosis of N0M0 Hepatocellular Carcinoma with Hepatic Resection Based on SEER Database

AIM

To develop and validate a simple-to-use nomogram for prediction of 3-/5-year survival in patients with N0M0 hepatocellular carcinoma after curative liver resection. Patients and Methods. Patients diagnosed HCC with hepatic resection in the Surveillance, Epidemiology, and End Results (SEER) database were included to identify prognostic factors of overall survival. Multivariate Cox regression were used to create a nomogram.

RESULTS

We identified 4856 HCC with hepatic resection from the SEER database. A nomogram to predict long-term survival with a C-index 0.667 (95% CI, 0.653 to 0.681) is more efficient than TNM staging with a lower C-index 0.613 (95% CI, 0.597 to 0.629). The C-index was confirmed to be 0.663 (95% CI, 0.640 to 0.686) through validation, suggesting a good discrimination and a good prediction capability.

CONCLUSIONS

The nomogram is a simple and effective screening tool for assessing the prognosis of HCC with hepatic resection and assists with the planning of individual postoperative surveillance protocols.

Indicator for local recurrence of hepatocellular carcinoma after proton beam therapy: analysis of attenuation difference between the irradiated tumor and liver parenchyma on contrast enhancement CT

OBJECTIVES

We aimed to identify dynamic CT features that can be used for prediction of local recurrence of hepatocellular carcinoma (HCC) after proton beam therapy (PBT).

METHODS

We retrospectively retrieved CT scans of patients with PBT-treated HCC, taken between January 2004 and December 2016. 17 recurrent lesions and 34 non-recurrent lesions were retrieved. The attenuation difference between irradiated tumor and irradiated parenchyma (AD_HCC-IP) was compared in the two groups by using the Mann-Whitney U test. Cut-off value of AD_HCC-IP was estimated by using the Youden index.

RESULTS

The follow-up time after PBT initiation ranged from 374 to 2402 days (median, 1069 days) in recurrent lesions, and 418 to 2923 days (median, 1091.5 days) in non-recurrent lesions (p = 0.892). The time until appearance of local recurrence after PBT initiation ranged from 189 to 2270 days (median, 497 days). AD_HCC-IP of recurrent lesions [mean, -21.8 Hounsfield units (HU); from -95 to -31 HU] was significantly greater than that of non-recurrent lesions (mean, -51.7 HU; from -117 to -12 HU) at 1-2 years in portal venous phase (p = 0.039). 5-year local tumor control rates were 0.93 and 0.56 in lesions with AD_HCC-IP at 1-2 years in PVP < -55 and ≥ -55 HU, respectively.

CONCLUSION

The attenuation difference between irradiated HCC and irradiated liver parenchyma in portal venous phase at 1-2 years after PBT can predict long-term local recurrence of HCC after treatment.

ADVANCES IN KNOWLEDGE

We identified a cut-off value for contrast enhancement of HCC after PBT that could predict future local recurrence.

Rethinking the Role of Radiation Therapy in the Treatment of Unresectable Hepatocellular Carcinoma: A Data Driven Treatment Algorithm for Optimizing Outcomes

Hepatocellular carcinoma (HCC) is the second most common cause of cancer death worldwide, with a majority of HCC patients not suitable for curative therapies. Approximately 70% of initially diagnosed patients cannot undergo surgical resection or transplantation due to locally advanced disease, poor liver function/underlying cirrhosis, or additional comorbidities. Local therapeutic options for patients with unresectable HCC, who are not suitable for thermal ablation, include transarterial embolization (bland, chemoembolization, radioembolization) and/or external beam radiation therapy (EBRT). Regarding EBRT specifically, technological advancements provide a means for safe and effective radiotherapy delivery in a wide spectrum of HCC patients. In multiple prospective studies, EBRT delivery in a variety of different fractionation schemes or in combination with transcatheter arterial chemoembolization (TACE) demonstrate improved outcomes, particularly with combination therapy. The Barcelona Clinic Liver Cancer classification provides a framework for treatment selection; however, given the growing complexity of treatment strategies, this classification system tends to simplify decision-making. In this review, we discuss the current literature regarding unresectable HCC and propose a modified treatment algorithm that emphasizes the role of radiation therapy for Child-Pugh score A or B patients with ≤3 nodules measuring >3 cm, multinodular disease or portal venous thrombosis.

Multidisciplinary approach for multifocal, bilobar hepatocellular carcinoma: A case report and literature review

BACKGROUND

Hepatocellular carcinoma (HCC) is the second most lethal malignancy worldwide. There has been virtually no change in the survivability of HCC in spite of improvement in therapies. Surgery is considered the ideal first, curative intervention, however most patients present in advanced stages with unresectable disease. Therefore, systemic and liver-directed non-operative therapies are initially offered to downstage the disease. To ensure optimal management, a multidisciplinary team approach is often warranted. Our case highlights the benefits of a multidisciplinary approach in a young woman with multifocal, bilobar HCC.

CASE SUMMARY

A 36-year-old Chinese woman with untreated hepatitis B was found to have large bilobar HCC during work up for abdominal pain. Her initial serum alpha-fetoprotein was significantly elevated to 311136 ng/mL. Computed tomography scan demonstrated bulky bilobar liver masses, consistent with intermediate stage HCC, Barcelona Clinic Liver Cancer Stage B. Her case was discussed and a personalized care plan was developed at the Multidisciplinary Center for Advanced Minimally Invasive Liver Oncologic Therapies at the University of Washington. She initially underwent bilobar transarterial chemoembolization with partial response of the left lobar tumor. Salvage hypofractionated proton beam radiation therapy was delivered to the right lobe followed by two additional transarterial chemoembolizations to the left lobe with good response. Finally, to remove left lobar residual disease, she was taken to the operating room for a left hepatectomy eleven months after her initial presentation. She continues to be without evidence of disease.

CONCLUSION

Coordinating the multiple HCC treatment modalities is complex and our case highlights the benefits of a multidisciplinary approach.

The association of changes in RAD51 and survivin expression levels with the proton beam sensitivity of Capan‑1 and Panc‑1 human pancreatic cancer cells

Fewer than 20% of patients diagnosed with pancreatic cancer can be treated with surgical resection. The effects of proton beam irradiation were evaluated on the cell viabilities in Panc‑1 and Capan‑1 pancreatic cancer cells. The cells were irradiated with proton beams at the center of Bragg peaks with a 6‑cm width using a proton accelerator. Cell proliferation was assessed with the MTT assay, gene expression was analyzed with semi‑quantitative or quantitative reverse transcription‑polymerase chain reaction analyses and protein expression was evaluated by western blotting. The results demonstrated that Capan‑1 cells had lower cell viability than Panc‑1 cells at 72 h after proton beam irradiation. Furthermore, the cleaved poly (ADP‑ribose) polymerase protein level was increased by irradiation in Capan‑1 cells, but not in Panc‑1 cells. Additionally, it was determined that histone H2AX phosphorylation in the two cell lines was increased by irradiation. Although a 16 Gy proton beam was only slightly up‑regulated cyclin‑dependent kinase inhibitor 1 (p21) protein expression in Capan‑1 cells, p21 expression levels in Capan‑1 and Panc‑1 cells were significantly increased at 72 h after irradiation. Furthermore, it was observed that the expression of DNA repair protein RAD51 homolog 1 (RAD51), a homogenous repair enzyme, was decreased in what appeared to be a dose‑dependent manner by irradiation in Capan‑1 cells. Contrastingly, the transcription of survivin in Panc‑1 was significantly enhanced. The results suggest that RAD51 and survivin are potent markers that determine the therapeutic efficacy of proton beam therapy in patients with pancreatic cancer.

Critical appraisal of the potential role of intensity modulated proton therapy in the hypofractionated treatment of advanced hepatocellular carcinoma

PURPOSE

To investigate the role of intensity modulated proton therapy (IMPT) for advanced hepatocellular carcinoma in comparison with volumetric modulated arc therapy (VMAT).

METHODS

An in-silico planning study was performed on 20 patients. The prescription dose was 60Gy in 6 fractions. Patients were planned with abdominal compression. IMPT plans were optimized with or without the inclusion of CT calibration (3%) and isocenter positioning (2,4,6mm) uncertainties. Plan robustness was appraised comparing rubust optimized plans vs standard plans and also in terms of the worst-case scenario. VMAT plans were optimized for 10FFF photon beams using 2 partial arcs.

RESULTS

Target coverage was fully achieved by both VMAT and IMPT plans with a significant improvement in homogeneity (~25%) with IMPT. Integral dose was reduced of ~60% with IMPT while the conformality of the dose distributions was similar among techniques. The sparing of the organs at risk was strongly improved with IMPT although all clinical objectives were met for both techniques. The inclusion of the uncertainties in the optimization lead to some deterioration in the target dose homogeneity (from 40 to 80% worse with 4 or 6mm position uncertainty) while none of the coverage parameters or OAR objective was violated. The worst-case scenario analysis demonstrated the risk of a major target underdosage only in the case of the most extreme errors (6mm) with D98% in average ~12% lower than the threshold.

CONCLUSION

IMPT with the support of abdominal compression, can be considered a viable solution also for advanced hepatocellular carcinoma patients. Great care shall be put in the minimization of the residual respiration and positioning uncertainties but the dosimetric advantage for organs at risk and the relative robustness on target coverage are promising factors.

Proton therapy for hepatocellular carcinoma: Current knowledges and future perspectives

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death, as few patients can be treated with currently available curative local modalities. In patients with HCC where curative modalities are not feasible, radiation therapy (RT) has emerged as an alternative or combination therapy. With the development of various technologies, RT has been increasingly used for the management of HCC. Among these advances, proton beam therapy (PBT) has several unique physical properties that give it a finite range in a distal direction, and thus no exit dose along the beam path. Therefore, PBT has dosimetric advantages compared with X-ray therapy for the treatment of HCC. Indeed, various reports in the literature have described the favorable clinical outcomes and improved safety of PBT for HCC patients compared with X-ray therapy. However, there are some technical issues regarding the use of PBT in HCC, including uncertainty of organ motion and inaccuracy during calculation of tissue density and beam range, all of which may reduce the robustness of a PBT treatment plan. In this review, we discuss the physical properties, current clinical data, technical issues, and future perspectives on PBT for the treatment of HCC.