Model-based dosimetry

OpenDose Calculator
Patient-specific dosimetry

OpenDose 3D
“OpenDose brings together resources and expertise to provide open access material for the benefit of Nuclear Medicine dosimetry through an international collaboration.”

Dosimetry in Nuclear Medicine (diagnostic or therapy) can be implemented using the
methodology introduced in the late 60s by the Medical Internal Radiation Dose (MIRD)
committee of the American Society of Nuclear Medicine (SNM). This methodology, known as
the *MIRD formalism* [1] can be expressed as:
\[ \overline{D}_{Target} = \sum_{Source} \widetilde{A}_{Source}
\times S_{\left( Target \leftarrow Source \right)} \]
where \( \overline{D}_{Target} \) is the absorbed dose (Gy) delivered to the target
(organ or tissue), \( \widetilde{A}_{Source} \) is the cumulated activity (i.e. the total
number of disintegrations, Bq.s) occurring in each source (organ or tissue) and
\( S_{\left( Target \leftarrow Source \right)} \) is the mean absorbed dose in a target
per nuclear disintegration in the source (*S value*,
Gy.Bq^{-1}.s^{-1}).
This formalism separates the determination of the absorbed dose in two independent tasks:
the estimation of the cumulated activity \(\widetilde{A}_{Source}\) and the calculation of
the *S value*. *S values* are obtained for an anthropomorphic model and for
a given radioisotope, and can be expressed as:
\[ S_{\left( Target \leftarrow Source \right)} =
\sum_i y_i E_i \Phi_{i \left( Target \leftarrow Source \right)} \]
where \( \Phi_{i \left( Target \leftarrow Source \right)} \) is the Specific Absorbed
Fraction (SAF, kg^{-1}) for radiation type i and \(y_i\), \(E_i\) are the yield
(Bq^{-1}.s^{-1}) and energy (J) of radiation type i, respectively.
The calculation of SAFs is done through intensive Monte Carlo simulations of
radiation transport in the anthropomorphic model, for every particle type (photons,
electrons) and energy.

The OpenDose project initially started as a collaborative effort to generate and
distribute free dosimetric data for the benefit of the Nuclear Medicine community
(Fig. 1). By sharing expertise and resources, the collaboration can produce data for one
anthropomorphic model in a few months. SAFs are produced independently using different
Monte Carlo codes with different radiation transport algorithms and physics models,
allowing data cross-verification. *S values* are then calculated using SAFs and
radioisotope decay characteristics. All data produced by OpenDose is provided with
statistical uncertainties.

The OpenDose collaboration has recently decided to develop dosimetric software in two directions (model-based and patient-specific dosimetry). We therefore welcome developers and clinical partners willing to test software with clinical data.

The OpenDose collaboration also aims at providing educational resources for professionals interested in radiopharmaceutical dosimetry.

[1] Loevinger R, Budinger TF, Watson EE. MIRD primer for absorbed dose calculations. Society of Nuclear Medicine, 1991.