Medulloblastoma is an undifferentiated tumor that originates from primitive, multidifferentiated potential medulloblast cells, i.e., neural tube cells that are embryonically located in the outer granular layer of the cerebellum. Traditionally, medulloblastoma is considered to be a tumor located in the posterior cranial fossa originating from the primitive ectoderm. Despite the controversy, the World Health Organization (WHO) retains the name “medulloblastoma” and considers primitive ectodermal tumor (PNET) on the screen as a specific undifferentiated embryonic tumor to distinguish it from the sequence of well-differentiated embryonic tumors (Table 2-1). In 70%-90% of children, the tumor can be completely or nearly completely resected to achieve better control of the tumor. The “staging” depends on the determination of the extent of the tumor during surgery, and the imaging diagnosis is now more helpful for accurate staging. Before the application of CT, CHANG (Table 2-2) had proposed a staging system based on the invasion site of the cerebrospinal lesion. The current data suggest that M-stage significantly affects prognosis, whereas a series of reports have concluded that local invasion of the tumor (T-stage, including T3b or brainstem invasion) does not result in significant differences in treatment outcomes after aggressive surgical resection is given. Radiation therapy often results in curative outcomes and thus becomes the mainstay of treatment for medulloblastoma. Medulloblastoma is sensitive to chemotherapy and has a high remission rate with alkylating agents (especially cyclophosphamide) and platinum-based drugs. Incomplete or inappropriate cerebrospinal irradiation (CSI) combined with overly intense chemotherapy results in a very high probability of cerebrospinal recurrence. Patients receiving pre-CSI chemotherapy have an increased risk of progression of cerebrospinal lesions with the continuation of chemotherapy. For patients with recurrence, a high-dose chemotherapy autologous bone marrow rescue regimen is sometimes effective. 2, radiation therapy The entire subarachnoid space is at risk of involvement, so whole brain and whole spinal cord irradiation must be given. The possibility of recurrence in the subfrontal lobe has been well established clinically, so it is important to include the subfrontal septum intact when irradiating the whole brain and spinal cord to prevent recurrence. The standard position for performing CSI is prone, and a body mold or vacuum immobilization device should be used as well. For whole-brain spinal cord irradiation, the head and neck are irradiated with two opposing fields on both sides, and the spinal cord is irradiated with a single posterior field adjacent to the head and neck field (in larger children, the spinal cord may be irradiated with two adjacent fields connected to the field). The articulation of the head and neck fields and the posterior spinal cord field is very important, and special settings are often required to make the dispersion beams in the superior direction of the posterior spinal cord field (with the head rotated at the appropriate angle for lateral field irradiation) and the dispersion beams in the inferior direction of both fields (with the bed rotated at the appropriate angle for lateral field irradiation) coincide with each other. Precise three-dimensional (3-D) articulation should be advantageous, as it eliminates the need for a gap between the fields and avoids the effects of dose disparity between the two fields by periodically moving the articulation. For CNS tumors requiring CSI irradiation, the posterior orbit need not be included in the field. The inferior border of the spinal subarachnoid space is at the level of sacral 2 or lower. The lateral border of the spinal cord irradiation field should include the entire width of the vertebral body and the intervertebral neural foramina. In young children, the thoracic portion of the spinal cord may not be irradiated to better protect the heart and lungs, and a sacral “spade field” is not necessary. The use of electron beam therapy for spinal cord irradiation has been reported, but the long-term results of treatment are unclear. The advantage of electron beam irradiation is that the amount of tissue outside the irradiated area is limited, but special attention should be paid to the accuracy of the depth of irradiation and the uniformity of the dose at the interface of the different fields. For posterior cranial fossa enrichment irradiation, all structures under the curtain should be included. The usual sequence of treatment is CSI irradiation followed by posterior cranial fossa dosing. If the patient has significant neurological symptoms and low blood levels that preclude fine CSI irradiation first, irradiation of the posterior cranial fossa should be performed first. Medulloblastoma is a tumor that is relatively sensitive to radiotherapy. The local control rate of tumor can be more than 80% with radiation therapy using fractionated doses of 1.6-1.8Gy and posterior cranial fossa doses up to 54-55Gy (45Gy posterior reduction field). For postoperative radiotherapy, the standard dose for cerebrospinal cord is 35-36Gy (fractionated dose of 1.6-1.8Gy). Second, embryonal tumors (PNET) WHO classification determines the taxonomic position of some specific histological types of tumors, such as medullary ependymoma, ventriculoblastoma or neuroblastoma of the brain. Clinically, pineoblastoma is classified as an embryonal tumor. 1. Treatment principles Supratentorial PNET, ventriculoblastoma, pinealoblastoma and columnar cell tumor are often difficult to be completely resected due to the extent and growth site of the tumor. Neuroblastomas of the brain are mostly well-defined lesions, and complete resection of the bulk of the tumor has been reported to be possible in more than 25% of patients. Postoperative radiation therapy to the entire cerebral spinal cord and additional doses of irradiation to the primary site are the standard of care for children older than 3-4 years of age. For tumors in the supratentorial or pineal region, radiation treatment techniques and doses are similar to those for medulloblastoma, and additional doses of local irradiation fields should be given in an additional 2-3 cm range depending on the preoperative tumor size and postoperative anatomic changes. Only a few reports support the feasibility of local field irradiation for neuroblastoma of the brain, and most studies still recommend CSI. For embryonal tumors in infants and young children, chemotherapy should generally be administered first: lomustine (CCNU), vincristine, and prednisone. Ventricular meningiomas originate from ventricular meningeal cells lining the ventricular system and can occur anywhere in the CNS. In children, 90% of ventricular meningiomas occur intracranially, with 60%-70% of these tumors occurring in the posterior cranial fossa, originating in the fourth ventricle. The typical lesion in the posterior cranial fossa occurs at the base of the fourth ventricle, and the lesion often invades the pontocerebellar horn of the cerebellum via the lateral foramen of the ventricles. In infants, ventricular meningiomas may originate in the pontocerebellar horn of the cerebellum, and 50% of lesions may extend through the foramen magnum, often presenting as a tongue-like protrusion to the C1-2 or C-2 level and progressing down to the C-5 level. Supratentorial ventricular meningiomas mainly occur in the frontal and parietal lobes and often extend to the ventricular system, but tumors occurring in the ventricles are rare. The first choice of treatment should be surgical removal of the tumor to the maximum extent possible. For infants and young children, chemotherapy should be given first. If chemotherapy is effective, surgery will have a greater chance of complete removal of the lesion. For supratentorial tumors, the size and location of the tumor reduces the likelihood of complete resection. Radiotherapy may improve local control of the tumor and survival. Two retrospective studies showed survival rates of 0% and 13% for surgery alone, compared to 45% and 59% for surgery combined with radiation therapy. Ventricular meningiomas are more sensitive to chemotherapy, especially alkylating agents and platinum-based drugs. Clinical trials with adjuvant applications of CCNU, vincristine and prednisone did not improve tumor control rates. Radiation therapy The extent of the target area for radiation therapy for intracranial ventricular meningioma is still controversial. Recent studies have shown that 3-16% of ventricular meningiomas in children have definite whole brain spinal cord dissemination at the time of diagnosis, and that the diagnosis is more commonly made by a positive cytologic finding alone than by imaging of the brain spinal cord. The failure rate of central nervous system treatment is about 12%. Studies have shown that there is no significant difference in tumor control rates with whole-cranial or CSI irradiation compared to local expanded field irradiation designed based on modern diagnostic imaging. The criterion for a locally expanded field for posterior cranial fossa ventricular meningioma is complete coverage of the entire posterior cranial fossa area. The irradiation field was identical to that of a localized expanded field for medulloblastoma at the same site, except for the lower border. The lower border of the irradiation field for ventricular meningioma is usually at the junction of the second and third vertebral bodies of the neck. If the tumor infiltrates the upper cervical medulla, the lower border of the irradiation field should include two more vertebral bodies downward according to the preoperative tumor extent, and irradiate up to 45Gy before reducing the field. Recently, it has been advocated that more limited radiation therapy may be used depending on the site of treatment failure in residual lesions or recurrent cases. Prospective studies will determine the target area based on the extent of the preoperative tumor lesion (rather than the posterior cranial fossa based on anatomic localization) and give reduced-field add-on irradiation to known sites of lesion invasion or residual lesions. For supratentorial ventricular meningioma, the size of the local expanded field should be determined based on the extent of the preoperative tumor lesion, but the displacement of normal brain structures after surgery should be taken into account, and the boundaries of the irradiated field should generally be radiated outward by 2-3 cm in accordance with the tumor margin. if the intracerebroventricular lesion has been clearly identified, the entire ventricle should receive a 45 Gy dose of radiotherapy. Current radiotherapy principles call for a total tumor dose of 50-55 Gy at the primary site, with an additional dose of radiotherapy to irradiate only the tumor bed after a 45 Gy field reduction. There are also recommendations to use small field additions to 55-65 Gy for residual lesions, but precise radiotherapy techniques are required. Malignant brain tumors in infants and young children About 20% of brain tumors occur in infants and young children under 3 years of age, and the younger the age, the more malignant the tumor is in terms of histology and clinical behavior. Supratentorial tumors (especially those occurring in children less than 1 year of age) often have metastases to the subarachnoid space present at the time of diagnosis. Infantile brain tumors are generally difficult to operate on, have limited efficacy with radiation therapy, and may increase distant neurological complications and lead to neurocognitive deficits; therefore, the irradiation dose should be reduced accordingly for children under 2-3 years of age. The results of treatment of medulloblastoma, ventricular meningioma and pineoblastoma show little good prognosis in children under 3-5 years of age. Supratentorial astrocytomas (especially in the optic cross/hypothalamic region) are also common in young children. The data show that surgery and chemotherapy can successfully treat a proportion of medulloblastomas and resected ventricular meningiomas without the need for radiotherapy. For patients with M0 who have completed 1-2 years of chemotherapy, a reduced dose of CNS radiation therapy has been given with fairly successful results. For patients with lesion progression during chemotherapy, or with residual tumor remaining after chemotherapy, aggressive CSI (30-35 Gy) can achieve a 5-year control rate of more than 50% with acceptable complications. Some success in tumor control has been achieved in malignant gliomas (3-year disease-free survival rate 45%), medulloblastomas (38%) and ventricular meningiomas (45%), but the prognosis for pineoblastomas is extremely poor (0%). The results of the Pediatric Clinical Oncology Collaborative Group (POG) and the Childhood Cancer Collaborative Group (CCG) showed that 1-2 years of chemotherapy followed by planned (POG) or selective (CCG) radiotherapy resulted in a 2-year disease-free survival rate of 37% (all malignant cell types, POG) and a 3-year disease-free survival rate of 23% (embryonal tumors and ventricular meningiomas, CCG). V. Low-grade malignant gliomas Approximately 40% of childhood brain tumors are low-grade malignant gliomas (astrocytomas, oligodendrogliomas, mixed glioblastomas, and mixed neuroepithelial tumors). Astrocytomas are the most common pathological type of supratentorial tumors; 60% occur in the mesencephalon (hypothalamus, optic nerve/optic pathway, and thalamus) and 40% in the cerebral hemispheres. Subscallosal astrocytomas occur mostly in the cerebellum and brainstem. Ninety percent of tumors of the optic pathway are low-grade malignant glioblastomas (mostly astrocytomas). A specific type of astrocytoma in children, juvenile pilocytic astrocytoma (JPA), is quite common and generally presents as a slowly developing, more well-defined tumor. Oligodendroglial cell tumors in children are rare. Mixed gliomas are most commonly a mixture of oligodendroglial and astrocytic components. Although low-grade malignant gliomas are characterized by limited location and well-defined borders, they may also present with multiple foci or disseminate. In patients diagnosed or recurring after treatment, JPA or typical astrocytomas can have multiple foci in up to 20% of patients. Typical astrocytomas in children, especially uncontrolled lesions, can develop or transform into malignant gliomas in 10-15% of cases. 1. Low-grade malignant mesencephalic glioma (optic cross/hypothalamic glioma, low grade malignant thalamic glioma) It is customary to name tumors invading the optic pathway (optic nerve or optic tract) in the saddle as “optic cross tumor”. Gliomas of the optic pathway are subdivided into anterior (40%, lesions invading the optic nerve or optic tract) and posterior (60%, lesions invading the optic tract and hypothalamus, with or without invasion of the optic tract) tumors. Thalamic gliomas can occur in children of any age and do not correlate specifically with neurofibromatosis type I (NF-1). (1) Principles of treatment Tumors of the visual pathway develop rather slowly or even asymptomatically, or may present with significant visual loss and signs of impaired mesencephalic function. The indications for treatment are: significant visual changes or neurological deficits, or objective evidence of tumor development based on periodic imaging and visual acuity testing. The medical strategy for optic nerve glioma includes observation or surgical resection, with the indications for surgical treatment being that the patient is blind or near blind and the tumor is located anterior to the optic cross. Recently, surgical resection of exophytic tumors in the optic chiasm/hypothalamus has been advocated, but radiation therapy is also very effective for these tumors. The surgical treatment of thalamic gliomas is still controversial. Long-term local control can be achieved in 50% of lesions treated with radiation. Prognosis is related to histologic type, with JPA having the best prognosis. In young children with optic cross/hypothalamic gliomas, it is believed that chemotherapy should be attempted because of the damaging nature that radiation can cause. (2) Radiation therapy For optic pathway and hypothalamic tumors, local field irradiation is often used. For tumors confined to the optic cross and hypothalamus, conventional arc or multi-arc coplanar irradiation techniques are used. Preliminary experience suggests that segmented stereotactic radiotherapy or three-dimensional conformal radiotherapy can be implemented to treat tumors in this area. Tumors of the optic pathway that invade the optic nerve or optic tract (sometimes progressing posteriorly, crossing the lateral corpus callosum knee and invading the optic radiation zone) need to be irradiated with high-energy radiation in both contralateral fields, and at least most of the dose can be given in this manner. Children with NF-1 often present with an “NF-1” lesion (characterized by a localized high signal image lacking enhancement on T2 images on MR scans) rather than a tumor sign. Such lesions are common in the basal ganglia and brainstem and do not need to be included in the irradiation field during radiotherapy. The recommended treatment dose is 50 Gy for children over 3 years of age; however, for infants, the dose should be reduced to 45 Gy. Local field irradiation techniques are often used for thalamic gliomas. If it is clear that the tumor has extravasated (into the midbrain or over the hydrazine body), the irradiation field should be expanded accordingly. Experience with 3-D planned therapy suggests that 3-D radiotherapy is more effective for limited low-grade malignant thalamic gliomas, with a recommended dose of 54 Gy. 2. Low-grade malignant hemispheric gliomas Histologically, these tumors are predominantly astrocytomas (JPA, typical astrocytoma); oligodendrogliomas are also more common. (1) Treatment principles For the majority of hemispheric gliomas, complete tumor resection should be pursued. Adjuvant radiotherapy is not necessary for completely resected low-grade malignant astrocytomas; similarly, postoperative radiotherapy is not necessary for completely resected oligodendrogliomas and oligodendroglial astrocytic cripples. Post-operative radiotherapy for incompletely resected tumors may provide long-term control. Connective tissue-producing brain tumors (astrocytomas, infantile gangliogliomas, and connective tissue-producing neuroepithelial tumors) often occur in infants and young children and present as superficial mass-shaped lesions that can usually be surgically resected despite the extent of the lesions. (2) Radiation therapy Local field irradiation should be used for low-grade malignant glioma. For lesions with clear boundaries, three-dimensional conformal or segmented stereotactic radiotherapy techniques are more suitable. The recommended dose is 54-55 Gy; in ongoing controlled studies, the dose of stereotactic radiotherapy is close to 60 Gy. 3. cerebellar astrocytoma Cerebellar astrocytoma is a benign tumor that often occurs in children aged 3-5 years. The tumor is often cystic in nature and approximately 85% of the lesions are histologically JPA. 80%-90% of patients have complete tumor resection and surgery becomes the treatment of choice. Local recurrence after gross tumor resection is relatively uncommon. A clear indication in the literature for postoperative radiotherapy remains unproven. Postoperative radiotherapy should be given for diffuse residual lesions limited to cerebellar astrocytomas (non-JPA), but it is not clear whether the best treatment can be achieved with local field split dose irradiation, because usually a larger field should be used for residual lesions developing along the brainstem. Malignant gliomas Malignant gliomas account for 7-10% of CNS tumors in children, and 15% are astrocytomas and common glial tumors. Histologically, 50%-60% are mesenchymal astrocytomas, 30%-40% are glioblastomas, and 10%-20% are mesenchymal oligodendrogliomas and malignant mixed gliomas. The tumor is characterized by local infiltration, and most data indicate that the probability of cerebrospinal dissemination has occurred at the time of diagnosis is 5% or 10%. The prognosis of malignant glioma in cerebral hemisphere is good after complete surgical resection. Thalamic tumors are usually given biopsy or limited resection surgery, and complete resection is rarely performed. Postoperative radiotherapy should be routine, but chemotherapy should be given first in young children under 3 years of age. The role of chemotherapy in the treatment of malignant gliomas in children has been confirmed by the CCG in clinical studies: postoperative radiotherapy and controlled studies of radiotherapy + chemotherapy (vincristine, CCNU and prednisone). 2. Radiation therapy As in adult patients, irradiation of local expanded fields should be recommended for malignant gliomas in the thalamus and cerebral hemispheres of children, depending on the preoperative tumor extent and in combination with changes after surgical resection. The field of irradiation should be based on the edge of the hypodense area on the T1 image of CT or MR, with an additional 2 cm of outreach. CSI is rarely required for malignant gliomas, and although the probability of disseminating lesions on the pediatric screen can be as high as 30-40%, no more than 10% of treatment failures are localized. The use of stereotactic interstitial tissue insertion or radiosurgery techniques with additive irradiation has been reported for malignant gliomas in children. However, because of the limited number of treatments, it is difficult to draw specific conclusions at this time, and therefore more experience with treatment in young patients needs to be drawn upon. The recommended dose is the same as that for adults (54-60 Gy with conventional split radiotherapy). Brainstem gliomas originate in the midbrain (including the peduncle and the parietal part of the midbrain, the pontine brain and the medulla oblongata. About 75% are pontocerebellar gliomas, which exhibit diffuse infiltrative extension lesions that grow mainly along the longitudinal axis (to the medulla oblongata or midbrain), and the well may invade the pontocerebellar peduncle of the cerebellum. Brain stem glioma mainly occurs in children aged 3-9 years old. 1.Treatment principles Pontine brain tumors may lead to certain complications even with biopsy, and there is a lack of histologically corresponding treatment options, so surgery is a rather difficult and non-essential option. Exophytic gliomas of the dorsal brainstem may be surgically resected as appropriate. A significant proportion of patients require a ventriculo-ventricular shunt (VP). For tumors occurring in the parietal region of the midbrain, biopsy is appropriate. Tumors occurring in the parietal region of the midbrain may block the cerebral aqueduct even if the tumor is small, so VP should be performed and closely monitored. For tumors occurring in the parietal region of the midbrain without obvious growth, they can usually be temporarily observed and not urgently biopsied, and then biopsied if there is objective evidence of tumor development that requires treatment. Endogenous tumors at the cervical medullary junction can be surgically removed in some neurosurgical centers. For rare highly malignant tumors, further treatment should be given after surgery. For small focal tumors in the pontine or midbrain, conventional coronal arc irradiation or newer three-dimensional irradiation techniques are best given. For brainstem gliomas originating from the pontine brain, radiation therapy is the treatment of choice. Radiotherapy can be effective, but the prognosis is poor, so clinical trials have been conducted to try to give hyper-segmentation for these tumors. Chemotherapy is basically ineffective for pontine glioma. The T2 image of MR is the most accurate way to determine the extent of lesions in the longitudinal axis (medulla oblongata and midbrain) and transverse axis (cerebellopontine peduncle and cerebellum). The most commonly used field of irradiation is the contralateral high-energy radiation field on both sides. Target area design for dorsal brainstem exophytic tumors should be limited to areas of residual postoperative lesions or areas of lesions progressing along the medulla oblongata, posterior and/or lateral to the pontocerebellum. Stereotactic radiotherapy or 3D conformal radiotherapy is the ideal treatment modality for brainstem gliomas. When a combination of tumor control and complications are considered, the recommended hyper-segmentation radiotherapy regimen is an irradiation with a fractionated dose of 1.17 Gy or 1 Gy and a total dose of 70.2 Gy or 70 Gy, respectively. For dorsal ependymal tumors or small focal tumors in the brainstem, the standard radiotherapy plan is: 50-55 Gy total with a fractionated dose of about 1.8 Gy. Late complications of high-dose hyper-segmentation irradiation modality include neurocognitive deficits, hearing loss, cerebral leukomalacia, micro diffuse hemorrhage and dystrophic calcifications as shown by MR, therefore, routine use of hyper-segmentation radiotherapy is not advocated for pontine glioma or brainstem tumors with a better prognosis. Craniopharyngioma is a benign tumor that arises from embryonic remnants of squamous cells in the cranial cheek bursa of the pituitary stalk (occurring in the gray matter nodes of the brain) during embryogenesis. Craniopharyngiomas present as suprasellar masses, with some calcification common within the tumor and often with intra-saddle lesions. Cystic or solid tumors may develop laterally into the middle cranial fossa and posteriorly into the posterior cranial fossa. At the time of diagnosis, 50%-90% of children show signs of hypoendocrine function, most commonly low levels of growth hormone, thyroid stimulating hormone (TSH), and adrenocorticotropic hormone (ACTH); 10%-15% of children show uremia. 1. Treatment principles The treatment of craniopharyngioma is still controversial. The preferred treatment option for the vast majority of patients is to try to obtain total tumor resection. Recurrence after surgical resection confirmed by imaging is relatively rare. Many recent reports put the rate of treatment failure between 10-30%. After total surgical tumor resection, postoperative imaging may still reveal residual calcification or significant tumor remnants in 15-25% of patients. Long-term tumor control is achieved in 80% of children treated with limited surgery and radiation therapy over a 20-year follow-up period. Numerous reports have shown that excellent disease-free survival rates of 10-20 years can be achieved after treatment. The efficacy of initial radiotherapy is superior to that of delayed radiotherapy. Postoperative radiotherapy should be administered to patients with incomplete tumor resection rather than waiting for tumor development. Because of the cystic nature of craniopharyngiomas, intracapsular brachytherapy can be performed with radioisotopes that emit beta lines, such as 90 yttrium or 32 phosphorus. Stereotactic radiosurgery has been reported for selected microscopic residual or recurrent lesions, and the preliminary results of segmented stereotactic radiotherapy are encouraging. There is no specific report on systemic chemotherapy for craniopharyngioma, but there are a few reports on the application of intracapsular bleomycin. 2.Radiation therapy The target area design of craniopharyngioma is more conservative to include the tumor volume, including the solid tumor and its cystic part. For lesions after needle aspiration of the cystic contents or limited resection, the target area should include the entire cystic wall. If the cystic lesion is large, it should be surgically resected first, and postoperative irradiation may target only the extent of the residual lesion. Two- or three-field fixed irradiation fields, high-energy photon radiotherapy, or coronal curvilinear irradiation techniques may be used. Stereotactic or three-dimensional conformal radiotherapy is advantageous in the treatment of craniopharyngioma, and local high-dose irradiation can be given to well-defined tumors. According to the literature, conventional fractionated (fractionated dose of 1.8 Gy once daily) irradiation with a total dose of 50-60 Gy improves local control of the tumor. Complications (including optic nerve damage and brain necrosis) are often associated with high-dose radiotherapy exceeding 60 Gy. Tumors of the pineal region and intracranial germ cell tumors Tumors of the pineal region include many pathological types of tumors originating in the posterior region of the third ventricle. Germ cell tumors (60-70%) and pineal parenchymal tumors (pineoblastoma or pineal cell tumor, 10%-20%) are the most common. For diagnostic imaging, tumors of the pineal region are more specific than many tumors originating in the third ventricle, such as astrocytomas, ventricular meningiomas, gliomas, and arachnoid cysts. Intracranial germ cell tumors present as midline third ventricular masses located in the pineal region (50%-60%) or suprasellar region (30%-35%) and, rarely, in the basal ganglia/thalamic region. The types of intracranial primary benign and malignant germ cell tumors present include: 60%-70% germ cell tumors; 15%-20% tumors that produce tumor markers (embryonal carcinoma, endodermal sinus tumors, yolk sac tumors, choriocarcinoma); and 15%-20% teratomas (benign, immature type, or malignant). Biochemical markers in both serum and cerebrospinal fluid (CSF) may be elevated: from elevated chorionic gonadotropin (p-hCG) (up to several thousand units in typical cases) associated with choriocarcinoma to endodermal sinus tumors or embryonal carcinomas with elevated alpha-fetoprotein (AFP). Marker indicators of up to 50-75 IU after radiotherapy may have a detrimental effect on prognosis, and marker measurement levels above 50 IU are a poor prognostic factor if chemotherapy is used first. Beta-hCG in serum and/or CSF may be mildly elevated in germ cell tumors. 1. Treatment principles For suprasellar tumors, especially those in the pineal region, biopsy is required for standard diagnostic and treatment procedures. Patients mostly need to undergo VP shunt. When the AFP level is elevated (diagnosing an aggressive or “malignant” germ cell tumor), the histologic diagnosis can be waived; in teenage boys presenting with multiple tumors in the midline third ventricle (diagnosing a germ cell tumor), the histologic diagnosis can be waived, but its reliability is poor. Treatment options of radiotherapy and adjuvant chemotherapy are reasonably available for histologically confirmed lesions. There is no clear benefit of surgical excision for germ cell tumors, and the role of surgical excision for other types of embryonal histiocytic tumors remains to be demonstrated. Recent literature suggests that there is no direct correlation between surgery and cerebrospinal or systemic dissemination. Radiotherapy is the standard treatment option for intracranial germ cell tumors. Although the dose and extent of radiation therapy are still highly controversial, radiation therapy can result in tumor control rates of more than 90%. The high radiosensitivity of germ cell tumors allows for a trial of diagnostic radiotherapy (20-25 Gy) for tumors in the pineal region that are not pathologically confirmed; if the tumor shrinks significantly, it is indicative of a germ cell tumor and treatment can be continued to completion. If the tumor is not sensitive to diagnostic radiotherapy, it should be considered an embryonal histiocytic tumor with poor prognosis or, more likely, another type of tumor, at which point local radiotherapy and/or surgery should be performed. The safety and accuracy of biopsy has led to a gradual abandonment of the idea of “diagnostic radiotherapy”. For other types of germ cell tumors, radiotherapy is part of a variety of treatment options, including stereotactic radiotherapy. Although pineal cell tumors in adults are benign, data suggest that pineal cell tumors in children are an indication for radiation therapy. Endocranial germ cell tumors are highly sensitive to chemotherapy, with high objective remission rates for alkylating agents, platinum compounds, and conventional chemotherapy regimens used for neuroectodermal tumors. 2. Radiation therapy The high probability of subventricular and cerebrospinal implantation in intracranial germ cell tumors has been the key to the debate of designing a reasonable irradiation field. Early data from Columbia University showed that the actual incidence of subarachnoid implantation was close to 37%, and the spinal cord failure rate for suprasellar germ cell tumors (up to 43% at 5 years) was significantly higher than that of clinically diagnosed pineal region tumors (10%). The probability of concurrent pineal and suprasellar lesions (multiple midline germ cell tumors) varies from 10% to more than 50%. positive CSF cytology findings are as high as 60% in Japanese cases, compared to 15% reported in North America. Results of CSI have been reported in the literature: several large number of case groups have reported tumor control rates of more than 90% with low-dose whole-brain spinal cord radiotherapy followed by localized field reduction with additional irradiation; others have reported a risk of spinal cord failure of no more than 10% after histologically confirmed germ cell tumors given only local or whole-brain irradiation. Despite the small number of pathologically confirmed germ cell tumors in the literature, control rates of 90% were achieved after local or large field brain irradiation only (without CSI). For all intracranial germ cell tumors in children older than 10-12 years, CSI is routinely given. radiotherapy to the whole cerebral spinal cord in young children (no definite lesion, standard dose of 25 Gy) can be dispensed with, and only local radiotherapy (high risk area for tumor recurrence) is advocated. Or a combination of local radiotherapy (often requiring a lower dose) and chemotherapy should be given according to the set study protocol. For other types of embryonal cell tumors, CSI has been the standard mode of treatment, but surgery and radiotherapy have been poor. The combination of radiotherapy and chemotherapy has some advantages, and some reports suggest that radiotherapy in combination with effective chemotherapy is sufficient for local field irradiation only. Although seminoma and histologically confirmed intracranial germ cell tumors also show a high sensitivity to radiotherapy, most radiotherapy sources recommend a dose of 50 Gy for the latter. If a combination of radiotherapy and chemotherapy is administered, the appropriate dose for the primary site is recommended to be 35-40 Gy. The dose for the whole cerebral spinal cord in M0 lesions should be limited to 25 Gy; in the presence of a well-defined lesion, irradiation of the whole cerebral spinal cord For malignant germ cell tumors, the treatment dose should be close to the tolerated dose, i.e., 54-55 Gy at the primary site and 35 Gy for the whole cerebrospinal cord. when there is a definite subarachnoid lesion, the whole cerebrospinal cord radiation dose should be 40 Gy.