Dosimetry of 131I-labeled 81C6 monoclonal antibody administered into surgically created resection cavities in patients with malignant brain tumors.
The objective of this study was to perform the dosimetry of 131I-labeled 81C6 monoclonal antibody (MAb) in patients with recurrent malignant brain tumors, treated by direct injections of MAb into surgically created resection cavities (SCRCs).


METHODS
Absorbed dose estimates were performed for nine patients. Dosimetry was performed retrospectively using probe counts (during patient isolation) and whole-body and SPECT images thereafter. Absorbed doses were calculated for the SCRC interface and for regions of interest (ROIs) 1 and 2 cm thick, measured from the margins of cavity interface. Also, mean absorbed doses were calculated for normal brain, liver, spleen, thyroid gland, stomach, bone marrow and whole body. The average residence time for the SCRC was 111 h (65-200h).


RESULTS
The average absorbed dose per unit injected activity (range) to the SCRC interface and ROIs 1 and 2 cm thick from the cavity interface were 31.9 (7.8-84.2), 1.9 (0.7-3.6) and 1.0 (0.4-1.8) cGy/MBq, respectively. Average absorbed doses per unit administered activity to brain, liver, spleen, thyroid, stomach, bone marrow and whole body were 0.18, 0.03, 0.08, 0.05, 0.02, 0.02 and 0.01 cGy/MBq, respectively. The high absorbed dose delivered to the SCRC interface may have produced an increase in cavity volume independent of tumor progression.


CONCLUSIONS
At the maximum tolerated dose of 3700 MBq 131I-labeled 81C6 MAb, the absorbed doses to the SCRC interface and ROIs of 1 and 2 cm thickness were estimated to be 1180, 71 and 39 Gy, respectively. The estimated average absorbed dose to the brain was 6.5 Gy. There was no neurological toxicity and minimal hematologic toxicity at this maximum tolerated administration level.
Akabani
G
G
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Reist
C J
CJ
Cokgor
I
I
Friedman
A H
AH
Friedman
H S
HS
Coleman
R E
RE
Zhao
X G
XG
Bigner
D D
DD
Zalutsky
M R
MR
D001932:Brain Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D003131:Combined Modality Therapy; D005909:Glioblastoma / Q000532:radiotherapy* / Q000601:surgery; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D009364:Neoplasm Recurrence, Local / Q000532:radiotherapy*; D016499:Radioimmunotherapy; D011879:Radiotherapy Dosage; D019063:Tenascin / Q000276:immunology*
D007457:Iodine Radioisotopes; D019063:Tenascin