|
|
Dosimetric Model for Locoregional
Treatments of Brain Tumors with 90Y-Conjugates: Clinical Application
with 90Y-DOTATOC
Ferrari M, Cremonesi M, Bartolomei M, Bodei L,
Chinol M, Fiorenza M, Tosi G, Paganelli G
Division of Nuclear Medicine, European Institute of Oncology, Milan,
Italy; and 2Medical Physics, European Institute of Oncology, Milan,
Italy.
Locoregional (LR) administration of (90)Y-conjugates after surgical
debulking is a promising therapeutic option of gliomas.
Dosimetry is highly recommended, as patient-specific parameters
influence the absorbed dose to target and normal tissues.
After tumor resection, the absorbed dose must be carefully evaluated
in the rim of tissue surrounding the resected area.
The aim of this study was to calculate and provide the S values,
according to the MIRD concept, for dosimetry of LR brain treatments
with several (90)Y-labeled compounds.
The S values thus obtained have been clinically applied in 12 patients
treated with (90)Y-labeled [DOTA(0),d-Phe(1),Tyr(3)]octreotide
((90)Y-DOTATOC).
Methods. An
anthropomorphic model for Monte Carlo simulations was developed to
evaluate absorbed doses in brain-adjacent tissue (BAT) and in normal
brain.
To adapt the model to single patients, S values were evaluated taking
into account
(i) different surgical resection cavity (SRC) volumes,
(ii) different percentages of conjugate binding to the cavity wall,
and
(iii) different depths of percolation of the conjugate trough the
cavity wall.
BAT was divided into 1-mm-thick consecutive adjacent shells to
evaluate the dose distribution around the cavity.
Corresponding S values were obtained to allow dosimetric evaluation in
brain LR therapy with (90)Y-conjugates.
In the clinical treatments, 0.4-1.1 GBq of (90)Y-DOTATOC were injected
into the SRC via an appropriate catheter.
The activity in the SRC was assumed to be the difference between the
total injected activity and the activity in the blood plus the
activity cumulatively eliminated with the urine.
Results. Assuming no
diffusion, with a mean residence time in SRC of 60 +/- 8 h, absorbed
doses to shell II were 0.25 and 0.03 Gy/MBq for SRC volumes of 7.2 and
65.4 mL, respectively.
Assuming a slight diffusion of 1 mm with a 7.2-mL SRC, absorbed dose
to shells I, II, and VI were consistently different: 5.32, 2.53, and
0.12 Gy/MBq, respectively.
Mean doses to normal brain, red marrow, bladder wall, and total body
were 0.015, 0.03, 1.22, and 0.006 MGy/MBq.
Conclusion. The model
proved to be suitable for the dosimetry of several LR therapies with
(90)Y-conjugates.
According to our results, LR treatment with (90)Y-DOTATOC can safely
deliver very high doses to target tissue, sparing normal organs
including brain.
|
