Abstract
Real‐time, 3D localization of the prostate for intensity‐modulated radiotherapy can be accomplished with passively charged radio frequency transmitters and superconducting quantum interference device (SQUID) magnetometers. The overall system design consists of an external dipole antenna as a power source for charging a microchip implant transmitter and SQUID magnetometers for signal detection. An external dipole antenna charges an on‐chip capacitor through inductive coupling in the near field region through a small implant inductor. The charge and discharge sequence between the external antenna and the implant circuit can be defined by half duplex, full duplex, or sequential operations. The resulting implant discharge current creates an alternating magnetic field through the inductor. The field is detected by the surrounding magnetometers, and the location of the implant transmitter can be calculated. Problems associated with this system design are interrelated with the signal strength at the detectors, detector sensitivity, and charge time of the implant capacitor. The physical parameters required for optimizing the system for real‐time applications are the operating frequency, implant inductance and capacitance, the external dipole current and loop radius, the detector distance, and mutual inductance. Consequently, the sequential operating mode is the best choice for real‐time localization for constraints requiring positioning within 1 s due to the mutual inductance and detector sensitivity. We present the theoretical foundation for designing a real‐time, 3D prostate localization system including the associated physical parameters and demonstrate the feasibility and physical limitations for such a system.PACS number: 87.53.‐j
Highlights
The goal of intensity-modulated radiotherapy (IMRT) is to minimize the dose to normal tissue surrounding the clinical target volume (CTV) and increase the tumor dose where possible
We developed an immobilization/localization system with an offline correction protocol, for prostate IMRT using the NOMOS Peacock system (NOMOS Corporation, Cranberry Township, PA).(18) The system design consists of a Styrofoam pellet filled vacuum bag (Vac-LokTM bag, MED-TEC, Orange City, IO) attached to a carrier box with specialized fiducials for pre- and posttreatment localization verification using lateral portal films
We investigated localizing the prostate for real-time radiotherapy treatment using the magnetic induction field as the source for calculating the position
Summary
The goal of intensity-modulated radiotherapy (IMRT) is to minimize the dose to normal tissue surrounding the clinical target volume (CTV) and increase the tumor dose where possible. Any deviations between the planned and treated position degrade the therapeutic ratio. The planning target volume is defined to include the CTV and associated treatment uncertainties that include but are not limited to patient setup and organ motion. For conditions where planning margins are not adequate, the tumor will be underdosed. Margins that are too large may lead to greater complications. While it is impossible to eliminate these errors, the goal in localization is to reduce the uncertainties where possible
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