ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
00:00 - 00:00
CyberKnife® patient plan verification with the SRS MapCHECKTM - First clinical experience
Sarah PETERS, Germany


CyberKnife® patient plan verification with the SRS MapCHECKTM - First clinical experience
Authors: Oliver Bislich.(Strahlenzentrum Hamburg / cyberknife center Hamburg, Radiotherapy, Hamburg, Germany), Fabian Fehlauer.(Strahlenzentrum Hamburg / cyberknife center Hamburg, Radiotherapy, Hamburg, Germany), Sarah Peters.(Strahlenzentrum Hamburg / cyberknife center Hamburg, Radiotherapy, Hamburg, Germany), Andreas A. Schönfeld.(Sun Nuclear, Research and Development, Neu-Isenburg, Germany)
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Purpose or Objective

The SRS MapCHECKTM (Sun Nuclear Corp., Melbourne, USA) is a two-dimensional diode array to be used in conjunction with the end-to-end phantom StereoPHANTM for metrological verification of treatment plans. The release of the SNC Patient Software 8.3 enables its use on CyberKnife® machines by removing the previous limit on the beam angle of incidence. This study aims to evaluate the performance of the device in the clinical routine. 10 treatment plans featuring different treatment sites, collimator sizes, number of gantry angles and delivery durations were tested.

Material and Methods

The SRS MapCHECKTM is equipped with 1013 Sun Point 2 diodes (0.48 x 0.48 mm²) distributed in a plane of 77 x 77 mm². The diagonal distance between the diodes is 2.47 mm. The specific arrangement of the diodes allows the measurement of the beam’s angle of incidence and the correction of the angular dependence of the detector response. For positioning on the CyberKnife®, 4 fiducial markers are integrated in the housing of the device.

To prepare the device for clinical use, a CT scan of the StereoPHANTM and the inserted SRS MapCHECKTM was taken. The suggested density overwrite was omitted in our tests. The array was calibrated in terms of absolute dose using a reference field. Two additional static beams were needed to calibrate for angular response.

The Precision® TPS (Accuray, Version was used to create the QA plans, and to export the DICOM RT Dose and reports.xml files. The 10 test plans included 9 different treatment sites, collimator sizes between 5 mm and 35 mm, 29 to 88 nodes and 61 to 314 beams.

The positioning of the device is performed via the integrated fiducials using x-ray imaging. After delivery, the SNC Patient Software applies the necessary corrections on a 50 ms frame base before summarizing the frames. The 6 degrees-of-freedom shift was calculated to evaluate the kV positioning accuracy, but not applied.

The setup of the phantom and the array on the treatment table takes about 3 minutes. The gamma criterion of 2% / 1mm > 90% and 3% / 1mm > 95% could be achieved in almost all test plans. 6 test plans achieved a gamma criterion of 1% / 1 mm > 90%. The rms of the calculated shifts between the delivered dose distribution and the planned dose distribution was below 0.4 mm in three dimensions.


The SRS MapCHECKTM allows easy and meaningful verification of patient plans without film, without restrictions of the angle of incidence and with little expenditure of time. The assembly and positioning of the phantom is without problem, except for cases with far posterior target volumes, where a relocation of the alignment center is recommended.