Hypoxia-Targeted Dose Painting in Radiotherapy

Retrospective analysis and IMRT replanning of a 3D-CRT murine dose painting study for preclinical oxygen-guided radiotherapy

A recent parallel-opposed 3D-conformal radiotherapy (3D-CRT) study in mice compared dose escalation (boost) in hypoxic (pO2 ≤ 10 torr) and non-hypoxic tumor subvolumes. They found a hypoxic boost led to significantly greater (p < 1e-4) tumor control probability than an equivalent non-hypoxic boost. We imported imaging and treatment data from this study for 31 SCC7 squamous carcinoma murine leg tumor cases-16 hypoxic boost and 15 non-hypoxic boost plans into a commercial treatment planning system for preclinical radiotherapy. Treatments were retrospectively recalculated with a fast Monte Carlo dose engine. We replanned cases with 3-field IMRT using an analogous uncertainty budget as 3D-CRT. Comparing both treatment groups, the hypoxic boost treatments had a significantly higher hypoxic fraction receive the boost prescription as planned in 3D-CRT (p < 1e-4) and IMRT (p < 1e-4). Surprisingly, retrospective 3D-CRT non-hypoxic boost treatments had a significantly lower non-hypoxic fraction receive the boost prescription (p < 1e-4). 3D-CRT non-hypoxic boost also substantially underdosed the entire tumor between 48-68 Gy compared to the "equivalent" hypoxic boost. In IMRT, the non-hypoxic volume receiving boost prescription was significantly higher in the non-hypoxic boost (p = 0.0215) and dosing in the entire tumor was identical between boost groups. This study displays IMRT's potential to advance the quality of preclinical dose painting studies.

Tumour hypoxia in driving genomic instability and tumour evolution

Intratumour hypoxia is a feature of all heterogenous solid tumours. Increased levels or subregions of tumour hypoxia are associated with an adverse clinical prognosis, particularly when this co-occurs with genomic instability. Experimental evidence points to the acquisition of DNA and chromosomal alterations in proliferating hypoxic cells secondary to inhibition of DNA repair pathways such as homologous recombination, base excision repair and mismatch repair. Cell adaptation and selection in repair-deficient cells give rise to a model whereby novel single-nucleotide mutations, structural variants and copy number alterations coexist with altered mitotic control to drive chromosomal instability and aneuploidy. Whole-genome sequencing studies support the concept that hypoxia is a critical microenvironmental cofactor alongside the driver mutations in MYC, BCL2, TP53 and PTEN in determining clonal and subclonal evolution in multiple tumour types. We propose that the hypoxic tumour microenvironment selects for unstable tumour clones which survive, propagate and metastasize under reduced immune surveillance. These aggressive features of hypoxic tumour cells underpin resistance to local and systemic therapies and unfavourable outcomes for patients with cancer. Possible ways to counter the effects of hypoxia to block tumour evolution and improve treatment outcomes are described.

Non-medicinal oral contrast in upper abdominal MRI for MR-guided radiotherapy: A scoping review

INTRODUCTION

Using non-medicinal oral contrast agents may aid safe delivery of magnetic resonance image-guided (MR-guided) radiotherapy by improving the ability to visualise and avoid excessive radiation dose to adjacent bowel/stomach. This scoping review aims to map the literature on non-medicinal oral contrasts used in upper-abdominal diagnostic or therapeutic magnetic resonance imaging (MRI) to find potential candidates for employing in MR-guided radiotherapy and identify gaps in knowledge for further study.

METHODS

A scoping review of non-medicinal oral contrast used in upper-abdominal MRI research followed a pre-defined protocol based on Arksey and O'Malley's framework. Data were charted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses for Scoping Reviews reporting guidelines.

RESULTS

Forty-seven studies from 1955 screened abstracts were charted. Thirty-one distinct non-medicinal oral contrast were identified, used primarily to enhance tissue visualisation (89 %) or observe motility (11 %) in diagnostic studies. All studies reported to be predominantly quantitative; only 13 % included participant experience via questionnaires and none used qualitative methods. No studies have examined the efficacy of non-medicinal oral contrasts in MR-guided radiotherapy planning or delivery.

CONCLUSION

Non-medicinal oral contrasts have been extensively investigated in diagnostic MRI to enhance gastrointestinal visualisation and assess motility. However, non-medicinal oral contrasts have not been investigated in the context of radiotherapy planning and treatment. Qualitative evaluation of the patient experience of non-medicinal oral contrasts in magnetic resonance image-guided radiotherapy should be considered alongside studies quantifying the potential clinical benefit.

IMPLICATIONS FOR PRACTICE

This review summarises the properties of non-medicinal oral contrasts and identifies critical gaps in the current evidence, particularly the absence of qualitative research in this domain and the unexplored potential for their application in MR-guided radiotherapy planning and delivery.

Biological effectiveness of uniform and nonuniform dose distributions in radiotherapy for tumors with intermediate oxygen levels

Objective. We propose a criterion of biological effectiveness of nonuniform hypoxia-targeted dose distributions in heterogeneous hypoxic tumors based on equivalent uniform aerobic dose (EUAD). We demonstrate the utility of this criterion by applying it to the model problems in radiotherapy for tumors with different levels of oxygen enhancement ratio (OER) and different degrees of dose nonuniformity.Approach. The EUAD is defined as the uniform dose that, under well-oxygenated conditions, produces equal integrated survival of clonogenic cells in radiotherapy for heterogeneous hypoxic tumors with a non-uniform dose distribution. We define the dose nonuniformity effectiveness (DNE) in heterogeneous tumors as the ratio of the EUAD(DN) for a non-uniform distributionDNand the reference EUAD(DU) for the uniform dose distributionDUwith equal integral tumor dose. The DNE concept is illustrated in a radiotherapy model problem for non-small cell lung cancer treated with hypoxia targeted dose escalation. A two-level cell population tumor model was used to consider the hypoxic and oxygenated tumor cells.Results. Theoretical analysis of the DNE shows that the entire region of the OER can be separated in two regions by a threshold OERth: (1) OER > OERthwhere DNE > 1 indicating higher effectiveness of nonuniform dose distributions and (2) OER < OERthwhere DNE < 1 indicating higher effectiveness of uniform dose distributions. Our simulations show that the value of the threshold OERthin radiotherapy with conventional fractionation is significant in the range of about 1.2-1.6 depending on selected radiotherapy parameters. In general, the OERthincreases with reoxygenation rate, relative hypoxic volume and dose escalation factor. The threshold value of OERthis smaller of about 1.1 for hypofractionated radiotherapy.Significance. The analysis of dose distributions using the DNE shows that the uniform dose distributions may improve biological cell killing effect in heterogeneous tumors with intermediate oxygen levels compared to targeted nonuniform dose distribution.

Modeling hypoxia-induced radiation resistance and the impact of radiation sources

Hypoxia contributes significantly to resistance in radiotherapy. Our research rigorously examines the influence of microvascular morphology on radiotherapy outcome, specifically focusing on how microvasculature shapes hypoxia within the microenvironment and affects resistance to a standard treatment regimen (30×2GyRBE). Our computational modeling extends to the effects of different radiation sources. For photons and protons, our analysis establishes a clear correlation between hypoxic volume distribution and treatment effectiveness, with vascular density and regularity playing a crucial role in treatment success. On the contrary, carbon ions exhibit distinct effectiveness, even in areas of intense hypoxia and poor vascularization. This finding points to the potential of carbon-based hadron therapy in overcoming hypoxia-induced resistance to RT. Considering that the spatial scale analyzed in this study is closely aligned with that of imaging data voxels, we also address the implications of these findings in a clinical context envisioning the possibility of detecting subvoxel hypoxia.

Tumor hypoxia and radiotherapy: A major driver of resistance even for novel radiotherapy modalities

Hypoxia in solid tumors is an important predictor of poor clinical outcome to radiotherapy. Both physicochemical and biological processes contribute to a reduced sensitivity of hypoxic tumor cells to ionizing radiation and hypoxia-related treatment resistances. A conventional low-dose fractionated radiotherapy regimen exploits iterative reoxygenation in between the individual fractions, nevertheless tumor hypoxia still remains a major hurdle for successful treatment outcome. The technological advances achieved in image guidance and highly conformal dose delivery make it nowadays possible to prescribe larger doses to the tumor as part of single high-dose or hypofractionated radiotherapy, while keeping an acceptable level of normal tissue complication in the co-irradiated organs at risk. However, we insufficiently understand the impact of tumor hypoxia to single high-doses of RT and hypofractionated RT. So-called FLASH radiotherapy, which delivers ionizing radiation at ultrahigh dose rates (> 40 Gy/sec), has recently emerged as an important breakthrough in the radiotherapy field to reduce normal tissue toxicity compared to irradiation at conventional dose rates (few Gy/min). Not surprisingly, oxygen consumption and tumor hypoxia also seem to play an intriguing role for FLASH radiotherapy. Here we will discuss the role of tumor hypoxia for radiotherapy in general and in the context of novel radiotherapy treatment approaches.

Hafnium (Hf)-Chelating Porphyrin-Decorated Gold Nanosensitizers for Enhanced Radio-Radiodynamic Therapy of Colon Carcinoma

X-ray-induced radiodynamic therapy (RDT) that can significantly reduce radiation dose with an improved anticancer effect has emerged as an attractive and promising therapeutic modality for tumors. However, it is highly significant to develop safe and efficient radiosensitizing agents for tumor radiation therapy. Herein, we present a smart nanotheranostic system FA-Au-CH that consists of gold nanoradiosensitizers, photosensitizer chlorin e6 (Ce6), and folic acid (FA) as a folate-receptor-targeting ligand for improved tumor specificity. FA-Au-CH nanoparticles have been demonstrated to be able to simultaneously serve as radiosensitizers and RDT agents for enhanced computed tomography (CT) imaging-guided radiotherapy (RT) of colon carcinoma, owing to the strong X-ray attenuation capability of high-Z elements Au and Hf, as well as the characteristics of Hf that can transfer radiation energy to Ce6 to generate ROS from Ce6 under X-ray irradiation. The integration of RT and RDT in this study demonstrates great efficacy and offers a promising therapeutic modality for the treatment of malignant tumors.

The PRX-1/TLR4 axis promotes hypoxia-induced radiotherapy resistance in non-small cell lung cancer by targeting the NF-κB/p65 pathway

Hypoxic lung cancer cells are highly resistant to radiation. Peroxiredoxin-1 (PRX-1), a transcriptional coactivator that enhances the DNA-binding activity of serum reactive factor, has been identified as a target for radiotherapy sensitization, but the underlying molecular mechanism remains unclear. This study aimed to investigate the influence of PRX-1 on radiotherapy sensitivity in hypoxic tumors. Hypoxic lung cancer cells exhibited radiotherapy-resistant phenotypes after irradiation, including increased proliferation, DNA damage repair, cell migration, invasion and stemness. Radio-resistant hypoxic lung cancer cells showed high expression levels of PRX-1. Furthermore, we observed that PRX-1 bound to the promoter region of TRL4 (-300 to -600) and promoted its transcription and expression and that PRX-1/TRL4 activated the NF-κB/p65 signaling pathway. Increased radiotherapy resistance of hypoxic lung cancer cells increased their ability to proliferate, migrate, and maintain stemness in vivo and in vitro. These findings suggest that PRX-1/TRL4 could be used as a target for the treatment of radiotherapy-resistant lung cancer cells and further provide a theoretical basis for the clinical treatment of hypoxic lung cancer cells.