Distribution of Brain Metastases in Relation to the Hippocampus: Implications for Neurocognitive Functional Preservation

Modulated Arc Therapy for hippocampal-avoidance whole brain radiation therapy: planning comparison with intensity modulated Radiation Therapy

This study aimed to evaluate the modulated arc therapy (mARC) technique as a planning and treatment option for hippocampal sparing whole brain radiotherapy (HS-WBRT) following the Radiation Therapy Oncology Group (RTOG) 0933 dosimetric criteria. Computed tomography (CT) and magnetic resonance imaging (MRI) were selected retrospectively for 15 patients. Two types of plans were created for each patient, namely an intensity-modulated radiation therapy (IMRT) and a mARC plan. IMRT and mARC plans were compared in terms of plan quality indices, absorbed dose to organs at risk (OARs), number of monitor units (MUs), and treatment time. All plans in both techniques were considered clinically acceptable for treatment. However, IMRT plans presented a higher conformity (p = 0.01) as well as a higher homogeneity as compared to mARC plans, but this difference was not statistically significant (p > 0.05). In terms of the preservation of the hippocampus, it was observed that the IMRT plans achieved significantly lower doses for both 100% of its volume and for its maximum dose (p < 0.001). The evaluation of the remaining OARs showed that the IMRT technique resulted in lower doses, and significant differences were observed for the following organs: left cochlea (p < 0.001), left eye (p < 0.001), right eye (p = 0.03), both lenses of the eye (p < 0.001), and right optic nerve (p = 0.02). Despite these differences, the absolute differences in all dosimetric parameters were low enough to bear any clinical relevance. A drastic (close to 65%) and significant (p < 0.001) decrease was observed in the number of MUs for the mARC plans. This resulted in a substantial decrease in treatment time (60.45%, p < 0.001). It is concluded that the mARC technique is a feasible planning and treatment solution for HS-WBRT that meets the RTOG 0933 criteria. The main advantage of using mARC over IMRT for HS-WBRT is the considerable reduction in MUs and treatment time.

Incidence of hippocampal and perihippocampal brain metastases and impact on hippocampal-avoiding radiotherapy: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

In patients requiring prophylactic cranial irradiation (PCI) or whole-brain radiotherapy (WBRT) for brain metastases (BMs), hippocampal avoidance (HA) has been shown to preserve neurocognitive function and quality of life. Here, we aim to estimate the incidence of hippocampal and perihippocampal BMs and the subsequent risk of local undertreatment in patients undergoing hippocampal sparing radiotherapy.

MATERIALS AND METHODS

MEDLINE, Embase, and Scopus were searched with the terms "Hippocampus", "Brain Neoplasms", and related terms. Trials reporting on the incidence of hippocampal and/or perihippocampal BMs or hippocampal failure rate after PCI or WBRT were included.

RESULTS

Forty records were included, encompassing a total of 5,374 patients with over 32,570 BMs. Most trials employed a 5 mm margin to define the HA zone. In trials reporting on BM incidence, 4.4 % (range 0 - 27 %) and 9.2 % (3 - 41 %) of patients had hippocampal and perihippocampal BMs, respectively. The most common risk factor for hippocampal BMs was the total number of BMs. The reported failure rate within the HA zone after HA-PCI or HA-WBRT was 4.5 % (0 - 13 %), salvageable with radiosurgery in most cases. SCLC histology was not associated with a higher risk of hippocampal failure (OR = 2.49; p = 0.23). In trials comparing with a conventional (non-HA) PCI or WBRT group, HA did not increase the hippocampal failure rate (OR = 1.90; p = 0.17).

CONCLUSION

The overall incidence of hippocampal and perihippocampal BMs is considerably low, with a subsequent low risk of local undertreatment following HA-PCI or HA-WBRT. In patients without involvement, the hippocampus should be spared to preserve neurocognitive function and quality of life.

Current dilemma and future directions over prophylactic cranial irradiation in SCLC: a systematic review in MRI and immunotherapy era

Small cell lung cancer (SCLC) is the most malignant pathological type of lung cancer with the highest mortality, and the incidence of brain metastasis (BM) is in high frequency. So far, prophylactic cranial irradiation (PCI) has been suggested as an effective treatment for preventing brain metastasis of SCLC. PCI has long been applied to limited-stage SCLC (LS-SCLC) patients who have achieved complete remission after radiotherapy and chemotherapy as a standard treatment. However, the neurocognitive decline is a major concern surrounding PCI. New therapeutic approaches targeting PCI-induced neurotoxicity, including hippocampal protection or memantine, have been increasingly incorporated into the therapeutic interventions of PCI. Helical tomotherapy, RapidArc, and Volumetric-modulated arc therapy (VMAT) with a head-tilting baseplate are recommended for hippocampal protection. Besides, in the MRI and immunotherapy era, the significance of PCI in SCLC patients is controversial. SCLC patients with PCI should be recruited in clinical trials since this is the only way to improve the existing standard of care. This review summarizes the current therapeutic strategy and dilemma over PCI for SCLC, providing a theoretical basis for clinical decision-making and suggestions for PCI practice in clinical.

Hippocampal avoidance whole-brain radiotherapy with simultaneous integrated boost in lung cancer brain metastases and utility of the Hopkins verbal learning test for testing cognitive impairment in Chinese patients: a prospective phase II study

BACKGROUND

This study aimed to evaluate the efficiency of hippocampal avoidance whole-brain radiotherapy with a simultaneous integrated boost (HA-WBRT-SIB) treating brain metastases (BM) and utility of the Hopkins Verbal Learning Test-Revised (HVLT-R) (Chinese version) in Chinese lung cancer patients.

METHODS

Lung cancer patients with BM undergone HA-WBRT-SIB at our center were enrolled. Brain magnetic resonance imaging, The HVLT total learning score, and side effects were evaluated before radiotherapy and 1, 3, 6, and 12 months after radiotherapy. This study analyzed the overall survival rate, progression-free survival rate, and changes in HVLT-R immediate recall scores.

RESULTS

Forty patients were enrolled between Jan 2016 and Jan 2020. The median follow-up time was 14.2 months. The median survival, progression-free survival, and intracranial progression-free survival of all patients were 14.8 months, 6.7 months and 14.8 months, respectively. Multivariate analysis indicated that male sex and newly diagnosed stage IV disease were associated with poor overall survival and progression-free survival, respectively. HVLT-R scores at baseline and 1, 3, and 6 months after radiotherapy were 21.94 ± 2.99, 20.88 ± 3.12, 20.03 ± 3.14, and 19.78 ± 2.98, respectively. The HVLT-R scores at 6 months after radiotherapy decreased by approximately 9.8% compared with those at baseline. No grade 3 toxicities occurred in the entire cohort.

CONCLUSIONS

HA-WBRT-SIB is of efficiency and cognitive-conserving in treating Chinese lung cancer BM.

TRIAL REGISTRATION

This study was retrospectively registered on ClinicalTrials.gov in 24th Feb, 2024. The ClinicalTrials.gov ID is NCT06289023.

Sparing the Hippocampus in Prophylactic Cranial Irradiation Using Three Different Linear Accelerators: A Comparative Study

Hippocampus protection, as an organ at risk in brain radiotherapy, might protect patients' quality of life. Prophylactic cranial irradiation (PCI) has been used traditionally in small cell lung cancer (SCLC) patients as it increases survival. This study aimed to discover the contributing parameters for a successful PCI with simultaneous protection of the hippocampus by using three different treatment machines. For this purpose, treatment plans were generated for 45 SCLC patients using three half-arcs in three linear accelerators (LINACs; Elekta Infinity, Synergy, and Axesse; Elekta Ltd, Stockholm, Sweden) with different radiation field sizes and multileaf collimator (MLC) leaf thickness characteristics. The prescribed dose was 25 Gy in 10 fractions. Thresholds for the hippocampus were calculated based on the Radiation Therapy Oncology Group 0933 dose constraints. The planning and treatment system templates were common to all three LINACs. Plan evaluation was based on the dosimetric target coverage by the 95% isodose, the maximum dose of the plan, the conformity index (CI), the degree of plan modulation (MOD), and the patient-specific quality assurance (QA) pass rate. The mean target coverage was highest for Infinity (97.3%), followed by Axesse (96.6%) and Synergy (95.5%). The mean maximum dose was higher for Synergy (27.5 Gy), followed by Infinity (27.0 Gy) and Axesse (26.9 Gy). Axesse plans had the highest CI (0.93), followed by Infinity (0.91) and Synergy (0.88). Plan MOD was lower for Synergy (2.88) compared with Infinity (3.07) and Axesse (3.69). Finally, patient-specific QA was successful in all Infinity plans, in all but one Synergy plan, and in 17/45 Axesse plans, as was expected from the field size in that treatment unit. Based on overall performance, the most favorable combination of target coverage, hippocampus sparing, and plan deliverability was obtained with the LINAC, which has the largest field opening and thinnest MLC leaves.

Exploration of anatomical distribution of brain metastasis from breast cancer at first diagnosis assisted by artificial intelligence

Objectives

This study aimed to explore the spatial distribution of brain metastases (BMs) from breast cancer (BC) and to identify the high-risk sub-structures in BMs that are involved at first diagnosis.

Methods

Magnetic resonance imaging (MRI) scans were retrospectively reviewed at our centre. The brain was divided into eight regions according to its anatomy and function, and the volume of each region was calculated. The identification and volume calculation of metastatic brain lesions were accomplished using an automatically segmented 3D BUC-Net model. The observed and expected rates of BMs were compared using 2-tailed proportional hypothesis testing.

Results

A total of 250 patients with BC who presented with 1694 BMs were retrospectively identified. The overall observed incidences of the substructures were as follows: cerebellum, 42.1 %; frontal lobe, 20.1 %; occipital lobe, 9.7 %; temporal lobe, 8.0 %; parietal lobe, 13.1 %; thalamus, 4.7 %; brainstem, 0.9 %; and hippocampus, 1.3 %. Compared with the expected rate based on the volume of different brain regions, the cerebellum, occipital lobe, and thalamus were identified as higher risk regions for BMs (P value ≤ 5.6*10-3). Sub-group analysis according to the type of BC indicated that patients with triple-negative BC had a high risk of involvement of the hippocampus and brainstem.

Conclusions

Among patients with BC, the cerebellum, occipital lobe and thalamus were identified as higher-risk regions than expected for BMs. The brainstem and hippocampus were high-risk areas of the BMs in triple negative breast cancer. However, further validation of this conclusion requires a larger sample size.

Neurotoxicity-sparing radiotherapy for brain metastases in breast cancer: a narrative review

Breast cancer brain metastasis (BCBM) has a devastating impact on patient survival, cognitive function and quality of life. Radiotherapy remains the standard management of BM but may result in considerable neurotoxicity. Herein, we describe the current knowledge on methods for reducing radiation-induced cognitive dysfunction in patients with BCBM. A better understanding of the biology and molecular underpinnings of BCBM, as well as more sophisticated prognostic models and individualized treatment approaches, have appeared to enable more effective neuroprotection. The therapeutic armamentarium has expanded from surgery and whole-brain radiotherapy to stereotactic radiosurgery, targeted therapies and immunotherapies, used sequentially or in combination. Advances in neuroimaging have allowed more accurate screening for intracranial metastases, precise targeting of intracranial lesions and the differentiation of the effects of treatment from disease progression. The availability of numerous treatment options for patients with BCBM and multidisciplinary approaches have led to personalized treatment and improved therapeutic outcomes. Ongoing studies may define the optimal sequencing of available and emerging treatment options for patients with BCBM.

High Radiation Dose to the Fornix Causes Symptomatic Radiation Necrosis in Patients with Anaplastic Oligodendroglioma

PURPOSE

Surgery, radiotherapy (RT), and chemotherapy have prolonged the survival of patients with anaplastic oligodendroglioma. However, whether RT induces long-term toxicity remains unknown. We analyzed the relationship between the RT dose to the fornix and symptomatic radiation necrosis (SRN).

MATERIALS AND METHODS

A total of 67 patients treated between 2009 and 2019 were analyzed. SRN was defined according to the following three criteria: 1) radiographic findings, 2) symptoms attributable to the lesion, and 3) treatment resulting in symptom improvement. Various contours, including the fornix, were delineated. Univariate and multivariate analyses of the relationship between RT dose and SRN, as well as receiver operating characteristic curve analysis for cut-off values, were performed.

RESULTS

The most common location was the frontal lobe (n=40, 60%). Gross total resection was performed in 38 patients (57%), and 42 patients (63%) received procarbazine, lomustine, and vincristine chemotherapy. With a median follow-up of 42 months, the median overall and progression-free survival was 74 months. Sixteen patients (24%) developed SRN. In multivariate analysis, age and maximum dose to the fornix were associated with the development of SRN. The cut-off values for the maximum dose to the fornix and age were 59 Gy (equivalent dose delivered in 2 Gy fractions) and 46 years, respectively. The rate of SRN was higher in patients whose maximum dose to the fornix was >59 Gy (13% vs. 43%, p=0.005).

CONCLUSION

The maximum dose to the fornix was a significant factor for SRN development. While fornix sparing may help maintain neurocognitive function, additional studies are needed.

Dosimetric comparison of helical tomotherapy and volumetric modulated arc therapy in hippocampal avoidance whole-brain radiotherapy

OBJECTIVE

This study aimed to discuss the dosimetric advantages of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) technology in hippocampal avoidance whole-brain radiotherapy and provide references for clinical selection of ideal radiotherapy technology.

METHODS

A total of 20 patients with hippocampal avoidance whole-brain radiotherapy were chosen randomly. Computed tomography (CT) and MRI scanning images were input into the treatment planning system (TPS). After the CT and enhanced magnetic resonance T1 weighted images were fused and registered, the same radiation therapy physician was invited to outline the tumor target volume. PTV-HS refers to the whole brain subtracted by 5 mm outward expansion of the hippocampus (HP). The prescribed dose was 30 Gy/10 fractions. HT and VMAT plans were designed for each patient in accordance with PTV. Under the premise that the 95% isodose curve covers the PTV, dose-volume histogram was applied to evaluate the PTV, conformal index (CI), heterogeneity index (HI), maximum dose (Dmax), mean dose (Dmean), minimum dose (Dmin) and absorbed doses of organs at risk (OARs) in HT and VMAT plans. Paired t-test was performed to compare the differences between two radiation therapy plans, and p  <  0.05 was considered statistically significant.

RESULTS

These two plans had no significant difference in PTV-HS (max, min, and mean). However, the HI and CI of the HT plan were significantly better than those of the VMAT plan, showing statistically significant difference (p < 0.05). The HT plan was significantly superior to the VMAT plan in terms of the Dmax, Dmin, and Dmean of HP, left and right eye lens, left and right eye, and spinal cord, showing statistically significant difference (p < 0.05). The HT plan was also better than the VMAT plan in terms of the Dmax of the left optic nerve. However, the two plans showed no obvious differences in terms of the absorbed doses of the right optic nerve and brainstem, without statistical significance.

CONCLUSIONS

Compared with the VMAT plan of hippocampal avoidance, HT technology has significant dosimetric advantages. HT plans significantly decreased the radiation dose and radiation volume of OARs surrounding the target area (e.g., surrounding eye lens and eye, especially hippocampal avoidance area) while increasing the CI and HI of PTV dose in whole brain radiotherapy (WBRT) greatly, thus enabling the decrease in the incidence rate of radioactive nerve function impairment.

Correlation between hippocampal radiation doses and psychological condition for patients with stage T1-2 nasopharyngeal carcinoma

BACKGROUND AND PURPOSE

The study aimed to investigate the correlation between radiation doses to the hippocampi and the psychological status of patients with stage T1-2 nasopharyngeal carcinoma (NPC) undergoing intensity modulated radiotherapy (IMRT) and recommend proper hippocampal dose limits for preserving patients' psychological well-being.

MATERIALS AND METHODS

A retrospective study was conducted involving 152 newly diagnosed NPC patients. The patients' psychological status was assessed using the Hospital Anxiety and Depression Scale (HADS) before and after radiotherapy. The hippocampi were manually delineated on treatment planning images, and dosimetric parameters were obtained from dose-volume histograms. Logistic regression analysis was performed to identify influential dosimetric factors associated with anxiety and depression.

RESULTS

The results showed that several dosimetric parameters to the hippocampi were significantly associated with anxiety but not depression. The optimal cut-off value for the independent predictor of anxiety was determined as D40 to hippocampi > 1500 cGy. Patients with D40 to hippocampi > 1500 cGy showed a higher probability for anxiety after radiotherapy.

CONCLUSION

This study provides insights into the relationship between radiation doses to the hippocampi and the psychological status of stage T1-2 NPC patients undergoing IMRT. It suggests the importance of hippocampal protection for preserving patients' psychological well-being. Further studies are needed to validate these results.

Pre-treatment Evaluation of Patients Eligible for Whole Brain Radiation Therapy: The Risk of Hippocampal Metastases in a Retrospective Study of 248 Cases at a Single Institution

Whole brain radiation therapy (WBRT) is effective for multiple brain metastases (BMs) but may impair neurocognitive function (NCF). The incidence of hippocampal metastasis (HM) is low, and the factors associated with the occurrence of HM remain unclear. This study aimed to assess the occurrence of limbic system metastasis (LSM), including HM, and to analyze the risk of HM. We retrospectively analyzed 248 patients who underwent three-dimensional conformal radiation therapy for BMs between May 2008 and October 2015. Gadolinium-enhanced brain MRI or CT scans were used for diagnosis. Statistical analysis involved assessing clinical factors, including age, gender, primary tumor, number of BMs, and maximum metastasis diameter, in relation to the presence of HMs using logistic regression and receiver operating characteristic (ROC) curve analysis. The median age at treatment was 62 years (range: 11-83 years). Primary lesion sites included the lung (n = 150; 60.5%), breast (n = 45; 18.1%), gastrointestinal tract (n = 18; 7.3%), and bone and soft tissue (n = 2; 0.8%). Histological cancer types included adenocarcinoma (n = 113; 45.6%), squamous cell carcinoma (n = 26; 10.5%), small cell carcinoma (n = 28; 11.3%), invasive ductal carcinoma (n = 35; 14.1%), sarcoma (n = 3; 1.2%), and others (n = 43; 17.3%). MRI or CT scans of the 248 patients were analyzed, indicating a total count of 2,163 brain metastases (median: five metastases per patient). HMs were identified in 18 (7.3%) patients. The most common location for LSMs was the cingulum/cingulate gyrus in 26 (10.5%) patients. In univariate and multivariate analyses, patients with 15 or fewer BMs had a significantly lower incidence of HMs (odds ratio (OR), 0.018 (95% confidence interval (CI), 0.030-0.24)) (p < 0.0001). A maximal tumor size of less than 2 cm significantly increased the incidence of HMs (OR, 13.8 (95%CI, 1.80-105.3)) (p = 0.0003). The presence of cingulum/cingulate gyrus metastases also demonstrated a significant increase in the incidence of HMs (OR, 9.42 (95%CI, 3.30-26.84)) (p < 0.0001). The present study has uncovered a novel association between a high number of metastases in the cingulate gyrus and the development of HMs. Patients with BMs eligible for WBRT with metastases in the cingulate gyrus may be at risk of developing HM.

May we routinely spare hippocampal region in primary central nervous system lymphoma during whole brain radiotherapy?

PURPOSE

One of the main limiting factors of whole-brain radiation therapy (WBRT) for primary central nervous system lymphoma (PCNSL) is the impairment of neurocognitive functions (NCFs), which is mainly caused by radiation-induced injury to the hippocampus. With a view to preventing NCF impairment and personalizing treatment, we explored the feasibility of sparing the hippocampus during WBRT by correlating the sites of PCNSL lesions with the hippocampus.

METHODS AND MATERIALS

Pre-treatment MR images from patients who underwent WBRT between 2010 and January 2020-and post-radiotherapy images in cases of relapse-were imported into the Varian Eclipse treatment-planning system and registered with the simulation CT. We constructed three 3-dimensional envelopes around the hippocampus at distances of 5, 10 and 15 mm and also contoured primary lesions and recurrences.

RESULTS

We analyzed 43 patients with 66 primary lesions: 9/66 (13.6%) involved the hippocampus and 11/66 (16.7%) were located within 5 mm of it. Thirty-six lesions (54.5%) were situated more than 15 mm from the hippocampus, while 10/66 (15.2%) were between 5 and 15 mm from it. The most common location was in deep brain structures (31%). Thirty-five of the 66 lesions relapsed: in field in 14/35 (40%) and outfield in 21/35 (60%) in different sites. Globally, 16/35 recurrences (45.7%) were located in the hippocampus or within 5 mm of it.

CONCLUSION

These data show that routinely sparing the hippocampus is not feasible. This approach could be considered in selected patients, when the lesion is more than 15 mm from the hippocampus.

Survival and complications following supra- and infratentorial brain metastasis resection

OBJECTIVE

15-30% of primary cancers metastasise to the brain. Of these, 10-25% involve the posterior fossa. It remains unclear whether patients undergoing resection for infratentorial brain metastases experience poorer prognosis than those with supratentorial lesions. We compare the post-operative outcomes of these two groups.

METHODS

We searched the electronic health records of all patients undergoing brain metastases resection at our regional neurosurgical centre between February 2014 and August 2019. Clinical data was collected on 85 consecutive patients (61 supratentorial, 24 infratentorial metastases). Outcome measures included overall survival, post-operative complications, and performance status. Patients were followed up until 21/04/2020.

RESULTS

Median post-operative survival of patients with supratentorial metastases was 323 days (95% CI 235-411), compared to 277 days (95% CI 195-359) for those with infratentorial metastases. These two groups experienced comparable survival (log rank = 0.276, p = 0.60) on univariate analysis. Infratentorial metastasis location was not associated with a change in survival using a Cox proportional hazards model incorporating age, sex and extracranial disease activity (HR = 1.39, 95% CI 0.777-2.486) (p = 0.27). However, neurological and non-neurological post-operative complications were more frequent in patients with infratentorial metastases (neurological = 21% vs 13%, non-neurological = 25% vs 2%, p = 0.002).

CONCLUSION

Patients with supra- and infratentorial metastases experienced comparable post-operative survival but posterior fossa metastasis location was associated with a 2.5 times higher risk of neurological and/or non-neurological post-operative complications. A better understanding of the precise indications for safe and effective surgical intervention for posterior fossa metastases is required.

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD₂) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower D_max and D_1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D_99% and D_min were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D_20%, D_40%, D_60% and D_80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the D_max in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

Treatment of breast cancer brain metastases: radiotherapy and emerging preclinical approaches

The breast is one of the common primary sites of brain metastases (BM). Radiotherapy for BM from breast cancer may include whole brain radiation therapy (WBRT), stereotactic radiosurgery (SRS), and stereotactic radiotherapy (SRT), but a consensus is difficult to reach because of the wide and varied protocols, indications, and outcomes of these interventions. Overall, dissemination of disease, patient functional status, and tumor size are all important factors in the decision of treatment with WBRT or SRS. Thus far, previous studies indicate that WBRT can improve tumor control compared to SRS, but increase side effects, however no randomized trials have compared the efficacy of these therapies in BM from breast cancer. Therapies targeting long non-coding RNAs and transcription factors, such as MALAT1, HOTAIR, lnc-BM, TGL1, and ATF3, have the potential to both prevent metastatic spread and treat BM with improved radiosensitivity. Given the propensity for HER2+ breast cancer to develop BM, the above-mentioned cell lines may represent an important target for future investigations, and the development of everolimus and pyrotinib are equally important.

Memantine in the Prevention of Radiation-Induced Brain Damage: A Narrative Review

Simple Summary

Decline in cognitive function is a major problem for patients undergoing whole-brain radiotherapy (WBRT). Scientific interest has increased due to the high dropout rate of patients in the first months after WBRT and the early onset of cognitive decline. Therefore, the study of antiglutamatergic pharmacological prophylaxis and hippocampal-sparing WBRT techniques has been deepened based on the knowledge of the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline. In order to provide a summary of the evidence in this field, and to foster future research in this setting, this literature review presents current evidence on the prevention of radiation-induced cognitive decline and particularly on the role of memantine.

Abstract

Preserving cognitive functions is a priority for most patients with brain metastases. Knowing the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline (CD) led to testing both the antiglutamatergic pharmacological prophylaxis and hippocampal-sparing whole-brain radiotherapy (WBRT) techniques. These studies showed a relative reduction in CD four to six months after WBRT. However, the failure to achieve statistical significance in one study that tested memantine alone (RTOG 0614) led to widespread skepticism about this drug in the WBRT setting. Moreover, interest grew in the reasons for the strong patient dropout rates in the first few months after WBRT and for early CD onset. In fact, the latter can only partially be explained by subclinical tumor progression. An emerging interpretation of the (not only) cognitive impairment during and immediately after WBRT is the dysfunction of the limbic and hypothalamic system with its immune and hormonal consequences. This new understanding of WBRT-induced toxicity may represent the basis for further innovative trials. These studies should aim to: (i) evaluate in greater detail the cognitive effects and, more generally, the quality of life impairment during and immediately after WBRT; (ii) study the mechanisms producing these early effects; (iii) test in clinical studies, the modern and advanced WBRT techniques based on both hippocampal-sparing and hypothalamic-pituitary-sparing, currently evaluated only in planning studies; (iv) test new timings of antiglutamatergic drugs administration aimed at preventing not only late toxicity but also acute effects.

Perihippocampal failure after hippocampal-avoidance whole-brain radiotherapy in cancer patients with brain metastases: Results of a retrospective analysis

Perihippocampal failure is a rare clinical scenario in brain metastatic cancer patients following hippocampal-avoidance (HA) whole-brain radiotherapy (HA-WBRT). The clinical features have not been fully identified because clinical data on intracranial failure after HA-WBRT are limited. It is thus necessary to accumulate clinical data.We retrospectively analyzed cancer patients with brain metastases who were diagnosed between January 2014 and September 2020 at a regional referral hospital. The medical records of patients who underwent HA-WBRT were reviewed. The clinical features of intracranial recurrence were described. Dosimetry parameters were compared in terms of deviation from the recommended protocol of the Radiation Therapy Oncology Report 0933.Twenty-four eligible patients with brain metastases who underwent HA-WBRT were identified; 13 (54%) were male. Seventeen patients (71%) had lung cancer, 6 (25%) had breast cancer, and 1 (4%) had liver cancer. The median overall survival was 12 months. Three patients developed intracranial failure during clinical follow-up, and 2 relapsed with intracranial failure in the perihippocampal region at 13 and 22 months, respectively. The perihippocampal failure rate was about 8%. One patient with small cell lung cancer received HA-prophylactic cranial irradiation; the minimum and maximum doses to the hippocampi were 6.8 and 10.7 Gy, respectively. Another patient with brain metastases from lung adenocarcinoma received HA-WBRT; the minimum and maximum doses to the hippocampi were 5.4 and 10.6 Gy, respectively.We reported unusual cases of intracranial failure in the perihippocampal region following HA-WBRT. Perihippocampal failure could be attributed to an under-dose of radiation partially or be resulted from aggressiveness of cancer per se. Further research on this topic is encouraged.

Intracranial Metastatic Disease: Present Challenges, Future Opportunities

Intracranial metastatic disease (IMD) is a prevalent complication of cancer that significantly limits patient survival and quality of life. Over the past half-century, our understanding of the epidemiology and pathogenesis of IMD has improved and enabled the development of surveillance and treatment algorithms based on prognostic factors and tumor biomolecular characteristics. In addition to advances in surgical resection and radiation therapy, the treatment of IMD has evolved to include monoclonal antibodies and small molecule antagonists of tumor-promoting proteins or endogenous immune checkpoint inhibitors. Moreover, improvements in the sensitivity and specificity of imaging as well as the development of new serological assays to detect brain metastases promise to revolutionize IMD diagnosis. In this review, we will explore current treatment principles in patients with IMD, including the emerging role of targeted and immunotherapy in select primary cancers, and discuss potential areas for further investigation.

Porous Se@SiO2 Nanoparticles Attenuate Radiation-Induced Cognitive Dysfunction via Modulating Reactive Oxygen Species

Radiotherapy has been widely used to manage primary and metastatic brain tumors. However, hippocampal damage and subsequent cognitive dysfunction are common complications of whole brain radiation (WBI). In this study, Se@SiO₂ nanoparticles (NPs) with antioxidant properties were synthesized. Se@SiO₂ NPs were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reactive oxygen species (ROS) scavenging ability of Se@SiO₂ NPs was assessed using a dichloro-dihydro-fluorescein diacetate (DCFH-DA) probe. Apoptosis of HT-22 cells treated with H₂O₂ and Se@SiO₂ NPs was assessed by annexin V-FITC/PI and JC-1 staining. Western blotting was used to evaluate inflammation-related signaling pathways. In vivo, the distribution and excretion of Se@SiO₂ NPs were assessed using in vivo imaging system (IVIS). The biosafety and antioxidant effects of Se@SiO₂ NPs were assessed. Neurogenesis in the hippocampus of mice was detected through neuron-specific nuclear protein (NeuN) and 5-bromo-2'-deoxyuridine (BrdU) immunofluorescence staining. The cognitive abilities of mice were also assessed using the Morris water maze test. Results showed that porous Se@SiO₂ NPs were successfully synthesized with uniform spherical structures. In vitro, Se@SiO₂ NPs inhibited ROS levels in mouse hippocampal neuronal cell line HT-22 treated with H₂O₂. Furthermore, Se@SiO₂ NPs suppressed the apoptotic rate of HT-22 cells by regulating apoptosis-related proteins. Se@SiO₂ NPs regulated the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, thereby reducing the expression of inflammatory factors. In vivo, Se@SiO₂ NPs showed high biocompatibility at a concentration of 1.25 μg/μL. Se@SiO₂ NPs inhibited ROS and promoted neurogenesis in the hippocampus, as well as improved cognitive ability in radiation-induced mice. In conclusion, Se@SiO₂ NPs protected the hippocampus from oxidative stress injury and neuroinflammation. Se@SiO₂ NPs treatment may be a potential therapeutic strategy for radiation-induced cognitive dysfunction.

Metastatic Neoplasm Volume Kinetics Following Two-Staged Stereotactic Radiosurgery

INTRODUCTION

Multisession staged stereotactic radiosurgery (2-SSRS) represents an alternative approach for management of large brain metastases (LBMs), with potential advantages over fractionated SRS. We investigated the clinical efficacy and safety of 2-SSRS in patients with LBMs.

METHODS

LBMs patients treated with 2-SSRS between 2014-2020 were evaluated. Demographic, clinical, and radiologic information was obtained. Volumetric measurements at first SSRS, second SSRS, and follow-up imaging studies were obtained. Characteristics that might predict response to 2-SSRS were evaluated through Fischer-exact or Mann-Whitney U test.

RESULTS

Twenty-four patients with 26 LBMs were included in the study. Median marginal doses for first and second SSRS were 15 Gy (14-18 Gy) and 15 Gy (12-16 Gy), respectively. Median tumor volumes at first SSRS, second SSRS, and 3-month follow-up were 8.1 cm³ (1.5-28.5 cm³), 3.3 cm³ (0.8-26.1 cm³), and 2.2 cm³ (0.2-10.1 cm³), respectively. Overall, 24/26 lesions (92%) demonstrated early local control following the first SSRS with 17 lesions (71%) demonstrating a decrease of >30% in the T1 post-contrast MRI volume before the second SSRS and 3 lesions (12%) remaining stable. Eventually, four lesions showed disease progression after 2-SSRS. The median time to local progression was not reached and the median time to intracranial progression was 9.1 months.

CONCLUSIONS

Our study supports the effectiveness and safety of 2-SSRS as a treatment modality for patients with large, symptomatic brain metastases, especially in poor surgical candidates. The local failure rate and low occurrence of adverse effects are comparable to other staged radiosurgery studies.

Anatomical and topographical variations in the distribution of brain metastases based on primary cancer origin and molecular subtypes: a systematic review

Background

While it has been suspected that different primary cancers have varying predilections for metastasis in certain brain regions, recent advances in neuroimaging and spatial modeling analytics have facilitated further exploration into this field.

Methods

A systematic electronic database search for studies analyzing the distribution of brain metastases (BMs) from any primary systematic cancer published between January 1990 and July 2020 was conducted using PRISMA guidelines.

Results

Two authors independently reviewed 1957 abstracts, 46 of which underwent full-text analysis. A third author arbitrated both lists; 13 studies met inclusion/exclusion criteria. All were retrospective single- or multi-institution database reviews analyzing over 8227 BMs from 2599 patients with breast (8 studies), lung (7 studies), melanoma (5 studies), gastrointestinal (4 studies), renal (3 studies), and prostate (1 study) cancers. Breast, lung, and colorectal cancers tended to metastasize to more posterior/caudal topographic and vascular neuroanatomical regions, particularly the cerebellum, with notable differences based on subtype and receptor expression. HER-2-positive breast cancers were less likely to arise in the frontal lobes or subcortical region, while ER-positive and PR-positive breast metastases were less likely to arise in the occipital lobe or cerebellum. BM from lung adenocarcinoma tended to arise in the frontal lobes and squamous cell carcinoma in the cerebellum. Melanoma metastasized more to the frontal and temporal lobes.

Conclusion

The observed topographical distribution of BM likely develops based on primary cancer type, molecular subtype, and genetic profile. Further studies analyzing this association and relationships to vascular distribution are merited to potentially improve patient treatment and outcomes.

Treatment planning of volumetric modulated arc therapy and positioning optimization for hippocampal-avoidance prophylactic cranial irradiation

BACKGROUND

Hippocampal-avoidance prophylactic cranial irradiation (HA-PCI) offers potential neurocognitive benefits but raises technical challenges to treatment planning. This study aims to improve the conventional planning method using volumetric modulated arc therapy (VMAT) technique and investigate a better patient's head positioning to achieve a high quality of HA-PCI treatment plans.

METHODS

The improved planning method set a wide expansion of hippocampus as a special region for dose decline. The whole brain target was divided into two parts according to whether the slice included hippocampus and their optimization objectives were set separately. Four coplanar full arcs with partial field sizes were employed to deliver radiation dose to different parts of the target. The collimator angle for all arcs was 90°. Tilting patient's head was achieved by rotating CT images. The improved planning method and tilted head positioning were verified using datasets from 16 patients previously treated with HA-PCI using helical tomotherapy (HT).

RESULTS

For the improved VMAT plans, the max and mean doses to hippocampus were 7.88 Gy and 6.32 Gy, respectively, significantly lower than those for the conventional VMAT plans (P < 0.001). Meanwhile, the improved planning method significantly improved the plan quality. Compared to the HT plans, the improved VMAT plans result in similar mean dose to hippocampus (P > 0.1) but lower max dose (P < 0.02). Besides, the target coverage was the highest for the improved VMAT plans. The tilted head positioning further reduced the max and mean doses to hippocampus (P < 0.05), significantly decreased the max dose to lens (P < 0.001) and resulted in higher plan quality as compared to nontilted head positioning.

CONCLUSIONS

The improved planning method enables the VMAT plans to meet the clinical requirements of HA-PCI treatment with high plan quality and convenience. The tilted head positioning provides superior dosimetric advantages over the nontilted head positioning, which is recommended for clinical application.

Intracranial failure after hippocampal-avoidance prophylactic cranial irradiation in limited-stage small-cell lung cancer patients

We evaluated intracranial failure after hippocampus-avoidance-prophylactic cranial irradiation (HA-PCI) for limited-stage small-cell lung cancer (SCLC). Data of 106 patients who received PCI with 25 Gy were retrospectively reviewed. The patients were divided into two groups based on whether they underwent HA-PCI: the HA-PCI group (n = 48) and the conventional PCI (C-PCI) group (n = 58). Twenty-one patients experienced intracranial failure: 11 and 10 patients in the C-PCI and HA-PCI groups, respectively. Using the log-rank test, the intracranial failure rate was not significantly different between the groups (p = 0.215). No clinical factor was significantly associated with intracranial failure in multivariate Cox regression analysis, but HA-PCI tended to be associated with increased incidence of intracranial failure (HR 2.87, 95% CI 0.86–9.58, p = 0.087). Among patients who received HA-PCI, two developed peri-hippocampal recurrence. A higher thoracic radiotherapy dose (≥ 60 Gy) was significantly associated with DFS (HR 0.52, p = 0.048) and OS (HR 0.35, p = 0.003). However, HA-PCI was associated with neither DFS nor OS. Although HA-PCI may be associated with an increased risk of intracranial failure, HA-PCI did not impair disease control or survival. Future prospective randomized trials are needed to reach a definite conclusion.

Edema-mass Ratio Based On Magnetic Resonance Imaging As A Preoperative Diagnostic Factor For Posterior Fossa Metastasis

BACKGROUND

Peritumoral edema of primary brain tumors is an important cause of morbidity and mortality. The number of studies currently available on the prognostic role of peritumoral brain edema in the posterior fossa is extremely limited.

OBJECTIVE

Based on the known importance of magnetic resonance imaging in diagnosing supratentorial metastases, this study aimed to investigate the effects of peritumoral edema on survival of patients with posterior fossa metastases and the preoperative diagnostic value of MRI.

METHODS

Edema and mass volumes of 49 patients with posterior fossa metastasis, who underwent surgery during 2012-2016, were measured using magnetic resonance imaging. The edema/mass indices were retrospectively calculated and interpreted by evaluating the demographic, clinical, and survival data.

RESULTS

The study consisted of 32 (65.3%) male and 17 (34.7%) female participants, with the mean age ± standard deviation of 47.25±29.25 (17-81) years. Among the 49 patients with posterior fossa metastases, 34 (69.4%) had carcinoma, while 15 (30.6%) had non-carcinoma metastases. The edema/mass indices of patients with carcinoma and non-carcinoma metastases were found to be 14.55±9.64 and 1.34±1.08, respectively, and the difference was statistically significant (p<0.001). The mean survival of patients with carcinoma and non-carcinoma metastases was found to be 642±11.52 days and 726±9.32 days, respectively; however, this difference was not statistically significant (p=0.787).

CONCLUSION

The edema/mass ratio was found to be a significant diagnostic factor for the prediction of posterior fossa metastases. Further detailed studies are warranted to investigate the effect of edema/mass ratio on survival rate.

Recommendation for the contouring of limbic system in patients receiving radiation treatment: A pictorial review for the everyday practice and education

AIMS

The limbic circuit (LC) is devoted to linking emotion to behavior and cognition. The injury this system results in post-RT cognitive dysfunction. The aim of this study is to create the first radiation oncologist's practical MR-based contouring guide for the delineation of the LC for the everyday clinical practice and education.

METHODS

An anonymized diagnostic 3.0 T T1-weighted BRAVO MRI sequence from a healthy patient with typical brain anatomy was used to delineate LC. For each structure key anatomical contours were completed by radiation oncologists, along with a neuro-radiologist to generate the final version of the LC atlas.

RESULTS

a step-by-step MR-based atlas of LC was created. Key structures of the LC, such as, cingulate gyrus, fornix, septal region, mammillary bodies, thalamus and the hippocampal-amygdala formation were contoured.

CONCLUSIONS

This article provides the recommendations for the first contouring atlas of LC in the setting of patients receiving RT and education.

The Capabilities and Characteristics of Helical Tomotherapy and Co-Planar Dual Arcs Volumetric-Modulated arc Therapy Associated with Hippocampal Sparing During Prophylactic Cranial Irradiation

Objective: To investigate the features of helical tomotherapy and co-planar dual Arcs volumetric-modulated arc therapy during prophylactic cranial irradiation associated with bilateral hippocampal tissue sparing. Materials and methods: Helical tomotherapy and co-planar dual arcs volumetric-modulated arc therapy treatment plans were generated with a dose of 30 Gy/10 fractions in 16 patients treated with prophylactic cranial irradiation. The dose to the bilateral hippocampal tissues, organs at risk, and planning target volume were determined when the average dose of bilateral hippocampal tissues was reduced by approximately 4 Gy as an observation point. Changes in dosimetry when sparing the bilateral hippocampal tissues were determined for both modalities. Results: When bilateral hippocampal tissues were restricted to 8 Gy, D40%mean-bilateral hippocampal tissues = 7.64 ± 0.41 Gy in helical tomotherapy, while D40%mean-bilateral hippocampal tissues = 10.96 ± 0.38 Gy in co-planar dual arcs volumetric-modulated arc therapy volumetric-modulated arc therapy. Helical tomotherapy was associated with significantly lower doses to organs at risk, including Dmean-bilateral hippocampal tissues (P = .03), D98%-bilateral hippocampal tissues (P = .01), D2%-bilateral hippocampal tissues (P = .01), Dmean-inner ear (P = .02), Dmean-parotid glands (P = .02), Dmax-lens (P = .02), and Dmax-brainstem (P = .02), but not Dmax-optic nerves (P = .87). Helical tomotherapy provided better target coverage, with lower average D2%-PTV (P = .02), higher average D98%-PTV (P = .02), and better conformal index (0.87 vs 0.84, P = .02) and homogeneity index (0.15 vs 0.21, P = .05). With smaller bilateral hippocampal tissues doses, the planning target volume dose changed across 3 dosimetry regions for both modalities; the plateau region (>20.0 Gy for helical tomotherapy versus >16.0 Gy for co-planar dual arcs volumetric-modulated arc therapy), gradient region (20.0-12.0 Gy vs 16.0-11.0 Gy), and falling region (<12.0 Gy vs <11.0 Gy). The average delivery duration of helical tomotherapy was almost 7.7 times longer than that of co-planar dual arcs volumetric-modulated arc therapy. Conclusions: Helical tomotherapy was better at sparing the bilateral hippocampal tissues and organs at risk and had better target coverage but a significantly longer treatment duration than co-planar dual arcs volumetric-modulated arc therapy. Further dose decreases in the bilateral hippocampal tissues would yield worse target dose coverage.

Treatment of stage III non-small cell lung cancer in the era of immunotherapy: pathological complete response to neoadjuvant pembrolizumab and chemotherapy

Non-small cell lung cancer (NSCLC) accounts for about 85% of all lung cancers. The expected 5-year survival of stage III NSCLC ranges from 13% to 36% for stage III. Due to the heterogeneity and poor efficacy of stage III patients, there is great controversy on how to optimize the therapy strategy. Immunotherapy is providing better clinical efficacy to more NSCLC patients, and is rapidly extending its range of care from advanced stage to locally advanced stage and early stage NSCLC. Due to the patient’s strong treatment intention, drug availability, and a few encouraging results from clinical trials (NADIM, NCT02716038, etc.), the authors observed a case of stage III NSCLC that achieved complete remission after receiving neoadjuvant chemotherapy combined with immunotherapy. In view of such a satisfactory result in neoadjuvant therapy, this article discusses how comprehensive treatment for stage III NSCLC patients may be conducted and the manner in which various therapeutic techniques can be mastered in the era of immunotherapy. Immunotherapy has opened the exploratory space for finding resolutions to numerous challenges of treating stage III NSCLC. Further clinical studies and exploration of personalized treatment, guided by imaging data, and clinical and pathological biomarkers are imperative for the benefit of these patients.

Initial Approach to the Patient with Multiple Newly Diagnosed Brain Metastases

Brain metastases are the most common intracranial tumor in adults, with increasing incidence owing to prolonged survival times. Roughly half of patients diagnosed with new brain metastases have greater than 1 brain metastasis at the time of diagnosis, raising the question of how to optimize patient care with multiple brain metastases. The authors review studies relevant to the care of patients with brain metastasis, with emphasis on those relevant to the care of patients with multiple brain metastases. They discuss evolving strategies involving multiple modalities and the benefit of surgical management in patients with a large symptomatic brain metastasis.

A low percentage of metastases in deep brain and temporal lobe structures

BACKGROUND

Whole-brain radiotherapy (WBRT) in patients with brain metastases (BM) is associated with neurocognitive decline. Given its crucial role in learning and memory, efforts to mitigate this toxicity have mostly focused on sparing radiation to the hippocampus. We hypothesized that BM are not evenly distributed across the brain and that several additional areas may be avoided in WBRT based on a low risk of developing BM.

METHODS

We contoured 2757 lesions in a large, single-institution database of patients with newly diagnosed BM. BM centroids were mapped onto a standard brain atlas of 55 anatomic subunits and the observed percentage of BM was compared with what would be expected based on that region's volume. A region of interest (ROI) analysis was performed in a validation cohort of patients from 2 independent institutions using equivalence and one-sample hypothesis tests.

RESULTS

The brainstem and bilateral thalami, hippocampi, parahippocampal gyri, amygdala, and temporal poles had a cumulative risk of harboring a BM centroid of 4.83% in the initial cohort. This ROI was tested in 157 patients from the validation cohort and was found to have a 4.1% risk of developing BM, which was statistically equivalent between the 2 groups (P < 1 × 10-6, upper bound).

CONCLUSION

Several critical brain structures are at a low risk of developing BM. A risk-adapted approach to WBRT is worthy of further investigation and may mitigate the toxicities of conventional radiation.

Feasibility of hippocampal avoidance whole brain radiation in patients with hippocampal involvement: Data from a prospective study

PURPOSE

Among patients with brain metastases, hippocampal avoidance whole brain radiation (HA-WBRT) preserves neurocognitive function relative to conventional WBRT but the feasibility of hippocampal sparing in patients with metastases in/near the hippocampus is unknown. We identified the incidence of hippocampal/perihippocampal metastases and evaluated the feasibility of HA-WBRT in such patients.

MATERIALS/METHODS

Dosimetric data from 34 patients randomized to HA-WBRT (30 Gy/10 fractions) in a phase III trial (NCT03075072) comparing HA-WBRT to stereotactic radiation in patients with 5 to 20 brain metastases were analyzed. Patients with metastases in/near the hippocampi received HA-WBRT with prioritization of tumor coverage over hippocampal avoidance. Target coverage and hippocampal sparing metrics were compared between patients with targets in/near the hippocampus versus not.

RESULTS

In total, 9 of 34 (26%) patients had targets in the hippocampus and an additional 5 of 34 (15%) patients had targets in the hippocampal avoidance zone (HAZ, hippocampus plus 5 mm expansion) but outside the hippocampus. Patients with targets within the hippocampus and those with targets in the HAZ but outside the hippocampus were spared 34% and 73% of the ipsilateral mean biologically equivalent prescription dose, respectively. Of the latter cohort, 88% and 25% met conventional hippocampal sparing metrics of Dmin ≤ 9 Gy and Dmax ≤ 16 Gy, respectively. Among 11 patients with unilateral hippocampal/perihippocampal involvement, the uninvolved/contralateral hippocampus was limited to Dmin ≤ 9 Gy and Dmax ≤ 17 Gy in all cases.

CONCLUSIONS

In this study, a substantial percentage of patients with 5 to 20 brain metastases harbored metastases in/near the hippocampus. In such cases, minimizing hippocampal dose while providing tumor coverage was feasible and may translate to neurocognitive protection.

Distribution of brain metastases: low-risk metastasis areas may be avoided when treating with whole-brain radiotherapy

Objective

Previous work has demonstrated that metastases are not uniformly distributed across the brain. This study aims to determine there are low-risk brain metastasis (BM) areas that may be avoided during whole-brain radiotherapy (WBRT) to reduce neurocognitive toxicity.

Methods

Clinical and magnetic resonance imaging (MRI) data of 991 metastases in 192 patients with advanced cancer were analyzed retrospectively. Eleven anatomically defined regions of interest (ROIs) were contoured, and the locations of the BMs were recorded. Using the same definition, ROIs were contoured in 20 healthy volunteers.The proportions of patients with BMs in different ROIs, proportion of BMs, and proportion of different ROI volumes relative to the total volume were calculated.

Results

The proportion of observed BMs was lower than expected in the brainstem, insula, diencephalon and internal structures, corpus callosum, and pituitary gland. The proportion of BMs was significantly higher than expected in the parietal lobe, occipital lobe, and cerebellum. For those patients with single BM, there was very low rate of low-risk ROIs involvement (0%), with 2–4 BMs, 6–13% of the patients had low-risk ROIs involvement, with ≥5 BMs, significant (> 30%) of the patients had low-risk ROIs involvement.

Conclusion

The brainstem, insula, diencephalon and internal structures, corpus callosum, and pituitary gland demonstrate low risk for metastatic involvement. Involvement of low risk areas occurs in patients with more than 1 BM.

Survival outcomes of breast cancer patients with brain metastases: A multicenter retrospective study in Korea (KROG 16-12)

PURPOSE

This study evaluated the influence of prognostic factors and whole brain radiotherapy (WBRT) on overall survival (OS) of breast cancer (BC) patients with brain metastases (BM).

METHODS AND MATERIALS

Medical records of 730 BC patients diagnosed with BM from 2000 to 2014 at 17 institutions were retrospectively reviewed. OS was calculated from BM diagnosis. Median follow-up duration was 11.9 months (range, 0.1-126.2).

RESULTS

Median OS was 15.0 months (95% CI: 14.0-16.9). Patients with different BC-specific graded prognostic assessment (GPA) scores showed significant differences (p < 0.001) in OS. In multivariate analysis, histologic grade 3 (p = 0.014), presence of extracranial metastasis (p < 0.001), the number of BM (>4; p = 0.002), hormone receptor negativity (p = 0.005), HER2-negativity (p = 0.003), and shorter time interval (<30 months) between BC and BM diagnosis (p = 0.007) were associated with inferior OS. By summing the β-coefficients of variables that were prognostic in multivariate analyses, we developed a prognostic model that stratified patients into low-risk (≤0.673) and high-risk (>0.673) subgroups; the high-risk subgroup had poorer median OS (10.1 months, 95% CI: 7.9-11.9 vs. 21.9 months, 95% CI: 19.5-27.1, p < 0.001). Univariate and multivariate analyses of propensity score-matched patients diagnosed with BM ≥ 30 months after BC diagnosis (n = 389, "late BM") revealed that WBRT-treated patients showed superior OS compared to non-WBRT-treated patients (p = 0.070 and 0.030, respectively).

CONCLUSION

Our prognostic model identified high-risk BC patients with BM who might benefit from increased surveillance; if validated, our model could guide treatment selection for such patients. Patients with late BM might benefit from WBRT as initial local treatment.

Radiation-induced hippocampal atrophy in patients with nasopharyngeal carcinoma early after radiotherapy: a longitudinal MR-based hippocampal subfield analysis

Increasing evidence indicates that radiation-induced injury to the hippocampus may play a critical role in neurocognitive dysfunction in patients with nasopharyngeal carcinoma (NPC). However, few studies have assessed RT-induced hippocampal structural alterations in these patients early after radiotherapy (RT). In this study, 58 NPC patients were longitudinally followed up prior to treatment initiation as well as 3 and 6 months after RT, respectively. Twenty comparable normal controls were recruited and followed up in parallel. A novel magnetic resonance imaging (MRI)-based automated method was used to label hippocampal subfields. The linear mixed model was employed to evaluate longitudinal changes in the volumes of the whole hippocampus and seven hippocampal subfields. Time-dependent volume reduction was observed in the bilateral hippocampus, as well as in the bilateral granule cell layer (GCL), bilateral cornu ammonis 1 (CA1), bilateral molecular layer (ML), and bilateral subiculum (SUB) in NPC patients, but not in controls. Moreover, volume deficits in the bilateral hippocampus, bilateral GCL, and right ML showed dose-dependent patterns, and high volume losses in the bilateral hippocampus, bilateral GCL, left SUB, and right ML were associated with a rapid decline in cognitive function. Our findings demonstrated that the hippocampal subfields were selectively injured by irradiation-related early neurotoxic effects, which might account for cognitive impairment in NPC patients at an early stage after RT. Further, structural MRI could serve as a potential noninvasive imaging biomarker for the early detection of radiation effects on the hippocampus in NPC patients after RT.

The Risk of Radiogenic Second Cancer Based on Differential DVH: Central Nervous System Malignant Tumor in Children

OBJECTIVES

To quantify the risk of radiogenic second cancer in pediatric patients receiving hippocampal-sparing craniospinal irradiation either with intensity-modulated radiation therapy or tomotherapy due to the development of a solid second cancer after radiotherapy using the concept of excess absolute risk.

METHODS

Computed tomography images of 15 pediatric patients who received craniospinal irradiation treatment were selected for this study. For each case, intensity-modulated radiation therapy and tomotherapy plans were computed. Then, the dosimetry parameters were analyzed. Differential dose-volume histograms were generated, and the excess absolute risks were calculated for each plan of each patient.

RESULTS

The tomotherapy group was superior to the intensity-modulated radiation therapy group in target area homogeneity index (P < .001). Tomotherapy offered greater hippocampal sparing than intensity-modulated radiation therapy in terms of D _2% (15.66 vs 23.05 Gy, P < .001) and D_mean (9.79 vs 20.29 Gy, P < .001). Tomotherapy craniospinal irradiation induced a much higher risk than intensity-modulated radiation therapy craniospinal irradiation to the thyroid and lungs (excess absolute risk: thyroid 28.7 vs 26.9 per 10 000 PY, P = .010; lung 20.5 vs 18.9 per 10 000 PY, P = .003). Both techniques conferred a higher risk to the stomach, but there was little difference. In addition, the 2 plans induced less carcinogenic risk to the liver (excess absolute risk 4.2 vs 4.0 per 10 000 PY, P = .020).

CONCLUSIONS

The tomotherapy plan has obvious advantages in the protection of the hippocampus for children undergoing craniospinal irradiation treatment. Tomotherapy increased the risk of radiogenic second cancer in organ at risk, and therefore, it is imperative to take the risk factor into consideration in the formulation of treatment protocols.

Propensity for different vascular distributions and cerebral edema of intraparenchymal brain metastases from different primary cancers

PURPOSE

This study seeks to ascertain whether different primary tumor types have a propensity for brain metastases (BMs) in different cerebral vascular territories and cerebral edema.

METHODS

Consecutive adult patients who underwent surgical resection of a BM at a tertiary care institution between 2001 and 2011 were retrospectively reviewed. Only patients with the most common primary cancers (lung, breast, skin-melanoma, colon, and kidney) were included. Preoperative MRIs were reviewed to classify all tumors by cerebral vascular territory (anterior cerebral artery-ACA, lenticulostriate, middle cerebral artery-MCA, posterior cerebral artery-PCA, posterior fossa, and watershed), and T2-weighted FLAIR widths were measured. Chi square analyses were performed to determine differences in cerebral vascular distribution by primary tumor type, and one-way ANOVA analyses were performed to determine FLAIR signal differences.

RESULTS

669 tumors from 388 patients were classified from lung (n = 316 BMs), breast (n = 144), melanoma (n = 119), renal (n = 47), and colon (n = 43). BMs from breast cancer were less likely to be located in PCA territory (n = 18 [13%]; χ² = 6.10, p = 0.01). BMs from melanoma were less likely to be located in cerebellar territory (n = 11 [9%]; χ² = 14.1, p < 0.001), and more likely to be located in lateral (n = 5 [4%]; χ² = 4.56, p = 0.03) and medial lenticulostriate territories (n = 2 [2%]; χ² = 6.93, p = 0.009). BMs from breast and melanoma had shorter T2-FLAIR widths, with an average [IQR] of 47.2 [19.6-69.2] mm (p = 0.01) and 41.2 [14.4-62.7] mm (p = 0.002) respectively. Conversely, BMs from renal cancer had longer T2-FLAIR widths (64.2 [43.6-80.8] mm, p = 0.002).

CONCLUSIONS

These findings suggest that different primary tumor types could have propensities for different cerebral vascular territories and cerebral edema.

Distribution of metastasis in the brain in relation to the hippocampus: a retrospective single-center analysis of 565 metastases in 116 patients

OBJECTIVE

To examine the distribution of brain metastases (BM) in relation to the hippocampus, so as to determine the risk of metastasis in the hippocampus, and thus provide experimental evidence for the hippocampal avoidance (HA) in patients with BM during radiotherapy.

METHODS

(1) For the retrospective analysis of 116 patients diagnosed with malignancies, confirmed as BM, from December 2014 to December 2016 at the First Affiliated Hospital of Bengbu Medical College. We obtained the T1-weighted, postcontrast axial, sagittal, and coronal Magnetic Resonance imaging (MRI) images f the patients, in supine position, using the head restraints and head thermoplastic masks to adjust the positioning, with computed tomography (CT) positioning scan ranging from the head to the mandible (layer thickness: 3 mm). CT and MRI images were fused on a Philips Pinnacle v9.8 treatment planning system;(2) Every metastasis of the 565 metastases was contoured;(3) hippocampus were contoured, and hippocampus with 5 mm expansion envelopes were analyzed;(4) Using the SPSS 16.0 software, we analyzed the relation between the distribution and age, sex, Karnofsky performance status (KPS), primary site, aggregate volume of intracranial metastases and the whole brain. The data were analyzed using a binary logistic regression analysis method, with two-sided P < 0.05 for statistical significance.

RESULTS

In this study, we recruited 116 patients with 565 metastases. Among them, 1.7% (n = 2) had metastases in the hippocampus, and 11.2% (n = 13) had metastases within 5 mm of the hippocampus, of which more than half were patients with non-small cell lung cancer (n = 7). Using a binary logistic regression to analyze the relation between the metastases located within 5 mm of the hippocampus and age (P = 0.395), sex (P = 0.139), KPS (P = 0.724), primary site (P = 0.894), aggregate volume of intracranial metastases (p = 0.093) and the whole brain (p = 0.998), and none of them showed statistically significant difference between them and the metastases location (P>0.05).

CONCLUSION

This study showed a low risk for the perihippocampal metastases (PHM) and no significant correlation between PHM and age, sex, KPS, primary site, aggregate volume of intracranial metastases and the whole brain. Accordingly, it is may be acceptable to avoid the perihippocampal region during whole brain radiotherapy.

Fatigue following radiation therapy in nasopharyngeal cancer survivors: A dosimetric analysis incorporating patient report and observer rating

PURPOSE

To explore for fatigue-related regions and the radiotherapy (RT) dose-fatigue relationship in nasopharyngeal cancer (NPC) survivors.

METHODS

Eighty disease-free NPC survivors completed the MD Anderson Symptom Inventory-Head and Neck module (MDASI-HN) after RT. Fatigue was evaluated by the MDASI-HN fatigue item (MDASI-HN-F) and Common Terminology Criteria for Adverse Events v3.0 (CTC-AE), between 6 and 36 months after RT to determine the presence of chronic fatigue. Skull base MRIs and planning CT/RT dose were retrievable for 56 patients. Dosimetric data were extracted for 10 MRI-defined potential fatigue at-risk structures (FARS): brainstem (BS), pituitary gland (PG), hypothalamus (HT), basal ganglia, internal capsule, pineal gland, sub-thalamic nuclei, thalamus, substantia nigra, and hippocampus (HC). Recursive partitioning analysis (RPA) was used to identify dose-volume effects associated with chronic fatigue.

RESULTS

56 pts formed the cohort. Thirty patients (54%) reported any fatigue per MDASI-HN-F. Thirty-three pts (59%) had any fatigue by CTC-AE. The maximum point doses (Dmax) for PG, BS, HC, and HT were numerically higher in patients with fatigue. Dmax and Dmean of the PG were significantly higher in patients with chronic fatigue, p ≤ 0.01. A dose-volume threshold of PG V52 Gy ≥16% (LogWorth 2.4, AUC 0.7) was identified on RPA, and potential sensitivity to the PG doses was observed in younger patients (<53 years-old).

CONCLUSION

A dose-fatigue relationship was identified for the pituitary gland, both patient-reported and observer ratings. We recommend limiting the Dmax of PG to <54 Gy and V52 Gy to <16%, particularly in young NPC patients, during plan optimization when achievable.

Dosimetric Comparison of Four Volumetric-Modulated Arc Therapy Beam Arrangements Utilized for Hippocampal-Sparing Whole-Brain Radiation Therapy

PURPOSE

In the present study, the performance of four VMAT beam arrangements used for hippocampal-sparing whole-brain radiation therapy is addressed.

MATERIAL AND METHODS

Data corresponding to 20 patients were utilized so as to generate plans for every beam configuration. A preliminary study was conducted to assess the optimal distance between optimization structures (PTVx) and hippocampi. V25, V30, D50%, D2%, D98%, homogeneity index (HI) and Paddick conformity factor (CF) were evaluated for PTV. D100% and Dmax were considered for hippocampi. All plans were required to perform at least as recommended in RTOG 0933 trial regarding organs at risk (OAR) sparing and PTV objectives.

RESULTS

Considerable hippocampi sparing alongside with a reasonably low decrease in PTV coverage was achieved using a 7 mm distance between hippocampi and PTV optimization structure. Beam setup 3 (comprised of two full arcs with 0° couch angle and two half arcs with 90° couch angle) achieved the best PTV coverage, HI and CF, while it performed the second-best sparing in hippocampi and lenses. Moreover, beam setup 3 was the second-fastest treatment, although it resulted in the highest number of delivered MU among all beam setups. Beam setup 1 (comprised of two full arcs with no couch angles) was the fastest and it delivered a significantly less amount of monitor units compared with the other beam setups evaluated. Furthermore, a higher robustness was obtained by using no couch angles. Although beam setup 1 was the least optimal considering OAR sparing, it still performed better than required in the RTOG 0933 trial.

CONCLUSIONS

Overall, beam setup 3 was considered to be the best. It is worth mentioning that, apart from our results, the election of one of these beam arrangements might be dependent on the amount of patient workload at a specific institution.

Incidence of Hippocampal Metastases: Laterality and Implications for Unilateral Hippocampal Avoiding Whole Brain Radiotherapy

Introduction

Hippocampi sparing whole brain radiotherapy (WBRT) is an evolving approach in the treatment of patients with multiple brain metastases, pursuing mitigation of verbal memory decline as a consequence of hippocampal radiation injury. Accumulating data are showing different postradiotherapy changes in the left and right hippocampus with a theoretical proposal of only unilateral (dominant, left) hippocampal sparing during WBRT.

Method

The aim of this retrospective study is to describe spatial distribution of brain metastases on MRI in a cohort of 260 patients (2595 metastases) and to evaluate distribution separately in the left and right hippocampus and in respective hippocampal avoiding zones (HAZ, region with subtherapeutic radiation dose), including evaluation of location of metastatic mass centre.

Results

The median number of brain metastases was three, with lung cancer being the most common type of primary tumour; 36% had single metastasis. Almost 8% of patients had metastasis within hippocampus (1.1% of all metastases) and 18.1% of patients within HAZ (3.3% of all metastases). No statistically significant difference was observed in the laterality of hippocampal involvement, also when the location of centre of metastases was analyzed. There were more patients presenting the centre of metastasis within left (15) versus right (6) HAZ approaching the borderline of statistical significance.

Conclusion

No significant difference in the laterality of BM seeding within hippocampal structures was observed. The hypothesized unilateral sparing WBRT would have theoretical advantage in about 50% reduction in the risk of subsequent recurrence within spared regions.

Prevention of Brain Metastases

The incidence of brain metastases is projected to rise because survival rates of lung cancer, breast cancer, and melanoma continue to improve (1). The brain is being identified as a sanctuary site for harboring metastases despite excellent control of extracranial disease. This is thought to occur because the drug therapies that control extracranial disease have limited central nervous system (CNS) penetration. The development of brain metastases is a devastating diagnosis affecting both quality of life (QOL) and survival. Symptoms after diagnosis can include headache, nausea, vomiting, seizure, neurocognitive decline, and focal neurologic deficit. Some of these symptoms can be irreversible even after successful treatment of intracranial disease. Treatment of brain metastases often necessitates surgery and radiation. There have been some reports of systemic therapies offering an intracranial response however long-term data is lacking. These treatments for CNS metastases can also lead to neurocognitive sequelae impacting quality of life. Therefore, preventing disease from spreading to the brain is a topic that has generated much interest in oncology. Prophylactic cranial Irradiation (PCI) has been used in leukemia, small cell lung cancer (SCLC), and non-small cell lung cancer (NSCLC). While showing effectiveness in preventing intracranial disease development, its carries with it side effects of neurocognitive decline that can affect QOL. There are Clinical trials exploring novel delivery of PCI and concurrent neuroprotective drug therapy to try to mitigate these neurocognitive sequelae. These will be important trials to complete, as PCI has shown promise in controlling disease and prolonging survival in select patient populations. There are also drug therapies that have shown efficacy in preventing CNS metastases development. This review will explore the current therapies available to prevent CNS metastases.

Posterior Fossa Metastasis-Associated Obstructive Hydrocephalus in Adult Patients: Literature Review and Practical Considerations from the Neuro-Oncology Club of the French Society of Neurosurgery

BACKGROUND

There is no consensus concerning the management of adult patients with posterior fossa metastasis-associated obstructive hydrocephalus, especially regarding surgical procedures. A literature review was performed to assess the surgical strategy in the management of patients with metastatic brain tumor.

METHODS

A literature search was conducted of PubMed in November 2017 to identify all studies concerning brain metastases and obstructive hydrocephalus in English. All studies (except case reports and pediatric studies) between December 1953 and November 2017 that were about posterior fossa metastasis-associated obstructive hydrocephalus in adult patients were eligible. Eligible studies were classified by level of evidence. We assessed epidemiology, clinical and imaging findings, neurosurgical management, and prognosis of adult patients with posterior fossa metastasis-associated obstructive hydrocephalus. We suggest some practical considerations and a management decision tree on behalf of the Neuro-oncology Club of the French Society of Neurosurgery, with evidence-based analysis.

RESULTS

Direct surgical resection could be considered for patients with asymptomatic obstructive hydrocephalus, and endoscopic third ventriculostomy seems to be a reasonable procedure for patients with symptomatic obstructive hydrocephalus. A ventriculoperitoneal or atrial shunt seems to be a valid alternative when patients have a history of central nervous system infection or ventricular hemorrhage, leptomeningeal carcinomatosis, or unfavorable anatomy for an endoscopic third ventriculostomy to be performed.

CONCLUSIONS

The Neuro-oncology Club of the French Society of Neurosurgery suggests a prospective assessment of these neurosurgical procedures to compare their safety and efficacy.

Inter-observer variation of hippocampus delineation in hippocampal avoidance prophylactic cranial irradiation

BACKGROUND

Hippocampal avoidance prophylactic cranial irradiation (HA-PCI) techniques have been developed to reduce radiation damage to the hippocampus. An inter-observer hippocampus delineation analysis was performed and the influence of the delineation variability on dose to the hippocampus was studied.

MATERIALS AND METHODS

For five patients, seven observers delineated both hippocampi on brain MRI. The intra-class correlation (ICC) with absolute agreement and the generalized conformity index (CI_gen) were computed. Median surfaces over all observers' delineations were created for each patient and regional outlining differences were analysed. HA-PCI dose plans were made from the median surfaces and we investigated whether dose constraints in the hippocampus could be met for all delineations.

RESULTS

The ICC for the left and right hippocampus was 0.56 and 0.69, respectively, while the CI_gen ranged from 0.55 to 0.70. The posterior and anterior-medial hippocampal regions had most variation with SDs ranging from approximately 1 to 2.5 mm. The mean dose (D_mean) constraint was met for all delineations, but for the dose received by 1% of the hippocampal volume (D_1%) violations were observed.

CONCLUSION

The relatively low ICC and CI_gen indicate that delineation variability among observers for both left and right hippocampus was large. The posterior and anterior-medial border have the largest delineation inaccuracy. The hippocampus D_mean constraint was not violated.

The role of radiosurgery in the acute management of fourth ventricle compression due to brain metastases

Background:

Approximately 20–30% of all intracranial metastases are located in the posterior fossa. The clinical evolution hinges on factors such as tumor growth dynamics, local topographic conditions, performance status, and prompt intervention. Fourth ventricle (V4) compression with secondary life-threatening obstructive hydrocephalus remains a major concern, often requiring acute surgical intervention. We have previously reported on the application of adaptive hypofractionated Gamma Knife Radiosurgery in the acute management of critically located metastases, a technique known to us as rapid rescue radiosurgery (3R). We report the results of 3R in the management of posterior fossa lesions and ensuing V4 decompression.

Case Descriptions:

Four patients with V4 compression due to posterior fossa metastases were treated with 3R by three separate gamma knife radiosurgical sessions (GKRS) over a period of seven days. Mean V4 volume was 1.02 cm³ at GKRS 1, 1.13 cm³ at GKRS 2, and 1.12 cm³ at GKRS 3. Mean tumor volume during the week of treatment was 10 cm³ at both GKRS 1 and 2 and 9 cm³ at GKRS 3. On average, we achieved a tumor volume reduction of 52% and a V4 size increase of 64% at the first follow-up (4 weeks after GKRS 3). Long-term follow-up showed continued local tumor control, stable V4 volume, and absence of hydrocephalus.

Conclusion:

For this series, 3R was effective in terms of rapid tumor ablation, V4 decompression, and limited radiation-induced toxicity. This surgical procedure may become an additional tool in the management of intractable posterior fossa metastasis with V4 compression.

Mechanisms and Therapy for Cancer Metastasis to the Brain

Advances in chemotherapy and targeted therapies have improved survival in cancer patients with an increase of the incidence of newly diagnosed brain metastases (BMs). Intracranial metastases are symptomatic in 60–70% of patients. Magnetic resonance imaging (MRI) with gadolinium is more sensitive than computed tomography and advanced neuroimaging techniques have been increasingly used in the detection, treatment planning, and follow-up of BM. Apart from the morphological analysis, the most effective tool for characterizing BM is immunohistochemistry. Molecular alterations not always reflect those of the primary tumor. More sophisticated methods of tumor analysis detecting circulating biomarkers in fluids (liquid biopsy), including circulating DNA, circulating tumor cells, and extracellular vesicles, containing tumor DNA and macromolecules (microRNA), have shown promise regarding tumor treatment response and progression. The choice of therapeutic approaches is guided by prognostic scores (Recursive Partitioning Analysis and diagnostic-specific Graded Prognostic Assessment-DS-GPA). The survival benefit of surgical resection seems limited to the subgroup of patients with controlled systemic disease and good performance status. Leptomeningeal disease (LMD) can be a complication, especially in posterior fossa metastases undergoing a “piecemeal” resection. Radiosurgery of the resection cavity may offer comparable survival and local control as postoperative whole-brain radiotherapy (WBRT). WBRT alone is now the treatment of choice only for patients with single or multiple BMs not amenable to surgery or radiosurgery, or with poor prognostic factors. To reduce the neurocognitive sequelae of WBRT intensity modulated radiotherapy with hippocampal sparing, and pharmacological approaches (memantine and donepezil) have been investigated. In the last decade, a multitude of molecular abnormalities have been discovered. Approximately 33% of patients with non-small cell lung cancer (NSCLC) tumors and epidermal growth factor receptor mutations develop BMs, which are targetable with different generations of tyrosine kinase inhibitors (TKIs: gefitinib, erlotinib, afatinib, icotinib, and osimertinib). Other “druggable” alterations seen in up to 5% of NSCLC patients are the rearrangements of the “anaplastic lymphoma kinase” gene TKI (crizotinib, ceritinib, alectinib, brigatinib, and lorlatinib). In human epidermal growth factor receptor 2-positive, breast cancer targeted therapies have been widely used (trastuzumab, trastuzumab-emtansine, lapatinib-capecitabine, and neratinib). Novel targeted and immunotherapeutic agents have also revolutionized the systemic management of melanoma (ipilimumab, nivolumab, pembrolizumab, and BRAF inhibitors dabrafenib and vemurafenib).

Hippocampal sparing in stereotactic radiotherapy for brain metastases: To contour or not contour the hippocampus?

PURPOSE

The aim of our study was to evaluate hippocampal irradiation in patients treated with fractionated stereotactic brain radiotherapy.

PATIENTS AND METHODS

Retrospective hippocampal dosimetric analysis performed on 22 patients with one to four brain metastases treated with fractionated stereotactic radiotherapy using volumetric intensity-modulated arc therapy. Original plans did not include hippocampus as avoidance structure in optimization criteria; hippocampus was retrospectively delineated on magnetic resonance coregistered with planning CT and using as reference the RTOG 0933 atlas. Hippocampus was defined both as a single and as pair organ. Constraints analysed were: Dmax<16Gy, D40%<7.3Gy, D100%=Dmin<9Gy. Assuming a α/β ratio of 2Gy, biologically equivalent dose in 2Gy fractions was calculated. Hippocampal-sparing plans were developed in cases where hippocampal constraints were not respected in the original plan.

RESULTS

Among constraints analysed Dmax and D40% have been exceeded in ten out of 22 cases. The constraints were not respected in patients with more than one metastatic lesion and in three patients with only one lesion. Considering all exceeded constraints values in non-hippocampal sparing plans, the 50% of them was respected after replanning. No significant differences were found among conformity and homogeneity index between non-hippocampal sparing and hippocampal sparing plans.

CONCLUSION

Volumetric intensity-modulated arc therapy hippocampal sparing plans significantly decreases dose to hippocampus assuring an equal target coverage and organs at risk avoiding.

Hippocampal-sparing and target volume coverage in treating 3 to 10 brain metastases: A comparison of Gamma Knife, single-isocenter VMAT, CyberKnife, and TomoTherapy stereotactic radiosurgery

PURPOSE

Our purpose was to evaluate hippocampal doses and target volume coverage with and without hippocampal sparing when treating multiple brain metastases using various stereotactic radiosurgery (SRS) platforms.

METHODS AND MATERIALS

We selected 10 consecutive patients with 14 separate treatments who had been treated in our department for 3 to 10 brain metastases and added hippocampal avoidance contours. All 14 treatments were planned with GammaPlan for Gamma Knife, Eclipse for single isocenter volumetric modulated arc therapy (VMAT), TomoTherapy Treatment Planning System (TPS) for TomoTherapy, and MultiPlan for CyberKnife. Initial planning was performed with the goal of planning target volume coverage of V100 ≥95% without hippocampal avoidance. If the maximum hippocampal point dose (Dmax) was <6.6 Gy in a single fraction and <40% of the hippocampi received ≤4.5 Gy, no second plan was performed. If either constraint was not met, replanning was performed with these constraints.

RESULTS

There was a median of 6 metastases per plan, with an average total tumor volume of 7.32 mL per plan. The median hippocampal Dmax (in Gy) without sparing averaged 1.65, 9.81, 4.38, and 5.46, respectively (P < .0001). Of 14 plans, 3 Gamma Knife and CyberKnife plans required replanning, whereas 13 VMAT and 8 TomoTherapy plans required replanning. The hippocampal constraints were not achievable in 1 plan on any platform when the tumor was bordering the hippocampus. The mean volume of brain receiving 12 Gy (in mL), which has been associated with symptomatic radionecrosis, was 23.57 with Gamma Knife, 76.77 with VMAT, 40.86 with CyberKnife, and 104.06 with TomoTherapy (P = .01). The overall average conformity indices for all plans ranged from 0.36 to 0.52.

CONCLUSIONS

Even with SRS, the hippocampi can receive a considerable dose; however, if the hippocampi are outlined as organs of risk, sparing these structures is feasible in nearly all situations with all 4 platforms, without detriment to target coverage, and should be considered in all patients undergoing SRS for multiple brain metastases.

SUMMARY

Hippocampi play an important role in memory, and sparing of these structures in whole brain radiation can improve neurocognitive outcomes. The hippocampi are not routinely spared when using stereotactic radiosurgery. We evaluated the incidental dose to the hippocampi when treating multiple brain metastases and sought to examine if hippocampal sparing is feasible without detriment to target coverage. We found that hippocampal sparing is possible without affecting coverage or conformality in most cases across treatment platforms.