Radiobiological rationale and clinical implications of hypofractionated radiation therapy

Comparison of Tumor Control and Skin Damage in a Mouse Model after Ultra-High Dose Rate Irradiation and Conventional Irradiation

Recent studies suggest ultra-high dose rate radiation treatment (UHDR-RT) reduces normal tissue damage compared to conventional radiation treatment (CONV-RT) at the same dose. In this study, we compared first, the kinetics and degree of skin damage in wild-type C57BL/6 mice, and second, tumor treatment efficacy in GL261 and B16F10 dermal tumor models, at the same UHDR-RT and CONV-RT doses. Flank skin of wild-type mice received UHDR-RT or CONV-RT at 25 Gy and 30 Gy. Normal skin damage was tracked by clinical observation to determine the time to moist desquamation, an endpoint which was verified by histopathology. Tumors were inoculated on the right flank of the mice, then received UHDR-RT or CONV-RT at 1 × 11 Gy, 1 × 15, 1 × 25, 3 × 6 and 3 × 8 Gy, and time to tumor tripling volume was determined. Tumors also received 1 × 11, 1 × 15, 3 × 6 and 3 × 8 Gy doses for assessment of CD8+/CD4+ tumor infiltrate and genetic expression 96 h postirradiation. All irradiations of the mouse tumor or flank skin were performed with megavoltage electron beams (10 MeV, 270 Gy/s for UHDR-RT and 9 MeV, 0.12 Gy/s for CONV-RT) delivered via a clinical linear accelerator. Tumor control was statistically equal for similar doses of UHDR-RT and CONV-RT in B16F10 and GL261 murine tumors. There were variable qualitative differences in genetic expression of immune and cell damage-associated pathways between UHDR and CONV irradiated B16F10 tumors. Compared to CONV-RT, UHDR-RT resulted in an increased latent period to skin desquamation after a single 25 Gy dose (7 days longer). Time to moist skin desquamation did not significantly differ between UHDR-RT and CONV-RT after a 30 Gy dose. The histomorphological characteristics of skin damage were similar for UHDR-RT and CONV-RT. These studies demonstrated similar tumor control responses for equivalent single and fractionated radiation doses, with variable difference in expression of tumor progression and immune related gene pathways. There was a modest UHDR-RT skin sparing effect after a 1 × 25 Gy dose but not after a 1 × 30 Gy dose.

Cellular bases of hypofractionated radiotherapy protocols for lung cancer

The extreme demand on health systems due to the COVID-19 pandemic has led to reconsider hypofractionation. Although the best clinical efficacy of these schemes is being demonstrated, the biological bases have not been established. Thus, after validating basic clinical parameters, through complementary in vitro models, we characterized the cellular and molecular mechanisms of hypofractionation protocols. Cell cultures of human lung cancer cell line A549 were irradiated with 0, 2, 4, 8, 12, 16 and 20 Gy. The clastogenic, cytotoxic, proliferative and clonogenic capacities and bystander effect were evaluated. In addition, we assessed survival and toxicity in a retrospective study of 49 patients with lung cancer. Our findings showed that the greater efficacy of ablative regimens should not only be attributed to events of direct cell death induced by genotoxic damage, but also to a lower cell repopulation and the indirect action of clastogenic factors secreted. These treatments were optimal in terms of 1- and 2-year overall survival (74 and 65%, respectively), and progression-free survival at 1 and 2 years (71 and 61%, respectively). The greater efficacy of high doses per fraction could be attributed to a multifactorial mechanism that goes beyond the 4Rs of conventional radiotherapy.

Establishment and Validation of CyberKnife Irradiation in a Syngeneic Glioblastoma Mouse Model

Simple Summary

Stereotactic radiosurgery (SRS) provides precise high-dose irradiation of intracranial tumors. However, its radiobiological mechanisms are not fully understood. This study aims to establish CyberKnife SRS on an intracranial glioblastoma tumor mouse model and assesses the early radiobiological effects of radiosurgery. Following exposure to a single dose of 20 Gy, the tumor volume was evaluated using MRI scans, whereas cellular proliferation and apoptosis, tumor vasculature, and immune response were evaluated using immunofluorescence staining. The mean tumor volume was significantly reduced by approximately 75% after SRS. The precision of irradiation was verified by the detection of DNA damage consistent with the planned dose distribution. Our study provides a suitable mouse model for reproducible and effective irradiation and further investigation of radiobiological effects and combination therapies of intracranial tumors using CyberKnife.

Abstract

CyberKnife stereotactic radiosurgery (CK-SRS) precisely delivers radiation to intracranial tumors. However, the underlying radiobiological mechanisms at high single doses are not yet fully understood. Here, we established and evaluated the early radiobiological effects of CK-SRS treatment at a single dose of 20 Gy after 15 days of tumor growth in a syngeneic glioblastoma-mouse model. Exact positioning was ensured using a custom-made, non-invasive, and trackable frame. One superimposed target volume for the CK-SRS planning was created from the fused tumor volumes obtained from MRIs prior to irradiation. Dose calculation and delivery were planned using a single-reference CT scan. Six days after irradiation, tumor volumes were measured using MRI scans, and radiobiological effects were assessed using immunofluorescence staining. We found that CK-SRS treatment reduced tumor volume by approximately 75%, impaired cell proliferation, diminished tumor vasculature, and increased immune response. The accuracy of the delivered dose was demonstrated by staining of DNA double-strand breaks in accordance with the planned dose distribution. Overall, we confirmed that our proposed setup enables the precise irradiation of intracranial tumors in mice using only one reference CT and superimposed MRI volumes. Thus, our proposed mouse model for reproducible CK-SRS can be used to investigate radiobiological effects and develop novel therapeutic approaches.

mNP hyperthermia and hypofractionated radiation activate similar immunogenetic and cytotoxic pathways

OBJECTIVE

The goal of this study is to better understand the immunogenetic expression and related cytotoxic responses of moderate but clinically relevant doses of hypofractionated radiation (1x15 Gy and 3x8 Gy) and magnetic nanoparticle hyperthermia (mNPH, CEM43 30).

METHODS

Genetic, protein, immunopathology and tumor growth delay assessments were used to determine the immune and cytotoxic responses following radiation and mNPH alone and in combination. Although the thermal dose used, 43 C°/30 min (CEM43 30), typically results in modest independent cytotoxicity, it has shown the ability to stimulate an immune response and enhance other cancer treatments. The radiation doses studied (15 Gy and 3x8 Gy) are commonly used in preclinical research and are effective in selected stereotactic and palliative treatment settings, however they are not commonly used as first-line primary tumor treatment regimens.

RESULTS

Our RNA-based genetic results suggest that while many of the cytotoxic and immune gene and protein pathways for radiation and hyperthermia are similar, radiation, at the doses used, results in a more consistent and expansive anti-cancer immune/cytotoxic expression profile. These results were supported by immunohistochemistry based cytotoxic T-cell tumor infiltration and tumor growth delay studies. When used together radiation and hyperthermia led to greater immune and cytotoxic activity than either modality alone.

CONCLUSION

This study clearly shows that modest, but commonly used hypofractionated radiation and hyperthermia doses share many important immune and cytotoxic pathways and that combining the treatments, as compared to either treatment alone, results in genetic and biological anti-cancer benefits.

Modern radiotherapy for head and neck cancer

Radiation therapy (RT) plays a key role in curative-intent treatments for head and neck cancers. Its use is indicated as a sole therapy in early stage tumors or in combination with surgery or concurrent chemotherapy in advanced stages. Recent technologic advances have resulted in both improved oncologic results and expansion of the indications for RT in clinical practice. Despite this, RT administered to the head and neck region is still burdened by a high rate of acute and late side effects. Moreover, about 50% of patients with high-risk disease experience loco-regional recurrence within 3 years of follow-up. Therefore, in recent decades, efforts have been dedicated to optimize the cost/benefit ratio of RT in this subset of patients. The aim of the present review was to highlight modern concepts of RT for head and neck cancers considering both the technological advances that have been achieved and recent knowledge that has informed the biological interaction between radiation and both tumor and healthy tissues.

[Irradiation in stereotactic conditions: prerequisites]

Indications of treatment by stereotactic body radiotherapy are dramatically increasing due to new potential indications. The conditions associated with the treatment delivery are multiple. The first step of the process is crucial. It is related to the validation of the indication proposed during the multidisciplinary meeting as regard the evidence-based proof of the concept. These emerging techniques mainly extracranial stereotactic body irradiation do not benefit from long-term evaluation in terms of efficiency as well as normal tissue late toxicities. Priority should be given to prospective independent clinical trials, validated by an independent scientific committee, performed under a relevant and well dedicated multicentric quality assurance program aiming to improve knowledge and selection of indications. The SFRO is still working with others professionals on the definition of the conditions for the implementation of such treatments and actively collaborates with the authorities to define the appropriate conditions to preserve the quality of the treatment delivery under these specific conditions.

Norm- and hypo-fractionated radiotherapy is capable of activating human dendritic cells

Despite the transient immunosuppressive properties of local radiotherapy (RT), this classical treatment modality of solid tumors is capable of inducing immunostimulatory forms of tumor-cell death. The resulting 'immunotoxicity' in the tumor, but not in healthy tissues, may finally lead to immune-mediated destruction of the tumor. However, little is known about the best irradiation scheme in this setting. This study examines the immunological effects of differently irradiated human colorectal tumor cells on human monocyte-derived dendritic cells (DC). Human SW480 tumor cells were irradiated with a norm-fractionation scheme (5 × 2 Gy), a hypo-fractionated protocol (3 × 5 Gy), and with a high single irradiation dose (radiosurgery; 1 × 15 Gy). Subsequently, human immature DC (iDC) were co-incubated with supernatants (SN) of these differently treated tumor cells. Afterwards, DC were analyzed regarding the expression of maturation markers, the release of cytokines, and the potential to stimulate CD4(+) T-cells. The co-incubation of iDC with SN of tumor cells exposed to norm- or hypo-fractionated RT resulted in a significantly increased secretion of the immune activating cytokines IL-12p70, IL-8, IL-6, and TNFα, compared to iDC co-incubated with SN of tumor cells that received a high single irradiation dose or were not irradiated. In addition, DC-maturation markers CD80, CD83, and CD25 were also exclusively elevated after co-incubation with the SN of fractionated irradiated tumor cells. Furthermore, the SN of tumor cells that were irradiated with norm- or hypo-fractionated RT triggered iDC to stimulate CD4(+) T-cells not only in an allogenic, but also in an antigen-specific manner like mature DC. Collectively, these results demonstrate that norm- and hypo-fractionated RT induces a fast human colorectal tumor-cell death with immunogenic potential that can trigger DC maturation and activation in vitro. Such findings may contribute to the improvement of irradiation protocols for the most beneficial induction of anti-tumor immunity.

[Alpha/beta ratio revisited in the era of hypofractionation]

Large doses per fraction are not recommended in daily radiotherapy due to a higher risk of late normal tissue injury. The technical refinements of modern radiotherapy and suggestions that some tumors could be sensitive to dose per fraction have renewed the interest in hypofractionated schedules. The estimation of α/β ratio value requires large samples of carefully evaluated patients in whom total and fractional doses have varied independently. Tumor repopulation has to be considered when the treatment duration is altered. Without setting aside conflicting publication, the α/β ratio values for prostate and breast (after lumpectomy) cancers could be as low as 2.5 Gy and 4 Gy, respectively. While it is too early to change our routine protocols, the time has come to conduct clinical trials comparing different fractionation schedules.

[Hypofractionated radiotherapy in prostate cancer]

Radiotherapy plays a central role in the management of localized prostate cancer, but the total duration of treatment of nearly 2 months poses not only problems of fatigue related to repetitive transports, especially for older patients, but also increases the overall cost of treatment including linear accelerators occupancy and patient transportation. To address this problem, various teams have developed hypofractionated radiotherapy protocols seeking to maintain the same efficacy and toxicity while reducing the total duration of treatment. These hypofractionated protocols require recent techniques such as image-guided radiation therapy (IGRT) and intensity-modulated radiation therapy (IMRT). Single centre series have validated the feasibility of "light" hypofractionation schemes at doses per fraction less than 6 Gy Similarly, different teams have shown the possibility of stereotactic irradiation for delivering "severe" hypofractionation schemes at doses greater than 6 Gy per fraction. Whatever the dose per fraction, the current clinical data support the conclusion that hypofractionated radiotherapy does not increase mid-term toxicity and could even improve biochemical control. Studies with the objective of demonstrating non-inferiority are expected to definitively validate the role of hypofractionated irradiation in the treatment of prostate cancer.

Present and future innovations in radiation oncology

The purpose of this article is to provide a review of innovations in radiation oncology that have been recently adopted as well as those that are likely to be adopted in the near future. Physics and engineering innovations, including image-guidance technologies and charged particle therapy, are discussed. Biologic innovations, including novel radiation sensitizers, functional imaging for use in treatment planning, and altered fractionation, are also discussed.

Probing early tumor response to radiation therapy using hyperpolarized [1-¹³C]pyruvate in MDA-MB-231 xenografts

Following radiation therapy (RT), tumor morphology may remain unchanged for days and sometimes weeks, rendering anatomical imaging methods inadequate for early detection of therapeutic response. Changes in the hyperpolarized [1-¹³C]lactate signals observed in vivo following injection of pre-polarized [1-¹³C]pyruvate has recently been shown to be a marker for tumor progression or early treatment response. In this study, the feasibility of using ¹³C metabolic imaging with [1-¹³C]pyruvate to detect early radiation treatment response in a breast cancer xenograft model was demonstrated in vivo and in vitro. Significant decreases in hyperpolarized [1-¹³C]lactate relative to [1-¹³C]pyruvate were observed in MDA-MB-231 tumors 96 hrs following a single dose of ionizing radiation. Histopathologic data from the treated tumors showed higher cellular apoptosis and senescence; and changes in the expression of membrane monocarboxylate transporters and lactate dehydrogenase B were also observed. Hyperpolarized ¹³C metabolic imaging may be a promising new tool to develop novel and adaptive therapeutic regimens for patients undergoing RT.