# ACNS0331: reduced-dose and reduced-volume radiotherapy with chemotherapy for average-risk medulloblastoma

Source: https://onco.cc/key-papers/paper-acns0331-michalski-jco-2021/  
OnCo record `paper-acns0331-michalski-jco-2021` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Reducing the radiotherapy boost to the tumour bed instead of the whole posterior fossa was safe in average-risk medulloblastoma, but lowering the craniospinal dose from 23.4 to 18 Gy in young children led to more relapses, so the standard dose was kept.

## Summary

Children's Oncology Group phase 3 trial of 464 children with average-risk medulloblastoma randomised to involved-field (tumour bed) versus whole posterior fossa boost, and, for children aged 3 to 7, to low-dose (18 Gy) versus standard-dose (23.4 Gy) craniospinal irradiation.

Five-year event-free survival was 82.5 percent with involved-field boost versus 80.5 percent with posterior fossa boost (non-inferior), but 71.4 percent with 18 Gy against 82.9 percent with 23.4 Gy craniospinal irradiation (inferior); WNT tumours did well regardless.

## Fields

- Kind: Key paper
- Last checked: 2026-09-17
- Journal: Journal of Clinical Oncology
- Year: 2021
- DOI: 10.1200/JCO.20.02730
- Authors: Michalski JM, Janss AJ, Vezina LG, et al.
- Findings: Involved-field boost non-inferior: five-year event-free survival 82.5 percent vs 80.5 percent.; 18 Gy craniospinal irradiation inferior: 71.4 percent vs 82.9 percent.
- What it means: Tumour-bed boost is standard in average-risk medulloblastoma, while craniospinal dose reduction is reserved for the WNT-activated subgroup in trials.
- Caveats: Molecular subgroup was determined retrospectively.; Neurocognitive outcomes were somewhat better with lower dose, highlighting the trade-off.

## Sources

- J Clin Oncol 2021: https://doi.org/10.1200/JCO.20.02730
- PubMed: https://pubmed.ncbi.nlm.nih.gov/34110925/

## Connected records

- cancers: [Group 3 and group 4 medulloblastoma (non-WNT/non-SHH)](https://onco.cc/cancers/medulloblastoma-group-3-4/), [WNT-activated medulloblastoma](https://onco.cc/cancers/medulloblastoma-wnt/)
- trials: [COG ACNS0331](https://onco.cc/trials/acns0331/)
- journals: [Journal of Clinical Oncology](https://onco.cc/journals/jco/)

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