Effect of Cobalt-60 Calibration Dose-Rate on Arteriovenous Malformation Obliteration after Stereotactic Radiosurgery

PURPOSE/OBJECTIVE(S)

Stereotactic radiosurgery (SRS) dose rate - how old the cobalt-60 sources are - is known to influence outcomes for some neurologic conditions and benign tumors, but it is not known if SRS dose rate influences arteriovenous malformation (AVM) obliteration. The objective of this study is to determine the association between cobalt-60 calibration dose rate and cerebral AVM obliteration in patients treated with SRS. Our hypothesis is that higher SRS dose rates are associated with increased incidence of cerebral AVM obliteration.

MATERIALS/METHODS

We performed a retrospective study of 361 patients undergoing 411 AVM-directed SRS treatments between 2005 and 2019 at a single institution. Obliteration was confirmed with digital subtraction angiogram or MRI (if patient refused angiography). Lesion characteristics, SRS treatment details, and post-treatment obliteration and toxicities were recorded. Univariate and multivariate proportional hazards regression models of AVM outcomes with regard to SRS dose rate were performed, controlling for factors such as Spetzler-Martin Grade, maximum AVM extent, prior hemorrhage and prior embolization.

RESULTS

At 10 years post-SRS, 68% of AVMs were obliterated on follow-up imaging. Dose rates >2.9 Gy/min were found to be significantly associated with AVM obliteration compared to those <2.1 Gy/min (p = 0.034, Gray's test). AVM size or Spetzler-Martin grade were also associated with obliteration, with obliteration more likely for smaller lesions, particularly those <3 cm in maximal diameter, or with lower Spetzler-Martin grade. Higher dose rates were not associated with development of post-SRS radiologic or symptomatic edema, though larger AVM volume was associated with both types of edema.

CONCLUSION

Patients with cerebral AVMs treated with higher SRS dose rates (from fresh cobalt-60 sources) experience higher incidences of obliteration, without a significant change in the risk of post-treatment edema. These findings suggest that clinics offering SRS for AVMs should regularly renew cobalt-60 radiation sources to maintain high therapeutic dose rates.

A Prospective Study of Machine Learning-Assisted Radiotherapy Planning for Patients Receiving 54 Gy to the Brain

PURPOSE/OBJECTIVE(S)

Radiotherapy (RT) planning is presently a semi-manual, iterative, labor-intensive process which may result in unnecessary variation in plan quality. To improve treatment plan quality and decrease RT planning time, we conducted a prospective, blinded study to compare machine learning-assisted planning with conventional manual planning for patients receiving 54 Gy in 30 fractions for a primary brain tumor.

MATERIALS/METHODS

From January 31, 2022 to January 10, 2023, 40 patients receiving 54 Gy for primary CNS tumors were prospectively enrolled (median age 50 years, range 4-78 years). Patients underwent standard CT/MR simulation and target/OAR delineation by the treating radiation oncologist. Each patient had one ML plan and 1-2 manual RT plans created by different planners. The reviewing oncologist was blinded to planning method by removing optimization and IMRT/VMAT beam arrangement details from all plans, which were then rated based on clinical acceptability, target coverage, OAR sparing, conformity, and dose-fall off. One preferred plan was chosen and used for clinical treatment.

RESULTS

A total of 115 plans for 40 patients were evaluated: 40 ML plans (35% of all plans), and 75 manual plans (65% of all plans; 5 and 35 patients had 1 and 2 manual plans created, respectively). ML plans required a mean planning time of 65 min as compared to 107 min for manual plans, with a mean time savings of 41 min per patient (paired t-test p = 0.002). 97% of ML plans (95% confidence interval [CI] 85-100) and 96% of manual plans (95% CI 87-99) were designated clinically acceptable by the treating radiation oncologist. While ML-assisted plans represented 35% of plans evaluated, they were chosen as preferred for clinical treatment in 43% of cases (17/40, 95% CI 29-58, p = 0.32). Median doses to the brain (10.8 Gy vs. 11.3 Gy, Wilcoxon rank-sum p = 0.012) and brain minus PTV (9.2 Gy vs 10.0 Gy, Wilcoxon rank-sum p = 0.009) were lower with ML planning versus manual planning, respectively. Doses to other structures, including hippocampi, cochlea, pituitary and hypothalamus were not statistically different.

CONCLUSION

In this prospective study with blinded oncologist evaluation, ML-assisted RT planning for primary CNS tumors was faster than manual planning, and produced a very high rate of acceptable plans with similar or superior OAR sparing. Future work will be undertaken to iteratively refine the ML model using the preferred cases from this study.

Dose Reductions to Critical Brain Organs-at-Risk and Better Cognition in Children with Medulloblastoma Receiving Proton Therapy

PURPOSE/OBJECTIVE(S)

Our group previously demonstrated an improvement in cognition among children with medulloblastoma treated with proton therapy, as compared to photon therapy. However, the reason for this cognitive improvement was unclear. In this study, our aim was to determine whether dose to critical brain structures acted as a mediator of improved cognition in patients treated with proton therapy.

MATERIALS/METHODS

In this retrospective study, a cohort of 75 children with medulloblastoma from two institutions was assembled (39 photon, 36 proton). Included patients were treated with similar radiation and cognitive follow-up protocols. Study endpoints were verbal comprehension (VCI), perceptual reasoning (PRI), working memory (WMI), processing speed (PSI) indices and full-scale IQ (FSIQ). Brain structures were segmented and dose comparisons by RT modality were compared using independent t-tests. Linear mixed effects models with random intercepts were created to evaluate cognitive endpoints using R version 4.2.2.

RESULTS

Median follow-up from RT to last cognitive assessment was 4.8 years. Total dose, including RT boost, was slightly lower in the proton cohort than the photon cohort (mean, 54.6 Gy vs. 56.1 Gy, respectively, p < 0.001). Eleven children (31%) treated with proton therapy received 36 Gy CSI, while 6 children (15%) treated with photon therapy received 36 Gy CSI (p = 0.07). Children treated with proton therapy had reduced total doses to the brain (mean, D40), left and right temporal lobes (mean, D40, D50), and left and right hippocampi (mean, D40, D50 - see Table). After adjustment for age at RT and posterior fossa syndrome, higher whole brain mean dose and time since RT were associated with greater decrease in VCI (p = 0.033), higher left temporal D50 and time since RT with greater decrease in PRI (p = 0.031), higher whole brain D40 and time since RT with greater decrease in PSI (p < 0.001) and FSIQ (p = 0.030).

CONCLUSION

Our study demonstrates that proton therapy for patients with medulloblastoma reduces dose to normal brain tissues, which is associated with better intellectual outcomes. Children with medulloblastoma who undergo RT should be treated with proton therapy, if available.

Requirement of PPARα in maintaining phospholipid and triacylglycerol homeostasis during energy deprivation

The peroxisome proliferator-activated receptor alpha (PPARalpha) has been implicated as a key control of fatty acid catabolism during the cellular fasting. However, little is known regarding changes of individual fatty acids in hepatic triacylglycerol (TG) and phospholipid (PL) as a result of starvation. In the present work, the effects of 72 h fasting on hepatic TG and PL fatty acid profiles in PPARalpha-null (KO) mice and their wild-type (WT) counterparts were investigated. Our results indicated that mice deficient in PPARalpha displayed hepatomegaly and hypoketonemia following 72 h starvation. Histochemical analyses revealed that severe fatty infiltration was observed in the livers of KO mice under fasted conditions. Furthermore, 72 h fasting resulted in a 2.8-fold higher accumulation of hepatic TG in KO mice than in WT mice fasted for the same length of time. Surprisingly, the total hepatic PL contents in fasted KO mice decreased by 45%, but no significant change in hepatic PL content was observed in WT mice following starvation. Gas chromatographic analysis indicated that KO mice were deprived of arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acids during fasting. Taken together, these results show that PPARalpha plays an important role in regulation of fatty acid metabolism as well as phospholipid homeostasis during energy deprivation.

Screening of chemopreventive tea polyphenols against PAH genotoxicity in breast cancer cells by a XRE-luciferase reporter construct

Polycyclic aromatic hydrocarbons (PAHs) are established cancer initiators that can be found in our food and environment. Some dietary plant polyphenols are strong inhibitors to PAH-induced mutagenesis, whereas others may not be as effective. To identify the chemopreventive compounds from a huge volume of dietary components, the development of an efficient screening method is required. In this study, a xenobiotic response element (XRE)-luciferase reporter plasmid was constructed to screen for some potential chemopreventive agents in tea against PAH-induced DNA damage. Tea is one of the most consumed beverages worldwide, and its beneficial effects on health have been documented. Previous studies have claimed that tea polyphenols could be protective against various cancers, and the rich database can be a source for comparison. Among the green and black tea polyphenols, the XRE-luciferase reporter assays suggested that only epigallocatechin gallate (EGCG) was effective in reducing XRE-driven luciferase assay in MCF-7 cells at the concentrations tested. Further study indicated EGCG could reduce CYP1A1 and CYP1B1 mRNA abundances and decrease the DMBA-DNA lesions. The results of DNA covalent binding of all tea polyphenols tested were consistent with the XRE-reporter assays. This study illustrated that the XRE-reporter assay was a viable screening test for dietary chemopreventive agents against PAH-initiated breast mutagenesis. It has the advantages of shorter sample processing time and producing no radioactive waste over directly measuring the CYP1A1/1B1 expressions, DNA lesion, or gel mobility shift assay.

Baicalein and genistein display differential actions on estrogen receptor (ER) transactivation and apoptosis in MCF-7 cells

Genistein is a soy isoflavone that has attracted much attention for its chemopreventive properties. Baicalein is a flavone found in Scutellaria species, and its structure is analogous to that of genistein. We examined the two flavones' antiestrogenicity by using a transient transfection model. Our results indicated that baicalein could suppress 17beta-estradiol-induced transactivation in cells expressing estrogen receptor alpha, whereas no antagonistic activity was seen in genistein. Cell death assay and flow cytometry analysis demonstrated that baicalein was a stronger apoptosis inducing agent than genistein. Considering all the criteria tested, baicalein could be a better chemopreventive agent than genistein.

Baicalein inhibits DMBA-DNA adduct formation by modulating CYP1A1 and CYP1B1 activities

Flavonoids are phenolic compounds isolated from plants, and several of them like genistein and quercetin, have been documented to be effective in preventing cancer. Baicalein, a flavonoid extracted from the root of Scutellaria species, is widely used as a health supplement and herbal medicine in Asian countries. In this study, the chemopreventive effect of baicalein on 7,12-dimethylbenz[a]anthracene (DMBA)-induced DNA damage was evaluated in an established cell culture model. In a preliminary screening, baicalein was identified to be a strong inhibitor to EROD activities induced by DMBA in MCF-7 cells. Subsequent enzyme kinetic analysis revealed that baicalein was a competitive inhibitor to EROD, and CYP1A1 and CYP1B1 gene expressions were also determined. Baicalein could reduce the CYP1A1/1B1 mRNA expressions induced by DMBA, and the mRNA abundance of CYP1A1 appeared to be more responsive than that of CYP1B1. A XRE-luciferase gene reporter assay indicated that AhR transactivation was suppressed. Since CYP1A1/1B1 were responsible for the biotransformation of polycyclic aromatic hydrocarbons, baicalein also demonstrated its ability to reduce DMBA-DNA adduct formation in MCF-7 cells. This study suggested that the natural occurring baicalein could be an agent preventing carcinogen-DNA adduct formation.