2286 - Feasibility Study of Lying-on-Gurney Position Total Skin Electron Therapy for Frail Patients
Presenter(s)
Z. Yang1, L. Skinner2, R. T. Hoppe1, M. S. Binkley1, and B. Han3; 1Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 2Department of Radiation Oncology, Stanford University, Palo Alto, CA, 3Department of Radiation Oncology, Stanford University, Stanford, CA
Purpose/Objective(s): To develop an easy-to-setup total skin electron (TSE) technique with enhanced patient comfort for treating frail patients who are unable to be treated in the conventional standing positions.
Materials/Methods: This technique was developed with a 9 MeV high dose rate electron beam with the collimator set to a field size of 40 cm. An in-house customized degrader made of tungsten, PLA and PMMA was employed to flatten the beam profile to improve field uniformity. Throughout the treatment, the patient remained lying on a gurney adjusted to its lowest position (SSD 160 cm). The whole procedure involved six sets of beams: 1) Two AP/PA six-fields: The gantry was set to 0°. The patient stayed lying on the gurney positioned transversely under the LINAC head at ±40cm along the Gun/Target direction to achieve patient lateral dose uniformity. Along the transverse direction, the gurney was first centered then shifted ±70cm to treat the patient with a total of 6 fields in both supine and prone positions. 2) Four oblique dual-fields: The gantry was set to 60°. The patient laid on the gurney in both prone and supine positions parallel to the longitudinal direction, 105 cm laterally from the central axis, and the gurney was then shifted ±80 cm along the longitudinal axis to deliver the dual-field beams. The gurney was then rotated 180° to treat the opposite side of the body, following the same set-up design. Optimal dose profiles along the patient’s vertical axis were determined by adjusting field weights and shifts based on the ion-chamber measurements. The weighting between the AP/PA six-fields and the oblique dual-fields were determined by OSLD measurements.
Results: For the AP/PA six-fields, the weights of two transversely centered beams were determined to be 0.65 relative to the ±70cm position beams. This will provide a relative dose profile ranged from 109% to 90% of the central axis dose in the patient superior-inferior direction over a length of 180 cm, while along the patient lateral direction the dose profile ranged from 95% to 105% over a length of 100cm. For the oblique dual-fields, the relative dose profile uniformity was also within ±10% over 180 cm along the patient’s longitudinal axis. The weight of the oblique dual-fields was determined as 0.1 relative to the AP/PA six-fields to provide a homogenous skin dose around the patient. For cases that require shorter treatment time, the four oblique dual-fields can be skipped while maintaining comparable dose uniformity.
Conclusion: The preliminary data demonstrated the feasibility of the proposed lying-on-gurney position TSE technique. Its quality and dose uniformity are clinically acceptable comparing with the conventional standing techniques, while offering improved patient comfort and a simpler, reproducible setup. This technique shows promise for frail patients who cannot safely maintain a standing position during treatment.