Room: Exhibit Hall | Forum 7
Purpose: To test the feasibility of using a three-dimensional (3D) printed patient-specific phantom for out-of-field dosimetry.
Methods: Louisiana State Universityâ€™s laboratory fabricated a 3D-printed phantom of the whole body of a 5â€™4â€? female. To evaluate out-of-field dose produced between photon, proton, and neutron therapies out-of-field absorbed dose was measured in organs and structures at risk of debilitating effects for intracranial fields ranging in size from 2.8x2.8 cmÂ² to 12.8x12.8 cmÂ². Photon therapy was delivered using an Elekta linear accelerator in 6 MV and flattening-filter-free (6FFF) modes and Varian Novalis Tx generated 6 MV fields. A clinical neutron therapy system delivered the neutron fields, and a clinical pencil beam scanning proton therapy system delivered the proton fields. The four out-of-field dose locations were the thyroid, pacemaker, esophagus, and fetus.
Results: The modality with the lowest out-of-field dose was proton therapy followed by the Elekta 6FFF, Elekta 6 MV, Varian 6 MV, and neutron therapy. For photon therapy, the Elekta 6FFF produced the lowest out-of-field dose, and in comparison to the Elekta 6 MV, it was on average 25%, 15%, 25%, and 45% lower in the thyroid, pacemaker, esophagus, and fetus, respectively. In comparison to proton therapy, the out-field-field dose from the Elekta 6FFF beam was on average 60% and 30% higher in the thyroid and pacemaker, respectively. Beyond the pacemaker, the out-of-field dose from proton therapy was indistinguishable from background for each field size.
Conclusion: We found that pencil beam scanning proton therapy offered the lowest out-of-field absorbed dose in comparison to photon and neutron modalities for intracranial fields of various field sizes. The study also demonstrated the feasibility of using an inexpensive 3D-printed patient-specific anthropomorphic phantom for out-of-field dosimetry. This is particularly important for quantifying the dose in organs, tissues, and electronics at risk for debilitating radiogenic effects.
Funding Support, Disclosures, and Conflict of Interest: Meagan Moore received funding from both the LSU Discover and LSU Foundation for the phantom fabrication.