Variables associated with the development of complications from radiosurgery of intracranial tumors

Dose-Volume Tolerance of the Brain and Predictors of Radiation Necrosis After 3-Fraction Radiosurgery for Brain Metastases: A Large Single-Institutional Analysis

PURPOSE

Stereotactic radiosurgery (SRS) is the current standard of care in patients with brain metastases and controlled extracranial disease. Radiation necrosis (RN) is the dose-limiting side effect of SRS, but the dose constraints especially for fractionated SRS remain poorly defined. We assessed the risk of RN after 3-fraction SRS with a goal to identify specific dose-volume constraints associated with grade 3 or higher RN (G3RN).

METHODS AND MATERIALS

A single-institutional retrospective review of patients treated with 3-fraction SRS was performed. The primary endpoint was G3RN, which was defined as severe symptoms with evidence of necrosis on magnetic resonance imaging with perfusion and/or biopsy confirmation. Tissue volume around each target lesion was contoured, and volumetric doses per lesion were recorded. Logistic regression models were used to estimate the relationship between RN and each volumetric dose, and normal tissue complication probability modeling was performed using a modified Lyman-Kutcher-Burman model.

RESULTS

From 2015 to 2021, 434 patients underwent 539 courses of linear accelerator-based SRS; 2518 lesions were treated. Median SRS dose was 24 Gy. Median follow-up after SRS was 7.9 months, and the median overall survival was 9 months. A total of 93 patients (17.2%) and 123 lesions (4.9%) developed any RN. Forty-two patients (7.8%) and 57 lesions (2.3%) developed G3RN. On logistic regression, V20 and V23 were best predictors of any grade RN and G3RN, respectively, with cutoff values of 4 cc, 10 cc, and 20 cc associated with <5%, <7.5%, and <10% risk of any RN, respectively, and V23 < 15 cc associated with <5% risk of G3RN. With constrained optimization of the normal tissue complication probability Lyman-Kutcher-Burman model for G3RN, we obtained a TD50 (uniform dose resulting in a 50% complication risk) of 31.4 Gy (95% CI, 27.8-35.1 Gy).

CONCLUSIONS

In patients receiving 3-fraction SRS, G3RN was seen in 7.8% of patients, and 2.3% of the lesions were treated. V20 and V23 were the most robust dosimetric parameters associated with RN. Further studies evaluating the outcomes and RN in patients treated with fractionated SRS compared with single-fraction SRS are warranted.

Hypofractionated proton therapy for benign tumors of the central nervous system: A systematic review of the literature

AIMS

Aim of the present analysis was to report results of a systematic review of the literature in the setting of patients treated with hypoF PT for benign lesions of the central nervous system (CNS).

METHODS

The methodology complied with the PRISMA recommendations. PubMed, EMBASE and Scopus databases were interrogated in September 2022.

RESULTS

Twelve papers have been selected including patients treated for base of the skull meningiomas (6 papers), vestibular schwannoma (3 papers) and pituitary adenomas (3 papers). Clinical outcomes were evaluated with both radiologic images and clinical parameters. Long-term toxicity was reported in all but one series with an incidence ranging from 2 % to 7 % in patients treated for base of skull meningioma and 1-9 % for schwannoma.

CONCLUSIONS

HypoF PT is a safe and effective treatment in selected benign tumors of the CNS. Further dosimetric and clinical comparisons are required to better refine the patients' selection criteria.

Advances in Radiotherapy for Brain Metastases

Radiotherapy remains a cornerstone treatment of brain metastases. With new treatment advances, patients with brain metastases are living longer, and finding solutions for mitigating treatment-related neurotoxicity and improving quality of life is important. Historically, whole-brain radiation therapy (WBRT) was widely used but treatment options such as hippocampal sparing WBRT and stereotactic radiosurgery (SRS) have emerged as promising alternatives. Herein, we discuss the recent advances in radiotherapy for brain metastases including the sparing of critical structures that may improve long-term neurocognitive outcomes (eg, hippocampus, fornix) that may improve long-term neurocognitive outcome, evidence supporting preoperative and fractionated-SRS, and treatment strategies for managing radiation necrosis.

Radiosurgery of limited brain metastases from primary solid tumor: results of the randomized phase III trial (NCT02355613) comparing treatments executed with a specialized or a C-arm linac-based platform

BACKGROUND

Comparative prospective data regarding different radiosurgery (SRS) modalities for treating brain metastases (BMs) from solid tumors are not available. To investigate with a single institute phase III randomized trial whether SRS executed with linac (Arm-B) is superior to a dedicated multi-source gamma-ray stereotactic platform (Arm-A).

METHODS

Adults patients with 1-4 BMs from solid tumors up to 30 mm in maximum diameter were randomly assigned to arms A and B. The primary endpoint was cumulative incidence of symptomatic (grade 2-3) radionecrosis (CIRN). Secondary endpoints were local progression cumulative incidence (CILP), distant brain failure, disease-free survival (DFS), and overall survival (OS).

RESULTS

A total of 251 patients were randomly assigned to Arm-A (121) or Arm-B (130). The 1-year RN cumulative incidence was 6.7% in whole cohort, 3.8% (95% CI 1.9-7.4%) in Arm-B, and 9.3% (95% CI 6.2-13.8%) in the Arm-A (p = 0.43). CIRN was influenced by target volume irradiated only for the Arm-A (p << 0.001; HR 1.36 [95% CI 1.25-1.48]). Symptomatic RN occurred in 56 cases at a median time of 10.3 months (range 1.15-54.8 months), 27 in the Arm-B at a median time of 15.9 months (range 4.9-54.8 months), and 29 in the Arm-A at a median time of 6.9 months (1.2-32.3 months), without statistically significant differences between the two arms. No statistically significant differences were recorded between the two arms in CILP, BDF, DFS or OS. The mean beam-on time to deliver SRS was 49.0 ± 36.2 min in Arm-A, and 3.1 ± 1.6 min in Arm-B.

CONCLUSIONS

Given the technical differences between the treatment platforms investigated in this single-institution study, linac-based SRS (Arm-B) did not lead to significantly lower grade 2-3 RN rates versus the multi-source gamma-ray system (Arm-A) in a population of patients with limited brain metastases of small volume. No significant difference in local control was observed between both arms. For Arm-B, the treatment delivery time was significantly lower than for Arm-A.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT02355613.

An Analysis of Risk Factors for Radiation Necrosis Following Cranial Radiation

Introduction Radiation necrosis in the brain is a frequent complication of brain radiation therapy (RT) and is characterized by various neurological symptoms including cognitive dysfunction, headaches, weakness, apraxia, aphasia, and numbness. These symptoms may be progressive and treatment-resistant. Currently, risk factors for radiation necrosis are not well characterized. The goal of this study is to identify risk factors for cerebral radiation necrosis in order to improve clinicians' ability to appropriately weigh the risks and benefits of brain RT. Methods A retrospective chart review was performed on patients who were diagnosed with brain tumors and received RT (3D conformal therapy, volumetric modulated arc therapy, stereotactic radiosurgery, or stereotactic radiotherapy) at the University of Arkansas for Medical Sciences from July 1, 2017, to July 1, 2019. Data regarding demographics, characteristics of cancer, chemotherapy status and class, comorbidities, and additional medications of patients were collected via EPIC. Total RT dose, fraction size, volume of brain receiving 12 Gy (V12), and retreatment of locally recurrent tumors were recorded from Eclipse. The diagnosis of radiation necrosis was based on MRI reports that were examined for a time period of 24 months following the completion of radiation treatment and confirmed, when possible, by biopsy. Cases that did not have an MRI available at least two months after the completion of RT were excluded. Statistical association analyses were used to identify candidate risk factors to radiation necrosis. These candidate risk factors were further used to assess their associations to demographics and other characteristics of cancer and treatments. Finally, adjusted and unadjusted logistic regression models were used to predict radiation necrosis using a single risk factor or multiple risk factors. ROC curves were used to evaluate the performance of prediction or discrimination of the logistic regression models. Results A total of 139 patients were studied. The mean ± standard deviation (SD) for age was 60.4 ± 13.6 years, female:male ratio was 71:68, and White:African American:other race ratio was 112:24:3. A total of 43 (30.9%) patients were diagnosed with radiation necrosis. Radiation adjuvant to surgery, concurrent systemic therapy status, total dose, and V12 were found to be significantly associated with radiation necrosis and considered candidate risk factors of radiation necrosis in the study. Predictive models showed adjusted odds ratios ([aORs] 95% confidence intervals or CIs) of 3.70 (1.01-13.56) and 8.19 (1.78-37.78) with radiation adjuvant to surgery and concurrent systemic therapy, respectively. For every one unit (log-transformed) increase of total dose and V12, the aORs (95% CI's) were 27.35 (3.74-200.16) and 1.63 (1.15-2.32), respectively. Conclusion Our study suggested a positive correlation of concurrent systemic therapy status and post-surgical adjuvant RT with the incidence of radiation necrosis. It further demonstrated that greater total RT dose and V12 were related to the risk of developing radiation necrosis following brain RT. Given the findings of this study, the aforementioned factors should be considered when weighing the risk of radiation necrosis with the benefits of treatment.

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.

Dose-Response Effect and Dose-Toxicity in Stereotactic Radiotherapy for Brain Metastases: A Review

Simple Summary

Brain metastases are one of the most frequent complications for cancer patients. Stereotactic radiosurgery is considered a cornerstone treatment for patients with limited brain metastases and the ideal dose and fractionation schedule still remain unknown. The aim of this literature review is to discuss the dose-effect relation in brain metastases treated by stereotactic radiosurgery, accounting for fractionation and technical considerations.

Abstract

For more than two decades, stereotactic radiosurgery has been considered a cornerstone treatment for patients with limited brain metastases. Historically, radiosurgery in a single fraction has been the standard of care but recent technical advances have also enabled the delivery of hypofractionated stereotactic radiotherapy for dedicated situations. Only few studies have investigated the efficacy and toxicity profile of different hypofractionated schedules but, to date, the ideal dose and fractionation schedule still remains unknown. Moreover, the linear-quadratic model is being debated regarding high dose per fraction. Recent studies shown the radiation schedule is a critical factor in the immunomodulatory responses. The aim of this literature review was to discuss the dose–effect relation in brain metastases treated by stereotactic radiosurgery accounting for fractionation and technical considerations. Efficacy and toxicity data were analyzed in the light of recent published data. Only retrospective and heterogeneous data were available. We attempted to present the relevant data with caution. A BED10 of 40 to 50 Gy seems associated with a 12-month local control rate >70%. A BED10 of 50 to 60 Gy seems to achieve a 12-month local control rate at least of 80% at 12 months. In the brain metastases radiosurgery series, for single-fraction schedule, a V12 Gy < 5 to 10 cc was associated to 7.1–22.5% radionecrosis rate. For three-fractions schedule, V18 Gy < 26–30 cc, V21 Gy < 21 cc and V23 Gy < 5–7 cc were associated with about 0–14% radionecrosis rate. For five-fractions schedule, V30 Gy < 10–30 cc, V 28.8 Gy < 3–7 cc and V25 Gy < 16 cc were associated with about 2–14% symptomatic radionecrosis rate. There are still no prospective trials comparing radiosurgery to fractionated stereotactic irradiation.

Risk of symptomatic radiation necrosis in patients treated with stereotactic radiosurgery for brain metastases

INTRODUCTIO

Stereotactic radiosurgery (SRS) is a treatment option in the initial management of patients with brain metastases. While its efficacy has been demonstrated in several prior studies, treatment-related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We thus examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases.

PATIENTS AND METHODS

We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. Diagnosis of symptomatic RN was determined by appearance on serial MRIs, MR spectroscopy, requirement of therapy, and the development of new neurological complaints without evidence of disease progression.

RESULTS

We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to symptomatic RN was 8.3 months. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001), V50% (p<0.0001), V12Gy (p<0.0001), and V10Gy (p=0.0002), compared to the rest of the cohort. Single-fraction treatment (p=0.0025) and diabetes (p=0.019) were also significantly associated with symptomatic RN.

CONCLUSION

SRS is an effective treatment option for patients with brain metastases; however, a subset of patients may develop symptomatic RN. We found that patients with larger tumor size, larger plan V100%, V50%, V12Gy, or V10Gy, who received single-fraction SRS, or who had diabetes were all at higher risk of symptomatic RN.

Internal dose escalation associated with increased local control for melanoma brain metastases treated with stereotactic radiosurgery

OBJECTIVE

The internal high-dose volume varies widely for a given prescribed dose during stereotactic radiosurgery (SRS) to treat brain metastases (BMs). This may be altered during treatment planning, and the authors have previously shown that this improves local control (LC) for non-small cell lung cancer BMs without increasing toxicity. Here, they seek to identify potentially actionable dosimetric predictors of LC after SRS for melanoma BM.

METHODS

The records of patients with unresected melanoma BM treated with single-fraction Gamma Knife RS between 2006 and 2017 were reviewed. LC was assessed on a per-lesion basis, defined as stability or a decrease in lesion size. Outcome-oriented approaches were utilized to determine optimal dichotomization for dosimetric variables relative to LC. Univariable and multivariable Cox regression analysis was implemented to evaluate the impact of collected parameters on LC.

RESULTS

Two hundred eighty-seven melanoma BMs in 79 patients were identified. The median age was 56 years (range 31-86 years). The median follow-up was 7.6 months (range 0.5-81.6 months), and the median survival was 9.3 months (range 1.3-81.6 months). Lesions were optimally stratified by volume receiving at least 30 Gy (V30) greater than or equal to versus less than 25%. V30 was ≥ and < 25% in 147 and 140 lesions, respectively. For all patients, 1-year LC was 83% versus 66% for V30 ≥ and < 25%, respectively (p = 0.001). Stratifying by volume, lesions 2 cm or less (n = 215) had 1-year LC of 82% versus 70% (p = 0.013) for V30 ≥ and < 25%, respectively. Lesions > 2 to 3 cm (n = 32) had 1-year LC of 100% versus 43% (p = 0.214) for V30 ≥ and < 25%, respectively. V30 was still predictive of LC even after controlling for the use of immunotherapy and targeted therapy. Radionecrosis occurred in 2.8% of lesions and was not significantly associated with V30.

CONCLUSIONS

For a given prescription dose, an increased internal high-dose volume, as indicated by measures such as V30 ≥ 25%, is associated with improved LC but not increased toxicity in single-fraction SRS for melanoma BM. Internal dose escalation is an independent predictor of improved LC even in patients receiving immunotherapy and/or targeted therapy. This represents a dosimetric parameter that is actionable at the time of treatment planning and warrants further evaluation.

Single- and hypofractionated stereotactic radiosurgery for large (> 2 cm) brain metastases: a systematic review

PURPOSE

Since frameless stereotactic radiosurgery (SRS) techniques have been recently introduced, hypofractionated SRS (HF-SRS) for large brain metastases (BMs) is gradually increasing. To verify the efficacy and safety of HF-SRS for large BMs, we aimed to perform a systematic review and compared them with SF-SRS.

METHODS

We systematically searched the studies regarding SF-SRS or HF-SRS for large (> 2 cm) BM from databases including PubMed, Embase, and the Cochrane Library on July 31, 2018. Biologically effective dose with the α/β ratio of 10 (BED₁₀), 1-year local control (LC), and radiation necrosis (RN) were compared between the two groups, with the studies being weighted by the sample size.

RESULTS

The 15 studies with 1049 BMs that described 1-year LC and RN were included. HF-SRS tended to be performed in larger tumors; however, higher mean BED₁₀ (50.1 Gy₁₀ versus 40.4 Gy₁₀, p < 0.0001) was delivered in the HF-SRS group, which led to significantly improved 1-year LC (81.6 versus 69.0%, p < 0.0001) and 1-year overall survival (55.1 versus 47.2%, p < 0.0001) in the HF-SRS group compared to the SF-SRS group. In contrast, the incidence of radiation toxicity was significantly decreased in the HF-SRS group compared to the SF-SRS group (8.0 versus 15.6%, p < 0.0001).

CONCLUSION

HF-SRS results in better LC of large BMs while simultaneously reducing RN compared to SF-SRS. Thus, HF-SRS should be considered a priority for SF-SRS in patients with large BMs who are not suitable to undergo surgical resection.

Radiation Necrosis from Stereotactic Radiosurgery-How Do We Mitigate?

OPINION STATEMENT

Intracranial stereotactic radiosurgery (SRS) is an effective and convenient treatment for many brain conditions. Data regarding safety come mostly from retrospective single institutional studies and a small number of prospective studies. Variations in target delineation, treatment delivery, imaging follow-up protocols and dose prescription limit the interpretation of this data. There has been much clinical focus on radiation necrosis (RN) in particular, as it is being increasingly recognized on follow-up imaging. Symptomatic RN may be treated with medical therapy (such as corticosteroids and bevacizumab) with surgical resection being reserved for refractory patients. Nevertheless, RN remains a challenging condition to manage, and therefore upfront patient selection for SRS remains critical to provide complication-free control. Mitigation strategies need to be considered in situations where the baseline risk of RN is expected to be high-such as large target volume or re-irradiation. These may involve reduction in the prescribed dose or hypofractionated stereotactic radiation therapy (HSRT). Recently published guidelines and international meta-analysis report the benefit of HSRT in larger lesions, without compromising control rates. However, careful attention to planning parameters and SRS techniques still need to be adhered, even with HSRT. In cases where the risk is deemed to be high despite mitigation, a combination approach of surgery with or without post-operative radiation should be considered.

The Judicious Use of Stereotactic Radiosurgery and Hypofractionated Stereotactic Radiotherapy in the Management of Large Brain Metastases

Simple Summary

Brain metastases are the most common cause of cancerous brain tumors in adults. Large brain metastases are an especially difficult clinical scenario as patients often have debilitating symptoms from these tumors, and large tumors are more difficult to control with traditional single treatment radiation regimens alone or after surgery. Hypofractionated stereotactic radiotherapy is a novel way to deliver the higher doses of radiation to control large tumors either after surgery (most common), alone (common), or potentially before surgery (uncommon). Herein, we describe how delivering high doses over three or five treatments may improve tumor control and decrease complication rates compared to more traditional single treatment regimens for brain metastases larger than 2 cm in maximum dimension.

Abstract

Brain metastases are the most common intracranial malignant tumor in adults and are a cause of significant morbidity and mortality for cancer patients. Large brain metastases, defined as tumors with a maximum dimension >2 cm, present a unique clinical challenge for the delivery of stereotactic radiosurgery (SRS) as patients often present with neurologic symptoms that require expeditious treatment that must also be balanced against the potential consequences of surgery and radiation therapy—namely, leptomeningeal disease (LMD) and radionecrosis (RN). Hypofractionated stereotactic radiotherapy (HSRT) and pre-operative SRS have emerged as novel treatment techniques to help improve local control rates and reduce rates of RN and LMD for this patient population commonly managed with post-operative SRS. Recent literature suggests that pre-operative SRS can potentially half the risk of LMD compared to post-operative SRS and that HSRT can improve risk of RN to less than 10% while improving local control when meeting the appropriate goals for biologically effective dose (BED) and dose-volume constraints. We recommend a 3- or 5-fraction regimen in lieu of SRS delivering 15 Gy or less for large metastases or resection cavities. We provide a table comparing the BED of commonly used SRS and HSRT regimens, and provide an algorithm to help guide the management of these challenging clinical scenarios.

Risk of symptomatic radiation necrosis in patients treated with stereotactic radiosurgery for brain metastases

INTRODUCTIO

Stereotactic radiosurgery (SRS) is a treatment option in the initial management of patients with brain metastases. While its efficacy has been demonstrated in several prior studies, treatment-related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We thus examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases.

PATIENTS AND METHODS

We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. Diagnosis of symptomatic RN was determined by appearance on serial MRIs, MR spectroscopy, requirement of therapy, and the development of new neurological complaints without evidence of disease progression.

RESULTS

We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to symptomatic RN was 8.3 months. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001), V50% (p<0.0001), V12Gy (p<0.0001), and V10Gy (p=0.0002), compared to the rest of the cohort. Single-fraction treatment (p=0.0025) and diabetes (p=0.019) were also significantly associated with symptomatic RN.

CONCLUSION

SRS is an effective treatment option for patients with brain metastases; however, a subset of patients may develop symptomatic RN. We found that patients with larger tumor size, larger plan V100%, V50%, V12Gy, or V10Gy, who received single-fraction SRS, or who had diabetes were all at higher risk of symptomatic RN.

Dosimetric comparison of iPlanⓇ Pencil Beam (PB) and Monte Carlo (MC) algorithms in stereotactic radiosurgery/radiotherapy (SRS/SRT) plans of intracranial arteriovenous malformations

Stereotactic radiosurgery/radiotherapy (SRS/SRT) is a hypofractionated treatment where accurate dose calculation is of prime importance. The accuracy of the dose calculation depends on the treatment planning algorithm. This study is a retrospective dosimetric comparison of iPlan^Ⓡ Monte Carlo (MC) and Pencil Beam (PB) algorithms in SRS/SRT plans of cranial arteriovenous malformations (AVMs). PB plans of 60 AVM patients who were already treated using 6 MV photons from a linear accelerator were selected and divided into 2 groups. Group-I consists of 30 patients who have undergone embolization procedure with high density Onyx^Ⓡ prior to radiosurgery whereas Group-II had 30 patients who did not have embolization. These plans were recalculated with MC algorithm while keeping parameters like beam orientation, multileaf collimator (MLC) positions, MLC margin, prescription dose, and monitor units constant. Several treatment coverage parameters, isodose volumes, plan quality metrics, dose to organs at risk, and integral dose were used for comparing the 2 algorithms. The isodose distribution generated by the 2 algorithms was also compared with gamma analysis using 1%/1 mm criterion. The difference between the 2 groups as well as the differences in dose calculation by PB and MC algorithms were tested for significance using independent t-test and paired t-test respectively at 5% level of significance. The results of the independent t-test showed that there is no significant difference between the Group-I and Group-II patients for PB as well as MC algorithm due to the presence of high density embolization material. However, results of the paired t-test showed that the differences between the PB and MC algorithms were significant for several parameters analyzed in both groups of patients. The gamma analysis results also showed differences in the dose calculated by the 2 algorithms especially in the low dose regions. The significant differences between the 2 algorithms are probably due to the incorrect representation of the loss of lateral charged particle equilibrium and lateral broadening of small photon beams by PB algorithm. MC algorithms are generally considered not essential for dose calculations for target volumes located in the brain. This study demonstrates PB algorithm may not be sufficiently accurate to predict dose distributions for small fields where there is loss of LCPE. The lateral broadening due to the loss of LCPE as predicted by the MC algorithm could be the main reason for significant differences in the parameters compared. Hence, an accurate MC algorithm if available may prove valuable for intracranial SRS treatment planning of such benign lesions where the long life expectancy of patients makes accurate dosimetry critical.

Intracranial Stereotactic Radiation Therapy With a Jawless Ring Gantry Linear Accelerator Equipped With New Dual Layer Multileaf Collimator

Purpose

To test the feasibility of a simplified, robust, workflow for intracranial stereotactic radiation therapy (SRT) using a ring gantry linear accelerator (RGLA) equipped with a dual-layer stacked, staggered, and interdigitating multileaf collimator.

Materials and Methods

Twenty recent clinical SRT cases treated using a radiosurgery c-arm linear accelerator were anonymized. From these data sets, a new planning workflow was developed and used to replan these cases, which then were compared to their clinical counterparts. Population-based dose-volume histograms were analyzed for target coverage and sparing of healthy brain. All plans underwent plan review and quality assurance and were delivered on an end-to-end verification phantom using image guidance to simulate treatment.

Results

The RGLA plans were able to meet departmental standards for target coverage and organ-at-risk sparing and showed plan quality similar to the clinical plans. RGLA plans showed increases in the 50% isodose in the axial plane but decreases in the sagittal and coronal planes. There were no statistically significant differences in the homogeneity index or number of monitor units between the 2 systems. There were statistically significant increases in conformity and gradient indices, with median values of 1.09 versus 1.11 and 2.82 versus 3.13, respectively, for the c-arm versus RGLA plans. These differences were not believed to be clinically significant because they met clinical goals. The population-based dose-volume histograms showed target coverage and organ-at-risk sparing similar to that of the clinical plans. All plans were able to meet the departmental quality assurance requirements and were delivered under image guidance on an end-to-end phantom with measurements agreeing within 3% of the expected value. RGLA plans showed a median reduction in delivery time of ≈50%.

Conclusions

This work describes a simplified and efficient workflow that could reduce treatment times and expand access to SRT to centers using an RGLA.

Single versus Multifraction Stereotactic Radiosurgery for Large Brain Metastases: An International Meta-analysis of 24 Trials

PURPOSE

Multifraction (MF) stereotactic radiosurgery (SRS) purportedly reduces radionecrosis risk over single-fraction (SF) SRS in the treatment of large brain metastases. The purpose of the current work is to compare local control (LC) and radionecrosis rates of SF-SRS and MF-SRS in the definitive (SF-SRS_D and MF-SRS_D) and postoperative (SF-SRS_P and MF-SRS_P) settings.

METHODS AND MATERIALS

Population, Intervention, Control, Outcomes, Study Design/Preferred Reporting Items for Systematic Reviews and Meta-analyses and Meta-analysis of Observational Studies in Epidemiology guidelines were used to select articles in which patients had "large" brain metastases (Group A: 4-14 cm³, or about 2-3 cm in diameter; Group B: >14 cm³, or about >3 cm in diameter); 1-year LC and/or rates of radionecrosis were reported; radiosurgery was administered definitively or postoperatively. Random effects meta-analyses using fractionation scheme and size as covariates were conducted. Meta-regression and Wald-type tests were used to determine the effect of increasing tumor size and fractionation on the summary estimate, where the null hypothesis was rejected for P < .05.

RESULTS

Twenty-four studies were included, published between 2008 and 2017, with 1887 brain metastases. LC random effects estimate at 1 year was 77.6% for Group A/SF-SRS_D and 92.9% for Group A/MF-SRS_D (P = .18). LC random effects estimate at 1 year was 77.1% for Group B/SF-SRS_D and 79.2% for Group B/MF-SRS_D (P = .76). LC random effects estimate at 1 year was 62.4% for Group B/SF-SRS_P and 85.7% for Group B/MF-SRS_P (P = .13). Radionecrosis incidence random effects estimate was 23.1% for Group A/SF-SRS_D and 7.3% for Group A/MF-SRS_D (P = .003). Radionecrosis incidence random effects estimate was 11.7% for Group B/SF-SRS_D and 6.5% for Group B/MF-SRS_D (P = .29). Radionecrosis incidence random effects estimate was 7.3% for Group B/SF-SRS_P and 7.5% for Group B/MF-SRS_P (P = .85). Metaregression assessing 1-year LC and radionecrosis as a continuous function of increasing tumor volume was not statistically significant.

CONCLUSIONS

Treatment for large brain metastases with MF-SRS regimens may offer a relative reduction of radionecrosis while maintaining or improving relative rates of 1-year LC compared with SF-SRS. These findings are hypothesis-generating and require validation by ongoing and planned prospective clinical trials.

Evaluation of Plan Quality Metrics in Stereotactic Radiosurgery/Radiotherapy in the Treatment Plans of Arteriovenous Malformations

Aim:

Several plan quality metrics are available for the evaluation of stereotactic radiosurgery/radiotherapy plans. This is a retrospective analysis of 60 clinical treatment plans of arteriovenous malformation (AVM) patients to study clinical usefulness of selected plan quality metrics.

Materials and Methods:

The treatment coverage parameters Radiation Therapy Oncology Group (RTOG) Conformity Index (CI_RTOG), RTOG Quality of Coverage (Q_RTOG), RTOG Homogeneity Index (HI_RTOG), Lomax Conformity Index (CI_Lomax), Paddick's Conformity Index (CI_Paddick), and dose gradient parameters Paddick's Gradient Index (GI_Paddick) and Equivalent Fall-off Distance (EFOD) were calculated for the cohort of patients. Before analyzing patient plans, the influence of calculation grid size on selected plan quality metrics was studied on spherical targets.

Results:

It was found that the plan quality metrics are independent of calculation grid size ≤2 mm. EFOD was found to increase linearly with increase in target volume, and a linear fit equation was obtained.

Conclusions:

The analysis shows that RTOG indices and EFOD would suffice for routine clinical radiosurgical treatment plan evaluation if a dose distribution is available for visual inspection.

Indications and Efficacy of Gamma Knife Stereotactic Radiosurgery for Recurrent Glioblastoma: 2 Decades of Institutional Experience

BACKGROUND

The role of stereotactic radiosurgery (SRS) for recurrent glioblastoma and the radionecrosis risk in this setting remain unclear.

OBJECTIVE

To perform a large retrospective study to help inform proper indications, efficacy, and anticipated complications of SRS for recurrent glioblastoma.

METHODS

We retrospectively analyzed patients who underwent Gamma Knife SRS between 1991 and 2013. We used the partitioning deletion/substitution/addition algorithm to identify potential predictor covariate cut points and Kaplan-Meier and proportional hazards modeling to identify factors associated with post-SRS and postdiagnosis survival.

RESULTS

One hundred seventy-four glioblastoma patients (median age, 54.1 years) underwent SRS a median of 8.7 months after initial diagnosis. Seventy-five percent had 1 treatment target (range, 1-6), and median target volume and prescriptions were 7.0 cm 3 (range, 0.3-39.0 cm 3 ) and 16.0 Gy (range, 10-22 Gy), respectively. Median overall survival was 10.6 months after SRS and 19.1 months after diagnosis. Kaplan-Meier and multivariable modeling revealed that younger age at SRS, higher prescription dose, and longer interval between original surgery and SRS are significantly associated with improved post-SRS survival. Forty-six patients (26%) underwent salvage craniotomy after SRS, with 63% showing radionecrosis or mixed tumor/necrosis vs 35% showing purely recurrent tumor. The necrosis/mixed group had lower mean isodose prescription compared with the tumor group (16.2 vs 17.8 Gy; P = .003) and larger mean treatment volume (10.0 vs 5.4 cm 3 ; P = .009).

CONCLUSION

Gamma Knife may benefit a subset of focally recurrent patients, particularly those who are younger with smaller recurrences. Higher prescriptions are associated with improved post-SRS survival and do not seem to have greater risk of symptomatic treatment effect.

Stereotactic Radiosurgical Treatment of Glomus Jugulare Tumors

OBJECTIVE

Determine treatment outcomes of stereotactic radiosurgery (SRS) for glomus jugulare tumors (GJT), focusing on three-dimensional volume change and symptoms before and after SRS, as well as complications related to SRS.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Thirty-eight patients treated with SRS between 2000 and 2015.

INTERVENTION

SRS treatment of GJT.

MAIN OUTCOME MEASURES

The tumor volumes on pre- and posttreatment imaging were compared utilizing the Leskell GammaPlan treatment plan software to assess tumor progression. Pre- and posttreatment symptoms, Fisch classification, and complications were recorded.

RESULTS

The mean radiographic follow-up was 39.1 months. The mean dose-to-tumor margin was 13.2 Gy. The mean tumor size at treatment was 5.8 and 5.2 cm at last follow-up. Thirty-three patients had follow-up imaging suitable for analysis. When defining both 10 and 15% tumor size increases as significant, 27 (82%) and 29 (88%) tumors decreased in size or remained stable, respectively. For the seven tumors with documented pre-SRS growth, treatment success was 86%. The mean marginal dose for treatment success and failure were 13.2 and 13.7 Gy, respectively. Patients receiving a higher margin dose had a greater risk of tumor progression (p = 0.0277). Fisch classification did not impact tumor progression rate. Initial tumor volume had no significance on tumor response to SRS.

CONCLUSIONS

SRS is an effective treatment option for GJT. Both initial tumor volume and Fisch classification did not impact tumor progression. There were no significant patient or lesion characteristics that distinguished treatment success and/or failure.

[Risk of radionecrosis after hypofractionated stereotactic radiotherapy targeting the postoperative resection cavity of brain metastases]

PURPOSE

To investigate the factors that potentially lead to brain radionecrosis after hypofractionated stereotactic radiotherapy targeting the postoperative resection cavity of brain metastases.

METHODS AND MATERIALS

A retrospective analysis conducted in two French centres, was performed in patients treated with trifractionated stereotactic radiotherapy (3×7.7Gy prescribed to the 70% isodose line) for resected brain metastases. Patients with previous whole-brain irradiation were excluded of the analysis. Radionecrosis was diagnosed according to a combination of criteria including clinical, serial imaging or, in some cases, histology. Univariate and multivariate analyses were performed to determine the predictive factors of radionecrosis including clinical and dosimetric variables such as volume of brain receiving a specific dose (V_8Gy-V_22Gy).

RESULTS

One hundred eighty-one patients, with a total of 189 cavities were treated between March 2008 and February 2015. Thirty-five patients (18.5%) developed radionecrosis after a median follow-up of 15 months (range: 3-38 months) after hypofractionated stereotactic radiotherapy. One third of patients with radionecrosis were symptomatic. Multivariate analysis showed that infra-tentorial location was predictive of radionecrosis (hazard ratio [HR]: 2.97; 95% confidence interval [95% CI]: 1.47-6.01; P=0.0025). None V_8Gy-V_22Gy was associated with appearance of radionecrosis, even if V_14Gy trended toward significance (P=0.059).

CONCLUSION

Analysis of patients and treatment variables revealed that infratentorial location of brain metastases was predictive for radionecrosis after hypofractionated stereotactic radiotherapy for postoperative resection cavities.

Design of a modulated orthovoltage stereotactic radiosurgery system

PURPOSE

To achieve stereotactic radiosurgery (SRS) dose distributions with sharp gradients using orthovoltage energy fluence modulation with inverse planning optimization techniques.

METHODS

A pencil beam model was used to calculate dose distributions from an orthovoltage unit at 250 kVp. Kernels for the model were derived using Monte Carlo methods. A Genetic Algorithm search heuristic was used to optimize the spatial distribution of added tungsten filtration to achieve dose distributions with sharp dose gradients. Optimizations were performed for depths of 2.5, 5.0, and 7.5 cm, with cone sizes of 5, 6, 8, and 10 mm. In addition to the beam profiles, 4π isocentric irradiation geometries were modeled to examine dose at 0.07 mm depth, a representative skin depth, for the low energy beams. Profiles from 4π irradiations of a constant target volume, assuming maximally conformal coverage, were compared. Finally, dose deposition in bone compared to tissue in this energy range was examined.

RESULTS

Based on the results of the optimization, circularly symmetric tungsten filters were designed to modulate the orthovoltage beam across the apertures of SRS cone collimators. For each depth and cone size combination examined, the beam flatness and 80-20% and 90-10% penumbrae were calculated for both standard, open cone-collimated beams as well as for optimized, filtered beams. For all configurations tested, the modulated beam profiles had decreased penumbra widths and flatness statistics at depth. Profiles for the optimized, filtered orthovoltage beams also offered decreases in these metrics compared to measured linear accelerator cone-based SRS profiles. The dose at 0.07 mm depth in the 4π isocentric irradiation geometries was higher for the modulated beams compared to unmodulated beams; however, the modulated dose at 0.07 mm depth remained <0.025% of the central, maximum dose. The 4π profiles irradiating a constant target volume showed improved statistics for the modulated, filtered distribution compared to the standard, open cone-collimated distribution. Simulations of tissue and bone confirmed previously published results that a higher energy beam (≥ 200 keV) would be preferable, but the 250 kVp beam was chosen for this work because it is available for future measurements.

CONCLUSIONS

A methodology has been described that may be used to optimize the spatial distribution of added filtration material in an orthovoltage SRS beam to result in dose distributions with decreased flatness and penumbra statistics compared to standard open cones. This work provides the mathematical foundation for a novel, orthovoltage energy fluence-modulated SRS system.

[Imaging methods used in the differential diagnosis between brain tumour relapse and radiation necrosis after stereotactic radiosurgery of brain metastases: Literature review]

After stereotactic radiosurgery for a cerebral metastasis, one of the dreaded toxicities is radionecrosis. In the follow-up of these patients, it is impossible to distinguish radiation necrosis from tumour relapse either clinically or with MRI. In current practice, many imaging methods are designed such as special sequences of MRI (dynamic susceptibility contrast perfusion and susceptibility-weighted imaging, diffusion), proton magnetic resonance spectroscopy, positron emission tomography, or more seldom 201-thallium single-photon emission computerized tomography. This article is a required literature analysis in order to establish a decision tree with the analysis of retrospective and prospective data.

Impact of the radiosurgery prescription dose on the local control of small (2 cm or smaller) brain metastases

OBJECTIVE The impact of the stereotactic radiosurgery (SRS) prescription dose (PD) on local progression and radiation necrosis for small (≤ 2 cm) brain metastases was evaluated. METHODS An institutional review board-approved retrospective review was performed on 896 patients with brain metastases ≤ 2 cm (3034 tumors) who were treated with 1229 SRS procedures between 2000 and 2012. Local progression and/or radiation necrosis were the primary end points. Each tumor was followed from the date of radiosurgery until one of the end points was reached or the last MRI follow-up. Various criteria were used to differentiate tumor progression and radiation necrosis, including the evaluation of serial MRIs, cerebral blood volume on perfusion MR, FDG-PET scans, and, in some cases, surgical pathology. The median radiographic follow-up per lesion was 6.2 months. RESULTS The median patient age was 56 years, and 56% of the patients were female. The most common primary pathology was non-small cell lung cancer (44%), followed by breast cancer (19%), renal cell carcinoma (14%), melanoma (11%), and small cell lung cancer (5%). The median tumor volume and median largest diameter were 0.16 cm³ and 0.8 cm, respectively. In total, 1018 lesions (34%) were larger than 1 cm in maximum diameter. The PD for 2410 tumors (80%) was 24 Gy, for 408 tumors (13%) it was 19 to 23 Gy, and for 216 tumors (7%) it was 15 to 18 Gy. In total, 87 patients (10%) had local progression of 104 tumors (3%), and 148 patients (17%) had at least radiographic evidence of radiation necrosis involving 199 tumors (7%; 4% were symptomatic). Univariate and multivariate analyses were performed for local progression and radiation necrosis. For local progression, tumors less than 1 cm (subhazard ratio [SHR] 2.32; p < 0.001), PD of 24 Gy (SHR 1.84; p = 0.01), and additional whole-brain radiation therapy (SHR 2.53; p = 0.001) were independently associated with better outcome. For the development of radiographic radiation necrosis, independent prognostic factors included size greater than 1 cm (SHR 2.13; p < 0.001), location in the corpus callosum (SHR 5.72; p < 0.001), and uncommon pathologies (SHR 1.65; p = 0.05). Size (SHR 4.78; p < 0.001) and location (SHR 7.62; p < 0.001)-but not uncommon pathologies-were independent prognostic factors for the subgroup with symptomatic radiation necrosis. CONCLUSIONS A PD of 24 Gy results in significantly better local control of metastases measuring < 2 cm than lower doses. In addition, tumor size is an independent prognostic factor for both local progression and radiation necrosis. Some tumor pathologies and locations may also contribute to an increased risk of radiation necrosis.

Technical Note: Dose gradients and prescription isodose in orthovoltage stereotactic radiosurgery

PURPOSE

The purpose of this work is to examine the trade-off between prescription isodose and dose gradients in orthovoltage stereotactic radiosurgery.

METHODS

Point energy deposition kernels (EDKs) describing photon and electron transport were calculated using Monte Carlo methods. EDKs were generated from 10  to 250 keV, in 10 keV increments. The EDKs were converted to pencil beam kernels and used to calculate dose profiles through isocenter from a 4π isotropic delivery from all angles of circularly collimated beams. Monoenergetic beams and an orthovoltage polyenergetic spectrum were analyzed. The dose gradient index (DGI) is the ratio of the 50% prescription isodose volume to the 100% prescription isodose volume and represents a metric by which dose gradients in stereotactic radiosurgery (SRS) may be evaluated.

RESULTS

Using the 4π dose profiles calculated using pencil beam kernels, the relationship between DGI and prescription isodose was examined for circular cones ranging from 4 to 18 mm in diameter and monoenergetic photon beams with energies ranging from 20 to 250 keV. Values were found to exist for prescription isodose that optimize DGI.

CONCLUSIONS

The relationship between DGI and prescription isodose was found to be dependent on both field size and energy. Examining this trade-off is an important consideration for designing optimal SRS systems.

Single-Fraction Versus Multifraction (3 × 9 Gy) Stereotactic Radiosurgery for Large (>2 cm) Brain Metastases: A Comparative Analysis of Local Control and Risk of Radiation-Induced Brain Necrosis

PURPOSE

To investigate the local control and radiation-induced brain necrosis in patients with brain metastases >2 cm in size who received single-fraction or multifraction stereotactic radiosurgery (SRS); factors associated with clinical outcomes and the development of brain radionecrosis were assessed.

METHODS AND MATERIALS

Two hundred eighty-nine consecutive patients with brain metastases >2.0 cm who received SRS as primary treatment at Sant'Andrea Hospital, University of Rome Sapienza, Rome, Italy, were analyzed. Cumulative incidence analysis was used to compare local control and radiation-induced brain necrosis between groups from the time of SRS. To achieve a balanced distribution of baseline covariates between treatment groups, a propensity score analysis was used.

RESULTS

The 1-year cumulative local control rates were 77% in the single-fraction SRS (SF-SRS) group and 91% in the multifraction SRS (MF-SRS) group (P=.01). Recurrences occurred in 25 and 11 patients who received SF-SRS or MF-SRS (P=.03), respectively. Thirty-one patients (20%) undergoing SF-SRS and 11 (8%) subjected to MF-SRS experienced brain radionecrosis (P=.004); the 1-year cumulative incidence rate of radionecrosis was 18% and 9% (P=.01), respectively. Significant differences between the 2 groups in terms of local control and risk of radionecrosis were maintained after propensity score adjustment.

CONCLUSIONS

Multifraction SRS at a dose of 27 Gy in 3 daily fractions seems to be an effective treatment modality for large brain metastases, associated with better local control and a reduced risk of radiation-induced radionecrosis as compared with SF-SRS.

Early and Late Complications Following Dynamic Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy

Between December 1986 and June 1990, 112 patients (116 lesions), underwent treatment with dynamic stereotactic radiosurgery at McGill University. Of the treated lesions, 59 were arteriovenous malformations and 53 were a variety of other neoplastic or non-neoplastic conditions. In 86 lesions, the treatment was delivered in a single fraction and the treatment of the remaining 30 lesions was fractionated. Complications attributed to treatment developed in seven of the 112 patients (6.3%). No relationship was found between complications and prescribed dose, fractionation, collimator diameter, type and anatomical region of the lesion that was treated, or previous irradiation. Although extensive clinical experience will be necessary to determine optimal total doses, the potential role of fractionated treatment, and the tolerance of critical structures to radiosurgery, the relatively low incidence of complications in our series allows us to conclude that radiosurgery is well tolerated by the vast majority of patients.

Long-term risk of radionecrosis and imaging changes after stereotactic radiosurgery for brain metastases

Radionecrosis is a well-characterized effect of stereotactic radiosurgery (SRS) and is occasionally associated with serious neurologic sequelae. Here, we investigated the incidence of and clinical variables associated with the development of radionecrosis and related radiographic changes after SRS for brain metastases in a cohort of patients with long-term follow up. 271 brain metastases treated with single-fraction linear accelerator-based SRS were analyzed. Radionecrosis was diagnosed either pathologically or radiographically. Univariate and multivariate Cox regression was performed to determine the association between radionecrosis and clinical factors available prior to treatment planning. After median follow up of 17.2 months, radionecrosis was observed in 70 (25.8%) lesions, including 47 (17.3%) symptomatic cases. 22 of 70 cases (31.4%) were diagnosed pathologically and 48 (68.6%) were diagnosed radiographically. The actuarial incidence of radionecrosis was 5.2% at 6 months, 17.2% at 12 months and 34.0% at 24 months. On univariate analysis, radionecrosis was associated with maximum tumor diameter (HR 3.55, p < 0.001), prior whole brain radiotherapy (HR 2.21, p = 0.004), prescription dose (HR 0.56, p = 0.02) and histology other than non-small cell lung, breast or melanoma (HR 1.85, p = 0.04). On multivariate analysis, only maximum tumor diameter (HR 3.10, p < 0.001) was associated with radionecrosis risk. This data demonstrates that with close imaging follow-up, radionecrosis after single-fraction SRS for brain metastases is not uncommon. Maximum tumor diameter on pre-treatment MR imaging can provide a reliable estimate of radionecrosis risk prior to treatment planning, with the greatest risk among tumors measuring >1 cm.

Outcome of cerebral arteriovenous malformations after linear accelerator reirradiation

Background:

The aim of this study was to evaluate the clinical outcome of patients undergoing single-dose reirradiation using the Linear Accelerator (LINAC) for brain arteriovenous malformations (AVM).

Methods:

A retrospective study of 37 patients with brain AVM undergoing LINAC reirradiation between April 2003 and November 2011 was carried out. Patient characteristics, for example, gender, age, use of medications, and comorbidities; disease characteristics, for example, Spetzler–Martin grading system, location, volume, modified Pollock–Flickinger score; and treatment characteristics, for example, embolization, prescription dose, radiation dose–volume curves, and conformity index were analyzed. During the follow-up period, imaging studies were performed to evaluate changes after treatment and AVM cure. Complications, such as edema, rupture of the blood–brain barrier, and radionecrosis were classified as symptomatic and asymptomatic.

Results:

Twenty-seven patients underwent angiogram after reirradiation and the percentage of angiographic occlusion was 55.5%. In three patients without obliteration, AVM shrinkage made it possible to perform surgical resection with a 2/3 cure rate. A reduction in AVM nidus volume greater than 50% after the first procedure was shown to be the most important predictor of obliteration. Another factor associated with AVM cure was a prescription dose higher than 15.5 Gy in the first radiosurgery. Two patients had permanent neurologic deficits. Factors correlated with complications were the prescription dose and maximum dose in the first procedure.

Conclusion:

This study suggests that single-dose reirradiation is safe and feasible in partially occluded AVM. Reirradiation may not benefit candidates whose prescribed dose was lower than 15.5 Gy in the first procedure and initial AVM nidus volume did not decrease by more than 50% before reirradiation.

Stereotactic radiosurgery (SRS) for brain metastases: a systematic review

In many patients with brain metastases, the primary therapeutic aim is symptom palliation and maintenance of neurologic function, but in a subgroup, long-term survival is possible. Local control in the brain, and absent or controlled extracranial sites of disease are prerequisites for favorable survival. Stereotactic radiosurgery (SRS) is a focal, highly precise treatment option with a long track record. Its clinical development and implementation by several pioneering institutions eventually rendered possible cooperative group randomized trials. A systematic review of those studies and other landmark studies was undertaken. Most clinicians are aware of the potential benefits of SRS such as a short treatment time, a high probability of treated-lesion control and, when adhering to typical dose/volume recommendations, a low normal tissue complication probability. However, SRS as sole first-line treatment carries a risk of failure in non-treated brain regions, which has resulted in controversy around when to add whole-brain radiotherapy (WBRT). SRS might also be prescribed as salvage treatment in patients relapsing despite previous SRS and/or WBRT. An optimal balance between intracranial control and side effects requires continued research efforts.

Cerebral radiation necrosis: a review of the pathobiology, diagnosis and management considerations

Radiation therapy forms one of the building blocks of the multi-disciplinary management of patients with brain tumors. Improved survival following radiation therapy may come with a cost, including the potential complication of radiation necrosis. Radiation necrosis impacts the quality of life in cancer survivors, and it is essential to detect and effectively treat this entity as early as possible. Significant progress in neuro-radiology and molecular pathology facilitate more straightforward diagnosis and characterization of cerebral radiation necrosis. Several therapeutic interventions, both medical and surgical, may halt the progression of radiation necrosis and diminish or abrogate its clinical manifestations, but there are still no definitive guidelines to follow explicitly that guide treatment of radiation necrosis. We discuss the pathobiology, clinical features, diagnosis, available treatment modalities, and outcomes in the management of patients with intracranial radiation necrosis that follows radiation used to treat brain tumors.

The use of RapidArc volumetric-modulated arc therapy to deliver stereotactic radiosurgery and stereotactic body radiotherapy to intracranial and extracranial targets

Twenty-three targets in 16 patients treated with stereotactic radiosurgery (SRS) or stereotactic body radiotherapy (SBRT) were analyzed in terms of dosimetric homogeneity, target conformity, organ-at-risk (OAR) sparing, monitor unit (MU) usage, and beam-on time per fraction using RapidArc volumetric-modulated arc therapy (VMAT) vs. multifield sliding-window intensity-modulated radiation therapy (IMRT). Patients underwent computed tomography simulation with site-specific immobilization. Magnetic resonance imaging fusion and optical tracking were incorporated as clinically indicated. Treatment planning was performed using Eclipse v8.6 to generate sliding-window IMRT and 1-arc and 2-arc RapidArc plans. Dosimetric parameters used for target analysis were RTOG conformity index (CI(RTOG)), homogeneity index (HI(RTOG)), inverse Paddick Conformity Index (PCI), D(mean) and D5-D95. OAR sparing was analyzed in terms of D(max) and D(mean). Treatment delivery was evaluated based on measured beam-on times delivered on a Varian Trilogy linear accelerator and recorded MU values. Dosimetric conformity, homogeneity, and OAR sparing were comparable between IMRT, 1-arc RapidArc and 2-arc RapidArc plans. Mean beam-on times ± SD for IMRT and 1-arc and 2-arc treatments were 10.5 ± 7.3, 2.6 ± 1.6, and 3.0 ± 1.1 minutes, respectively. Mean MUs were 3041, 1774, and 1676 for IMRT, 1-, and 2-arc plans, respectively. Although dosimetric conformity, homogeneity, and OAR sparing were similar between these techniques, SRS and SBRT fractions treated with RapidArc were delivered with substantially less beam-on time and fewer MUs than IMRT. The rapid delivery of SRS and SBRT with RapidArc improved workflow on the linac with these otherwise time-consuming treatments and limited the potential for intrafraction organ and patient motion, which can cause significant dosimetric errors. These clinically important advantages make image-guided RapidArc useful in the delivery of SRS and SBRT to intracranial and extracranial targets.

Treatment of cavernous sinus tumors with linear accelerator radiosurgery

Since 1989, 79 patients with benign or malignant cavernous sinus tumors, have been treated at Stanford University with linear accelerator (linac) radiosurgery. Radiosurgery has been used as (1) a planned second-stage procedure for residual tumor following surgery, (2) primary treatment for patients whose medical conditions preclude surgery, (3) palliation of malignant lesions, and (4) definitive treatment for small, well-localized, poorly accessible tumors. Mean patient age was 52 years (range, 18 to 88); there were 28 males and 51 females. Sixty-one patients had benign tumors; 18 had malignant tumors. Mean tumor volume was 6.8 cm(3) (range 0.5 to 22.5 cm(3)) covered with an average of 2.3 isocenter (range, 1 to 5). Radiation dose averaged 17.1 Gy. Mean follow-up was 46 months. Tumor control or shrinkage, or both, varied with pathology. Radiographic tumor improvement was most pronounced in malignant lesions, with greater than 85% showing reduction in tumor size; benign tumors (meningiomas and schwannomas) had a 63% control rate and 37% shrinkage rate, with none enlarging. We concluded that stereotactic radiosurgery is a valuable tool in managing cavernous sinus tumors. There was excellent control and stabilization of benign tumors and palliation of malignant lesions.

Stereotactic Radiotherapy of Central Nervous System and Head and Neck Lesions, Using a Conformal Intensity-Modulated Radiotherapy System (Peacocktrade mark System)

The objective of this article is to evaluate single-fraction or fractionated stereotactic radiotherapy of central nervous system (CNS) and head and neck lesions using intensity-modulated radiotherapy (IMRT) with a commercially available system (Peacocktrade mark, Nomos Corporation, Sewickley, PA). This system allows tomotherapeutic delivery of intensity-modulated radiation, that is, the slice-by-slice treatment of the volume of interest with an intensity-modulated beam, making the delivery of highly conformal radiation to the target possible in both single or multiple fractions mode. During an 18-month period, 43 (21 males and 22 females) patients were treated, using a removable cranial screw-fixation device. Ages ranged from 10 to 77 years (mean, 52.2; median, 53.5). Intra- and extra-axial lesions, including head and neck malignancies and spine metastases, were treated. Clinical target volume ranged from 0.77 to 195 cm(3) (mean, 47.8; median, 29.90). The dose distribution was normalized to the maximum and was prescribed, in most cases, at the 80% or 90% isodose line (range, 65 to 96%; median, 85%; mean, 83.4%) and ranged from 14 to 80 Gy (mean, 48; median, 50). The number of fractions ranged from 1 to 40 (mean, 23; median, 25). In all but one patient, 90% of the prescription isodose line covered 100% of the clinical target volume. The heterogeneity index (the ratio between the maximum radiation dose and the prescribed dose) ranged between 1.0 and 1.50, whereas the conformity index (the ratio between the volume encompassed by the prescription isodose line and the clinical target volume) ranged between 1.0 and 4.5. There were no complications related to the radiation treatment. With a median follow-up of 6 months, more than 70% of our patients showed decreased lesion size. Stereotactic IMRT of CNS and head and neck lesions can be delivered safely and accurately. The Peacock system delivers stereotactic radiation in single or multiple fractions and has no volume limitations. It has been used to treat intracranial, head and neck, and spinal lesions. The option of fractionation, the lack of volume constraint, and the capability of treating intracranial, head and neck, and spinal pathology make stereotactic IMRT a valuable adjunct to established stereotactic radiotherapy systems delivering convergent-beam irradiation using the Linac or Gamma Knife. In a clinical setting that offers Linac, Gamma Knife radiosurgery, and conformal stereotactic radiotherapy, the latter may have advantages for treating large (> 25-cm(3)) and irregular lesions, especially when fractionation is considered useful.

Stereotactic radiosurgery for brain metastases: analysis of outcome and risk of brain radionecrosis

Purpose

to investigate the factors affecting survival and toxicity in patients treated with stereotactic radiosurgery (SRS), with special attention to volumes of brain receiving a specific dose (V10 - V16 Gy) as predictors for brain radionecrosis.

Patients and Methods

Two hundred six consecutive patients with 310 cerebral metastases less than 3.5 cm were treated with SRS as primary treatment and followed prospectively at University of Rome La Sapienza Sant'Andrea Hospital. Overall survival, brain control, and local control were estimated using the Kaplan-Meier method calculated from the time of SRS. Univariate and multivariate analysis using a Cox proportional hazards regression model were performed to determine the predictive value of prognostic factors for treatment outcome and SRS-related complications.

Results

Median overall survival and brain control were 14.1 months and 10 months, respectively. The 1-year and 2-year survival rates were 58% and 24%, and respective brain control were 43% and 22%. Sixteen patients recurred locally after SRS, with 1-year and 2-year local control rates of 92% and 84%, respectively. On multivariate analysis, stable extracranial disease and KPS >70 were associated with the most significant survival benefit. Neurological complications were recorded in 27 (13%) patients. Severe neurological complications (RTOG Grade 3 and 4) occurred in 5.8% of patients. Brain radionecrosis occurred in 24% of treated lesions, being symptomatic in 10% and asymptomatic in 14%. On multivariate analysis, V10 through V16 Gy were independent risk factors for radionecrosis, with V10 Gy and V12 Gy being the most predictive (p = 0.0001). For V10 Gy >12.6 cm³ and V12 Gy >10.9 cm³ the risk of radionecrosis was 47%.

Conclusions

SRS alone represents a feasible option as initial treatment for patients with brain metastases, however a significant subset of patients may develop neurological complications. Lesions with V12 Gy >8.5 cm³ carries a risk of radionecrosis >10% and should be considered for hypofractionated stereotactic radiotherapy especially when located in/near eloquent areas.

Clinical and pathological characteristics of brain metastasis resected after failed radiosurgery

OBJECTIVE

This study evaluates the tumor histopathology and clinical characteristics of patients who underwent resection of their brain metastasis after failed gamma knife radiosurgery.

METHODS

This study was a retrospective review from a prospective database. A total of 1200 brain metastases in 912 patients were treated by gamma knife radiosurgery during a 7-year period. Fifteen patients (1.6% of patients, 1.2% of all brain metastases) underwent resective surgery for either presumed tumor progression (6 patients) or worsening neurological symptoms associated with increased mass effect (9 patients). Radiographic imaging, radiosurgical and surgical treatment parameters, histopathological findings, and long-term outcomes were reviewed for all patients.

RESULTS

The mean age at the time of radiosurgery was 57 years (age range, 32-65 years). Initial pathological diagnoses included metastatic non-small cell lung carcinoma in 8 patients (53%), melanoma in 4 patients (27%), renal cell carcinoma in 2 patients (13%), and squamous cell carcinoma of the tongue in 1 patient (7%). The mean time interval between radiosurgery and surgical extirpation was 8.5 months (range, 3 weeks to 34 months). The mean treatment volume for the resected lesion at the time of radiosurgery was 4.4 cm(3) (range, 0.6-8.4 cm(3)). The mean dose to the tumor margin was 21Gy (range, 18-24 Gy). In addition to the 15 tumors that were eventually resected, a total of 32 other metastases were treated synchronously, with a 78% control rate. The mean volume immediately before surgery for the 15 resected lesions was 7.5 cm(3) (range, 3.8-10.2 cm(3)). Histological findings after radiosurgery varied from case to case and included viable tumor, necrotic tumor, vascular hyalinization, hemosiderin-laden macrophages, reactive gliosis in surrounding brain tissue, and an elevated MIB-1 proliferation index in cases with viable tumor. The mean survival for patients in whom viable tumor was identified (9.4 months) was significantly lower than that of patients in whom only necrosis was seen (15.1 months; Fisher's exact test, P < 0.05).

CONCLUSION

Radiation necrosis and tumor radioresistance are the most common causes precipitating a need for surgical resection after radiosurgery in patients with brain metastasis.

The place of interstitial brachytherapy and radiosurgery for low-grade gliomas

Even though stereotactic brachytherapy has been used for treatment of complex located low-grade glioma for many years, its place within modern treatment concepts is still debated and only a few centers have gained experience with this complex treatment modality. The current article reviews selection criteria, treatment protocols, radiobiology, treatment effects, risk models and side effects of stereotactic brachytherapy. Potentially alternative techniques such as radiosurgery were also reviewed under consideration of radiobiological similarities and differences.

Irradiated volume as a predictor of brain radionecrosis after linear accelerator stereotactic radiosurgery

PURPOSE

To investigate the correlation between volume of brain irradiated by stereotactic radiosurgery (SRS) and the incidence of symptomatic and asymptomatic brain radionecrosis (RN).

METHODS AND MATERIALS

A retrospective analysis was performed of patients treated with single-fraction SRS for brain metastases at our institution. Patients with at least 6-month imaging follow-up were included and diagnosed with RN according to a combination of criteria, including appearance on serial imaging and histology. Univariate and multivariate analyses were performed to determine the predictive value of multiple variables, including volume of brain receiving a specific dose (V8 Gy-V18 Gy).

RESULTS

Sixty-three patients were reviewed, with a total of 173 lesions. Most patients (63%) had received previous whole-brain irradiation. Mean prescribed SRS dose was 18 Gy. Symptomatic RN was observed in 10% and asymptomatic RN in 4% of lesions treated. Multivariate regression analysis showed V8 Gy-V16 Gy to be most predictive of symptomatic RN (p < 0.0001). Threshold volumes for significant rise in RN rates occurred between the 75th and 90th percentiles, with a midpoint volume of 10.45 cm(3) for V10 Gy and 7.85 cm(3) for V12 Gy.

CONCLUSIONS

Analysis of patient and treatment variables revealed V8 Gy-V16 Gy to be the best predictors for RN using linear accelerator-based single-fraction SRS for brain metastases. We propose that patients with V10 Gy >10.5 cm(3) or V12 Gy >7.9 cm(3) be considered for hypofractionated rather than single-fraction treatment, to minimize the risk of symptomatic RN.

Prediction of volumetric change in the "triple ring" caused by glioma I-125 brachytherapy

The aim of this study was to reveal the volumetric changes in tumor necrosis, reactive zone, and edema referred to as the "triple ring" appearing after low-dose-rate iodine-125 (I-125) interstitial irradiation of 20 inoperable low-grade gliomas. To enable prediction of these volumetric changes, we provide mathematical expressions that describe the dynamics of the triple ring. Volumes of the three regions on image-fused control CT/MR images were measured for a 24-month period. The delivered dose on the tumor surface was 50-60 Gy. Dose planning and image fusion were performed with Brain-Lab Target 1.19 software; mathematical and statistical computations were carried out with Matlab numeric computation and visualization software. To determine the volumes, control images with the triple rings were fused with the planning images. Relative volumes normalized with respect to the volume of reference dose were calculated and plotted in the time domain. First, the mean values of volumes were determined from the patients' measured data; then, polynomials were fitted to the mean values using the polynomial curve-fitting method. The accuracy of our results was verified by correlating the predicted data with the measured ones. The polynomial prediction approach proposed here reveals the dynamics of the triple ring. These polynomials will assist with (1) designing the best treatment, (2) following the patient's condition, and (3) planning reirradiation if necessary.

Conformity of LINAC-based stereotactic radiosurgery using dynamic conformal arcs and micro-multileaf collimator

PURPOSE

To assess the conformity of dynamic conformal arc linear accelerator-based stereotactic radiosurgery and to describe a standardized method of isodose surface (IDS) selection.

METHODS AND MATERIALS

In 174 targets, the conformity index (CI) at the prescription IDS used for treatment was calculated as CI = (PIV/PVTV)/(PVTV/TV), where TV is the target volume, PIV (prescription isodose volume) is the total volume encompassed by the prescription IDS, and PVTV is the TV encompassed by the IDS. In addition, a "standardized" prescription IDS (sIDS) was chosen according to the following criteria: 95% of the TV was encompassed by the PIV and 99% of TV was covered by 95% of the prescription dose. The CIs at the sIDS were also calculated.

RESULTS

The median CI at the prescription IDS and sIDS was 1.63 and 1.47, respectively (p < 0.001). In 132 of 174 cases, the volume of normal tissue in the PIV was reduced by the prescription to the sIDS compared with the prescription IDS, in 20 cases it remained unchanged, and in 22 cases it was increased.

CONCLUSION

The CIs obtained with linear accelerator-based stereotactic radiosurgery are comparable to those previously reported for gamma knife stereotactic radiosurgery. Using a uniform method to select the sIDS, adequate target coverage was usually achievable with prescription to an IDS greater than that chosen by the treating physician (prescription IDS), providing sparing of normal tissue. Thus, the sIDS might aid physicians in identifying a prescription IDS that balances coverage and conformity.

High-dose, single-fraction image-guided intensity-modulated radiotherapy for metastatic spinal lesions

PURPOSE

To report tumor control and toxicity for patients treated with image-guided intensity-modulated radiotherapy (RT) for spinal metastases with high-dose single-fraction RT.

METHODS AND MATERIALS

A total of 103 consecutive spinal metastases in 93 patients without high-grade epidural spinal cord compression were treated with image-guided intensity-modulated RT to doses of 18-24 Gy (median, 24 Gy) in a single fraction between 2003 and 2006. The spinal cord dose was limited to a 14-Gy maximal dose. The patients were prospectively examined every 3-4 months with clinical assessment and cross-sectional imaging.

RESULTS

The overall actuarial local control rate was 90% (local failure developed in 7 patients) at a median follow-up of 15 months (range, 2-45 months). The median time to local failure was 9 months (range, 2-15 months) from the time of treatment. Of the 93 patients, 37 died. The median overall survival was 15 months. In all cases, death was from progression of systemic disease and not local failure. The histologic type was not a statistically significant predictor of survival or local control. The radiation dose was a significant predictor of local control (p = 0.03). All patients without local failure also reported durable symptom palliation. Acute toxicity was mild (Grade 1-2). No case of radiculopathy or myelopathy has developed.

CONCLUSION

High-dose, single-fraction image-guided intensity-modulated RT is a noninvasive intervention that appears to be safe and very effective palliation for patients with spinal metastases, with minimal negative effects on quality of life and a high probability of tumor control.

CHAINED LIGHTNING, PART II

THE FUNDAMENTAL PRINCIPLE in the radiosurgical treatment of neurological conditions is the delivery of energy to a lesion with minimal injury to surrounding structures. The development of radiosurgical techniques from Leksell's original design has focused on the refinement of various methodologies to achieve energy containment within a target. This article is the second in a series reviewing the evolution of radiosurgical instruments with respect to issues of energy beam generation and delivery for improved conformal therapy.

Continuing with concepts introduced in an earlier article, this article examines specific aspects of beam delivery and the emergence of stereotactic radiosurgery as a measure for focusing energy beams within a target volume. The application of stereotactic principles and devices to gamma ray and linear accelerator-based energy sources provides the methodology by which energy beams are generated and targeted precisely in a focal lesion. Advanced technological systems are reviewed, including fixed beams, dynamic radiosurgery, multileaf collimation, beam shaping, and robotics as various approaches for manipulating beam delivery. Radiosurgical instruments are also compared with regard to mechanics, geometry, and dosimetry. Finally, new radiosurgical designs currently on the horizon are introduced. In exploring the complex history of radiosurgery, it is evident that the discovery and rediscovery of ideas invariably leads to the development of innovative technology for the next generation.

Stereotactic Radiosurgery: Adjacent Tissue Injury and Response after High-Dose Single Fraction Radiation—Part II: Strategies for Therapeutic Enhancement, Brain Injury Mitigation, and Brain Injury Repair

IN THE FIRST part of this series, we reviewed the histological, radiographic, and molecular data gathered regarding the brain parenchymal response to radiosurgery and suggested future studies that could enhance our understanding of the topic. With this article, we begin by addressing methods of potentiating the effect of radiosurgery on target lesions of the central nervous system. Much of the work on potentiating the effects of cranial radiation has been performed in the field of whole-brain radiotherapy. Data from Phase III trials evaluating the efficacy of various agents as radiosensitizers or radioenhancers in whole-brain radiotherapy are reviewed, and trials for investigating certain agents as enhancers of radiosurgery are suggested. The roles of gene therapy and nanotechnology in enhancing the therapeutic efficacy of radiosurgery are then addressed. Focus is then shifted to a discussion of strategies of protecting healthy tissue from the potentially deleterious aspects of the brain's response to radiosurgery that were presented in the first article of this series. Finally, comments are made regarding the role of neural progenitor or stem cells in the repair of radiation-induced brain injury after radiosurgery. The importance of both the role of the extracellular matrix and properly directed axonal regrowth leading to appropriate target reinnervation is highlighted.