Design of a phantom for verification of IORT treatments and in vivo dosimetry simulation.
PO-1319
Abstract
Design of a phantom for verification of IORT treatments and in vivo dosimetry simulation.
Authors: Lozares|, Sergio(1)*[sergiolozares@hotmail.com];Gandía|, Almudena(1);Villa|, David(1);Hernández|, Mónica(1);Jiménez|, Sara(1);Alba|, Verónica(1);Font|, José Antonio(1);
(1)Miguel Servet University Hospital, Física y Protección Radiológica, Zaragoza, Spain;
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Purpose or Objective
A phantom was designed for verification of IORT treatments treated with low energy X-rays with the Axxent equipment (Xoft Inc.).
The goal is to estimate doses in risk organs such as heart and lung in which it is not possible to place a detector to perform proper in vivo dosimetry.
Material and Methods
It was designed with a 3D design software phantom suitable to accommodate the balloon-shaped applicator used in IORT breast treatments performed with Axxent. The balloon is housed in the area where the tumor is removed. Dosimetry measurements can be made in vivo in the prescription area (with the detector attached to the balloon in the case of radiochromic films) and in the skin area, but not in the heart (left breast) or lung. The phantom was been designed (fig 1) in such a way that it can fit with the pieces of solid water (RW3) and be able to recreate the design to measure doses at the distances between the lung and the heart, as well as being able to add materials of different density to the complete design.
Doses to the patient''s lungs and heart were estimated from measurements of distances to these organs performed in a pre-treatment CT study.
The measurements were made with properly calibrated XR-RV3 radiochromic film scanning the films before and after irradiation following the triple channel method (radiochromic.com).
The phantom can accommodate balloons with a volume of 30 and 35 cc, which are the volumes most used in the treatment of patients (65% of cases), and for these cases were made the measures "pseudo in-vivo".
The simulated patients correspond to treatments of the upper quadrant, both internal and external.
The doses are estimated for the minimum distance at which the TPS tells us that the organ is located, so we would estimate the maximum dose to that organ.
Results
The results show the maximum doses calculated with radiochromic film for left lung and heart of 20 patients treated from the left breast measured retrospectively.
The data shown correspond to the average of these measures separated by applicator volume and treatment location (breast quadrant), since depending on the location the distance to the risk organs is different.
Conclusion
3D printing is a very useful tool for simulating in vivo dosimetry situations that cannot otherwise be accessed. The control of the density of the materials and the adaptation of the design to our needs are turning this technique into a fundamental ally of the medical physicist. In this case was possible to measure and verify the doses in lung and heart for IORT treatments. With a CT study of the patient we could measure a priori the doses in these organs to recommend a particular type of treatment.