Proton versus photon radiotherapy for common pediatric brain tumors: comparison of models of dose characteristics and their relationship to cognitive function.
BACKGROUND
To determine whether proton radiotherapy has clinical advantages over photon radiotherapy, we modeled the dose characteristics of both to critical normal tissue volumes using data from patients with four types of childhood brain tumors.


METHODS
Three-dimensional imaging and treatment planning data, including targeted tumor and normal tissues contours, were acquired for 40 patients, 10 each with optic pathway glioma (OPG), craniopharyngioma (CR), infratentorial ependymoma (EP), or medulloblastoma (MB). Dose-volume data were collected for the entire brain, temporal lobes, cochlea, and hypothalamus from each patient. The data were averaged and compared based on treatment modality (protons vs. photons) using dose-cognitive effects models. Outcomes were estimated over 5 years.


RESULTS
Relatively small critical normal tissue volumes such as the cochlea and hypothalamus may be spared from radiation exposure when not adjacent to the primary tumor volume. Larger normal tissue volumes such as the supratentorial brain or temporal lobes receive less of the low and intermediate doses. When applied to longitudinal models of radiation dose-cognitive effects, these differences resulted in clinically significant higher IQ scores for patients with MB and CR and academic reading scores in patients with OPG. Extreme differences between proton and photon dose distributions precluded meaningful comparison of protons and photons for patients with EP.


CONCLUSIONS
Differences in the overall dose distributions, as indicated by modeling changes in cognitive function, showed that a reduction in the lower-dose volumes or mean dose would have long-term, clinical advantages for children with MB, CR, and OPG.
Merchant
Thomas E
TE
Division of Radiation Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA. thomas.merchant@stjude.org
Hua
Chia-Ho
CH
Shukla
Hemant
H
Ying
Xiaofei
X
Nill
Simeon
S
Oelfke
Uwe
U
D001932:Brain Neoplasms / Q000150:complications / Q000532:radiotherapy*; D002648:Child; D003071:Cognition / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D034381:Hearing Loss / Q000209:etiology; D006801:Humans; D007027:Hypothalamic Diseases / Q000209:etiology; D021621:Imaging, Three-Dimensional; D017785:Photons; D011522:Protons; D011878:Radiotherapy / Q000009:adverse effects; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal
D011522:Protons