Assessment of the role of multimodality imaging for treatment volume definition of intracranial ependymal tumors: An original article

Ependymomas refer to glial tumors arising from ependymal tissue of Central Nervous System (CNS). These tumors may be derived from the radial glial cells in subventricular zone . Ependymomas comprise approximately one fourth of primary tumors originating in spinal cord, and less than 10% of CNS tumors. There may be an increased incidence of intramedullary spinal cord ependymoma in cases of neurofi bromatosis type 2. While the location is typically intracranial in children, adult ependymomas mostly have spinal location. Patient presentation and symptomatology depend on lesion localization. Fourth ventricle is a very common location for Abstract


Introduction
Ependymomas refer to glial tumors arising from ependymal tissue of Central Nervous System (CNS). These tumors may be derived from the radial glial cells in subventricular zone . Ependymomas comprise approximately one fourth of primary tumors originating in spinal cord, and less than 10% of CNS tumors. There may be an increased incidence of intramedullary spinal cord ependymoma in cases of neurofi bromatosis type 2. While the location is typically intracranial in children, adult ependymomas mostly have spinal location. Patient presentation and symptomatology depend on lesion localization. Fourth ventricle is a very common location for intracranial ependymomas, and extension into subarachnoid Surgery may be used for management of intracranial ependymal tumors, however, other therapeutic modalities including Radiation Therapy (RT) and chemotherapy may be utilized [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. RT may have a role as part of primary treatment, as adjuvant therapy, or for management of recurrences [3][4][5][6][7][8][9][10][11][12][13][14][15]. In recent years, there is a rising trend towards reducing the adverse effects of RT by incorporation of modernized techniques. Accurate and precise RT treatment volume is essential for optimization of treatment results. Herein, we evaluated RT target defi nition for intracranial ependymal tumors.

Materials and methods
In this study, irradiation target volume defi nition was assessed for 15 patients with intracranial ependymal tumors.
Patient characteristics are summarized in Table 1.

Results
Contemporary RT treatment planning systems at our tertiary referral institution were used. Optimal target coverage and minimal exposure of normal tissues was considered as priority. Ground truth target volume was determined after meticulous assessment of physicians. Target determination was assessed. An overlap of 100% has been detected between CT-MR fusion based target defi nition and ground truth target volume determination by the board certifi ed radiation oncologists following meticulous assessment, colleague peer review, collaboration, and ultimate consensus. As the primary result, it was found that the ground truth target voume was identical with target determination with CT-MR fusion based imaging. Table 2 demonstrates treatment characteristics and comparative analysis of target determination with CT-MR fusion based imaging and ground truth target voume defi nition.

Discussion
Incorporation of contemporary technologies may reduce adverse effects of RT in the millennium era. Using effective doses of radiation with optimal sparing of critical structures may improve treatment outcomes for patients suffering from intracranial ependymoma. In this regard, accurate treatment volume determination is an indispensable aspect of contemporary irradiation strategies. There has been signifi cant progress with excellent improvements regarding radiation oncology practice by introduction of modernized treatment equipment, contemporary and adaptive irradiation strategies [16][17][18][19][20]. With regard to radiotherapeutic management of intracranial ependymomas, accumulating data suggest promising treatment results [3][4][5][6][7][8][9][10][11][12][13][14][15]. With this in mind, precision in target designation becomes essential for optimized irradiation protocols with the incorporation of recent RT delivery techniques and modalities. More focused irradiation of well defi ned targets has been possible by use of radiosurgical techniques with stereotactic immobilization and image guidance, however, extreme hypofractionation with sophisticated technologies necessiates improved precision and accuracy in treatment volume determination to avoid geographic misses, treatment failures, and radiation induced adverse effects. While defi nition of huge treatment volumes could result in increased doses to surrounding normal tissues with resultant toxicity, determination of inadequate treatment volumes can result in treatment failures. In this regard, there is an obvious need for optimization of target volume determination. In the literature, there is accumulating of evidence in support of CT-MR fusion based target volume determination for several indications [21][22][23][24][25]. However, there is paucity of data regarding the utility of multimodality imaging for RT planning of intracranial ependymal tumors. Within this context, our study may add to accumulating data on multimodality imaging based treatment volume determination for radiotherapeutic management of intracranial ependymal tumors.
In conclusion, precision and accuracy in target and treatment volume defi nition of intracranial ependymomas