Exhibit Hall | Forum 6
Purpose: One of our clinics lost/misplaced immobilization devices produced from a full day of CT simulations. Four patients received CT simulation during that day, including a right lung, SBRT pelvis, SBRT clavicle, and a breast e-boost case. This would normally require rescheduling the patients for re-simulation and re-planning on the new simulation scan. However, due to the importance of minimizing unnecessary contact to prevent Covid-19 transmissions, a previously developed and tested in-house image-based immobilization technique was utilized instead, eliminating the need for patients to physically return for re-simulation.
Methods: The original CT simulation scan was used to fabricate a custom machine-milled Styrofoam mold for each patient. First step was contouring the patient’s external, then extracting the patient posterior and lateral surface, adding the isocenter markings as part of the fabricated mold contour, and finally saving the final mold contour in STL file format. This file was loaded to a computer numerical controlled (CNC) milling machine to fabricate the immobilization device within hours.
Results: All four patients received their immobilization devices for their first setup/treatment day. The replacement molds length varied from 78-35 cm, based on the length of the original CT scan. Therapists were able to setup and immobilize all four patients using the replacement molds without difficulty. Physicists and clinicians reviewed the setups and imaging prior to the treatments and found that setup errors were within the acceptable range for treatment. Based on the OBI match results, the mean overall shift (couch shift vector length) was 0.76 ±0.34 cm for the two SBRT cases.
Conclusion: Creating replacement immobilization devices from CT simulation scans offers a feasible and efficient alternative to re-simulation due to lost or damaged immobilization devices. Patient setup was reproduceable, comfortable, and comparable to our standard of care.
TH- RT Interfraction Motion Management: setup errors, immobilization, localization