# Patient-Specific Dosimetry Evaluations in Theranostics Software for Internal Radiotherapy
## 2 Materials and Methods
The resulting dose maps and dose-volume-histograms are then internally elaborated to provide the mean doses absorbed by the structures delineated on SPECT-CT images (organs and lesions). These values may be compared to the absorbed doses calculated by OLINDA 2.0. Figure 1: _Cont._  
**Phantom**  
The manlike phantom Liqui-Phill (The Phantom Laboratory, Greenwich, NY, USA) provided with 4 inserts (Left kidney, Right kidney, Liver and Spleen) was chosen to evaluate Velocity Theranostics. For this purpose in each insert a specific \({}^{177}\)Lu activity concentration was injected, as shown in Table 1. This antropomorphic phantom was acquired once with a SPECT/CT tomograph (Figure 2), while later on a set of 4 SPECT/CT images was generated (using Matlab, The MathWorks Inc., Natick, MI, USA) for the purpose of simulating radiopharmaceutical bio-kinetics. The time points were generated to simulate scans at 1 h, 4 h, 24 h, 48 h and 70 h post injection. During the preparation of the phantom, to ensure the accurate measure of the volumes, a calibrated scale was used to measure the weight of phantom and inserts (before and after refilling). The density of the solution of water and radioactivity was considered as 1 g/mL. HCl (0.1 M) was injected to water as a carrier solution so as to avoid \({}^{177}\)Lu deposition on the phantom walls and to ensure a more uniform radioactive solution. Figure 1: Workflow of the Velocity Theranostics calculations. Figure 2: SPECT-CT scan of Liqui-Phill phantom. **Cohort of Patients**  
Velocity Theranostics was evaluated with a cohort of clinical cases (15), who were extracted from the group of patients enrolled in a clinical PRRT trial (EURRACT 2015-00546-63) at AUSL-IRCCS of Reggio Emilia (Italy), who gave written informed consent for dosimetry calculations. Dosimetry was scheduled on the occasion of the first course of therapy following a therapeutic administration of \({}^{177}\)Lu-labelled peptides. Each patient underwent 4 SPECT/CT scans at approximately 1, 24, 40 and 75 h post injection for dosimetry purpose. Absorbed doses were calculated for liver, spleen and kidneys. **Image Acquisition and Reconstruction**  
A SPECT-CT scanner (Symbia T2, Siemens Healthineers Headquarters, Forchheim, Germany, 3/8\" NaI(Tl)-detector) which was previously calibrated for \({}^{177}\)Lu (CF = 28.5 Bq/count) [19] was used to perform image acquisitions of phantom and patients through a clinical protocol for body studies. It uses: MEHR collimators; 128 \(\times\) 128 matrix; zoom = 1; views = 32 \(\times\) 2; time/view = 30 s; step and shoot mode; degree of rotation = 180\({}^{\circ}\); non-circular orbit; detector configuration = 180\({}^{\circ}\). The first clinical CT image was acquired with 130 kV and 90 mAs, using tube current modulation. The following CT images were acquired at 130 kV with a fixed value of 40 mAs to respect the safety of the patient. The slice thickness of reconstructed images was 5 mm. A smooth reconstruction kernel was used (B08s; Siemens Medical Solution, Germany). The iterative algorithm Flash 3D (10 it. ; 8 sub. ; Gaussian filter 4.8 mm; cubic voxel size 4.8 mm) [20] was used to reconstruct SPECT images in Siemens E-Soft workstation (Syngo, MI Application version 32B, Siemens Healthineers Headquarters, Forchheim, Germany) with CT based attenuation correction, scatter correction and collimator-detector response correction. **Data Analysis and Statistics**  
The absorbed doses were computed independently with OLINDA 2.0 and Velocity Theranostics (organ-level option) using the same set of images for both for the anthropomorphic Liqui-Phill phantom and for clinical cases. The Time-Integrated Activity used for OLINDA 2.0 absorbed dose calculations were computed in Matlab using a bi-exponential curve to fit the time-activities data extrapolated from Velocity segmentation tool.