Pediatric Medulloblastoma Treatment & Management
- Author: Tobey J MacDonald, MD; Chief Editor: Max J Coppes, MD, PhD, MBA more...
Standard therapy for medulloblastoma consists of aggressive surgery followed by radiation to the entire craniospinal axis with boost to both the primary tumor site and focal CNS metastatic sites. Recently, adjuvant chemotherapy has also been shown to be beneficial.
Reducing the amount of craniospinal radiation in an attempt to decrease morbidity without jeopardizing survival appears to be successful in this group. In a report by the International Society of Pediatric Oncology, children with average-risk medulloblastoma randomly received either the standard 36 Gy or a reduced dose of 24 Gy to the neuraxis. It was found that no statistical difference in progression-free survival rates was demonstrated between the groups as long as the initiation of radiotherapy was not delayed by the administration of chemotherapy before radiation.
The dose for average-risk medulloblastoma patients enrolled on Children's Oncology Group (COG) last completed trial was 23.4 Gy to the craniospinal axis followed by 32.4 Gy boost directly to the primary tumor site. In both the poor-risk and average-risk groups, the total radiation dose to sites of known disease is 55.8 Gy. An ongoing study is investigating further reduction of the craniospinal dose to 18 Gy in a subset of children with average-risk disease.
Verma et al conducted a retrospective study comparing results obtained with prone positioning for craniospinal irradiation with results obtained with supine positioning in the treatment of medulloblastoma. The study cohort consisted of 46 children, 23 of whom were irradiated in the prone positioning, and 23 in the supine position. The median ages for each group was 8.1 years and 7.2 years, respectively. Data were collected with regard to age; sex; risk group; need for general anesthesia; radiation therapy dose and fractionation; acceptance or rejection of weekly port films during treatment; and outcomes, including neuraxis recurrence and possible complications, such as myelitis. High-risk disease was seen in 26% of patients receiving irradiation in the prone position and in 35% of those receiving irradiation in the supine position. There was no difference in use of general anesthesia between the 2 groups. The rejection rate of cranial port films was significantly higher for patients treatedintheprone position (35%) than for patients in patients in the supine position (8%). The rate for 5-year progression-free survival was 62% for patients in the prone position and 76% for supine patients. The rate for overall survival was 67% for patients in the prone position and 84% for supine patients. There were no isolated junctional failures or occurrences of radiation myelitis in either group. The investigators concluded that irradiation positioning had no bearing on survival outcomes but that prone positioning was associated with a higher rate of rejection of cranial port films.
Min et al conducted a study of the relationship between the skin dose of proton irradiation and permanent alopecia in pediatric patients with medellublastoma. The study cohort comprised 12 children (aged 4-15 years) with medulloblastoma. Permanent alopecia was assessed and graded after completion of therapy. Skin threshold doses of permanent alopecia were calculated on the basis of skin dose from the craniospinal irradiation plan, using the concept of generalized equivalent uniform dose. The investigators took into account the intensity of chemotherapy that was employed. Monte Carlo simulations were used to assess uncertainties associated with beam range prediction and the presence of secondary particles. The investigators found that increasing the dose of the irradiation field or the dose given by the boost field to the posterior fossa increased total skin dose delivered in that region. It was found that permanent alopecia correlated with irradiation dose with a threshold of about 21 Gy (relativebiological effectiveness) with high-dose chemotherapy and 30 Gy with conventional chemotherapy. The investigators concluded that the risk for permanent alopecia could be predicted on the basis of the information in the treatment plan.
The current recommendation is 36 Gy to the craniospinal axis, followed by a boost of 19.8 Gy to the primary tumor site and an additional 19.8 Gy to focal metastatic sites. The amount of boost that can be given is limited by the presence of the optic nerves within the radiation field or if more than two thirds of the supratentorial compartment volume is within the radiation field.
Spinal disease that is visible after 30.6 Gy of the prescribed 36 Gy to the craniospinal axis receives an additional boost up to a total of 45 Gy if the tumor is located above the termination of the spinal cord and as much as 50.4 Gy if the tumor is located below the termination of the cord.
Radiotherapy for patients younger than 3 years, the poorest risk group, remains controversial. Because the effects of radiotherapy on intellectual development are most severe in this age group, attempts have been made to delay or omit radiation by using chemotherapy. However, in the most recent COG study, infants receiving chemotherapy alone had a 29% 3-year progression-free survival rate for those without dissemination and only 11% for those with metastasis. The Pediatric Oncology Group (POG) reported that, in infants with medulloblastoma treated initially with chemotherapy followed by delayed radiation, the 2-year progression-free survival rate was 34%.
Trials are currently underway to avoid or delay radiotherapy in this population by using cycles of high-dose chemotherapy followed by autologous stem cell rescue. Initial reports have indicated a good response rate to chemotherapy, and, although overall survival (30-40%) is comparable to prior studies, most patients who survived in the latest trials did not receive radiotherapy. Infants with desmoplastic tumor treated with chemotherapy fare better than those with classic tumors because 70% or more can be successfully treated without radiotherapy.
The most encouraging results with adjuvant chemotherapy have been reported in children with nondisseminated medulloblastoma receiving 8 cycles of lomustine (CCNU), vincristine, and cisplatin chemotherapy for approximately 1 year following conventional dose radiotherapy and concomitant vincristine.
Latest trials indicate that children aged 3-10 years who received this regimen with reduced-dose craniospinal radiation have a superior survival rate compared to those who received standard radiation alone. The current 3-year progression-free survival rate for those receiving adjuvant chemotherapy is approximately 80%.
Chemotherapeutic agents that have been found to be most effective for this disease are cisplatin, carboplatin, cyclophosphamide, and vincristine.
To improve survival rates in this group, current trials are investigating the use of high-dose chemotherapy (most commonly using carboplatinum and thiotepa-containing regimens) and autologous stem cell rescue after a course of conventional craniospinal radiotherapy and chemotherapy.
Studies using chemotherapy (carboplatin and vincristine) concurrent with radiotherapy are also underway.
Retinoic acid as a maturation agent following radiation is under investigation in a randomized trial.
In children younger than 3 years, evidence suggests that some do respond, at least partially, to chemotherapy. In patients with minimal residual postoperative disease, this response may be long-lasting.
Ongoing trials are investigating high-dose chemotherapy (carboplatin and thiotepa) and stem cell rescue, following induction with chemotherapeutic agents similar to those used in the treatment for older children with poor-risk disease. Whether radiotherapy can be safely delayed or omitted altogether in certain subgroups has not yet been determined.
Methotrexate, both intrathecally and intravenously, is being added to more conventional chemotherapy in some studies; primarily for infants with partially resected and/or disseminated tumors.
Current studies investigating the use of biologic agents that specifically target the most common molecular alterations described in this disease, such as tyrosine kinase inhibitors that block the function of EBB2, are ongoing.
Because the tumor is often friable, gentle suction is used. Microdissection is used to remove adherent portions.
Modern neurosurgical techniques permit complete or near-complete resection with little or no significant increase in morbidity and mortality rates compared with more conservative surgery.
Because surgical estimates of the extent of resection may not be reliable, postoperative MRI evaluation for residual disease is required within several days of the procedure.
As many as 40% of patients have some degree of new neurologic dysfunction postoperatively. One ill-defined syndrome is posterior fossa syndrome, characterized by mutism, cerebellar dysfunction, supranuclear cranial nerve palsy, and hemiparesis that occurs 12-48 hours after surgery. As many as 50% of patients have residual deficits.
Approximately 50% of patients require placement of a ventriculoperitoneal shunt at the time of operation (or shortly thereafter) because of unresolving obstructive hydrocephaly. Third ventriculostomy is increasingly used to avoid the placement of a permanent ventricular shunt.
As a direct result of the tumor and/or therapy, many patients are referred to occupational, physical, hearing, and speech therapists for rehabilitation of common neurologic dysfunction. Neurophthalmologists may also be consulted after successful treatment to evaluate persistent gaze palsies that may effect visual development.
Team members for the care of all patients should include specialists from each of the following:
Pediatric oncology and/or neuro-oncology
No specific dietary restrictions or requirements are indicated.
Patients who develop severe anorexia or weight loss as a result of therapy may need supplemental nutrition to maintain daily requirements. Most patients can tolerate enteral supplementation, but some may need parenteral support.
Most patients have no restrictions on activity other than limitations from neurologic deficits caused by the tumor and treatment.
Patients with ventriculoperitoneal shunts may be restricted from performing high-impact sports (eg, diving).
School performance needs to be carefully monitored, as most children, especially those younger than 7 years at diagnosis, require added support at school.
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