Effective radiotherapeutic treatment intensification in patients with pancreatic cancer: higher doses alone, higher RBE or both?

High-LET charged particles: radiobiology and application for new approaches in radiotherapy

The number of patients treated with charged-particle radiotherapy as well as the number of treatment centers is increasing worldwide, particularly regarding protons. However, high-linear energy transfer (LET) particles, mainly carbon ions, are of special interest for application in radiotherapy, as their special physical features result in high precision and hence lower toxicity, and at the same time in increased efficiency in cell inactivation in the target region, i.e., the tumor. The radiobiology of high-LET particles differs with respect to DNA damage repair, cytogenetic damage, and cell death type, and their increased LET can tackle cells' resistance to hypoxia. Recent developments and perspectives, e.g., the return of high-LET particle therapy to the US with a center planned at Mayo clinics, the application of carbon ion radiotherapy using cost-reducing cyclotrons and the application of helium is foreseen to increase the interest in this type of radiotherapy. However, further preclinical research is needed to better understand the differential radiobiological mechanisms as opposed to photon radiotherapy, which will help to guide future clinical studies for optimal exploitation of high-LET particle therapy, in particular related to new concepts and innovative approaches. Herein, we summarize the basics and recent progress in high-LET particle radiobiology with a focus on carbon ions and discuss the implications of current knowledge for charged-particle radiotherapy. We emphasize the potential of high-LET particles with respect to immunogenicity and especially their combination with immunotherapy.

Neoadjuvant Treatment for Resectable and Borderline Resectable Pancreatic Cancer: Chemotherapy or Chemoradiotherapy?

Worldwide, there is a shifting paradigm from immediate surgery with adjuvant treatment to a neoadjuvant approach for patients with resectable or borderline resectable pancreatic cancer (RPC or BRPC). Comparison of neoadjuvant and adjuvant studies is extremely difficult because of a great difference in patient selection. The evidence from randomized studies shows that overall survival by intention-to-treat improves after neoadjuvant gemcitabine-based chemoradiotherapy or chemotherapy (various regimens), as compared to immediate surgery followed by adjuvant chemotherapy. Radiotherapy appears to play an important role in mediating locoregional effects. Yet, since more effective chemotherapy regimens are currently available, in particular FOLFIRINOX and Gemcitabine/Nab-paclitaxel, these chemotherapy regimens should be investigated in future randomized trials combined with (stereotactic) radiotherapy to further improve outcomes of RPC and BRPC.

Physics and biomedical challenges of cancer therapy with accelerated heavy ions

Radiotherapy should have low toxicity in the entrance channel (normal tissue) and be very effective in cell killing in the target region (tumour). In this regard, ions heavier than protons have both physical and radiobiological advantages over conventional X-rays. Carbon ions represent an excellent combination of physical and biological advantages. There are a dozen carbon-ion clinical centres in Europe and Asia, and more under construction or at the planning stage, including the first in the USA. Clinical results from Japan and Germany are promising, but a heated debate on the cost-effectiveness is ongoing in the clinical community, owing to the larger footprint and greater expense of heavy ion facilities compared with proton therapy centres. We review here the physical basis and the clinical data with carbon ions and the use of different ions, such as helium and oxygen. Research towards smaller and cheaper machines with more effective beam delivery is necessary to make particle therapy affordable. The potential of heavy ions has not been fully exploited in clinics and, rather than there being a single 'silver bullet', different particles and their combination can provide a breakthrough in radiotherapy treatments in specific cases.

The Role of Particle Therapy for the Treatment of Skull Base Tumors and Tumors of the Central Nervous System (CNS)

Radiation therapy (RT) is a mainstay in the interdisciplinary treatment of brain tumors of the skull base and brain. Technical innovations during the past 2 decades have allowed for increasingly precise treatment with better sparing of adjacent healthy tissues to prevent treatment-related side effects that influence patients' quality of life. Particle therapy with protons and charged ions offer favorable kinetics with sharp dose deposition in a well-defined depth (Bragg-Peak) and a steep radiation fall-off beyond that maximum. This review highlights the role of particle therapy in the management of primary brain tumors and tumors of the skull base.

4DMRI-based investigation on the interplay effect for pencil beam scanning proton therapy of pancreatic cancer patients

BACKGROUND

Time-resolved volumetric magnetic resonance imaging (4DMRI) offers the potential to analyze 3D motion with high soft-tissue contrast without additional imaging dose. We use 4DMRI to investigate the interplay effect for pencil beam scanning (PBS) proton therapy of pancreatic cancer and to quantify the dependency of residual interplay effects on the number of treatment fractions.

METHODS

Based on repeated 4DMRI datasets for nine pancreatic cancer patients, synthetic 4DCTs were generated by warping static 3DCTs with 4DMRI deformation vector fields. 4D dose calculations for scanned proton therapy were performed to quantify the interplay effect by CTV coverage (v95) and dose homogeneity (d5/d95) for incrementally up to 28 fractions. The interplay effect was further correlated to CTV motion characteristics. For quality assurance, volume and mass conservation were evaluated by Jacobian determinants and volume-density comparisons.

RESULTS

For the underlying patient cohort with CTV motion amplitudes < 15 mm, we observed significant correlations between CTV motion amplitudes and both the length of breathing cycles and the interplay effect. For individual fractions, tumor underdosage down to v95 = 70% was observed with pronounced dose heterogeneity (d5/d95 = 1.3). For full × 28 fractionated treatments, we observed a mitigation of the interplay effect with increasing fraction numbers. On average, after seven fractions, a CTV coverage with 95-107% of the prescribed dose was reached with sufficient dose homogeneity. For organs at risk, no significant differences were found between the static and accumulated dose plans for 28 fractions.

CONCLUSION

Intrafractional organ motion exhibits a large interplay effect for PBS proton therapy of pancreatic cancer. The interplay effect correlates with CTV motion, but can be mitigated efficiently by fractionation, mainly due to different breathing starting phases in fractionated treatments. For hypofractionated treatments, a further restriction of motion may be required. Repeated 4DMRI measurements are a viable tool for pre- and post-treatment evaluations of the interplay effect.

Proton Beam Therapy and Carbon Ion Radiotherapy for Hepatocellular Carcinoma

Charged particle therapy with proton beam therapy (PBT) and carbon ion radiotherapy (CIRT) has emerged as a promising radiation modality to minimize radiation hepatotoxicity while maintaining high rates of tumor local control. Both PBT and CIRT deposit the majority of their dose at the Bragg peak with little to no exit dose, resulting in superior sparing of normal liver tissue. CIRT has an additional biological advantage of increased relative biological effectiveness, which may allow for increased hypofractionation regimens. Retrospective and prospective studies have demonstrated encouragingly high rates of local control and overall survival and low rates of hepatotoxicity with PBT and CIRT. Ongoing randomized trials will evaluate the value of PBT over photons and other standard liver-directed therapies and future randomized trials are needed to assess the value of CIRT over PBT.

Evaluation of radiation-related invasion in primary patient-derived glioma cells and validation with established cell lines: impact of different radiation qualities with differing LET

PURPOSE

Glioblastoma multiforme (GBM) is the most common primary brain tumor and has a very poor overall prognosis. Multimodal treatment is still inefficient and one main reason is the invasive nature of GBM cells, enabling the tumor cells to escape from the treatment area causing tumor progression. This experimental study describes the effect of low- and high-LET irradiation on the invasion of primary GBM cells with a validation in established cell systems.

METHODS

Seven patient derived primary GBM as well as three established cell lines (LN229, LN18 and U87) were used in this study. Invasion was investigated using Matrigel® coated transwell chambers. Irradiation was performed with low- (X-ray) and high-LET (alpha particles) radiation. The colony formation assay was chosen to determine the corresponding alpha particle dose equivalent to the X-ray dose.

RESULTS

4 Gy X-ray irradiation increased the invasive potential of six patient derived GBM cells as well as two of the established lines. In contrast, alpha particle irradiation with an equivalent dose of 1.3 Gy did not show any effect on the invasive behavior. The findings were validated with established cell lines.

CONCLUSION

Our results show that in contrast to low-LET irradiation high-LET irradiation does not enhance the invasion of established and primary glioblastoma cell lines. We therefore suggest that high-LET irradiation could become an alternative treatment option. To fully exploit the benefits of high-LET irradiation concerning the invasion of GBM further molecular studies should be performed.