Advantage of protons compared to IMRT in the treatment of medulloblastoma

James Metz, MD
OncoLink Associate Editor
Last Modified: October 24, 2000

Presenter: W. H. St. Clair
Affiliation: Massachusetts General Hospital

Background:

There is continued interest in finding ways to reduce the radiation related toxicity associated with the treatment of medulloblastoma. Both proton radiotherapy and intensity modulated radiation therapy (IMRT) have been shown to reduce the amount of normal tissue that receives a high dose of radiation. This study was performed to compare conventional photons, proton radiotherapy, and IMRT for the treatment of medulloblastoma.

Materials and Methods:

Conventional photon, proton, and IMRT plans were compared for the treatment of a single patient with a diagnosis of medulloblatoma.
The target volume was the entire craniospinal axis followed by a boost to the posterior fossa.
Dose volume histograms (DVH) were compared for a variety of normal tissues for each of the dosimetry plans

Results:

There was substantial normal tissue dose sparing for both the IMRT and proton plans when compared to the conventional photon plan
Protons were clearly superior to both IMRT and conventional photons.
Treatment with IMRT resulted in more exposure to normal tissues when the low dose region was evaluated for some DVH's, although there was sparing at the high dose regions when compared to conventional photons.

Authors' Conclusions

There was a continuous improvement in dose deposition with improvements in technology (photons-->IMRT-->protons), with protons showing the best results.
Because of the better dose distribution of protons, there may be significant decreases in late toxicity when using this modality compared to the others.

Clinical/Scientific Implications:

This is a small study with only one patient analyzed, thus the results must be taken with caution.
Because IMRT uses multiple field arrangements to decrease the amount of normal tissue receiving a high dose of radiation, there may be exposure of more normal tissues to a low dose of radiation then with conventional photons.
Other reports have previously supported the use of protons over conventional photons in the treatment of medulloblastoma.