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Benjamin CG, Gurewitz J, Kavi A, Bernstein K, Silverman J, Mureb M, Donahue B, Kondziolka D. Survival and outcomes in patients with ≥ 25 cumulative brain metastases treated with stereotactic radiosurgery. J Neurosurg 2022; 137:571-581. [PMID: 34952524 DOI: 10.3171/2021.9.jns21882] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 09/16/2021] [Indexed: 11/06/2022]
Abstract
OBJECTIVE In the era in which more patients with greater numbers of brain metastases (BMs) are being treated with stereotactic radiosurgery (SRS) alone, it is critical to understand how patient, tumor, and treatment factors affect functional status and overall survival (OS). The authors examined the survival outcomes and dosimetry to critical structures in patients treated with Gamma Knife radiosurgery (GKRS) for ≥ 25 metastases in a single session or cumulatively over the course of their disease. METHODS A retrospective analysis was conducted at a single institution. The institution's prospective Gamma Knife (GK) SRS registry was queried to identify patients treated with GKRS for ≥ 25 cumulative BMs between June 2013 and April 2020. Ninety-five patients were identified, and their data were used for analysis. Treatment plans for dosimetric analysis were available for 89 patients. Patient, tumor, and treatment characteristics were identified, and outcomes and OS were evaluated. RESULTS The authors identified 1132 patients with BMs in their institutional registry. Ninety-five patients were treated for ≥ 25 cumulative metastases, resulting in a total of 3596 tumors treated during 373 separate treatment sessions. The median number of SRS sessions per patient was 3 (range 1-12 SRS sessions), with nearly all patients (n = 93, 98%) having > 1 session. On univariate analysis, factors affecting OS in a statistically significant manner included histology, tumor volume, tumor number, diagnosis-specific graded prognostic assessment (DS-GPA), brain metastasis velocity (BMV), and need for subsequent whole-brain radiation therapy (WBRT). The median of the mean WB dose was 4.07 Gy (range 1.39-10.15 Gy). In the top quartile for both the highest cumulative number and highest cumulative volume of treated metastases, the median of the mean WB dose was 6.14 Gy (range 4.02-10.15 Gy). Seventy-nine patients (83%) had all treated tumors controlled at last follow-up, reflecting the high and durable control rate. Corticosteroids for tumor- or treatment-related effects were prescribed in just over one-quarter of the patients. Of the patients with radiographically proven adverse radiation effects (AREs; 15%), 4 were symptomatic. Four patients required subsequent craniotomy for hemorrhage, progression, or AREs. CONCLUSIONS In selected patients with a large number of cumulative BMs, multiple courses of SRS are feasible and safe. Together with new systemic therapies, the study results demonstrate that the achieved survival rates compare favorably to those of larger contemporary cohorts, while avoiding WBRT in the majority of patients. Therefore, along with the findings of other series, this study supports SRS as a standard practice in selected patients with larger numbers of BMs.
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Affiliation(s)
| | - Jason Gurewitz
- 2Department of Radiation Oncology, NYU Langone Medical Center, New York
| | - Ami Kavi
- 2Department of Radiation Oncology, NYU Langone Medical Center, New York
| | - Kenneth Bernstein
- 2Department of Radiation Oncology, NYU Langone Medical Center, New York
| | - Joshua Silverman
- 2Department of Radiation Oncology, NYU Langone Medical Center, New York
| | - Monica Mureb
- 3Department of Neurosurgery, Westchester Medical Center, Valhalla
| | - Bernadine Donahue
- 2Department of Radiation Oncology, NYU Langone Medical Center, New York
- 5Department of Radiation Oncology, Maimonides Medical Center, Brooklyn, New York
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Ganz JC. Cerebral metastases. PROGRESS IN BRAIN RESEARCH 2022; 268:229-258. [PMID: 35074082 DOI: 10.1016/bs.pbr.2021.10.034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Brain metastases are common and deadly. Over the last 25 years GKNS has been established as an invaluable treatment. It may be used as a primary treatment or after either surgery or WBRT. Patients are assessed using one of a number of available scales. GKNS may be repeated for new metastases and for unresponsive tumors. Prescription doses are usually between 18 and 20Gy. The use of advanced MR techniques to highlight sensitive structures like the hippocampi have extended the efficacy of the treatment. More recently GKNS has been used with different target therapies with improved results. More recently frameless treatments have become more popular in this group of very sick patients. GKNS controls tumors in between 80% and over 95% of cases and may even be used for brainstem tumors.
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Affiliation(s)
- Jeremy C Ganz
- Department of Neurosurgery, Haukeland University Hospital, Bergen, Norway.
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Kavi A, Gurewitz J, Benjamin CG, Silverman JS, Bernstein K, Mureb M, Oh C, Sulman EP, Donahue B, Kondziolka D. Hippocampal sparing in patients receiving radiosurgery for ≥25 brain metastases. Radiother Oncol 2021; 161:65-71. [PMID: 34052342 DOI: 10.1016/j.radonc.2021.05.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Revised: 05/19/2021] [Accepted: 05/20/2021] [Indexed: 10/21/2022]
Abstract
PURPOSE/OBJECTIVES To report our dosimetric analysis of the hippocampi (HC) and the incidence of perihippocampal tumor location in patients with ≥25 brain metastases who received stereotactic radiosurgery (SRS) in single or multiple sessions. MATERIALS/METHODS Analysis of our prospective registry identified 89 patients treated with SRS for ≥25 brain metastases. HC avoidance regions (HA-region) were created on treatment planning MRIs by 5 mm expansion of HC. Doses from each session were summed to calculate HC dose. The distribution of metastases relative to the HA-region and the HC was analyzed. RESULTS Median number of tumors irradiated per patient was 33 (range 25-116) in a median of 3 (range1-12) sessions. Median bilateral HC Dmin (D100), D40, D50, Dmax, and Dmean (Gy) was 1.88, 3.94, 3.62, 16.6, and 3.97 for all patients, and 1.43, 2.99, 2.88, 5.64, and 3.07 for patients with tumors outside the HA-region. Multivariate linear regression showed that the median HC D40, D50, and Dmin were significantly correlated with the tumor number and tumor volume (p < 0.001). Of the total 3059 treated tumors, 83 (2.7%) were located in the HA-region in 57% evaluable patients; 38 tumors (1.2%) abutted or involved the HC itself. CONCLUSIONS Hippocampal dose is higher in patients with tumors in the HA-region; however, even for patients with a high burden of intracranial disease and tumors located in the HA-regions, SRS affords hippocampal sparing. This is particularly relevant in light of our finding of eventual perihippocampal metastases in more than half of our patients.
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Affiliation(s)
- Ami Kavi
- Department of Radiation Oncology, State University of New York Downstate Health Sciences University, Brooklyn, USA; Department of Radiation Oncology, Maimonides Cancer Center, Brooklyn, USA.
| | - Jason Gurewitz
- Marian University College of Osteopathic Medicine, USA; Department of Radiation Oncology, NYU Grossman School of Medicine, New York, USA
| | | | - Joshua S Silverman
- Brain and Spine Tumor Center, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, USA; Department of Radiation Oncology, NYU Grossman School of Medicine, New York, USA
| | - Kenneth Bernstein
- Brain and Spine Tumor Center, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, USA; Department of Radiation Oncology, NYU Langone Health, New York, USA
| | - Monica Mureb
- Department of Neurosurgery, Westchester Medical Center, Valhalla, USA
| | - Cheongeun Oh
- Department of Population Health, Division of Biostatistics, NYU Langone Health, New York, USA.
| | - Erik P Sulman
- Brain and Spine Tumor Center, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, USA; Department of Radiation Oncology, NYU Grossman School of Medicine, New York, USA
| | - Bernadine Donahue
- Brain and Spine Tumor Center, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, USA; Department of Radiation Oncology, NYU Grossman School of Medicine, New York, USA; Department of Radiation Oncology, Maimonides Cancer Center, Brooklyn, USA
| | - Douglas Kondziolka
- Department of Neurosurgery, NYU Grossman School of Medicine, New York, USA; Brain and Spine Tumor Center, Laura and Isaac Perlmutter Cancer Center, NYU Langone Health, New York, USA; Department of Radiation Oncology, NYU Grossman School of Medicine, New York, USA
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Riina MD, Stambaugh CK, Huber KE. Hippocampal Dosimetry and the Necessity of Hippocampal-Sparing in Gamma Knife Stereotactic Radiosurgery for Extensive Brain Metastases. Adv Radiat Oncol 2020; 5:180-188. [PMID: 32280817 PMCID: PMC7136666 DOI: 10.1016/j.adro.2019.10.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/15/2019] [Accepted: 10/19/2019] [Indexed: 11/18/2022] Open
Abstract
PURPOSE To characterize hippocampal dosimetry in Gamma Knife stereotactic radiosurgery (GK-SRS) for extensive brain metastases and evaluate the need for hippocampal-sparing in GK-SRS treatment planning. METHODS AND MATERIALS We reviewed 75 GK-SRS plans for the treatment of 4 to 30 brain metastases generated without consideration of the hippocampi. The mean dose, maximum dose to 100% of the volume (D100), maximum dose to 40% of the volume (D40), and maximum point dose (Dmax, 0.03 cm3) were obtained for the unilateral and bilateral hippocampi and compared between plans with 4 to 9 and ≥10 lesions. The rate at which plans met hippocampal dose constraints (D100 ≤ 4.21 Gy, D40 ≤ 4.50 Gy, and Dmax ≤ 6.65 Gy) was compared between groups, and each was examined for risk factors associated with excessive hippocampal dosing. For plans that exceeded constraints, we attempted replanning to spare the hippocampi. RESULTS Compared with those for the treatment of 4 to 9 brain metastases, GK-SRS plans with ≥10 lesions were associated with significantly greater median bilateral mean dose (1.0 vs 2.0, P = .001), D100 (0.4 vs 0.8, P = .003), D40 (0.9 vs 1.9, P = .001), and Dmax (2.0 vs 4.9, P = .0005). These plans also less frequently met hippocampal constraints, with this difference trending toward significance (80% vs 93%; P = .1382; odds ratio 0.29; 95% CI, 0.06-1.4). Risk factors for exceeding constraints included greater total disease volume and closer approach of the nearest metastasis to the hippocampi, both of which depended upon the number of metastases present. Seven plans failed to meet constraints and were successfully replanned to spare the hippocampi with minimal increases in treatment time and without compromise to target coverage or conformity. CONCLUSIONS Patients with extensive brain metastases treated with GK-SRS are at increased risk for excessive hippocampal dosing when ≥10 lesions are present or when lesions are in close proximity to the hippocampi and may benefit from hippocampal-avoidant treatment planning.
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Affiliation(s)
| | | | - Kathryn E. Huber
- Department of Radiation Oncology, Tufts Medical Center, Boston, Massachusettes
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Di Carlo C, Trignani M, Caravatta L, Vinciguerra A, Augurio A, Perrotti F, Di Tommaso M, Nuzzo M, Giancaterino S, Falco MD, Genovesi D. Hippocampal sparing in stereotactic radiotherapy for brain metastases: To contour or not contour the hippocampus? Cancer Radiother 2018; 22:120-125. [PMID: 29576492 DOI: 10.1016/j.canrad.2017.08.113] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 05/23/2017] [Accepted: 08/10/2017] [Indexed: 11/27/2022]
Abstract
PURPOSE The aim of our study was to evaluate hippocampal irradiation in patients treated with fractionated stereotactic brain radiotherapy. PATIENTS AND METHODS Retrospective hippocampal dosimetric analysis performed on 22 patients with one to four brain metastases treated with fractionated stereotactic radiotherapy using volumetric intensity-modulated arc therapy. Original plans did not include hippocampus as avoidance structure in optimization criteria; hippocampus was retrospectively delineated on magnetic resonance coregistered with planning CT and using as reference the RTOG 0933 atlas. Hippocampus was defined both as a single and as pair organ. Constraints analysed were: Dmax<16Gy, D40%<7.3Gy, D100%=Dmin<9Gy. Assuming a α/β ratio of 2Gy, biologically equivalent dose in 2Gy fractions was calculated. Hippocampal-sparing plans were developed in cases where hippocampal constraints were not respected in the original plan. RESULTS Among constraints analysed Dmax and D40% have been exceeded in ten out of 22 cases. The constraints were not respected in patients with more than one metastatic lesion and in three patients with only one lesion. Considering all exceeded constraints values in non-hippocampal sparing plans, the 50% of them was respected after replanning. No significant differences were found among conformity and homogeneity index between non-hippocampal sparing and hippocampal sparing plans. CONCLUSION Volumetric intensity-modulated arc therapy hippocampal sparing plans significantly decreases dose to hippocampus assuring an equal target coverage and organs at risk avoiding.
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Affiliation(s)
- C Di Carlo
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - M Trignani
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - L Caravatta
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - A Vinciguerra
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - A Augurio
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - F Perrotti
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - M Di Tommaso
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - M Nuzzo
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - S Giancaterino
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - M D Falco
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy
| | - D Genovesi
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Via Dei Vestini, 66100 Chieti, Italy.
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Daniela Falco M, Giancaterino S, D'Andrea M, Gimenez De Lorenzo R, Trignani M, Caravatta L, Di Carlo C, Di Biase S, Allajbej A, Genovesi D. Hippocampal sparing approach in fractionated stereotactic brain VMAT radio therapy: A retrospective feasibility analysis. J Appl Clin Med Phys 2017; 19:86-93. [PMID: 29125239 PMCID: PMC5768008 DOI: 10.1002/acm2.12216] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 09/13/2017] [Accepted: 10/05/2017] [Indexed: 11/16/2022] Open
Abstract
Volumetric Modulated Arc Therapy (VMAT) techniques for fractioned stereotactic brain radiotherapy (FSBRT) can achieve highly conformal dose distribution to intracranial lesions. However, they can potentially increase the dose to hippocampus (H) causing neurocognitive toxicity during the first four months after irradiation. The purpose of this study was to assess the feasibility of hippocampal‐sparing (HS) treatment plans in 22 patients with brain metastasis treated with VMAT technique. Firstly, we retrospectively analyzed hippocampal doses in all 22 VMAT original (not hippocampal‐sparing, NHS) plans. Plans with hippocampal dose exceeding constraints (9 out of 22) were re‐planned considering dose constraints on the hippocampus (H) and on hippocampal avoidance zone (HAZ) generated using 5 mm isotropic margin to the hippocampus. Conformity (CI) and homogeneity indexes (HI) on the target and MUs, were maintained as close as possible to the original plans. Mean CINHS and CIHS obtained were: 0.79 ± 0.11 and 0.81 ± 0.10, respectively (P = 0.75); mean HINHS and HIHS were 1.05 ± 0.02 and 1.04 ± 0.01 respectively (P = 0.72). In both sets of plans, the mean MU values were similar: 1033 ± 275 and 1022 ± 234 for NHS and HS respectively. In HS plans, the mean hippocampal dose was decreased by an average of 35%. After replanning, the Dmax (21.3 Gy) for HAZ and H was met by 45% (4/9) and 78% (7/9) of the NHS plans, respectively. The worst results were obtained for cases with target volumes extention closer than 12 mm to H, because of the difficulty to spare hippocampus without compromising target coverage. After replanning D40% constraint value (7.3 Gy) was met by all the 9 NHS plans. In conclusion, this study suggests that an hippocampal‐sparing approach to FSBRT is feasible resulting in a decrease in the dose to the hippocampus without any loss in conformity or increase in treatment time.
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Affiliation(s)
- Maria Daniela Falco
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Stefano Giancaterino
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Marco D'Andrea
- Laboratory of Medical Physics and Expert Systems, National Cancer Center Institute Regina Elena, Rome, Italy
| | - Ramon Gimenez De Lorenzo
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Marianna Trignani
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Luciana Caravatta
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Clelia Di Carlo
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Saide Di Biase
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Albina Allajbej
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
| | - Domenico Genovesi
- Department of Radiation Oncology, "G. D'Annunzio" University of Chieti, SS. Annunziata Hospital, Chieti, Italy
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Fiorentino A, Tebano U, Sicignano G, Ricchetti F, Di Paola G, Aiello D, Giaj-Levra N, Mazzola R, Fersino S, Ruggieri R, Alongi F. Hippocampal dose during Linac-based stereotactic radiotherapy for brain metastases: An observational study. Phys Med 2017; 49:135-138. [PMID: 28951047 DOI: 10.1016/j.ejmp.2017.09.129] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 09/11/2017] [Accepted: 09/17/2017] [Indexed: 11/19/2022] Open
Abstract
INTRODUCTION Aim of the present study is to evaluate homolateral and contralateral hippocampus (H-H, C-H, respectively) dose during Fractionated Stereotactic Radiotherapy (FSRT) or Radiosurgery (SRS) for brain metastases (BM). MATERIALS & METHODS Patients with BM<5, size≤30mm, KPS≥80 and a life expectancy>3months, were considered for SRS/FSRT (total dose 15-30Gy, 1-5 fractions). For each BM, a Flattening Filter Free (FFF) Volumetric Modulated Arc Therapy (VMAT) plan was generated with one or two arcs. Hippocampi were not considered during optimizations phase and were contoured and evaluated retrospectively in terms of dose: the Dmedian, Dmean, D0.1cc and the V1Gy, V2Gy, V5Gy and V10Gy were analyzed. RESULTS From April 2014 to December 2015, 81 BM were treated with FFF-FSRT/SRS. For the H-H, the average values of Dmedian, Dmean and D0.1cc were 1.5Gy, 1.54Gy and 2.2Gy, respectively, while the V1Gy, V2Gy, V5Gy and V10Gy values were 25%, 8.9%, 8.9% and 2.1%, respectively. For the C-H, the average Dmedian, Dmean and D0.1cc were 0.7Gy, 0.7Gy, 0.9Gy, respectively, while the average values of V1Gy, V2Gy, V5Gy and V10Gy were 18%, 10.2%, 2.8% and 1.4%, respectively. Tumor dimension, tumor cranial-caudal length and the distance between BM and H-H were correlated to Dmedian, Dmean and D0.1cc. For C-H, only the distance from PTV was correlated with a dose reduction. CONCLUSION During FFF-FSRT/SRS, hippocampus received a negligible dose. Despite its clinical significance is still under evaluation, in patients with a long life expectancy, H-H should be considered during Linac-based FSRT/SRS.
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Affiliation(s)
- Alba Fiorentino
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Umberto Tebano
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy.
| | | | | | | | - Dario Aiello
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Niccolò Giaj-Levra
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Rosario Mazzola
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Sergio Fersino
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Ruggero Ruggieri
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy
| | - Filippo Alongi
- Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy; University of Brescia, Brescia, Italy
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Hippocampal dose from stereotactic radiosurgery for 4 to 10 brain metastases: Risk factors, feasibility of dose reduction via re-optimization, and patient outcomes. Med Dosim 2017; 42:310-316. [PMID: 28760560 DOI: 10.1016/j.meddos.2017.06.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Revised: 05/26/2017] [Accepted: 06/26/2017] [Indexed: 01/08/2023]
Abstract
This study aimed to report hippocampal dose from single-fraction stereotactic radiosurgery (SRS) for 4 to 10 brain metastases and determine feasibility of hippocampal-sparing SRS. Patients with 4 to 10 brain metastases receiving single-isocenter, multi-target single-fraction SRS were identified. Hippocampi were contoured using the Radiation Therapy Oncology Group (RTOG) 0933 atlas. RTOG 0933 dose constraints were converted to a biologically effective dose using an alpha/beta of 2 (D100 421 cGy, Dmax 665 cGy). Number of metastases, total target volume, prescribed dose, and distance of nearest metastasis (dmin) were analyzed as risk factors for exceeding hippocampal constraints. If hippocampi exceeded constraints, the SRS plan was re-optimized. Key dosimetric parameters were compared between original and re-optimized plans. To determine if a single target can exceed constraints, all targets but the closest metastasis were removed from the plan, and dosimetry was compared. Forty plans were identified. Fifteen hippocampi (19%) exceeded constraints in 12 SRS plans. Hippocampal sparing was achieved in 10 of 12 replanned cases (83%). Risk factors associated with exceeding hippocampal constraints were decreasing dmin (24.0 vs 8.0 mm, p = 0.002; odds ratio [OR] 1.14, 95% confidence interval [CI] 1.04 to 1.26) and total target volume (5.46 cm3vs 1.98 cm3, p = 0.03; OR 1.14, 95% CI 1.00 to 1.32). There was no difference in exceeding constraints for 4 to 5 vs 6 to 10 metastases (27% vs 21%, p = 0.409) or prescribed dose (18 Gy, p = 0.58). For re-optimized plans, there were no significant differences in planning target volume (PTV) coverage (99.6% vs 99.0%, p = 0.17) or conformality index (1.47 vs 1.4, p = 0.78). Six (50%) plans exceeded constraints with a single target. A substantial minority of hippocampi receive high radiation dose from SRS for 4 to 10 brain metastases. Decreasing distance of the closest metastasis and total target volume are associated with exceeding hippocampal constraints. Re-optimizing these plans yielded hippocampal-sparing SRS plans with acceptable dosimetry. Prospective evaluation of the impact of hippocampal dose from SRS on neurocognition merits consideration.
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