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Hearing loss after radiosurgery-blame it on Cochlear dose or the radiation tool!

Hearing loss after radiosurgery-blame it on Cochlear dose or the radiation tool! While sudden hearing loss after stereotactic radiosurgery has been demonstrated in some cases a recent article by Linge et al. and have demonstrated the need for further discussion on this topic. We attempt to delineate the fact that the type of dosing regimen or technology used will not affect the hearing or radio-graphical control outcomes and thus should not be a consideration while administering treatment. Also we discuss the role of location of the lesion and vascularity and potential new therapies for this unexpected outcome after radiosurgery. Keywords: Vestibular schwannoma, Gamma knife, Stereotactic radiosurgery, Hearing loss Dear Editor, remarkable track record of functional preservation and We read with great interest the article by Linge et al. tumor growth control with gamma knife radiosurgery [1] regarding the loss of functional hearing in patients (GKRS). Regarding the radiosurgical technology used, with vestibular schwannomas (VS) after fractionated there is no difference in the radiographic tumor control stereotactic radiotherapy (FSRT) and Cyberknife stereo- rate among the options available. Radiographic control tactic radiosurgery (SRS). They reported that after 1 year ranged from 88.5–100% in LINAC-based series, and 71– after treatment, 84% of the SRS patients and 71% of the 100% in GK series [3]. With longer follow up, tumor FSRT patients had preservation of useful hearing. At 3 control rates decrease regardless of the technology used. years, a useful hearing had been retained in 27% of the Only tumor size had an impact on radiographic control, SRS patients and 50% of the FSRT patients. Linge et al. with smaller tumors (< 3 cm) showing the highest tumor [1] noted that preservation of Gardener-Robertson hear- control rate at comparable time intervals, regardless of ing class I or II had not differed significantly between the technology. the two treatment groups. For larger tumors, including Analogous to radiographic control, hearing preserva- medium-size ones, SRS should be considered first-line tion decreased with longer follow-up irrespective of the therapy. Tuleasca et al. [2] state that acute and subacute technology. Combs et al. [4] reported hearing preserva- complications after SRS for VS are independent of the tion of 90% at 1 year, which subsequently decreased to used radiosurgery device. They also state that a vestibu- 69% at 10 years using LINAC-based technology. GKRS lar dose of more than 8 Gy was responsible for the ap- based series such as those by Hasegawa et al. [5]reported pearance of vestibular symptoms and that corticosteroid a decrease in hearing preservation from 54% at 3 years to use in these cases almost always results in resolution of 34% at 8 years. Various series have reported hearing loss the symptoms. akin to presbycusis post-GKRS [3]. Also, hearing loss in VS comprise 8% of all primary brain neoplasms and sporadic and neurofibromatosis type 2 (NF2) cases needs 16% of all benign brain lesions and are inherently slow to be differentiated, as sporadic cases are usually unilateral growing in nature thus allowing the great potential of thus have better word recognition scores as compared to treatment by radiosurgery. Perhaps no other intracranial NF2 cases where the hearing loss in the functionally nor- pathology garnered such enthusiasm as VS after its mal ear could be disastrous. In addition to the often-discussed mechanism of coch- lear spearing, other factors influence hearing preserva- * Correspondence: drmanjultripathi@gmail.com 2 tion. A higher auditory function at baseline and young Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India age can favorably contribute to higher rates of hearing Full list of author information is available at the end of the article © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Deora and Tripathi Radiation Oncology (2019) 14:186 Page 2 of 3 preservation after SRS while an injury to the vasa In this article for single-dose treatments, a dose of 12 nervosa of the cochlear nerve can secondarily cause Gy was prescribed at the 80% isodose surrounding the radiation-induced tumor edema and lead to acute hear- PTV. For fractionated treatments, a dose of 54 Gy was ing loss. Hasegawa et al. [5] reported that in patients prescribed at the 100% isodose with the 95% isodose sur- receiving < 4 Gy to the cochlea, hearing preservation at rounding the PTV. Here, FSRT was delivered in 30 daily 3 years was 80 and 70% at 8 years (in contrast to 55 and fractions of 1.8 Gy over a period of 6 weeks. Within a 34%, respectively, with higher cochlear dose). Bashnagel range of doses used in various series, a lower dose had et al. [6] reported a cochlear dose < 3 Gy to have favor- little to no appreciable difference in progression-free able prognostic outcome on hearing preservation while survival, and generally high rates of progression-free sur- Boari et al. [7] reported the highest hearing preservation vival were reported across a wide range of delivered in patients < 55 years of age with Gardner–Robertson doses [4–8]. Thus, level 3 evidence-based guideline by (GR) Class 1 hearing prior to SRS, 93% compared to Germano et al. [3] states that a dose of ≤13 Gy achieves 71% in patients > 55 years of age, and 49% for the overall radiographic control while minimizing adverse effects population, independent of GR class and age. Similarly, hence should be used while planning SRS for VSs. While Franzin et al. [6] associated GR Class 1 hearing and recent changes have allowed us to use a fractionated age < 54 years old as favorable prognostic factors for dose regimen and thus increase the total dose thus hearing preservation. Thus, it is the basal turn of the allowing time for normal cells to repair themselves cochlea, which needs protection. The final dose should between treatments, thereby reducing side effects to the not be more than 4 Gy to more than 10% of the cochlea surrounding tissues such as brainstem, cerebellum, coch- [4–8]. The importance of the location of the tumor as lea. In the present paper, those who received 54 Gy were cited by the author is controversial at best. Moffat et al. divided into 30 daily fractions of 1.8 Gy over a period of [7] reported acute SNHL secondary to the sudden rise in 6 weeks. Therefore, in terms of biological effects, the pre- intracanalicular pressure in 28/139 patients of medically scribed radiation is more than 90gy. Yet where possible arising VS while Sauvaget et al. and others [8–10] re- we believe that the dosing should be according to the ported the similar phenomenon in lateral arising tumors. Noren’s policy, i.e., ‘the lowest irradiation doses that are The safest modality of the radiosurgery tool is a matter therapeutically effective”. The author’s intention to give a of heated debate among various treatment modalities. higher dose in few cases is unexplained and needs to be However, most long-term results are from GK series. A understood in terms of his fractionation method used and systematic comparison by Gaevert et al. [11] have shown if the same had any effect on the cochlear dose too. that introduction of new LINAC based technologies In addition to the effect of steroids on the treatment of (high definition multi-leaf collimation, intensity modula- acute hearing loss, the role of Bevacizumab needs to be tion) has reduced the gap between GKRS and LINAC highlighted. Treatment with Bevacizumab results in a based technologies, in terms of dose planning. The clinically relevant tumor-volume reduction and hearing beauty of SRS lies in maintaining high conformity while improvement in some but not all patients treated with minimizing dose spillage to the surrounding organs at some possible treatment-related side effects. It is also risk. For this purpose, GKRS Perfexion and ICON sys- useful to note that NF2 pathologic specimens stain for tems comply with all the planning objectives. With the VEGF. Although the mechanism of action is unknown, it use of multiple non-isocentric-modulated beams (Cyber- is presumed that bevacizumab inhibits VEGF-mediated knife) or intensity-modulated beams instead of multiple angiogenesis within the tumor, resulting in its effect [3]. isocenters (LGK-PFX) or dynamic arcs (NTx-DCA), a With our own experience with Bevacizumab resulting in lower dose will be spread around the lesion. Finally, the hearing improvement on 2 cases, we understand that use of inverse planning will accomplish the most homo- radiation induces an inflammatory reaction, characterized geneous treatment plannings. For neurosurgeons, the by an increase in the activated microglia, and cytokine Gamma Knife is a simple and effective tool. LINAC release. This inflammatory reaction leads to a cycle of based SRS, on the other hand, requires several QA further cellular toxicity and tissue damage. A sudden checks by radiation technologists and physicists. Dose increase in the intracanalicular component of VS may plan is also more conformal with GK because the multi- lead to a rise in intracanalicular pressure compromising isocenter plan can be generated and delivered. With the vascular supply of VII-VIII nerve complex. Bevaci- most LINACs (except newer LINACs with high dose zumab is a humanized monoclonal antibody against rate) dose delivery of multi-isocenter plans takes a VEGF and inhibits the blood-brain barrier (BBB) very long time, which is not practical for the manage- permeability and over-pruning of blood vessels. Bevaci- ment. That is the reason most LINAC plans are 3–5 zumab has been reported to induce both tumor regres- isocenter plans but it adversely affects the selectivity sion and hearing improvement in patients with NF2 of the plan. associated VS. Deora and Tripathi Radiation Oncology (2019) 14:186 Page 3 of 3 Abbreviations 8. Franzin A, Spatola G, Serra C, et al. Evaluation of hearing function after FSRT: Fractionated stereotactic radiotherapy; GKRS: Gamma Knife gamma knife surgery of vestibular schwannomas. Neurosurg Focus. 2009; Radiosurgery; LINAC: Linear accelarator; SRS: Stereotactic radiosurgery; 27(6):E3. VS: Vestibular schwanomma 9. Moffat DA, Baguley DM, von Blumenthal H, Irving RM, Hardy DG. Sudden deafness in vestibular schwannoma. J Laryngol Otol. 1994;108:116–9. 10. Sauvaget E, Kici S, Kania R, Herman P, Tran Ba Huy P. Sudden sensorineural Acknowledgements hearing loss as a revealing symptom of vestibular schwannoma. Acta None. Otolaryngol. 2005;125:592–5. 11. Gevaert T, Levivier M, Lacornerie T, Verelen D, Engels B, Reynaert N, Tournerl Note K, Duchateau M, Reynders T, Depuvdt T, Collen C, Lartigau E, Ridder MD. No portion of the contents of the paper have been presented (not Dosimetric comparision of different treatment modalities for stereotactic published) previously. radiosurgery of arteriovenous malformations and acoustic neuromas. Radiother Oncol. 2013;106:192–7. Authors’ contributions Harsh Deora and Manjul Tripathi: Preparation of manusript and review and Publisher’sNote editing of manuscript. Both authors read and approved the final manuscript. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Funding None. Availability of data and materials Not applicable. Ethics approval and consent to participate Ethics approval was not needed for this letter to editor. No patient data was used and hence no consent was taken. Consent for publication No patient data was used and hence no consent was taken. Competing interests The authors declare that they have no competing interest. Author details Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, India. Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India. Received: 26 June 2019 Accepted: 4 October 2019 References 1. van Linge A, van Os R, Hoekstra N, et al. Progression of hearing loss after LINAC-based stereotactic radiotherapy for vestibular schwannoma is associated with cochlear dose, not with pre-treatment hearing level. Radiat Oncol. 2018;13(1):253. Published 2018 Dec 24. doi:https://doi.org/10.1186/ s13014-018-1202-z. 2. Tuleasca C, George M, Faouzi M, Schiappacasse L, Leroy HA, Zeverino M, et al. Acute clinical adverse radiation effects after gamma knife surgery for vestibular schwannomas. J Neurosurg. 2016;125:73–82. 3. Germano IM, Sheehan J, Parish J, et al. Congress of neurological surgeons systematic review and evidence-based guideline on the role of radiosurgery and radiation therapy in the management of patients with vestibular schwannomas. Neurosurgery. 2018;82(2):00. 4. Combs SE, Welzel T, Kessel K, et al. Hearing preservation after radiotherapy for vestibular schwannomas is comparable to hearing deterioration in healthy adults and is accompanied by local tumor control and a highly preserved quality of life (QOL) as patients’ self-reported outcome. Radiother Oncol. 2013;106(2):175–80. 5. Hasegawa T, Kida Y, Kato T, Iizuka H, Yamamoto T. Factors associated with hearing preservation after gamma knife surgery for vestibular schwannomas in patients who retain serviceable hearing. J Neurosurg. 2011;115(6):1078–86. 6. Baschnagel AM, Chen PY, Bojrab D, et al. Hearing preservation in patients with vestibular schwannoma treated with gamma knife surgery. J Neurosurg. 2013;118(3):571–8. 7. Boari N, Bailo M, Gagliardi F, et al. Gamma knife radiosurgery for vestibular schwannoma:clinical results at long-term follow-up in a series of 379 patients. J Neurosurg. 2014;121(suppl):123–42. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Oncology Springer Journals

Hearing loss after radiosurgery-blame it on Cochlear dose or the radiation tool!

Radiation Oncology , Volume 14 (1) – Oct 30, 2019

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Springer Journals
Copyright
Copyright © 2019 by The Author(s).
Subject
Biomedicine; Cancer Research; Oncology; Radiotherapy; Imaging / Radiology
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1748-717X
DOI
10.1186/s13014-019-1390-1
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Abstract

While sudden hearing loss after stereotactic radiosurgery has been demonstrated in some cases a recent article by Linge et al. and have demonstrated the need for further discussion on this topic. We attempt to delineate the fact that the type of dosing regimen or technology used will not affect the hearing or radio-graphical control outcomes and thus should not be a consideration while administering treatment. Also we discuss the role of location of the lesion and vascularity and potential new therapies for this unexpected outcome after radiosurgery. Keywords: Vestibular schwannoma, Gamma knife, Stereotactic radiosurgery, Hearing loss Dear Editor, remarkable track record of functional preservation and We read with great interest the article by Linge et al. tumor growth control with gamma knife radiosurgery [1] regarding the loss of functional hearing in patients (GKRS). Regarding the radiosurgical technology used, with vestibular schwannomas (VS) after fractionated there is no difference in the radiographic tumor control stereotactic radiotherapy (FSRT) and Cyberknife stereo- rate among the options available. Radiographic control tactic radiosurgery (SRS). They reported that after 1 year ranged from 88.5–100% in LINAC-based series, and 71– after treatment, 84% of the SRS patients and 71% of the 100% in GK series [3]. With longer follow up, tumor FSRT patients had preservation of useful hearing. At 3 control rates decrease regardless of the technology used. years, a useful hearing had been retained in 27% of the Only tumor size had an impact on radiographic control, SRS patients and 50% of the FSRT patients. Linge et al. with smaller tumors (< 3 cm) showing the highest tumor [1] noted that preservation of Gardener-Robertson hear- control rate at comparable time intervals, regardless of ing class I or II had not differed significantly between the technology. the two treatment groups. For larger tumors, including Analogous to radiographic control, hearing preserva- medium-size ones, SRS should be considered first-line tion decreased with longer follow-up irrespective of the therapy. Tuleasca et al. [2] state that acute and subacute technology. Combs et al. [4] reported hearing preserva- complications after SRS for VS are independent of the tion of 90% at 1 year, which subsequently decreased to used radiosurgery device. They also state that a vestibu- 69% at 10 years using LINAC-based technology. GKRS lar dose of more than 8 Gy was responsible for the ap- based series such as those by Hasegawa et al. [5]reported pearance of vestibular symptoms and that corticosteroid a decrease in hearing preservation from 54% at 3 years to use in these cases almost always results in resolution of 34% at 8 years. Various series have reported hearing loss the symptoms. akin to presbycusis post-GKRS [3]. Also, hearing loss in VS comprise 8% of all primary brain neoplasms and sporadic and neurofibromatosis type 2 (NF2) cases needs 16% of all benign brain lesions and are inherently slow to be differentiated, as sporadic cases are usually unilateral growing in nature thus allowing the great potential of thus have better word recognition scores as compared to treatment by radiosurgery. Perhaps no other intracranial NF2 cases where the hearing loss in the functionally nor- pathology garnered such enthusiasm as VS after its mal ear could be disastrous. In addition to the often-discussed mechanism of coch- lear spearing, other factors influence hearing preserva- * Correspondence: drmanjultripathi@gmail.com 2 tion. A higher auditory function at baseline and young Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India age can favorably contribute to higher rates of hearing Full list of author information is available at the end of the article © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Deora and Tripathi Radiation Oncology (2019) 14:186 Page 2 of 3 preservation after SRS while an injury to the vasa In this article for single-dose treatments, a dose of 12 nervosa of the cochlear nerve can secondarily cause Gy was prescribed at the 80% isodose surrounding the radiation-induced tumor edema and lead to acute hear- PTV. For fractionated treatments, a dose of 54 Gy was ing loss. Hasegawa et al. [5] reported that in patients prescribed at the 100% isodose with the 95% isodose sur- receiving < 4 Gy to the cochlea, hearing preservation at rounding the PTV. Here, FSRT was delivered in 30 daily 3 years was 80 and 70% at 8 years (in contrast to 55 and fractions of 1.8 Gy over a period of 6 weeks. Within a 34%, respectively, with higher cochlear dose). Bashnagel range of doses used in various series, a lower dose had et al. [6] reported a cochlear dose < 3 Gy to have favor- little to no appreciable difference in progression-free able prognostic outcome on hearing preservation while survival, and generally high rates of progression-free sur- Boari et al. [7] reported the highest hearing preservation vival were reported across a wide range of delivered in patients < 55 years of age with Gardner–Robertson doses [4–8]. Thus, level 3 evidence-based guideline by (GR) Class 1 hearing prior to SRS, 93% compared to Germano et al. [3] states that a dose of ≤13 Gy achieves 71% in patients > 55 years of age, and 49% for the overall radiographic control while minimizing adverse effects population, independent of GR class and age. Similarly, hence should be used while planning SRS for VSs. While Franzin et al. [6] associated GR Class 1 hearing and recent changes have allowed us to use a fractionated age < 54 years old as favorable prognostic factors for dose regimen and thus increase the total dose thus hearing preservation. Thus, it is the basal turn of the allowing time for normal cells to repair themselves cochlea, which needs protection. The final dose should between treatments, thereby reducing side effects to the not be more than 4 Gy to more than 10% of the cochlea surrounding tissues such as brainstem, cerebellum, coch- [4–8]. The importance of the location of the tumor as lea. In the present paper, those who received 54 Gy were cited by the author is controversial at best. Moffat et al. divided into 30 daily fractions of 1.8 Gy over a period of [7] reported acute SNHL secondary to the sudden rise in 6 weeks. Therefore, in terms of biological effects, the pre- intracanalicular pressure in 28/139 patients of medically scribed radiation is more than 90gy. Yet where possible arising VS while Sauvaget et al. and others [8–10] re- we believe that the dosing should be according to the ported the similar phenomenon in lateral arising tumors. Noren’s policy, i.e., ‘the lowest irradiation doses that are The safest modality of the radiosurgery tool is a matter therapeutically effective”. The author’s intention to give a of heated debate among various treatment modalities. higher dose in few cases is unexplained and needs to be However, most long-term results are from GK series. A understood in terms of his fractionation method used and systematic comparison by Gaevert et al. [11] have shown if the same had any effect on the cochlear dose too. that introduction of new LINAC based technologies In addition to the effect of steroids on the treatment of (high definition multi-leaf collimation, intensity modula- acute hearing loss, the role of Bevacizumab needs to be tion) has reduced the gap between GKRS and LINAC highlighted. Treatment with Bevacizumab results in a based technologies, in terms of dose planning. The clinically relevant tumor-volume reduction and hearing beauty of SRS lies in maintaining high conformity while improvement in some but not all patients treated with minimizing dose spillage to the surrounding organs at some possible treatment-related side effects. It is also risk. For this purpose, GKRS Perfexion and ICON sys- useful to note that NF2 pathologic specimens stain for tems comply with all the planning objectives. With the VEGF. Although the mechanism of action is unknown, it use of multiple non-isocentric-modulated beams (Cyber- is presumed that bevacizumab inhibits VEGF-mediated knife) or intensity-modulated beams instead of multiple angiogenesis within the tumor, resulting in its effect [3]. isocenters (LGK-PFX) or dynamic arcs (NTx-DCA), a With our own experience with Bevacizumab resulting in lower dose will be spread around the lesion. Finally, the hearing improvement on 2 cases, we understand that use of inverse planning will accomplish the most homo- radiation induces an inflammatory reaction, characterized geneous treatment plannings. For neurosurgeons, the by an increase in the activated microglia, and cytokine Gamma Knife is a simple and effective tool. LINAC release. This inflammatory reaction leads to a cycle of based SRS, on the other hand, requires several QA further cellular toxicity and tissue damage. A sudden checks by radiation technologists and physicists. Dose increase in the intracanalicular component of VS may plan is also more conformal with GK because the multi- lead to a rise in intracanalicular pressure compromising isocenter plan can be generated and delivered. With the vascular supply of VII-VIII nerve complex. Bevaci- most LINACs (except newer LINACs with high dose zumab is a humanized monoclonal antibody against rate) dose delivery of multi-isocenter plans takes a VEGF and inhibits the blood-brain barrier (BBB) very long time, which is not practical for the manage- permeability and over-pruning of blood vessels. Bevaci- ment. That is the reason most LINAC plans are 3–5 zumab has been reported to induce both tumor regres- isocenter plans but it adversely affects the selectivity sion and hearing improvement in patients with NF2 of the plan. associated VS. Deora and Tripathi Radiation Oncology (2019) 14:186 Page 3 of 3 Abbreviations 8. Franzin A, Spatola G, Serra C, et al. Evaluation of hearing function after FSRT: Fractionated stereotactic radiotherapy; GKRS: Gamma Knife gamma knife surgery of vestibular schwannomas. Neurosurg Focus. 2009; Radiosurgery; LINAC: Linear accelarator; SRS: Stereotactic radiosurgery; 27(6):E3. VS: Vestibular schwanomma 9. Moffat DA, Baguley DM, von Blumenthal H, Irving RM, Hardy DG. Sudden deafness in vestibular schwannoma. J Laryngol Otol. 1994;108:116–9. 10. Sauvaget E, Kici S, Kania R, Herman P, Tran Ba Huy P. Sudden sensorineural Acknowledgements hearing loss as a revealing symptom of vestibular schwannoma. Acta None. Otolaryngol. 2005;125:592–5. 11. Gevaert T, Levivier M, Lacornerie T, Verelen D, Engels B, Reynaert N, Tournerl Note K, Duchateau M, Reynders T, Depuvdt T, Collen C, Lartigau E, Ridder MD. No portion of the contents of the paper have been presented (not Dosimetric comparision of different treatment modalities for stereotactic published) previously. radiosurgery of arteriovenous malformations and acoustic neuromas. Radiother Oncol. 2013;106:192–7. Authors’ contributions Harsh Deora and Manjul Tripathi: Preparation of manusript and review and Publisher’sNote editing of manuscript. Both authors read and approved the final manuscript. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Funding None. Availability of data and materials Not applicable. Ethics approval and consent to participate Ethics approval was not needed for this letter to editor. No patient data was used and hence no consent was taken. Consent for publication No patient data was used and hence no consent was taken. Competing interests The authors declare that they have no competing interest. Author details Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, India. Department of Neurosurgery, Post Graduate Institute of Medical Education and Research, Chandigarh 160012, India. Received: 26 June 2019 Accepted: 4 October 2019 References 1. van Linge A, van Os R, Hoekstra N, et al. Progression of hearing loss after LINAC-based stereotactic radiotherapy for vestibular schwannoma is associated with cochlear dose, not with pre-treatment hearing level. Radiat Oncol. 2018;13(1):253. Published 2018 Dec 24. doi:https://doi.org/10.1186/ s13014-018-1202-z. 2. Tuleasca C, George M, Faouzi M, Schiappacasse L, Leroy HA, Zeverino M, et al. Acute clinical adverse radiation effects after gamma knife surgery for vestibular schwannomas. J Neurosurg. 2016;125:73–82. 3. Germano IM, Sheehan J, Parish J, et al. Congress of neurological surgeons systematic review and evidence-based guideline on the role of radiosurgery and radiation therapy in the management of patients with vestibular schwannomas. Neurosurgery. 2018;82(2):00. 4. Combs SE, Welzel T, Kessel K, et al. Hearing preservation after radiotherapy for vestibular schwannomas is comparable to hearing deterioration in healthy adults and is accompanied by local tumor control and a highly preserved quality of life (QOL) as patients’ self-reported outcome. Radiother Oncol. 2013;106(2):175–80. 5. Hasegawa T, Kida Y, Kato T, Iizuka H, Yamamoto T. Factors associated with hearing preservation after gamma knife surgery for vestibular schwannomas in patients who retain serviceable hearing. J Neurosurg. 2011;115(6):1078–86. 6. Baschnagel AM, Chen PY, Bojrab D, et al. Hearing preservation in patients with vestibular schwannoma treated with gamma knife surgery. J Neurosurg. 2013;118(3):571–8. 7. Boari N, Bailo M, Gagliardi F, et al. Gamma knife radiosurgery for vestibular schwannoma:clinical results at long-term follow-up in a series of 379 patients. J Neurosurg. 2014;121(suppl):123–42.

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Radiation OncologySpringer Journals

Published: Oct 30, 2019

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