When to start radiotherapy in a 19-year-old patient with a history of right frontal lobe ependymoma (grade 3) who received proton therapy (56.8 Gy) and underwent re-operation for a small recurrence 23 months later?

When to Start Radiotherapy After Re-operation for Recurrent Grade 3 Frontal Lobe Ependymoma

Radiotherapy should be initiated 2-3 weeks after re-operation, once post-operative staging with craniospinal MRI and CSF cytology has been completed to assess for metastatic disease and finalize the radiation field. 1, 2

Immediate Post-operative Steps (First 2-3 Weeks)

• Obtain post-operative MRI within 48-72 hours to document the extent of resection, as this is the single most critical prognostic factor determining survival 1

• Wait at least 2-3 weeks post-surgery before performing CSF cytology and craniospinal MRI with contrast to assess for metastatic disease 1, 2

  • This staging is mandatory before finalizing the re-irradiation plan, as the presence of disseminated disease would alter the radiation field 1
  • Do not proceed with radiotherapy planning until this staging is complete

Re-irradiation Strategy

Re-irradiation achieves durable responses and should be administered even after complete resection in grade 3 ependymomas. 1, 2

Radiation Dose and Technique

• Use focal fractionated re-irradiation with doses of 54-60 Gy to the tumor bed 1

  • This patient previously received 56.8 Gy, so cumulative dose constraints to organs at risk must be carefully reconstructed 3

• Re-irradiation can be delivered with curative intent if adequate coverage of target volumes can be achieved without exceeding estimated dose constraints on organs at risk 3

  • The radiation plan must be based on accurate reconstruction of the previous proton therapy dose distribution 3
  • The degree of recovery from initial radiation is difficult to estimate, but preliminary data suggest some tissue recovery occurs over time 3

Critical Considerations for Re-irradiation

• The 23-month interval since initial radiation may allow for some normal tissue recovery, making re-irradiation more feasible 3

• For brain re-irradiation, particular caution is warranted as there is currently insufficient data to recommend an optimal dose and fractionation scheme 3

  • However, the site of recurrence in the operated bed may be partially outside the previously irradiated high-dose volume, potentially allowing adequate treatment 3

• If re-irradiation cannot achieve sufficiently high-dose or adequate coverage without exceeding dose constraints, then other treatment modalities are preferable 3

Why Not Delay Radiotherapy Further?

• The main cause of death in ependymoma patients is intracranial failure at the primary site 4

• Re-irradiation still provides benefit even after complete resection in grade 3 ependymomas, as these are high-grade tumors with significant risk of local recurrence 1

• Among patients with recurrent ependymoma, 5-year event-free survival after re-operation is only 19% with gross total resection and 14% with incomplete resection 1, 2

  • These poor outcomes underscore the need for adjuvant re-irradiation

Common Pitfalls to Avoid

• Do not proceed with radiotherapy before completing staging workup (craniospinal MRI and CSF cytology at 2-3 weeks post-op), as this may result in inadequate treatment fields if metastatic disease is present 1, 2

• Do not assume chemotherapy is an alternative to re-irradiation - chemotherapy should only be considered when both surgical and radiotherapy options have been exhausted 1, 2

• Do not use low-dose palliative re-irradiation - this patient requires curative-intent treatment given the isolated recurrence in the operative bed 3

• Do not delay radiotherapy beyond 4-6 weeks post-operatively once staging is complete, as this may compromise local control

Timeline Summary

1. Days 1-3 post-op: Obtain MRI to assess extent of resection 1
2. Weeks 2-3 post-op: Perform craniospinal MRI and CSF cytology 1, 2
3. Weeks 3-4 post-op: Complete radiation planning with careful dose reconstruction from prior proton therapy 3
4. Week 4-6 post-op: Initiate re-irradiation (54-60 Gy focal fractionated radiotherapy) 1