The Actual Whole Brain Dose Measurement Under The Protocol Of Limiting The Skull Dose To 12 J

Kiyoshi Nakazaki1, Yasue Tanaka2, Yoshinobu Sekihara2, Norihiro Ishii Mitiyoshi Sato2, Akira Sano2, Hiroyuki Nakagaki2, Katuya Goto2, Shinzo Ota2

1Fukuyama, Japan 2Brain Attack Center, Oota Memorial Hospital, Fukuyama, Japan

Keywords: gamma knife, radiosurgery, brain metastasis, Radiation Therapy, dose delivery

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     The safe skull dose is considered 10-12J that is equivalent to 3Gy of whole brain radiation. However, the cumulative irradiation dose to the whole brain (WB dose) under this protocol has not been measured in the common Gamma knife (GK) planning.
     We studied the difference between the WB dose and the skull dose, and estimated the dose distribution on the normal brain about all procedures.
     Among 89 patients (96 procedures) who underwent GK surgery between January 2009 and October 2009, 82 patients (89 procedures) could have the WB CT or MRI images.
     The skull dose in all procedures was under 12 J. In all procedures taken the WB images, the WB dose was computed using a Gamma Plan. The cases of brain metastasis were studied in detail because of the possibility of the re-treatment.
     The mean skull dose was 3.9 (range 0.5-11.2) J. The mean WB dose was 2.7 (range 0.3-7.0) J. The mean proportion of the WB dose to the skull dose was 0.57(range 0.28-0.75). In the cases of brain metastasis (52 procedures), the mean numbers of tumors were 6 (range 1-32), the mean total volume of all tumors was 7.7 (range 0.05-26.5) cc, and the mean WB dose was 2.69(range 0.28-6.41) J. The mean proportion of the WB dose to the skull dose was 0.56 (range 0.28-0.64). The mean proportion of volumes receiving >3Gy, >6Gy, >10Gy in the WB was 19.5 (range 0.2-86.2) %., 5.8 (0.1-21.7) %, 1.9 (range 0.0-7.9) %. In cases (8 procedures) with more than 10 (range 12-32) tumors, the mean WB dose was 5.4 (range 3.68-6.41) J.
     This is a retrospective study.
     This result assures that the effect of GK to the normal brain is low under this protocol.
     It may be said that repeated GK could be performed with small risk.


Project Roles:

K. Nakazaki (), Y. Tanaka (), Y. Sekihara (), N. Sato (), A. Sano (), H. Nakagaki (), K. Goto (), S. Ota ()