total resection or less than 1.5 cm2 residual disease
The standard of care for children older than 5 years with low risk (also called standard risk) disease is low dose RT (23.4 Gy in 180 cGy fractions) to the craniospinal axis with a chemotherapy regimen outside of a study:
- Low dose craniospinal RT (23.4 Gy in 180 cGy fractions) plus chemotherapy. The posterior fossa is then boosted to 54 Gy in 180 cGy fractions plus chemotherapy.
- The boost is usually given to encompass the original tumor volume with adequate margins. Some centers recommend treating the whole posterior fossa, but there is no evidence that this is improves local control.
- This combined modality approach has allowed an improved survival in spite of decreasing the craniospinal axis dose to 23.4 Gy in standard risk medulloblastoma eg COG 9961 study demonstrated an 81% EFS at 5 years and overall survival of 86%.
- Decreasing the dose of craniospinal axis RT to 23.4 Gy has been shown to decrease long-term neurocognitive morbidity.
There are trials currently underway investigating whether chemotherapy can be used in standard risk patients between the ages of 3 and 8 in order to decrease the craniospinal component of the radiation dose even further and to assess if RT boost to the entire posterior fossa improves local control.
The Children’s Oncology Group ACNS0331 trial was a phase 3 Study that randomized patients with standard risk medulloblastoma twice:
- A first randomization (for children aged 3 to 8 years old) was to a standard dose craniospinal RT (23.4 Gy in 180 cGy size fractions) versus a 25% dose reduction craniospinal RT (18 Gy in 180 cGy size fractions).
- A second randomization was between a boost to the whole posterior fossa versus conformal RT to the tumor bed plus a margin.
- All patients received concomitant vincristine during RT.
- They then received multiagent chemotherapy, namely alternating cycles of vincristine/cisplatin/lomustine (CCNU) and vincristine/cyclophosphamide.
This study is now closed and preliminary results are available.
- Survival rates following reduced radiation boost volumes were comparable to treatment of the whole posterior fossa.
- The reduced dose of craniospinal RT was associated with higher adverse event rates and worse survival