Principles of radiobiology of stereotactic radiosurgery and clinical applications in the central nervous system

How Does the Number of Brain Metastases Correlate With Normal Brain Exposure in Single-Isocenter Multitarget Multifraction Stereotactic Radiosurgery

Purpose

To investigate the relationship between normal brain exposure in LINAC-based single-isocenter multitarget multifraction stereotactic radiosurgery or stereotactic radiation therapy (SRT) and the number or volume of treated brain metastases, especially for high numbers of metastases.

Methods and Materials

A cohort of 44 SRT patients with 709 brain metastases was studied. Renormalizing to a uniform prescription of 27 Gy in 3 fractions, normal brain dose volume indices, including V23 Gy (volume receiving >23 Gy), V18 Gy (volume receiving >18 Gy), and mean dose, were evaluated on these plans against the number and the total volume of targets for each plan. To compare with exposures from whole-brain radiation therapy (WBRT), the SRT dose distributions were converted to equivalent dose in 3 Gy fractions (EQD3) using an alpha-beta ratio of 2 Gy.

Results

With increasing number of targets and increasing total target volume, normal brain exposures to dose ≥18 Gy increases, and so does the mean normal brain dose. The factors of the number of targets and the total target volume are both significant, although the number of targets has a larger effect on the mean normal brain dose and the total target volume has a larger effect on V23 Gy and V18 Gy. The EQD3 mean normal brain dose with SRT planning is lower than conventional WBRT. On the other hand, SRT results in higher hot spot (ie, maximum dose outside of tumor) EQD3 dose than WBRT.

Conclusions

Based on clinical SRT plans, our study provides information on correlations between normal brain exposure and the number and total volume of targets. As SRT becomes more greatly used for patients with increasingly extensive brain metastases, more clinical data on outcomes and toxicities is necessary to better define the normal brain dose constraints for high-exposure cases and to optimize the SRT management for those patients.

Novel MRI-guided focussed ultrasound stimulated microbubble radiation enhancement treatment for breast cancer

Preclinical studies have demonstrated focused ultrasound (FUS) stimulated microbubble (MB) rupture leads to the activation of acid sphingomyelinase-ceramide pathway in the endothelial cells. When radiotherapy (RT) is delivered concurrently with FUS-MB, apoptotic pathway leads to increased cell death resulting in potent radiosensitization. Here we report the first human trial of using magnetic resonance imaging (MRI) guided FUS-MB treatment in the treatment of breast malignancies. In the phase 1 prospective interventional study, patients with breast cancer were treated with fractionated RT (5 or 10 fractions) to the disease involving breast or chest wall. FUS-MB treatment was delivered before 1st and 5th fractions of RT (within 1 h). Eight patients with 9 tumours were treated. All 7 evaluable patients with at least 3 months follow-up treated for 8 tumours had a complete response in the treated site. The maximum acute toxicity observed was grade 2 dermatitis in 1 site, and grade 1 in 8 treated sites, at one month post RT, which recovered at 3 months. No RT-related late effect or FUS-MB related toxicity was noted. This study demonstrated safety of combined FUS-MB and RT treatment. Promising response rates suggest potential strong radiosensitization effects of the investigational modality.Trial registration: clinicaltrials.gov, identifier NCT04431674.

Is single fraction the future of stereotactic body radiation therapy (SBRT)? A critical appraisal of the current literature

Stereotactic Body Radiation Therapy (SBRT) is a standard of care for many localizations but the question of the optimal fractionation remains a matter of concern. If single fraction sessions are routinely used for intracranial targets, their utilization for mobile extracranial lesions is a source of debate and apprehension. Single session treatments improve patient comfort, provide a medico-economic benefit, and have proven useful in the context of the SARS-CoV 2 pandemic. However, both technical and radiobiological uncertainties remain. Experience from intracranial radiosurgery has shown that the size of the target, its proximity to organs at risk, tumor histology, and the volume of normal tissue irradiated are all determining factors in the choice of fractionation. The literature on the use of single fraction for extracranial sites is still scarce. Only primary and secondary pulmonary tumors have been evaluated in prospective randomized trials, allowing the integration of these fractionation schemes in daily practice, for highly selected cases and in trained teams. The level of evidence for the other organs is mainly based on dose escalation or retrospective trials and calls for caution, with further studies being needed before routine use in clinical practice.

Stereotactic ablative radiotherapy for acquired resistance to EGFR therapy in metastatic non-small cell lung cancer

The advent of targeted therapy has transformed the treatment paradigm and survival of patients with metastatic non-small cell lung cancer (NSCLC) with driver mutations. The development of acquired resistances during treatment with tyrosine kinase inhibitors (TKIs) impedes a prolonged survival in many patients. This fact is leading to the use of locally ablative therapies such as stereotactic ablative radiotherapy (SABR) to counter these resistances. SABR is a non-invasive treatment that can be delivered in multiple locations and has already proven effective in oligometastatic disease. Clinical evidence suggests that the combination of SABR with TKIs prolongs progression-free survival (PFS) in metastatic NSCLC patients with mutations in epidermal growth factor receptor (EGFR), with international guidelines recommending their use in unfavorable scenarios such as oligoprogressive disease. In this publication, we have reviewed the available evidence on EGFR-TKIs resistance mechanisms and the combination of SABR with TKI in metastatic NSCLC with EGFR mutations. We also describe the utility and clinical recommendations of this combination in oligometastatic and oligoprogressive disease.

Local Control With Single-Fraction Lung Stereotactic Body Radiotherapy is not influenced by Non-Small Cell Lung Cancer Histologic Subtype

INTRODUCTION/BACKGROUND

For early stage medically inoperable lung cancer treated with fractionated stereotactic body radiotherapy (SBRT), higher local failure is associated with squamous carcinoma (SqC) compared to adenocarcinoma (AC). This study explored whether histology influences single-fraction SBRT local control.

MATERIALS AND METHODS

We surveyed our prospective data registry from 12/2009 to 12/2019 for SF-SBRT cases with biopsy-proven AC or SqC only. Outcomes of interest included local (LF), nodal (NF), distant (DF) failure rates and overall survival (OS), as well as treatment-related toxicity.

RESULTS

For the 10-year interval surveyed, 113 patients met study criteria. There was no association between histology and dose received (34 Gy or 30 Gy). Median follow up was 22.9 months. Patient characteristics were balanced between histologic cohorts. Median tumor size was 1.9 cm. Comparing total AC vs. SqC cohorts, 2-year LF rates (%) were 7.3 vs. 9.6, respectively (P = .9805). In %, 2-year LF, NF, DF and OS rates for AC for 30 Gy and 34 Gy, respectively, were 10.8 vs. 6.4; 10.5 vs. 16.2; 15.8 vs. 13.0; 77.9 vs.71.2 (all P = non-significant). In %, 2-year LF, NF, DF, and OS rates for SqC for 30 Gy and 34 Gy, respectively, were 11.8 vs. 8.1; 5.9 vs. 18.0; 23.5 vs. 9.7; 70.6 vs. 77.1 (all P = non-significant). When considering toxicities, there were no grade 4/5 toxicities and no significant differences in any other toxicity rate by histology or dose.

CONCLUSION

SF-SBRT local control was not associated with histology, unlike fractionated schedules. This novel finding adds to the evolving understanding of this treatment schedule.

Pre-operative Stereotactic Radiosurgery for Cerebral Metastatic Disease: A Retrospective Dose-Volume Study

BACKGROUND AND PURPOSE

Stereotactic radiosurgery (SRS) after maximal safe resection is an accepted treatment strategy for patients with cerebral metastatic disease. Despite its high conformality profile, the incidence of radionecrosis (RN) remains high. SRS delivered pre-operatively could be associated with a reduced incidence of RN. We sought to evaluate whether neoadjuvant SRS could reduce radiotherapy doses in a cohort of patients treated with post-operative SRS.

METHODS

A cohort of 47 brain metastases (BM) treated at 2 academic institutions was retrospectively analyzed. Subjects underwent surgical extirpation of BMs and subsequent SRS to surgical bed. Post-operative volumetric and dosimetric data was collected from records or recreations of delivered plans; pre-operative data were derived from hypothetical radiotherapy courses and compared using Wilcoxon signed-rank tests.

RESULTS

Higher planned tumor volume post-operatively (median[IQR] 12.28 [6.54, 18.69]cc vs. 10.20 [4.53, 21.70]cc respectively, p=0.4150) was observed. The median prescribed radiotherapy dose (DRx) was 16Gy pre-operatively and 24Gy post-operatively(p<0.0001). Further investigations revealed improved pre-operative conformity index (1.23[1.20, 1.29] vs. 1.29[1.23, 1.39], p=0.0098) and gradient index (2.72[2.59, 2.98] vs. 2.94[2.69, 3.47], p=0.0004). A significant difference was found in normal brain tissue exposed to 10Gy (12.97[6.78, 25.54]cc vs. 32.13[19.42, 48.40]cc, p<0.0001), 12Gy (9.31[4.56, 17.43]cc vs. 23.80[14.74, 36.56]cc, p<0.0001), and 14Gy (5.62[3.23, 11.61]cc vs. 17.47[9.00, 28.31]cc, p<0.0001), favoring pre-operative SRS.

CONCLUSIONS

Neoadjuvant SRS is associated reduced DRx, better conformality profile and decreased radiation to normal tissue. These findings could support the use of neoadjuvant SRS for the treatment of BMs.

Management Strategies for Large Brain Metastases

Brain metastases represent the most common intracranial neoplasm and pose a significant disease burden on the individual and the healthcare system. Although whole brain radiation therapy was historically a first line approach, subsequent research and technological advancements have resulted in a larger armamentarium of strategies for treatment of these patients. While chemotherapeutic options remain limited, surgical resection and stereotactic radiosurgery, as well as their combination therapies, have shifted the paradigms for managing intracranial metastatic disease. Ultimately, no single treatment is shown to be consistently effective across patient groups in terms of overall survival, local and distant control, neurocognitive function, and performance status. However, close consideration of patient and tumor characteristics may help delineate more favorable treatment strategies for individual patients. Here the authors present a review of the recent literature surrounding surgery, whole brain radiation therapy, stereotactic radiosurgery, and combination approaches.

Stereotactic ablative radiation therapy for spinal metastases: experience at a single Brazilian institution

Background

This study aims to assess the clinical outcomes of patients with spine metastases who underwent stereotactic ablative radiation therapy (SABR) as part of their treatment. SABR has arisen as a contemporary treatment option for spinal metastasis patients with good prognoses.

Materials and methods

Between November 2010 and September 2018, Spinal SABR was performed in patients with metastatic disease in different settings: radical (SABR only), postoperative (after decompression and/or fixation surgery), and reirradiation. Local control (LC), pain control, overall survival (OS) and toxicities were reported.

Results

Eighty-five patients (corresponding to 96 treatments) with spine metastases were included. The median age was 59 years (range, 23-91). In most SA BR (82.3%, n = 79) was performed as the first local spine treatment, while in 12 settings (12.5%), fixation and/or decompression surgery was performed prior to SABR. Two-year overall survival rate was 74.1%, and median survival was 19 months. The LC rate at 2 years was 72.3%. With regard to pain control, among 67 patients presenting with pain before SA BR, 83.3% had a complete response, 12.1% had a partial response, and 4.6% had progression. Vertebral compression fractures occurred in 10 patients (11.7%), of which 5 cases occurred in the reirradiation setting. Radiculopathy and myelopathy were not observed. No grade III or IV toxicities were seen.

Conclusion

This is the first study presenting a Brazilian experience with spinal SA BR, and the results confirm its feasibility and safety. SABR was shown to produce good local and pain control rates with low rates of adverse events.

A Volumetric Dosimetry Analysis of Vertebral Body Fracture Risk after Single Fraction Spine Stereotactic Body Radiotherapy

PURPOSE

Vertebral compression fractures (VCF) are a common and severe complication of spine stereotactic body radiotherapy (SBRT). We sought to analyze how volumetric dosimetry and clinical factors were associated with the risk of VCF.

METHODS AND MATERIALS

We evaluated 173 spinal segments undergoing single fraction SBRT in 85 patients from a retrospective database. Vertebral bodies were contoured and dosimetric values were calculated. Competing risk models were used to evaluate the effect of clinical and dosimetry variables on the risk of VCF.

RESULTS

Our primary endpoint was development of a post SBRT VCF. New or progressive fractures were noted in 21/173 vertebrae (12.1%); the median time to fracture was 322 days. Median follow up time was 426 days. Upon multivariable analysis, the percentages of vertebral body volume receiving >20 Gy and >24 Gy were significantly associated with increased risk of VCF (HR: 1.036, 1.104; p = 0.029, 0.044 respectively). No other patient or treatment factors were found to be significant on multivariable analysis. Sensitivity analysis revealed that the percentages of vertebral body volume receiving >20 Gy and >24 Gy required to obtain 90% sensitivity for predicting vertebral body fracture were 24% and 0%, respectively.

CONCLUSIONS

VCF is a common complication after SBRT with a crude incidence of 12.1%. Treatment plans that permit higher volumes receiving doses >20 Gy and >24 Gy to the vertebral body are associated with increased risk of VCF. In order to achieve 90% sensitivity for predicting VCF post SBRT, the percentage of vertebral volume receiving >20 Gy should be <24% and maximum point dose should be <24 Gy. These results may help guide clinicians when evaluating spine SBRT treatment plans to minimize the risk of developing post-treatment VCF.

Responses in the diffusivity and vascular function of the irradiated normal brain are seen up until 18 months following SRS of brain metastases

Background

MRI may provide insights into longitudinal responses in the diffusivity and vascular function of the irradiated normal-appearing brain following stereotactic radiosurgery (SRS) of brain metastases.

Methods

Forty patients with brain metastases from non-small cell lung cancer (N = 26) and malignant melanoma (N = 14) received SRS (15–25 Gy). Longitudinal MRI was performed pre-SRS and at 3, 6, 9, 12, and 18 months post-SRS. Measures of tissue diffusivity and vascularity were assessed by diffusion-weighted and perfusion MRI, respectively. All maps were normalized to white matter receiving less than 1 Gy. Longitudinal responses were assessed in normal-appearing brain, excluding tumor and edema, in the LowDose (1–10 Gy) and HighDose (>10 Gy) regions. The Eastern Cooperative Oncology Group (ECOG) performance status was recorded pre-SRS.

Results

Following SRS, the diffusivity in the LowDose region increased continuously for 1 year (105.1% ± 6.2%; P < .001), before reversing toward pre-SRS levels at 18 months. Transient reductions in microvascular cerebral blood volume (P < .05), blood flow (P < .05), and vessel densities (P < .05) were observed in LowDose at 6–9 months post-SRS. Correspondingly, vessel calibers in LowDose transiently increased at 3–9 months (P < .01). The responses in HighDose displayed similar trends as in LowDose, but with larger interpatient variations. Vascular responses followed pre-SRS ECOG status.

Conclusions

Our results imply that even low doses of radiation to normal-appearing brain following cerebral SRS induce increased diffusivity and reduced vascular function for up until 18 months. In particular, the vascular responses indicate the reduced ability of the normal-appearing brain tissue to form new capillaries. Assessing the potential long-term neurologic effects of SRS on the normal-appearing brain is warranted.

Fractionated Stereotactic Radiotherapy for Pituitary Adenomas: Single-Center Experience in 75 Consecutive Patients

BACKGROUND

Early results of postoperative fractionated stereotactic radiotherapy (FSRT) for functional and nonfunctional pituitary adenomas appear promising, but the majority of available evidence draws from small series with insufficient follow-up data to draw meaningful conclusions.

OBJECTIVE

To evaluate the long-term outcomes of a large series of patients undergoing FSRT for both functional and nonfunctional pituitary adenomas with the Novalis system (BrainLAB, Heimstetten, Germany).

METHODS

Chart data for 75 consecutive patients undergoing FSRT for a pituitary tumor (21 functional and 54 nonfunctional adenomas) at our institution between January 2004 and June 2013 were reviewed.

RESULTS

Radiographic progression-free survival was 100% over a mean of 47.8 months of radiographic follow-up (range, 12.0-131.2 months). Hormonal normalization was seen in 69.2% of patients with functional adenomas after FSRT, whereas 30.8% experienced partial hormonal control. Mild, grade I acute adverse effects were observed during radiotherapy treatment in 36 patients (48%), and objective, persistent worsening of vision occurred in a single patient (1.5%) after FSRT. New hormonal deficits were seen in 28.0% of patients after FSRT. Radiographic responses were inversely related to tumor volume.

CONCLUSION

FSRT delivers radiographic and functional outcomes similar to those seen with stereotactic radiosurgery and conventional radiotherapy with less resultant toxicity. FSRT is most beneficial for smaller tumors (those <3 cm in diameter).

ABBREVIATIONS

EBRT, external beam radiotherapyFSRT, fractionated stereotactic radiotherapyOR, odds ratioPTV, planning target volumeSRS, stereotactic radiosurgery.

Impact of 2-staged stereotactic radiosurgery for treatment of brain metastases ≥ 2 cm

OBJECTIVE Stereotactic radiosurgery (SRS) is the primary modality for treating brain metastases. However, effective radiosurgical control of brain metastases ≥ 2 cm in maximum diameter remains challenging and is associated with suboptimal local control (LC) rates of 37%-62% and an increased risk of treatment-related toxicity. To enhance LC while limiting adverse effects (AEs) of radiation in these patients, a dose-dense treatment regimen using 2-staged SRS (2-SSRS) was used. The objective of this study was to evaluate the efficacy and toxicity of this treatment strategy. METHODS Fifty-four patients (with 63 brain metastases ≥ 2 cm) treated with 2-SSRS were evaluated as part of an institutional review board-approved retrospective review. Volumetric measurements at first-stage stereotactic radiosurgery (first SSRS) and second-stage SRS (second SSRS) treatments and on follow-up imaging studies were determined. In addition to patient demographic data and tumor characteristics, the study evaluated 3 primary outcomes: 1) response at first follow-up MRI, 2) time to local progression (TTP), and 3) overall survival (OS) with 2-SSRS. Response was analyzed using methods for binary data, TTP was analyzed using competing-risks methods to account for patients who died without disease progression, and OS was analyzed using conventional time-to-event methods. When needed, analyses accounted for multiple lesions in the same patient. RESULTS Among 54 patients, 46 (85%) had 1 brain metastasis treated with 2-SSRS, 7 patients (13%) had 2 brain metastases concurrently treated with 2-SSRS, and 1 patient underwent 2-SSRS for 3 concurrent brain metastases ≥ 2 cm. The median age was 63 years (range 23-83 years), 23 patients (43%) had non-small cell lung cancer, and 14 patients (26%) had radioresistant tumors (renal or melanoma). The median doses at first and second SSRS were 15 Gy (range 12-18 Gy) and 15 Gy (range 12-15 Gy), respectively. The median duration between stages was 34 days, and median tumor volumes at the first and second SSRS were 10.5 cm³ (range 2.4-31.3 cm³) and 7.0 cm³ (range 1.0-29.7 cm³). Three-month follow-up imaging results were available for 43 lesions; the median volume was 4.0 cm³ (range 0.1-23.1 cm³). The median change in volume compared with baseline was a decrease of 54.9% (range -98.2% to 66.1%; p < 0.001). Overall, 9 lesions (14.3%) demonstrated local progression, with a median of 5.2 months (range 1.3-7.4 months), and 7 (11.1%) demonstrated AEs (6.4% Grade 1 and 2 toxicity; 4.8% Grade 3). The estimated cumulative incidence of local progression at 6 months was 12% ± 4%, corresponding to an LC rate of 88%. Shorter TTP was associated with greater tumor volume at baseline (p = 0.01) and smaller absolute (p = 0.006) and relative (p = 0.05) decreases in tumor volume from baseline to second SSRS. Estimated OS rates at 6 and 12 months were 65% ± 7% and 49% ± 8%, respectively. CONCLUSIONS 2-SSRS is an effective treatment modality that resulted in significant reduction of brain metastases ≥ 2 cm, with excellent 3-month (95%) and 6-month (88%) LC rates and an overall AE rate of 11%. Prospective studies with larger cohorts and longer follow-up are necessary to assess the durability and toxicities of 2-SSRS.

Skull base bony lesions: Management nuances; a retrospective analysis from a Tertiary Care Centre

Background:

Skull base lesions are not uncommon, but their management has been challenging for surgeons. There is large no of bony tumors at the skull base which has not been studied in detail as a group. These tumors are difficult not only because of their location but also due to their variability in the involvement of important local structure. Through this retrospective analysis from a Tertiary Care Centre, we are summarizing the details of skull base bony lesions and its management nuances.

Materials and Methods:

The histopathologically, radiologically, and surgically proven cases of skull base bony tumors or lesions involving bone were analyzed from the neurosurgery, neuropathology record of our Tertiary Care Institute from January 2009 to January 2014. All available preoperative and postoperative details were noted from their case files. The extent of excision was ascertained from operation records and postoperative magnetic resonance imaging if available.

Results:

We have surgically managed 41 cases of skull base bony tumors. It includes 11 patients of anterior skull base, 13 middle skull base, and 17 posterior skull base bony tumors. The most common bony tumor was chordoma 15 (36.6%), followed by fibrous dysplasia 5 (12.2%), chondrosarcoma (12.2%), and ewings sarcoma-peripheral primitive neuroectodermal tumor (EWS-pPNET) five cases (12.2%) each. There were more malignant lesions (n = 29, 70.7%) at skull base than benign (n = 12, 29.3%) lesions. The surgical approach employed depended on location of tumor and pathology. Total mortality was 8 (20%) of whom 5 patients were of histological proven EWS-pPNET.

Conclusions:

Bony skull base lesion consists of wide variety of lesions, and requires multispecialty management. The complex lesions required tailored approaches surgery of these lesions. With the advent of microsurgical and endoscopic techniques, and use of navigation better outcomes are being seen, but these lesions require further study for development of proper management plan.

Prospective evaluation of anxiety, depression and quality of life in medically inoperable early stage non-small cell lung cancer patients treated with stereotactic ablative radiotherapy

AIM

The aim of this prospective study was to evaluate the level of anxiety, depression, and quality of life (QoL) in medically inoperable patients with early stage non-small cell lung cancer (NSCLC) treated with stereotactic ablative radiotherapy (SABR).

BACKGROUND

Prolonged survival is equally important as maintaining high QoL and good psychological functioning during the treatment of lung cancer. Nowadays available SABR has markedly changed clinical care and outcomes in the group of medically inoperable patients. To our knowledge, analysis of QoL and psychological state has not been performed in Polish patients with early NSCLC treated with SABR.

MATERIALS AND METHODS

Research group consisted of medically inoperable, early NSCLC (T1-2aN0M0) patients qualified to SABR. Patients were asked to complete Polish versions of the European Organization for Research and Treatment of Cancer Quality of Life - Core Questionnaire (EORTC QLQ-C30) with the Lung Cancer Questionnaire (LC13) and Hospital Anxiety and Depression Scale (HAD). These questionnaires were repeated 2 weeks and then 3 months after treatment completion.

RESULTS

We enrolled 51 patients who met the inclusion criteria. SABR did not deteriorate QoL and psychological functioning. On the contrary, clinically meaningful improvement was observed in emotional functioning, level of insomnia, anxiety and depression. Significantly worse improvement was shown in patients with chronic obstructive pulmonary disease (COPD).

CONCLUSIONS

Our results confirm that SABR is well tolerated and does not have a deleterious effect on QoL and psychological state. Results of our study indicate the importance of additional psychological care in the group of patients with COPD.

The impact of tumor biology on survival and response to radiation therapy among patients with non-small cell lung cancer brain metastases

PURPOSE

To investigate the natural history and response to radiation therapy among ALK-rearranged, EGFR-mutated, wild-type adenocarcinoma, and squamous cell non-small cell lung cancer (NSCLC) brain metastases.

METHODS AND MATERIALS

Patients with NSCLC brain metastasis diagnosed from 1989 through 2014 at a single tertiary-care institution were included. The primary outcome was overall survival, whereas secondary outcomes included local failure, distant intracranial failure, and radiation necrosis. Cox proportional hazards regression was used to model overall survival; multivariate competing risks regression was used to model secondary outcomes.

RESULTS

Within the study period, 1920 patients presented with 6312 brain metastases. Squamous histology was associated with poorer median survival compared with adenocarcinomas (5.4 vs 8.8 months, P < .01). Median survival was greatest among ALK+ patients (49.2 months), followed by EGFR+ (20.3 months), and wild-type adenocarcinomas (10.0 months, P < .01). Treatment with estimated glomerular filtration rate inhibitors (hazard ratio [HR], 0.66; P < .01) and vascular endothelial growth factor antibodies (HR, 0.65; P < .01) increased survival independent of mutational status. Among 2056 lesions treated with stereotactic radiosurgery, the 12-month cumulative incidence of local failure was significantly greater among squamous cell carcinomas relative to adenocarcinomas (15% vs 10%, HR, 1.26; P = .04). Patients with ALK+ metastases experienced higher rates of local failure (10%; HR, 2.00; P = .05), distant failure (39%; HR, 2.94; P < .01), and radiation necrosis (18%; HR, 5.77; P < .01), whereas EGFR+ patients experienced the lowest rates of local failure (5%; HR, 0.46; P = .04) and distant failure (3%; HR, 0.13; P = .04).

CONCLUSIONS

Advances in precision medicine have increased survival among select patients with NSCLC. In the present investigation, ALK+ and EGFR+ status were associated with improved survival. However, patients with ALK+ metastases have poor intracranial control relative to EGFR+ metastases, possibly because of limited intracranial penetration of crizotinib compared with estimated glomerular filtration rate inhibitors. Future investigations are warranted to determine the optimal management of ALK+ brain metastases with the introduction of second-generation ALK inhibitors.

Spine stereotactic radiosurgery with concurrent tyrosine kinase inhibitors for metastatic renal cell carcinoma

OBJECT

Systemic control of metastatic renal cell carcinoma (mRCC) has substantially improved with the development of VEGF, mTOR, and checkpoint inhibitors. The current first-line standard of care is a VEGF tyrosine kinase inhibitor (TKI). In preclinical models, TKIs potentiate the response to radiotherapy. Such improved efficacy may prolong the time to salvage therapies, including whole-brain radiotherapy or second-line systemic therapy.

As the prevalence of mRCC has increased, the utilization of spine stereotactic radiosurgery (SRS) has also increased. However, clinical outcomes following concurrent treatment with SRS and TKIs remain largely undefined. The purpose of this investigation was to determine the safety and efficacy of TKIs when delivered concurrently with SRS. The authors hypothesized that first-line TKIs delivered concurrently with SRS significantly increase local control compared with SRS alone or TKIs alone, without increased toxicity.

METHODS

A retrospective cohort study of patients undergoing spine SRS for mRCC was conducted. Patients undergoing SRS were divided into 4 cohorts: those receiving concurrent first-line TKI therapy (A), systemic therapy–naïve patients (B), and patients who were undergoing SRS with (C) or without (D) concurrent TKI treatment after failure of first-line therapy. A negative control cohort (E) was also included, consisting of patients with spinal metastases managed with TKIs alone. The primary outcome was 12-month local failure, defined as any in-field radiographic progression. Multivariate competing risks regression was used to determine the independent effect of concurrent first-line TKI therapy upon local failure.

RESULTS

One hundred patients who underwent 151 spine SRS treatments (232 vertebral levels) were included. At the time of SRS, 46% were receiving concurrent TKI therapy. In each SRS cohort, the median prescription dose was 16 Gy in 1 fraction. Patients in Cohort A had the highest burden of epidural disease (96%, p < 0.01).

At 12 months, the cumulative incidence of local failure was 4% in Cohort A, compared with 19%–27% in Cohorts B–D and 57% in Cohort E (p < 0.01). Multivariate competing risks regression demonstrated that concurrent first-line TKI treatment (Cohort A) was independently associated with a local control benefit (HR 0.21, p = 0.04). In contrast, patients treated with TKIs alone (Cohort E) experienced an increased rate of local failure (HR 2.43, p = 0.03). No toxicities of Grade 3 or greater occurred following SRS with concurrent TKI treatment, and the incidence of post-SRS vertebral fracture (overall 21%) and pain flare (overall 17%) were similar across cohorts.

CONCLUSIONS

The prognosis for patients with mRCC has significantly improved with TKIs. The present investigation suggests a local control benefit with the addition of concurrent first-line TKI therapy to spine SRS. These results have implications in the oligometastatic setting and support a body of preclinical radiobiological research.

Single-Fraction Spine Stereotactic Body Radiation Therapy for the Treatment of Chordoma

PURPOSE

Chordoma is a radioresistant tumor that presents a therapeutic challenge with spine involvement, as high doses of radiation are needed for local control while limiting dose to the spinal cord. The purpose of this study is to determine the efficacy and safety of single-fraction spine stereotactic body radiation therapy for the treatment of spine chordoma.

METHODS

A retrospective review of our institutional database from 2006 to 2013 identified 8 patients (12 cases) with chordoma of the spine who were treated with spine stereotactic body radiation therapy. Surgical resection was performed in 7 of the 12 cases. The treatment volume was defined by the bony vertebral level of the tumor along with soft tissue extension appreciated on magnetic resonance imaging fusion. Medical records and imaging were assessed for pain relief and local control. Treatment toxicity was evaluated using Common Terminology Criteria for Adverse Events version 4.0.

RESULTS

Median age was 59 years (range, 17-91). Median target volume was 48 cm³ (1-304), and median prescription dose was 16 Gy (11-16). Median conformality index was 1.44 (1.14-3.21), and homogeneity index was 1.12 (1.05-1.19). With a median follow-up time of 9.7 months (.5-84), local control was achieved in 75% of the cases treated. One patient developed limited grade 2 spinal cord myelopathy that resolved with steroids. There were no other treatment toxicities from spine stereotactic body radiation therapy.

CONCLUSION

Single-fraction spine stereotactic body radiation therapy can be safely delivered to treat chordoma of the spine with the potential to improve pain symptoms. Although the early data are suggestive, long-term follow-up with more patients is necessary to determine the efficacy of spine stereotactic body radiation therapy in the treatment of chordoma of the spine.

The Rationale for Targeted Therapies and Stereotactic Radiosurgery in the Treatment of Brain Metastases

Brain metastases are the most common intracranial malignancy. Many approaches, including radiation therapy, surgery, and cytotoxic chemotherapy, have been used to treat patients with brain metastases depending on the patient's disease burden and symptoms. However, stereotactic surgery (SRS) has revolutionized local treatment of brain metastases. Likewise, targeted therapies, including small-molecule inhibitors and monoclonal antibodies that target cancer cell metabolism or angiogenesis, have transformed managing systemic disease. Prospective data on combining these treatments for synergistic effect are limited, but early data show favorable safety and efficacy profiles. The combination of SRS and targeted therapy will further individualize treatment, potentially obviating the need for cytotoxic chemotherapy or whole-brain radiation. There is a great need to pursue research into these exciting modalities and novel combinations to further improve the treatment of patients with brain metastases. This article discusses reported and ongoing clinical trials assessing the safety and efficacy of targeted therapy during SRS.

IMPLICATIONS FOR PRACTICE

Treatment of patients with brain metastases requires a multidisciplinary approach. Stereotactic radiosurgery is increasingly used in the upfront setting to treat new brain metastasis. Targeted therapies have revolutionized systemic treatment of many malignancies and may sometimes be used as initial treatment in metastatic patients. There is sparse literature regarding safety and efficacy of combining these two treatment modalities. This article summarizes the supporting literature and highlights ongoing clinical trials in combining radiosurgery with targeted therapy.

Stereotactic radiosurgery of glomus jugulare tumors: current concepts, recent advances and future perspectives

Stereotactic radiosurgery (SRS), a very highly focused form of therapeutic irradiation, has been widely recognized as a viable treatment option in the management of intracranial pathologies including benign tumors, malign tumors, vascular malformations and functional disorders. The applications of SRS are continuously expanding thanks to the ever-increasing advances and corresponding improvements in neuroimaging, radiation treatment techniques, equipment, treatment planning and delivery systems. In the context of glomus jugulare tumors (GJT), SRS is being more increasingly used both as the upfront management modality or as a complementary or salvage treatment option. As its safety and efficacy is being evident with compiling data from studies with longer follow-up durations, SRS appears to take the lead in the management of most patients with GJT. Herein, we address current concepts, recent advances and future perspectives in SRS of GJT in light of the literature.

Medical linear accelerator mounted mini-beam collimator: design, fabrication and dosimetric characterization

The goal of this work was to design, build and experimentally characterize a linear accelerator mounted mini-beam collimator for use at a nominal 6 MV beam energy. Monte Carlo simulation was used in the design and dosimetric characterization of a compact mini-beam collimator assembly mounted to a medical linear accelerator. After fabrication, experimental mini-beam dose profiles and central axis relative output were measured and the results used to validate the simulation data. The simulation data was then used to establish traceability back to an established dosimetric code of practice. The Monte Carlo simulation work revealed that changes in collimator blade width have a greater influence on the valley-to-peak dose ratio than do changes in blade height. There was good agreement between the modeled and measured profile data, with the exception of small differences on either side of the central peak dose. These differences were found to be systematic across all depths and result from limitations associated with the collimator fabrication. Experimental mini-beam relative output and simulation data agreed to better than ± 2.0%, which is well within the level of uncertainty required for dosimetric traceability of non-standard field geometries. A mini-beam collimator has now been designed, built and experimentally characterized for use with a commercial linear accelerator operated at a nominal 6 MV beam energy.

Multi-modality management of craniopharyngioma: a review of various treatments and their outcomes

Craniopharyngioma is a rare tumor that is expected to occur in ∼400 patients/year in the United States. While surgical resection is considered to be the primary treatment when a patient presents with a craniopharyngioma, only 30% of such tumors present in locations that permit complete resection. Radiotherapy has been used as both primary and adjuvant therapy in the treatment of craniopharyngiomas for over 50 years. Modern radiotherapeutic techniques, via the use of CT-based treatment planning and MRI fusion, have permitted tighter treatment volumes that allow for better tumor control while limiting complications. Modern radiotherapeutic series have shown high control rates with lower doses than traditionally used in the two-dimensional treatment era. Intracavitary radiotherapy with radio-isotopes and stereotactic radiosurgery may have a role in the treatment of recurrent cystic and solid recurrences, respectively. Recently, due to the exclusive expression of the Beta-catenin clonal mutations and the exclusive expression of BRAF V600E clonal mutations in the overwhelming majority of adamantinomatous and papillary tumors respectively, it is felt that inhibitors of each pathway may play a role in the future treatment of these rare tumors.

Quantification of the In Vitro Radiosensitivity of Mung Bean Sprout Elongation to 6MV X-Ray: A Revised Target Model Study

In this study, a revised target model for quantifying the in vitro radiosensitivity of mung bean sprout elongation to 6-MV X-rays was developed. The revised target model, which incorporated the Poisson prediction for a low probability of success, provided theoretical estimates that were highly consistent with the actual data measured in this study. The revised target model correlated different in vitro radiosensitivities to various effective target volumes and was successfully confirmed by exposing mung beans in various elongation states to various doses of 6-MV X-rays. For the experiment, 5,000 fresh mung beans were randomly distributed into 100 petri dishes, which were randomly divided into ten groups. Each group received an initial watering at a different time point prior to X-ray exposure, resulting in different effective target volumes. The bean sprouts were measured 70 hr after X-ray exposure, and the average length of the bean sprouts in each group was recorded as an index of the mung bean in vitro radiosensitivity. Mung beans that received an initial watering either six or sixteen hours before X-ray exposure had the shortest sprout length, indicating that the maximum effective target volume was formed within that specific time period. The revised target model could be also expanded to interpret the "two-hit" model of target theory, although the experimental data supported the "one-hit" model. If the "two-hit" model was sustained, theoretically, the target size would be 2.14 times larger than its original size to produce the same results.

Hypofractionated stereotactic radiation therapy in skull base meningiomas

To investigate the role of hypo-fractionated stereotactic radiation treatment (HSRT) in the management of skull base meningioma. Twenty-six patients were included in the study and treated with a dose of 30 Gy in 5 fractions with volumetric modulated arc therapy (RapidArc). Eighteen patients were symptomatic before treatment. Endpoints were local toxicity and relief from symptoms. Tumors were located in anterior skull base in 4/27 cases, in middle skull base in 12/27 and in posterior skull base in 11/27. HSRT was performed as first treatment in 17 (65 %) patients, in 9 (35 %) patients it followed a previous partial resection. Median follow up was 24.5 months (range 5-57 months). clinical remission of symptoms, complete or partial, was obtained in the vast majority of patients after treatment. Out of the 18 symptomatic patients, partial remission occurred in 9 (50 %) patients and complete remission in 9 (50 %). All asymptomatic patients retained their status after treatment. No severe neurologic toxicity grade III-IV was recorded. No increase of meningioma in the same site of treatment occurred; 16 (62 %) patients had stable disease and 9 (38 %) patients had tumor reduction. The mean tumor volume after treatment was 10.8 ± 17.8 cm(3) compared with 13.0 ± 19.1 cm(3) before treatment (p = 0.02). The mean actuarial OS was 54.4 ± 2.8 months. The 1- and 2-years OS was 92.9 ± 0.7 %. HSRT proved to be feasible for these patients not eligible to full surgery or to ablative radiation therapy. Local control and durability of results suggest for a routine application of this approach in properly selected cases.

Recurrent malignant gliomas

In almost all patients, malignant glioma recurs following initial treatment with maximal safe resection, conformal radiotherapy, and temozolomide. This review describes the many options for treatment of recurrent malignant gliomas, including reoperation, alternating electric field therapy, chemotherapy, stereotactic radiotherapy or radiosurgery, or some combination of these modalities, presenting the evidence for each approach. No standard of care has been established, though the antiangiogenic agent, bevacizumab; stereotactic radiotherapy or radiosurgery; and, perhaps, combined treatment with these 2 modalities appear to offer modest benefits over other approaches. Clearly, randomized trials of these options would be advantageous, and novel, more efficacious approaches are urgently needed.

Stereotactic radiation therapy for treatment of canine intracranial meningiomas

The objective of this study is to determine the rate of toxicity, median survival time (MST) and prognostic factors in dogs with presumed intracranial meningiomas that were treated with stereotactic radiation therapy (SRT). Patient demographics, neurological history, details of SRT plans and response to treatment (including toxicity and survival times) were examined for potential prognostic factors. Overall MST (MST) due to death for any cause was 561 days. There was a mild to moderate exacerbation of neurological symptoms 3-16 weeks following SRT treatments in 11/30 (36.7%) of dogs. This presumed adverse event was treated with corticosteroids, and improvement was seen in most of these dogs. Death within 6 months of treatment as a result of worsening neurologic signs was seen in 4/30 (13.3%) of dogs. Volume of normal brain that received full dose at a prescription of 8Gy × 3 fractions was predictive of death due to neurological problems within this 6-month period.

Radiosurgery with photons or protons for benign and malignant tumours of the skull base: a review

Stereotactic radiosurgery (SRS) is an important treatment option for intracranial lesions. Many studies have shown the effectiveness of photon-SRS for the treatment of skull base (SB) tumours; however, limited data are available for proton-SRS.Several photon-SRS techniques, including Gamma Knife, modified linear accelerators (Linac) and CyberKnife, have been developed and several studies have compared treatment plan characteristics between protons and photons.The principles of classical radiobiology are similar for protons and photons even though they differ in terms of physical properties and interaction with matter resulting in different dose distributions.Protons have special characteristics that allow normal tissues to be spared better than with the use of photons, although their potential clinical superiority remains to be demonstrated.A critical analysis of the fundamental radiobiological principles, dosimetric characteristics, clinical results, and toxicity of proton- and photon-SRS for SB tumours is provided and discussed with an attempt of defining the advantages and limits of each radiosurgical technique.

Single-fraction stereotactic body radiotherapy for spinal metastases from renal cell carcinoma

Object

Stereotactic body radiotherapy (SBRT) has emerged as an important treatment option for spinal metastases from renal cell carcinoma (RCC) as a means to overcome RCC's inherent radioresistance. The authors reviewed the outcomes of SBRT for the treatment of RCC metastases to the spine at their institution, and they identified factors associated with treatment failure.

Methods

Fifty-seven patients (88 treatment sites) with RCC metastases to the spine received single-fraction SBRT. Pain relief was based on the Brief Pain Inventory and was adjusted for narcotic use according to the Radiation Therapy Oncology Group protocol 0631. Toxicity was scored according to Common Toxicity Criteria for Adverse Events version 4.0. Radiographic failure was defined as infield or adjacent (within 1 vertebral body [VB]) failure on follow-up MRI. Multivariate analyses were performed to correlate outcomes with the following variables: epidural, paraspinal, single-level, or multilevel disease (2–5 sites); neural foramen involvement; and VB fracture prior to SBRT. Kaplan-Meier analysis and Cox proportional hazards modeling were used for statistical analysis.

Results

The median follow-up and survival periods were 5.4 months (range 0.3–38 months) and 8.3 months (range 1.5–38 months), respectively. The median time to radiographic failure and unadjusted pain progression were 26.5 and 26.0 months, respectively. The median time to pain relief (from date of simulation) and duration of pain relief (from date of treatment) were 0.9 months (range 0.1–4.4 months) and 5.4 months (range 0.1–37.4 months), respectively. Multivariate analyses demonstrated that multilevel disease (hazard ratio [HR] 3.5, p = 0.02) and neural foramen involvement (HR 3.4, p = 0.02) were correlated with radiographic failure; multilevel disease (HR 2.3, p = 0.056) and VB fracture (HR 2.4, p = 0.046) were correlated with unadjusted pain progression. One patient experienced Grade 3 nausea and vomiting; no other Grade 3 or 4 toxicities were observed. Twelve treatment sites (14%) were complicated by subsequent vertebral fractures.

Conclusions

Stereotactic body radiotherapy for RCC metastases to the spine offers fast and durable pain relief with minimal toxicity. Stereotactic body radiotherapy seems optimal for patients who have solitary or few spinal metastases. Patients with neural foramen involvement are at an increased risk for failure.

Stereotactic body radiation therapy for metastasis in the lung: an undervalued treatment option with future prospects

SUMMARY The lung is a common site of metastatic disease from solid tumors. Most cancers can develop lung metastases, and sarcoma and epithelial (especially colorectal) malignancies are prone to metastasize to the lung. In particular, the International Registry of Lung Metastases describes 5206 cases of lung metastasectomy, of which 43% were epithelial and 42% were sarcomatoid. Common presenting symptoms include cough, hemoptysis, shortness of breath, chest pain and back pain. Data in the literature suggest the existence of an oligometastatic state, where metastases are limited in number and location. For selected patients with lung oligometastases, local therapy such as surgery, stereotactic body radiotherapy (SBRT) and radiofrequency ablation may potentially yield prolonged survival. Data from retrospective series and prospective trials on the use of SBRT for lung metastases are emerging, showing promising results. Most studies show high local control rates rivaling those found in studies of surgical management (the usual treatment of choice) for lung metastases, while SBRT also has the benefit of low rates of significant toxicities. This review will provide an overview of the utilization of SBRT in the management of lung oligometastases.