Clinical Outcomes and Patterns of Failure in Patients with High-Risk Atypical Meningioma Treated with Single Fraction vs. Hypofractionated Gamma Knife Radiosurgery

PURPOSE/OBJECTIVE(S)

The recently completed RTOG 0539 supports fractionated radiation therapy for patients categorized as having intermediate (3 yr PFS 93.8%) or high-risk (3 yr LC 68.9%) meningiomas. Stereotactic radiosurgery (SRS) has not been widely established in the treatment of WHO grade 2 atypical meningiomas given concern that there is a greater risk of microscopic infiltration and therefore requires larger margins than safely achievable with SRS. We look to review a consecutive cohort of patients at our institution who have been diagnosed with atypical meningioma treated with either single fraction Gamma Knife SRS (GK-sfSRS) or hypofractionated Gamma Knife SRS (GK-hfSRS). We review both control rates and patterns of failure.

MATERIALS/METHODS

Patients diagnosed with intermediate or high-risk WHO grade 2 meningioma per RTOG 0539 classification, without a history of prior radiation (RT) and treated with either GK-sfSRS or GK-hfSRS between 2014 to 2021 at our institution, were included. Patient charts were reviewed, and follow-up data were analyzed for local control (LC) and failure patterns. Local failure was defined as tumor recurrence within the prescription isodose line, marginal was ≤5 mm outside the prescription isodose line, and distant was >5 mm outside of the prescription isodose line Primary outcome was LC, and secondary outcomes were overall survival (OS) and progression free survival (PFS).

RESULTS

We identified 47 pathologically confirmed WHO grade 2 meningiomas in 27 patients. 33 lesions were treated with GK-sfSRS and 14 lesions with GK-hfSRS. 6 lesions were intermediate risk, and 41 were high-risk per RTOG 0539. With a median follow up of 36 months (range 2-86 mo), the 3yr LC was 82.7%, PFS was 83.1%, and OS was 96.3%. A total of 4 patients with 8 lesions failed treatment - all with high-risk disease. All failures were local (4) or marginal (4). The 4 local failures were all from a single patient with 4 distinct meningiomas that were treated with GK-sfSRS without surgical resection. The 4 marginal failures were all in patients treated with GK-sfSRS. There were no failures in patients treated with GK-hfSRS.

CONCLUSION

Our institutional data for patients with atypical meningiomas treated with radiosurgical techniques compare favorably to the patients treated with EBRT in RTOG 0539, though longer follow-up is needed to confirm these findings. Outside of one patient, no patients developed recurrence within the prescription volume. There were 4 tumors with marginal failures, suggesting that additional dural margins than what were prescribed may be meaningful. At our institution, we are increasingly moving to hypofractionated radiosurgery with 5 mm of dural margin when using radiosurgical techniques for high-risk atypical meningioma. However, longer term follow-up is needed to validate the use of radiosurgical techniques in atypical meningioma.

Prioritizing Radiation and Targeted Systemic Therapy in Patients with Resected Brain Metastases from Lung Cancer Primaries with Targetable Mutations: A Report from a Multi-Site Single Institution

PURPOSE/OBJECTIVE(S)

Brain metastases (BrM) are a common complication of non-small cell lung cancer (NSCLC), present in up to 50% of patients. While treatment of BrM requires a multidisciplinary approach with surgery, radiotherapy (RT), and systemic therapy, advances in sequencing have improved outcomes with targetable alterations in PDL-1, EGFR, ALK, and KRAS mutations. With a push towards molecular characterization of cancers, we sought out to examine outcomes by treatment modalities at our institution with respect to prioritizing RT and targeted therapies.

MATERIALS/METHODS

After IRB approval, we identified patients treated with a surgical resection of BrM from NSCL primaries between 2011 to 2022 at 5 sites at our institution. Tumor molecular profiles were reviewed and patients with PDL-1, EGFR, ALK, and KRAS mutations were evaluated by a treatment modality: surgery alone or in combination with RT (SRS, WBRT) and/or systemic therapy (TKIs -1st-3rd generations, immunotherapy). The primary endpoints were in-brain freedom from progression (FFP) and overall survival (OS). SAS Studio version 4.4 was used to perform statistical analyses.

RESULTS

We identified 272 patients with 162/272 (60%) patients with adequate follow-up included in this analysis. The median follow-up was 27.8 months (range, 0.43 - 134.45 months). There were 59.2% females and 40.7% males, with median ages at diagnosis of 67 years for females and 66 for males, respectively. Of the entire cohort, 102/162 (63%) patients received adjuvant combination RT and systemic therapy, and 60/162 (37%) received adjuvant monotherapy (p <0.0001). The use of systemic therapy was associated with 9.89 months median time to progression vs 4.87 months without it (p = 0.077), respectively. Similarly, patients treated with a combination of RT and systemic therapy had a median FFP time of 9.77 months vs 5.28 months (p = 0.064). No significant difference in OS was found with or without systemic therapy.

CONCLUSION

After resection of BrM from NSCLC with PDL-1, EGFR, ALK, and KRAS mutations, we found that systemic therapy, including TKIs and immunotherapy, may have an increasing role in delaying time to progression. At our institution, as we continue to identify actionable mutations, a statistically significant number of patients continue to be treated with a combination of RT and systemic therapies with a trend toward superior FFP.

The Association of Chemoradiation Induced Lymphopenia with Racial Disparity and Its Prognostic Impact on Survival for Anal Cancer

PURPOSE/OBJECTIVE(S)

While the association between chemoradiation induced lymphopenia (CIL) and poor overall survival (OS) is established in multiple solid malignancies, it has not been studied in anal cancer. Racial and socioeconomic disparities as potential predictors of lymphopenia have not been reported. We hypothesize that race and socioeconomic status is associated with increased incidence of severe CIL, which can predict worse overall survival for patients with anal cancer.

MATERIALS/METHODS

A cohort of 75 patients treated with definitive chemoradiation (CRT) for squamous cell anal cancer from January 2014 to December 2020 was reviewed. Total lymphocyte counts (TLC) at baseline and TLC nadir at 1 month post-CRT were analyzed. Logistic regression was used to identify associations between race, gender, ethnicity, median household income by zip code, marital status, baseline hematopoietic cell counts, and post-CRT Grade 3+ lymphopenia (TLC <0.5k/μL). Kaplan-Meier method and Cox regression model were used to perform survival analysis.

RESULTS

Of the 75 patients identified, mean age was 66.9 years and median follow-up time was 37.1 months. There were 63 females, 53 non-Hispanic whites, 22 minorities (12 Blacks, 9 Hispanics, 1 Asians) Radiation dose ranged from 41.4 Gray to 56 Gray. At 1 month post CRT, 85.3% developed lymphopenia (G1 9.3%, G2 26.7%, G3 37.3%, G4 12.0%). On multivariate logistic regression, non-white race demonstrated a trend to have more Grade 3+ lymphopenia (OR = 3.5, p = 0.07). On univariate Cox regression, poorer overall survival was associated with race (HR 3.7, p = 0.04), baseline white blood count (HR 1.3, p = 0.04), baseline hemoglobin (HR 0.6, p = 0.04), and post-CRT Grade 3+ lymphopenia (HR 5.8, p = 0.03). On multivariate Cox regression, only post-CRT Grade 3+ lymphopenia was associated with worse OS (HR 7.5, p = 0.049). 5-year OS significantly differed between patients with and without post-CRT Grade 3+ lymphopenia (62.3% vs 94.7%, P = 0.01).

CONCLUSION

Lymphopenia is commonly observed after chemoradiation for anal cancer. Racial disparity is associated with severe lymphopenia induced by chemoradiation, which is a robust predictor of poor survival in anal cancer. More attention to lymphopenia induced by chemoradiation for anal cancer is needed, particularly in racial minorities.

Determining Combined Modality Dosimetric Constraints by Integration of IMRT and LDR Prostate Brachytherapy Dosimetry and Correlation with Toxicity

Purpose

Intermediate- and high-risk prostate cancer patients undergoing combination external beam radiation therapy (EBRT) and low dose rate (LDR) brachytherapy have demonstrated increased genitourinary (GU) toxicity. We have previously demonstrated a method to combine EBRT and LDR dosimetry. In this work, we use this technique for a sample of patients with intermediate- and high-risk prostate cancer, correlate with clinical toxicity, and suggest preliminary summed organ-at-risk constraints for future investigation.

Methods and Materials

Intensity modulated EBRT and ¹⁰³Pd-based LDR treatment plans were combined for 138 patients using biological effective dose (BED) and deformable image registration. GU and gastrointestinal (GI) toxicity were compared with combined dosimetry for the urethra, bladder, and rectum. Differences between doses in each toxicity grade were assessed by analysis of variance (α = 0.05). Combined dosimetric constraints are proposed using the mean organ-at-risk dose, subtracting 1 standard deviation for a conservative recommendation.

Results

The majority of our 138-patient cohort experienced grade 0 to 2 GU or GI toxicity. Six grade 3 toxicities were noted. Mean prostate BED D90 (± 1 standard deviation) was 165.5±11.1 Gy. Mean urethra BED D10 was 230.3±33.9 Gy. Mean bladder BED was 35.2±11.0 Gy. Mean rectum BED D2cc was 85.6±24.3 Gy. Significant dosimetric differences between toxicity grades were found for mean bladder BED, bladder D15, and rectum D50, but differences between individual means were not statistically significant. Given the low incidence of grade 3 GU and GI toxicity, we propose urethra D10 <200 Gy, rectum D2cc <60 Gy, and bladder D15 <45 Gy as preliminary dose constraints for combined modality therapy.

Conclusions

We successfully applied our dose integration technique to a sample of patients with intermediate- and high-risk prostate cancer. Incidence of grade 3 toxicity was low, suggesting that combined doses observed in this study were safe. We suggest preliminary dose constraints as a conservative starting point to investigate and escalate prospectively in a future study.

LET-Dependent Low Dose and Synergistic Inhibition of Human Angiogenesis by Charged Particles: Validation of miRNAs that Drive Inhibition

Space radiation inhibits angiogenesis by two mechanisms depending on the linear energy transfer (LET). Using human 3D micro-vessel models, blockage of the early motile stage of angiogenesis was determined to occur after exposure to low LET ions (<3 KeV/AMU), whereas inhibition of the later stages occurs after exposure to high LET ions (>8 KeV/AMU). Strikingly, the combined effect is synergistic, detectible as low as 0.06 Gy making mixed ion space radiation more potent. Candidates for bystander transmission are microRNAs (miRNAs), and analysis on miRNA-seq data from irradiated mice shows that angiogenesis would in theory be downregulated. Further analysis of three previously identified miRNAs showed downregulation of their targets associated with angiogenesis and confirmed their involvement in angiogenesis pathways and increased health risks associated with cardiovascular disease. Finally, synthetic molecules (antagomirs) designed to inhibit the predicted miRNAs were successfully used to reverse the inhibition of angiogenesis.

Treatment Outcomes and Dose Rate Effects Following Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannomas

BACKGROUND

Gamma Knife radiosurgery (GKRS; Elekta AB) remains a well-established treatment modality for vestibular schwannomas. Despite highly effective tumor control, further research is needed toward optimizing long-term functional outcomes. Whereas dose-rate effects may impact post-treatment toxicities given tissue dose-response relationships, potential effects remain largely unexplored.

OBJECTIVE

To evaluate treatment outcomes and potential dose-rate effects following definitive GKRS for vestibular schwannomas.

METHODS

We retrospectively reviewed 419 patients treated at our institution between 1998 and 2015, characterizing baseline demographics, pretreatment symptoms, and GKRS parameters. The cohort was divided into 2 dose-rate groups based on the median value (2.675 Gy/min). Outcomes included clinical tumor control, radiographic progression-free survival, serviceable hearing preservation, hearing loss, and facial nerve dysfunction (FND). Prognostic factors were assessed using Cox regression.

RESULTS

The study cohort included 227 patients with available follow-up. Following GKRS 2-yr and 4-yr clinical tumor control rates were 98% (95% CI: 95.6%-100%) and 96% (95% CI: 91.4%-99.6%), respectively. Among 177 patients with available radiographic follow-up, 2-yr and 4-yr radiographic progression-free survival rates were 97% (95% CI: 94.0%-100.0%) and 88% (95% CI: 81.2%-95.0%). The serviceable hearing preservation rate was 72.2% among patients with baseline Gardner-Robertson class I/II hearing and post-treatment audiological evaluations. Most patients experienced effective relief from prior headaches (94.7%), tinnitus (83.7%), balance issues (62.7%), FND (90.0%), and trigeminal nerve dysfunction (79.2%), but not hearing loss (1.0%). Whereas GKRS provided effective tumor control independently of dose rate, GKRS patients exposed to lower dose rates experienced significantly better freedom from post-treatment hearing loss and FND (P = .044).

CONCLUSION

Whereas GKRS provides excellent tumor control and effective symptomatic relief for vestibular schwannomas, dose-rate effects may impact post-treatment functional outcomes. Further research remains warranted.

Rectal balloon use limits vaginal displacement, rectal dose, and rectal toxicity in patients receiving IMRT for postoperative gynecological malignancies

Pelvic radiotherapy for gynecologic malignancies traditionally used a 4-field box technique. Later trials have shown the feasibility of using intensity-modulated radiotherapy (IMRT) instead. But vaginal movement between fractions is concerning when using IMRT due to greater conformality of the isodose curves to the target and the resulting possibility of missing the target while the vagina is displaced. In this study, we showed that the use of a rectal balloon during treatment can decrease vaginal displacement, limit rectal dose, and limit acute and late toxicities. Little is known regarding the use of a rectal balloon (RB) in treating patients with IMRT in the posthysterectomy setting. We hypothesize that the use of an RB during treatment can limit rectal dose and acute and long-term toxicities, as well as decrease vaginal cuff displacement between fractions. We performed a retrospective review of patients with gynecological malignancies who received postoperative IMRT with the use of an RB from January 1, 2012 to January 1, 2015. Rectal dose constraint was examined as per Radiation Therapy Oncology Group (RTOG) 1203 and 0418. Daily cone beam computed tomography (CT) was performed, and the average (avg) displacement, avg magnitude, and avg magnitude of vector were calculated. Toxicity was reported according to RTOG acute radiation morbidity scoring criteria. Acute toxicity was defined as less than 90 days from the end of radiation treatment. Late toxicity was defined as at least 90 days after completing radiation. Twenty-eight patients with postoperative IMRT with the use of an RB were examined and 23 treatment plans were reviewed. The avg rectal V40 was 39.3% ± 9.0%. V30 was65.1% ± 10.0%. V50 was 0%. Separate cone beam computed tomography (CBCT) images (n = 663) were reviewed. The avg displacement was as follows: superior 0.4 + 2.99 mm, left 0.23 ± 4.97 mm, and anterior 0.16 ± 5.18 mm. The avg magnitude of displacement was superior/inferior 2.22 ± 2.04 mm, laterally 3.41 ± 3.62 mm, and anterior/posterior 3.86 ± 3.45 mm. The avg vector magnitude was 6.60 ± 4.14 mm. For acute gastrointestinal (GI) toxicities, 50% experienced grade 1 toxicities and 18% grade 2 GI toxicities. For acute genitourinary (GU) toxicities, 21% had grade 1 and 18% had grade 2 toxicities. For late GU toxicities, 7% had grade 1 and 4% had grade 2 toxicities. RB for gynecological patients receiving IMRT in the postoperative setting can limit V40 rectal dose and vaginal displacement. Although V30 constraints were not met, patients had limited acute and late toxicities. Further studies are needed to validate these findings.

Whole-brain Irradiation Field Design: A Comparison of Parotid Dose

Whole-brain radiation therapy (WBRT) plays an important role in patients with diffusely metastatic intracranial disease. Whether the extent of the radiation field design to C1 or C2 affects parotid dose and risk for developing xerostomia is unknown. The goal of this study is to examine the parotid dose based off of the inferior extent of WBRT field to either C1 or C2. Patients treated with WBRT with either 30 Gy or 37.5 Gy from 2011 to 2014 at a single institution were examined. Parotid dose constraints were compared with Radiation Therapy Oncology Group (RTOG) 0615 nasopharyngeal carcinoma for a 33-fraction treatment: mean <26 Gy, volume constraint at 20 Gy (V20) < 20 cc, and dose at 50% of the parotid volume (D50) < 30 Gy. Biologically effective dose (BED) conversions with an α/β of 3 for normal parotid were performed to compare with 10-fraction and 15-fraction treatments of WBRT. The constraints are as follows: mean < BED 32.83 Gy, V15.76 (for 10-fraction WBRT) or V17.35 (for 15-fraction WBRT) < 20 cc, and D50 < BED 39.09 Gy. Nineteen patients treated to C1 and 26 patients treated to C2 were analyzed. Comparing WBRT to C1 with WBRT to C2, the mean left, right, and both parotids' doses were lower when treated to C1. Converting mean dose to BED₃, the parotid doses were lower than BED₃ constraint of 32.83 Gy: left (30.12 Gy), right (30.69 Gy), and both parotids (30.32 Gy). V20 to combined parotids was lower in patients treated to C1. When accounting for fractionation of WBRT received, the mean corrected V20 volume was less than 20 cc when treating to C1. D50 for C1 was lower than C2 for the left parotid, right parotid, and both parotids. BED₃ conversion for the mean D50 of the left, right, and both parotids was less than 39.09 Gy. In conclusion, WBRT to C1 limits parotid dose, and parotid dose constraints are achievable compared with inferior border at C2. A possible mean parotid dose constraint with BED₃ should be less than 32.83 Gy.

Targeted cytoplasmic irradiation and autophagy

The effect of ionizing irradiation on cytoplasmic organelles is often underestimated because the general dogma considers direct DNA damage in the nuclei to be the primary cause of radiation induced toxicity. Using a precision microbeam irradiator, we examined the changes in mitochondrial dynamics and functions triggered by targeted cytoplasmic irradiation with α-particles. Mitochondrial dysfunction induced by targeted cytoplasmic irradiation led to activation of autophagy, which degraded dysfunctional mitochondria in order to maintain cellular energy homeostasis. The activation of autophagy was cytoplasmic irradiation-specific and was not detected in nuclear irradiated cells. This autophagic process was oxyradical-dependent and required the activity of the mitochondrial fission protein dynamin related protein 1 (DRP1). The resultant mitochondrial fission induced phosphorylation of AMP activated protein kinase (AMPK) which leads to further activation of the extracellular signal-related kinase (ERK) 1/2 with concomitant inhibition of the mammalian target of rapamycin (mTOR) to initiate autophagy. Inhibition of autophagy resulted in delayed DNA damage repair and decreased cell viability, which supports the cytoprotective function of autophagy. Our results reveal a novel mechanism in which dysfunctional mitochondria are degraded by autophagy in an attempt to protect cells from toxic effects of targeted cytoplasmic radiation.

Cytoplasmic Irradiation Induces Metabolic Shift in Human Small Airway Epithelial Cells via Activation of Pim-1 Kinase

The unique cellular and molecular consequences of cytoplasmic damage caused by ionizing radiation were studied using a precision microbeam irradiator. Our results indicated that targeted cytoplasmic irradiation induced metabolic shift from an oxidative to glycolytic phenotype in human small airway epithelial cells (SAE). At 24 h postirradiation, there was an increase in the mRNA expression level of key glycolytic enzymes as well as lactate secretion in SAE cells. Using RNA-sequencing analysis to compare genes that were responsive to cytoplasmic versus nuclear irradiation, we found a glycolysis related gene, Pim-1, was significantly upregulated only in cytoplasmic irradiated SAE cells. Inhibition of Pim-1 activity using the selective pharmaceutic inhibitor Smi-4a significantly reduced the level of lactate production and glucose uptake after cytoplasmic irradiation. In addition, Pim-1 also inhibited AMPK activity, which is a well-characterized negative regulator of glycolysis. Distinct from the glycolysis induced by cytoplasmic irradiation, targeted nuclear irradiation also induced a transient and minimal increase in glycolysis that correlated with increased expression of Hif-1α. In an effort to explore the underline mechanism, we found that inhibition of mitochondria fission using the cell-permeable inhibitor mdivi-1 suppressed the induction of Pim-1, thus confirming Pim-1 upregulation as a downstream effect of mitochondrial dysfunction. Our data show and, for the first time, that cytoplasmic irradiation mediate expression level of Pim-1, which lead to glycolytic shift in SAE cells. Additionally, since glycolysis is frequently linked to cancer cell metabolism, our findings further suggest a role of cytoplasmic damage in promoting neoplastic changes.