SU‐E‐T‐02: 90Y Microspheres Dosimetry Calculation with Voxel‐S‐Value Method: A Simple Use in the Clinic

Abstract

Purpose: To present a simple and feasible method of voxel‐S‐value (VSV) dosimetry calculation for daily clinical use in radioembolization (RE) with 90Y microspheres. Dose distributions are obtained and visualized over CT images. Methods: Spatial dose distributions and dose in liver and tumor are calculated for RE patients treated with Sirtex Medical miscrospheres at our center. Data obtained from the previous simulation of treatment were the basis for calculations: Tc‐99m maggregated albumin SPECT‐CT study in a gammacamera (Infinia, General Electric Healthcare.). Attenuation correction and ordered‐subsets expectation maximization (OSEM) algorithm were applied.For VSV calculations, both SPECT and CT were exported from the gammacamera workstation and registered with the radiotherapy treatment planning system (Eclipse, Varian Medical systems). Convolution of activity matrix and local dose deposition kernel (S values) was implemented with an in‐house developed software based on Python code. The kernel was downloaded from http://www.medphys.it. Final dose distribution was evaluated with the free software Dicompyler. Results: Liver mean dose is consistent with Partition method calculations (accepted as a good standard). Tumor dose has not been evaluated due to the high dependence on its contouring. Small lesion size, hot spots in health tissue and blurred limits can affect a lot the dose distribution in tumors. Extra work includes: export and import of images and other dicom files, create and calculate a dummy plan of external radiotherapy, convolution calculation and evaluation of the dose distribution with dicompyler. Total time spent is less than 2 hours. Conclusion: VSV calculations do not require any extra appointment or any uncomfortable process for patient. The total process is short enough to carry it out the same day of simulation and to contribute to prescription decisions prior to treatment. Three‐dimensional dose knowledge provides much more information than other methods of dose calculation usually applied in the clinic.

Dosimetry and prescription in liver radioembolization with90Y microspheres: 3D calculation of tumor-to-liver ratio from global99mTc-MAA SPECT information

“…It was used corre sponding to 90 Y with a spacing of 2.21 mm. Manipulation of DICOM files, transformation of counts in accumulated activity and convolution were carried out with in-house software developed with the Python programming language (Mañeru et al 2015). Once the spatial dose distribution was known, the tumor was identified by locating the area with the highest dose until the known tumor size was reached.…”