Hyperthermic enhancement of tumour growth inhibition by accelerated carbon-ions in transplantable human esophageal cancer

A systematic review on the usage of averaged LET in radiation biology for particle therapy

Linear Energy Transfer (LET) is widely used to express the radiation quality of ion beams, when characterizing the biological effectiveness. However, averaged LET may be defined in multiple ways, and the chosen definition may impact the resulting reported value. We review averaged LET definitions found in the literature, and quantify which impact using these various definitions have for different reference setups. We recorded the averaged LET definitions used in 354 publications quantifying the relative biological effectiveness (RBE) of hadronic beams, and investigated how these various definitions impact the reported averaged LET using a Monte Carlo particle transport code. We find that the kind of averaged LET being applied is, generally, poorly defined. Some definitions of averaged LET may influence the reported averaged LET values up to an order of magnitude. For publications involving protons, most applied dose averaged LET when reporting RBE. The absence of what target medium is used and what secondary particles are included further contributes to an ill-defined averaged LET. We also found evidence of inconsistent usage of averaged LET definitions when deriving LET-based RBE models. To conclude, due to commonly ill-defined averaged LET and to the inherent problems of LET-based RBE models, averaged LET may only be used as a coarse indicator of radiation quality. We propose a more rigorous way of reporting LET values, and suggest that ideally the entire particle fluence spectra should be recorded and provided for future RBE studies, from which any type of averaged LET (or other quantities) may be inferred.

Differential response of esophageal cancer cells to particle irradiation

Background

Radiation therapy is a mainstay in the treatment of esophageal cancer (EC) patients, and photon radiotherapy has proved beneficial both in the neoadjuvant and the definitive setting. However, regarding the still poor prognosis of many EC patients, particle radiation employing a higher biological effectiveness may help to further improve patient outcomes. However, the influence of clinically available particle radiation on EC cells remains largely unknown.

Methods

Patient-derived esophageal adenocarcinoma and squamous cell cancer lines were treated with photon and particle irradiation using clinically available proton (¹H), carbon (¹²C) or oxygen (¹⁶O) beams at the Heidelberg Ion Therapy Center. Histology-dependent clonogenic survival was calculated for increasing physical radiation doses, and resulting relative biological effectiveness (RBE) was calculated for each radiation modality. Cell cycle effects caused by photon and particle radiation were assessed, and radiation-induced apoptosis was measured in adenocarcinoma and squamous cell EC samples by activated caspase-3 and sub-G1 populations. Repair kinetics of DNA double strand breaks induced by photon and particle radiation were investigated.

Results

While both adenocarcinoma EC cell lines demonstrated increasing sensitivities for ¹H, ¹²C and ¹⁶O radiation, the two squamous cell carcinoma lines exhibited a more heterogeneous response to photon and particle treatment; average RBE values were calculated as 1.15 for ¹H, 2.3 for ¹²C and 2.5 for ¹⁶O irradiation. After particle irradiation, squamous cell EC samples reacted with an increased and prolonged block in G2 phase of the cell cycle compared to adenocarcinoma cells. Particle radiation resulted in an incomplete repair of radiation-induced DNA double strand breaks in both adenocarcinoma and squamous cell carcinoma samples, with the levels of initial strand break induction correlating well with the individual cellular survival after photon and particle radiation. Similarly, EC samples demonstrated heterogeneous levels of radiation-induced apoptosis that also corresponded to the observed cellular survival of individual cell lines.

Conclusions

Esophageal cancer cells exhibit differential responses to irradiation with photons and ¹H, ¹²C and ¹⁶O particles that were independent of tumor histology. Therefore, yet unknown molecular markers beyond histology may help to establish which esophageal cancer patients benefit from the biological effects of particle treatment.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1326-9) contains supplementary material, which is available to authorized users.

The dependence of p53 on the radiation enhancement of thermosensitivity at different let

PURPOSE

The aim of this study is to investigate the dependence of p53-gene status on the radiation enhancement of thermosensitivity at different levels of linear energy transfer (LET).

METHODS AND MATERIALS

We used two kinds of human glioblastoma transfectants of A-172 cells bearing the wild-type p53 gene, A-172/neo cells with control vector containing the neo gene and A-172/mp53 cells with both the dominant negative mutated p53 gene and neo gene. We exposed these cells to X-rays and accelerated carbon-ion (C-) beams (13-200 KeV/microm) followed by heating at 44 degrees C. Cellular sensitivities were determined using clonogenic assay.

RESULTS

The radiation enhancement of thermosensitivity was LET-dependent for the A-172/neo cells, but this was not clearly demonstrated in the A-172/mp53 cells. The supraadditive radiation enhancement of thermosensitivity was observed in A-172/neo cells at the LET range of 13 to 70 KeV/microm, though only an additive effect was observed at higher LET. In A-172/mp53 cells, only an additive effect was observed through all the LET examined.

CONCLUSION

These results indicate that the radiation enhancement of thermosensitivity is p53- and LET-dependent. Our results suggest that the combined use of high-LET radiation and hyperthermia brings useful application for cancer therapeutic purposes.