A comparative study of dose distribution of PBT, 3D-CRT and IMRT for pediatric brain tumors
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RESEARCH
Open Access
A comparative study of dose distribution of PBT, 3D-CRT and IMRT for pediatric brain tumors Daichi Takizawa1*, Masashi Mizumoto1, Tetsuya Yamamoto2, Yoshiko Oshiro1, Hiroko Fukushima3, Takashi Fukushima3, Toshiyuki Terunuma4, Toshiyuki Okumura1, Koji Tsuboi1 and Hideyuki Sakurai1
Abstract Introduction: It was reported that proton beam therapy (PBT) reduced the normal brain dose compared with X-ray therapy for pediatric brain tumors. We considered whether there was not the condition that PBT was more disadvantageous than intensity modulated photon radiotherapy (IMRT) and 3D conventional radiotherapy (3D-CRT) for treatment of pediatric brain tumors about the dose reduction for the normal brain when the tumor location or tumor size were different. Methods: The subjects were 12 patients treated with PBT at our institute, including 6 cases of ependymoma treated by local irradiation and 6 cases of germinoma treated by irradiation of all four cerebral ventricles. IMRT and 3D-CRT treatment plans were made for these 12 cases, with optimization using the same planning conditions as those for PBT. Model cases were also compared using sphere targets with different diameters or locations in the brain, and the normal brain doses with PBT, IMRT and 3D-CRT were compared using the same planning conditions. Results: PBT significantly reduced the average dose to normal brain tissue compared to 3D-CRT and IMRT in all cases. There was no difference between 3D-CRT and IMRT. The average normal brain doses for PBT, 3D-CRT, and IMRT were 5.1–34.8% (median 14.9%), 11.0–48.5% (23.8%), and 11.5–53.1% (23.5%), respectively, in ependymoma cases; and 42.3–61.2% (48.9%), 54.5–74.0% (62.8%), and 56.3–72.1% (61.2%), respectively, in germinoma cases. In the model cases, PBT significantly reduced the average normal brain dose for larger tumors and for tumors located at the periphery of the brain. Conclusion: PBT reduces the average dose to normal brain tissue, compared with 3D-CRT and IMRT. The effect is higher for a tumor that is larger or located laterally. Keywords: Brain, 3D-CRT, IMRT, PBT, Pediatric tumor
Introduction Deterioration of intelligence after radiotherapy is an important problem in growing children. The degree of deterioration is affected by the irradiation dose, volume, site, and age at irradiation [1]. A major concern of brain irradiation in pediatric patients is subsequent deterioration of intelligence [6–10], since neurodevelopment is affected by the treatment dose and age at irradiation [1, 11, 12]. In 4 patients among 27 children with medulloblastoma treated
with craniospinal irradiation with a posterior fossa boost, Walter et al. [8] found an IQ decline of 3.9 points per year during a median observation period of 4.8 years, and cognitive losses did not seem to have reached a plateau. Merchant et al. analysed the correlation with the degree of deterioration and DVH of the whole brain and suggested that IQ can be obtained from the following formula [1]: IQ ¼ 93:11 ð0:028 age ‐ 0:0095 average dose t
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