Copenhagen, Denmark

ESTRO 2022

Session Item

Poster (digital)
Radioluminesence imaging for CyberKnife® dosimetry and quality assurance
Antonello Spinelli, Italy


Radioluminesence imaging for CyberKnife® dosimetry and quality assurance

Antonello Spinelli1, Zahra Shakarami1, Sara Broggi2, Antonella del Vecchio2, Claudio Fiorino2

1San Raffaele Scientific Institute, Experimental Imaging Center, Milan, Italy; 2San Raffaele Scientific Institute, Medical Physics, Milan, Italy

Show Affiliations
Purpose or Objective

To investigate the applicability of radioluminescence imaging (RLI) as a novel 2D quality assurance (QA) dosimetry system for CyberKnife®.

Material and Methods

We developed a real time dose measurement system based on a commercial complementary metal oxide semiconductor (CMOS) camera facing a radioluminescence screen located at the isocenter (Figure.1). The radioluminescence light collected by a lens was used to measure 2D dose distributions. An image transformation procedure, based on two reference phantoms (square and star), was developed to correct for projective distortion due to the angle (15 degrees) between the optical and the radiation beam main axis. Dose profiles were measured for field sizes ranging from 10 mm to 60 mm using fixed circular and Iriscollimators and compared against gafchromic film (GC). The corresponding full width at half maximum (FWHM) was measured using the RLI and benchmarked against GC film. Small shift of the isocenter position were introduced on purpose to test the sensitivity of the RLI system to field size variations.

Figure 1: RLI acquisition setup. The radiation beam (yellow) impinged on

 the scintillation screen, which then emits light collected by the camera (orange).


The FWHM measurements using the RLI system indicated strong agreement with GC film with maximum absolute difference equal to 0.131 mm for fixed collimators and 0.049 mm for the Iris (Table.1). A 2D analysis of RLI with respect to GC film indicated that the differences in the central region are negligible, while small discrepancies are in the penumbra region (30%-70%). Changes in field sizes of up to 0.2 mm were detectable by RLI.

Table 1: FWHM (mm) obtained from the RLI line profiles and compared with the GC films.

Field Size (mm)FWHM (mm)

RLIGC Filmmm%

Circle 1010.03910.108-0.069-0.68
Circle 4041.20641.269-0.063-0.15
Circle 6061.8861.820.060.097


Circle 1010.71410.753-0.039-0.36
Circle 4041.14841.259-0.111-0.26
Circle 6061.98461.8530.1310.211

Two facing sides

Iris 109.789.80-0.02-0.2
Iris 4037.05237.095-0.043-0.11
Iris 6056.81756.866-0.049-0.086


The first application of a novel RLI approach for CyberKnife® dosimetry was presented and tested. Results are in agreement with GC film measurements. The sensitivity, sub-mm spatial resolution, simple setup, immediate availability of the data and full automation of the readout and processing, make this optical system as an useful and effective tool for robotic radiosurgery quality assurance.

Key words: Radioluminescence imaging, CyberKnife, Quality assurance.