Abstract
PurposeThe aim of this work was to evaluate the use of an angularly independent silicon detector (edgeless diodes) developed for dosimetry in megavoltage radiotherapy for Cyberknife in a phantom and for patient quality assurance (QA).MethodThe characterization of the edgeless diodes has been performed on Cyberknife with fixed and IRIS collimators. The edgeless diode probes were tested in terms of basic QA parameters such as measurements of tissue‐phantom ratio (TPR), output factor and off‐axis ratio. The measurements were performed in both water and water‐equivalent phantoms. In addition, three patient‐specific plans have been delivered to a lung phantom with and without motion and dose measurements have been performed to verify the ability of the diodes to work as patient‐specific QA devices. The data obtained by the edgeless diodes have been compared to PTW 60016, SN edge, PinPoint ionization chamber, Gafchromic EBT3 film, and treatment planning system (TPS).ResultsThe TPR measurement performed by the edgeless diodes show agreement within 2.2% with data obtained with PTW 60016 diode for all the field sizes. Output factor agrees within 2.6% with that measured by SN EDGE diodes corrected for their field size dependence. The beam profiles’ measurements of edgeless diodes match SN EDGE diodes with a measured full width half maximum (FWHM) within 2.3% and penumbra widths within 0.148 mm. Patient‐specific QA measurements demonstrate an agreement within 4.72% in comparison with TPS.ConclusionThe edgeless diodes have been proved to be an excellent candidate for machine and patient QA for Cyberknife reproducing commercial dosimetry device measurements without need of angular dependence corrections. However, further investigation is required to evaluate the effect of their dose rate dependence on complex brain cancer dose verification.
Highlights
Stereotactic radiosurgery (SRS) is a modern radiotherapy technique that employs multiple narrow beams to deliver conformed and precise high radiation dose to the target from different directions in single or few fractions.[1,2] It requires an accurate target localization and identification which can be achieved by physical stereotactic immobilization devices registering patient to a fixed frame (e.g., Gammaknife) or by imaging‐guided methods.[3]
Real‐time dosimetry and quality assurance (QA) of SRS treatments performed by the means of a robotic linear accelerator are challenging due to the small field sizes and nonisocentric beam delivery
A diode manufactured by an innovative technology named “edgeless” has been tested to estimate the diode's accuracy for small field dosimetry and its use as a real‐time device for patient‐specific QA of SRS treatments delivered by Cyberknife
Summary
Stereotactic radiosurgery (SRS) is a modern radiotherapy technique that employs multiple narrow beams to deliver conformed and precise high radiation dose to the target from different directions in single or few fractions.[1,2] It requires an accurate target localization and identification which can be achieved by physical stereotactic immobilization devices registering patient to a fixed frame (e.g., Gammaknife) or by imaging‐guided methods (such as Cyberknife Synchrony).[3]. Most predominant challenges are related to the dimensions of the detectors relative to the radiation field size which leads to a volume averaging effect and the fluence perturbation caused by the materials adopted for fabrication of the devices. The detectors used for QA in robotic SRS equipment such as Cyberknife should be energy, dose rate, and angular independent. They should have the ability to obtain high spatial resolution measurement without perturbing the radiation beam.[4,12,13,14]
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