Purpose: To compare two commercial systems, Sun Nuclear SRS MapCHECK and iRT Systems Integral Quality Monitor(IQM), on quality assurance(QA) of single isocenter(ISO) multiple metastases(Mets) stereotactic radiosurgery(SRS) and stereotactic radiation therapy(SRT) plans.
Methods: Single ISO multiple Mets SRS/SRT plans with multiple arcs were created in Brainlab Multiple Mets Elements(MME). The SRS MapCHECK is a 2D diode array of 77mmx77mm. It was designed to be inserted into StereoPHAN secured on a designated base mounted on a Linac couch. The SRS MapCHECK/StereoPHAN system was CT scanned and imported into Brainlab MME as a patient-specific QA phantom. Gamma pass rates per Met was analyzed. IQM is a single large-area 550cc ionization chamber mounted onto the Linac head. It has a sensitive area of 40cmx40cm projected at the isocenter, which only needs one plan delivery regardless of Mets number. With IQM, the measured signal per segment and cumulative signal per arc are compared to the calculated.
Results: The patient-specific QA on three clinical plans totaling 13 Mets and 24 arcs were performed with both systems and all passed QA. With the SRS MapCHECK, the Gamma passing rates @3%/1mm criteria per Met were 90%- 100% (mean 96.9%±3.4%). With IQM, the difference between calculated and measured signal per Arc was mostly within 3%, except for the smallest segments, in which the deviations increased up to 4-7%, but well within the acceptable tolerance. The time to complete the measurements was on average 120 minutes for SRS MapCHECK and 15 minutes for IQM. The difference in time was due to the fact that with a limited measurement size, the SRS MapCHECK had to be irradiated multiple times to cover all of the Mets.
Conclusion: There was good agreement between the QA results on both systems. The QA time was dramatically decreased with IQM by approximately a factor of 10.