Acute and Long-Term Complications of Therapeutic Radiation for Skull Base Tumors

Prospective assessment of peripapillary microvasculature using optical coherence tomography angiography in para-optic intracranial and sinonasal tumors treated with proton therapy

PURPOSE

Radiation-induced optic neuropathy (RION) is rare but may lead to blindness. The mechanisms by which this occurs include endothelial and neuronal damage, but RION has been assessed very little in the case of extraocular tumors treated with high-energy proton therapy, the use of which is expanding worldwide. We assessed peripapillary microvascular changes by optical coherence tomography angiography (OCT-A) in patients undergoing high-energy proton therapy for para-optic intracranial or head and neck tumors.

MATERIALS AND METHODS

In this prospective institutional review board approved study, patients receiving>40Gy_RBE maximal PBT dose to their optic nerve between 2018 and 2020 underwent quantitative OCT-A analyses. ImageJ software was used to assess changes in the peripapillary superficial vascular complex (SVC) using vascular area density (VAD), vessel length density (VLD) and fractal dimension (FDsk). Uni- and multivariate analyses were performed.

RESULTS

Of 47 patients (78 eyes) with 29±6 months of follow-up (range 18-42), 29 patients (61.7%) had previously undergone surgery and 18 (32.1%) had microvascular abnormalities prior to proton therapy. Total radiotherapy dose was the most relevant factor in decreased peripapillary microvasculature. Duration of follow-up was associated with lower VAD (P=0.005) and mean retinal nerve fiber layer (RNFLm) thickness also decreased. There was no significant correlation between OCT-A changes and mean visual defect.

CONCLUSION

Peripapillary microvasculature changes may occur from tumor compression or surgery and proton therapy for extraocular tumors. OCT-A may provide quantitative and mechanistic insights into RION before the occurrence of clinical symptoms.

New Concepts in the Diagnosis and Management of Optic Nerve Sheath Meningioma

Optic nerve sheath meningiomas are by far the most common tumors of the optic nerve sheath. The diagnosis can be suspected in most cases from clinical findings and supported by the results of neuroimaging, obviating tissue biopsy in the majority of cases. Observation may be appropriate in patients with mild or no visual deficit or in whom visual loss is not progressing, whereas stereotactic fractionated radiation therapy has been demonstrated to improve or stabilize vision in progressive or advanced cases. Attempts at surgical excision, and even biopsy, of optic nerve sheath meningiomas are associated with a high risk of blindness and should be reserved for the rare case of an anteriorly located, primarily exophytic tumor with focal involvement of the dural sheath.

New Concepts in the Management of Optic Nerve Sheath Meningiomas

Introduction: Primary optic nerve sheath meningiomas (ONSMs) are the most common primary tumours of the optic nerve sheath. The diagnosis and management of ONSMs have changed dramatically in the last decade. In this review article, we discuss the latest information regarding these issues. Materials and Methods: References for this manuscript were obtained by searching the database PubMed using the phrase “optic nerve sheath meningioma”. Approximately 150 articles were identified and reviewed. These articles served as reference sources for other articles, books and chapters on the subject. The results were combined with our personal experience, which includes over 100 cases of ONSMs that have been observed or treated with one or more of the modalities described below. Results: The diagnosis of ONSM can be suspected in most cases from clinical findings and supported by the results of neuroimaging, obviating tissue biopsy in the majority of cases. Management depends on several factors. Observation may be appropriate in patients with mild or no visual deficit or in whom visual loss is not progressing, whereas stereotactic fractionated radiation therapy has been documented to improve or stabilise vision in progressive or advanced cases. Attempts at excision of ONSMs are associated with a high risk of blindness and should be reserved for the rare case of an anteriorly located, primarily exophytic tumour with focal involvement of the dural sheath. Rare patients with acute visual deterioration may benefit from optic nerve sheath fenestration. Conclusion: The majority of ONSMs can be suspected on clinical grounds and diagnosed with readily available non-invasive neuroimaging. Stereotactic fractionated radiotherapy is currently the treatment of choice for ONSMs that require therapy. Key words: Meningioma, Optic nerve, Optic nerve sheath, Radiotherapy

Detection and treatment of optic nerve sheath meningioma

Optic nerve sheath meningioma is an uncommon tumor of middle age. Patients most often present with progressive visual loss, mild proptosis, and, occasionally, ocular motility defect. With modern neuroimaging, these tumors are relatively easy to diagnose. However, the computed tomography scan or magnetic resonance imaging scan obtained must be a high-resolution study focused on the optic nerve. Clinical observation may be appropriate for patients with relatively preserved vision. However, when vision deteriorates, fractionated stereotactic radiotherapy is indicated and can often restore or preserve visual function.

Radiation tolerance of functioning pituitary tissue in gamma knife surgery for pituitary adenomas

OBJECTIVE

This study is intended to contribute to a determination of the sensitivity of preserved hypophyseal function to focal radiation in pituitary adenomas.

METHODS

We compared two subgroups of patients followed up for a median of 5 years after gamma knife surgery (GKS). Subgroup 1 (n = 30) showed postirradiation hypopituitarism. Subgroup 2 (n = 33) was continually eupituitary. These subgroups were taken from a previously published study relating to a larger group of 163 patients with pituitary adenomas treated by GKS and evaluated after a median follow-up period of 2 years. A relatively high treatment dose was used in this larger group (median, 20 Gy to the tumor margin for growth control in nonfunctioning adenomas; median, 35 Gy for hypersecreting adenomas). Early results approached those of microsurgery, and there were only a few side effects. In the present study, we compared 16 different variables in the same two subgroups to discover the relationships that caused a delayed appearance of postirradiation hypopituitarism. The main pretreatment and treatment parameters were measured on reconstructed treatment plans. This database was used for statistical evaluation.

RESULTS

The relationship between the mean dose and the volume of functioning hypophysis was stronger in terms of worsening of pituitary function than that of the spot dose to different intrasellar structures. We found that for our group of patients, the safe mean dose of radiation to the hypophysis was 15 Gy for gonadotropic and thyrotropic functions and 18 Gy for adrenocorticotropic function. The worsening of pituitary function was also significantly dependent on the dose to different anatomic levels of the infundibulum, but we did not succeed in fully characterizing this relationship. In addition, we discovered significant levels of dependency of postirradiation pituitary damage to different pretreatment and treatment variables.

CONCLUSION

Knowledge of the radiation tolerance of functioning pituitary structures subjected to GKS can ensure better preservation of pituitary function after irradiation. This is valid for the group of patients we studied. Our study's findings can be used as a guideline for GKS treatment of new patients with pituitary adenomas, and it can serve for comparison with the experience of other gamma knife centers.

Radiation injury to the nervous system

This article reviews the current knowledge with regard to neurotoxicity of conventional radiation, including recent understanding of the pathophysiology, molecular biology, diagnostic evaluation and clinical presentations, as well as proposed treatment modalities and possible protective agents.