Reirradiation vs. Systemic Therapy vs. Combination Therapy for Recurrent High-Grade Glioma: A Meta-Analysis of Survival and Toxicity

PURPOSE/OBJECTIVE(S)

To compare the effects of reirradiation, systemic therapy and combination therapy (reirradiation + systemic therapy) on overall survival (OS), progression-free survival (PFS) and adverse effects (AEs) in patients with recurrent high-grade glioma (rHGG).

MATERIALS/METHODS

A search was performed on PubMed, Scopus, Embase and CENTRAL on 18 March 2022, and repeated on 1 November 2022. Studies comparing OS, PFS and AEs in patients with rHGG, and encompassing the following four groups were included; reirradiation vs systemic therapy, combination therapy vs systemic therapy, combination therapy vs reirradiation, and reirradiation + bevacizumab-based systemic therapy vs reirradiation +/- non-bevacizumab-based systemic therapy. Risk of bias was assessed using the Cochrane RoB 2 tool for randomized control trials (RCTs) and the ROBINS-I tool for non-randomized studies. The logHR and SE (logHR) for OS and PFS, and logRR and SE (logRR) for AEs were extracted or estimated if not reported. Meta-analyses were performed for each comparator group using a random effects model. Subgroup analysis was performed on only RCTs if ≥ 2 studies were available.

RESULTS

Thirty-three studies comprising of 2201 participants were included. In the reirradiation vs systemic therapy group, there was no difference in PFS (2 studies, 185 participants; HR 0.87 (95% CI 0.61-1.22)) and OS (3 studies, 237 participants; HR 0.94 (95% CI 0.67-1.31)). In the combination therapy vs systemic therapy group, combination therapy improved PFS (6 studies, 605 participants; HR = 0.70 (95% CI 0.59-0.82)) and OS (6 studies, 537 participants; HR 0.73 (95% CI 0.56-0.96)), and there was no difference in grade 3+ AEs (4 studies, 398 participants; RR 1.03 (95% CI 0.57-1.86)). Subgroup analysis of only RCTs (2 studies, 205 participants) similarly showed no difference in grade 3+ AEs (RR 1.13 (95% CI 0.71-1.82)), though no significant improvements in PFS (HR 0.51 (95% CI 0.22-1.19)) or OS (HR 0.90 (95% CI 0.65-1.26)) were demonstrated. In the combination therapy vs reirradiation group, combination therapy improved PFS (5 studies, 259 participants; HR 0.50 (95% CI 0.37-0.69)) and OS (13 studies, 713 participants; HR 0.59 (95% CI 0.47-0.74)). In the reirradiation + bevacizumab-based systemic therapy vs reirradiation +/- non-bevacizumab-based systemic therapy group, combining reirradiation with bevacizumab improved PFS (2 studies, 104 participants; HR 0.46 (95% CI 0.27-0.77)) and OS (5 studies, 256 participants; HR 0.42 (95% CI 0.24-0.72)), and reduced radionecrosis (RN) (5 studies, 353 participants; RR 0.17 (95% CI 0.06-0.48)).

CONCLUSION

Combination therapy may improve OS and PFS with acceptable toxicity in select patients with rHGG. Further RCTs comparing systemic therapy to combination therapy, particularly with bevacizumab-based systemic therapy, are needed. The limitations of previous RCTs must be addressed; namely inadequate accrual of appropriate patients, and exclusion of FLAIR abnormalities from target delineation.

Reirradiation versus systemic therapy versus combination therapy for recurrent high-grade glioma: a systematic review and meta-analysis of survival and toxicity

PURPOSE

This review compares reirradiation (reRT), systemic therapy and combination therapy (reRT & systemic therapy) with regards to overall survival (OS), progression-free survival (PFS), adverse effects (AEs) and quality of life (QoL) in patients with recurrent high-grade glioma (rHGG).

METHODS

A search was performed on PubMed, Scopus, Embase and CENTRAL. Studies reporting OS, PFS, AEs and/or QoL and encompassing the following groups were included; reirradiation vs systemic therapy, combination therapy vs systemic therapy, combination therapy vs reRT, and bevacizumab-based combination therapy vs reRT with/without non-bevacizumab-based systemic therapy. Meta-analyses were performed utilising a random effects model. Certainty of evidence was assessed using GRADE.

RESULTS

Thirty-one studies (three randomised, twenty-eight non-randomised) comprising 2084 participants were included. In the combination therapy vs systemic therapy group, combination therapy improved PFS (HR 0.57 (95% CI 0.41-0.79); low certainty) and OS (HR 0.73 (95% CI 0.56-0.95); low certainty) and there was no difference in grade 3 + AEs (RR 1.03 (95% CI 0.57-1.86); very low certainty). In the combination therapy vs reRT group, combination therapy improved PFS (HR 0.52 (95% CI 0.38-0.72); low certainty) and OS (HR 0.69 (95% CI 0.52-0.93); low certainty). In the bevacizumab-based combination therapy vs reRT with/without non-bevacizumab-based systemic therapy group, adding bevacizumab improved PFS (HR 0.46 (95% CI 0.27-0.77); low certainty) and OS (HR 0.42 (95% CI 0.24-0.72; low certainty) and reduced radionecrosis (RR 0.17 (95% CI 0.06-0.48); low certainty).

CONCLUSIONS

Combination therapy may improve OS and PFS with acceptable toxicities in patients with rHGG compared to reRT or systemic therapy alone. Particularly, combining bevacizumab with reRT prophylactically reduces radionecrosis.

REGISTRATION

CRD42022291741.

Radioprotective effects of induced astronaut torpor and advanced propulsion systems during deep space travel

BACKGROUND

Human metabolic suppression is not a new concept, with 1950s scientific literature and movies demonstrating its potential use for deep space travel (Hock, 1960). An artificially induced state of metabolic suppression in the form of torpor would improve the amount of supplies required and therefore lessen weight and fuel required for missions to Mars and beyond (Choukèr et al., 2019). Transfer habitats for human stasis to Mars have been conceived (Bradford et al., 2018). Evidence suggests that animals, when hibernating, demonstrate relative radioprotection compared to their awake state. Experiments have also demonstrated relative radioprotection in conditions of hypothermia as well as during sleep (Bellesi et al., 2016 and Andersen et al., 2009). Circadian rhythm disrupted cells also appear to be more susceptible to radiation damage compared to those that are under a rhythmic control (Dakup et al., 2018). An induced torpor state for astronauts on deep space missions may provide a biological radioprotective state due to a decreased metabolism and hypothermic conditions. A regular enforced circadian rhythm might further limit DNA damage from radiation. The As Low As Reasonably Achievable (A.L.A.R.A.) radiation protection concept defines time, distance and shielding as ways to decrease radiation exposure. Whilst distance cannot be altered in space and shielding either passively or actively may be beneficial, time of exposure may be drastically decreased with improved propulsion systems. Whilst chemical propulsion systems have superior thrust to other systems, they lack high changes in velocity and fuel efficiency which can be achieved with nuclear or electric based propulsion systems. Radiation toxicity could be limited by reduced transit times, combined with the radioprotective effects of enforced circadian rhythms during a state of torpor or hibernation.

OBJECTIVES

1. Investigate how the circadian clock and body temperature may contribute to radioprotection during human torpor on deep space missions. 2. Estimate radiation dose received by astronauts during a transit to Mars with varying propulsion systems.

METHODS

We simulated three types of conditions to investigate the potential radioprotective effect of the circadian clock and decreased temperature on cells being exposed to radiation such that may be the case during astronaut torpor. These conditions were: - Circadian clock strength: strong vs weak. - Light exposure: dark-dark vs light-dark cycle - Body temperature: 37C vs hypothermia vs torpor. We estimated transit times for a mission to Mars from Earth utilizing chemical, nuclear and electrical propulsion systems. Transit times were generated using the General Mission Analysis Tool (GMAT) and Matlab. These times were then input into the National Aeronautics and Space Administration (NASA) Online Tool for the Assessment of Radiation In Space (OLTARIS) computer simulator to estimate doses received by an astronaut for the three propulsion methods.

RESULTS

Our simulation demonstrated an increase in radioprotection with decreasing temperature. The greatest degree of radioprotection was shown in cells that maintained a strong circadian clock during torpor. This was in contrast to relatively lower radioprotection in cells with a weak clock during normothermia. We were also able to demonstrate that if torpor weakened the circadian clock, a protective effect could be partially restored by an external drive such as lighting schedules to aid entrainment i.e.: Blue light exposure for periods of awake and no light for rest times For the propulsion simulation, estimated transit times from Earth to Mars were 258 days for chemical propulsion with 165.9mSv received, 209 days for nuclear propulsion with 134.4mSv received and 80 days for electrical propulsion with 51.4mSv received.

CONCLUSION

A state of torpor for astronauts on deep space missions may not only improve weight, fuel and storage requirements but also provide a potential biological radiation protection strategy. Moreover, maintaining a controlled circadian rhythm during torpor conditions may aid radioprotection. In the not too distant future, propulsion techniques will be improved to limit transit time and hence decrease radiation dose to astronauts. Limiting exposure time and enhancing physiological radioprotection during transit could provide superior radioprotection benefits compared with active and passive radiation shielding strategies alone.

Microsatellite variation and fine-scale population structure in the wood frog (Rana sylvatica)

We investigated genetic population structure in wood frogs (Rana sylvatica) from a series of Prairie Pothole wetlands in the northern Great Plains. Amphibians are often thought to exist in demographic metapopulations, which require some movement between populations, yet genetic studies have revealed strong subdivision among populations, even at relatively fine scales (several km). Wood frogs are highly philopatric and studies of dispersal suggest that they may exhibit subdivision on a scale of approximately 1-2 km. We used microsatellites to examine population structure among 11 breeding assemblages separated by as little as 50 m up to approximately 5.5 km, plus one population separated from the others by 20 km. We found evidence for differentiation at the largest distances we examined and among a few neighbouring ponds, but most populations were strikingly similar in allele frequencies, suggesting high gene flow among all but the most distant populations. We hypothesize that the few significant differences among neighbouring populations at the finest scale may be a transient effect of extinction-recolonization founder events, driven by periodic drying of wetlands in this hydrologically dynamic landscape.