Protons in posterior fossa ependymoma- a dosimetric comparison with photons
Kannikanti, D. H. Charlwood, Frances C Clarke, Matthew F Colaco, Rovel J Pan, Shermaine Saunders, Daniel Sitch, Peter Thorp, N. Whitfield, Gillian A Rasool, M.
Kannikanti, D. H.
Charlwood, Frances C
Clarke, Matthew F
Colaco, Rovel J
Pan, Shermaine
Saunders, Daniel
Sitch, Peter
Thorp, N.
Whitfield, Gillian A
Rasool, M.
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Abstract
Purpose or Objective
Adjuvant radiotherapy in ependymoma improves both local control and survival outcomes. The 5 year overall survival in
paediatric ependymoma is around 85%. With such outcomes, the late effects of treatment assume prime importance.
Protons when compared with photons have the potential to spare organs at risk (OARs), and thereby decrease late
complications. This study was designed to compare the dosimetry of proton with photon radiotherapy plans in patients with
posterior fossa ependymoma, in order to understand the potential for reduced late effects.
Materials and Methods
Data were extracted for ten patients with posterior fossa ependymoma treated with protons who had Volumetric Modulated
Arc Therapy (VMAT) photon plans prepared in case of cyclotron downtime. Five were single phase plans to a total dose of
59.4Gy in 33 fractions, with appropriate limitation of dose at spinal cord level, and 5 were two phase plans, to 54Gy in 30
fractions followed by a boost of 5.4Gy in 3 fractions to the volume above the foramen magnum. Clinically relevant
dosimetric variables of target and routinely outlined OARs for data collection were selected based on our clinical practice
and with reference to the European Particle Therapy Network (EPTN) consensus on radiation dose constraints for OARs in
neuro-oncology. Mean values were compared between proton and photon plans using a two tailed paired sample t-test. P
values of less than 0.05 were considered statistically significant. Results
Of ten patients, 7 were females. The median age was 7 years (range 3 to 17 years). For almost all dosimetric variables,
proton plans showed a statistically significant dosimetric advantage in OAR variables, including to the optic nerves and
chiasm, cochleae, pituitary gland, hypothalamus, hippocampi, temporal lobes, brain and brainstem. The mean D0.03cc for
brainstem, skin and spinal cord were not statistically significantly different between modalities (Figure 1). The mean
integral dose was significantly lower in protons compared to photons (p=0.00) with a median proton to photon integral dose
ratio of 0.55 (range-0.41 to 0.74). The mean percentage of the PTV receiving 95% of prescription dose and the mean
homogeneity index were not statistically significantly different between proton and photon plans (p=0.11 and p=0.98 respectively. Conclusion
This study showed marked dosimetric advantage for protons in OAR sparing and lowered integral doses, while maintaining
similar target volume coverage. This is anticipated to reduce the risk of late effects, particularly hearing loss, endocrine
dysfunction, neurocognitive effects, and second malignancies, while maintaining the established high rates of local control
with photons.
Description
Date
2022
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Kannikanti DH, Charlwood F, Clarke M, Colaco R, Pan S, Saunders D, et al. Protons in posterior fossa ependymoma- a dosimetric comparison with photons. Radiotherapy and Oncology. 2022 May;170:S984-S5. PubMed PMID: WOS:000806764200636.