Evaluation of a complementary metal oxide semiconductor detector as a tool for stereotactic body radiotherapy plan quality assurance

Highlights

• •

  Signal increased linearly with dose (r ² = 1) and output factors agreed within 0.5 % of chamber measurements for field sizes of 1 × 1 cm and above.

• •

  The detector exhibited angular and dose rate dependencies.

• •

  Detector demonstrated mean gamma pass rates using parameters 2 %/2 mm and 3 %/1 mm of 98.5 % ± 2.3 % and 97.2 % ± 3.1 %, respectively, relative to planned doses.

• •

  Detector demonstrated mean gamma pass rate of 99.2 % ± 1.0 % relative to radiochromic film for measuring clinical doses.

• •

  We report the detector's sensitivity to 1 mm single Multi Leaf Collimator offsets.

Abstract

Background and purpose

A sub-mm resolution Complementary Metal Oxide Semiconductor sensor has been developed for stereotactic radiotherapy quality assurance. Herein we evaluate its basic dosimetric performance and its application for linac C-arm stereotactic body radiotherapy (SBRT) plan quality assurance.

Materials and methods

The detector was integrated into its accompanying phantom or in Water Equivalent Plastic (WEP). The measurement reproducibility, stability, dose linearity and dependence on angularity, dose rate and field size were investigated. Clinical plan measurements were compared to our radiotherapy treatment planning system and radiochromic film. Sensitivity to introduced Multi Leaf Collimator (MLC) offsets was evaluated by simulating single MLC offsets in SBRT plans and comparing measurements to expected doses.

Results

Signal reproducibility was within ± 0.1 % and output calibration was stable over a 6 month period. Detector showed good linearity with dose (r ² = 1). Signal decreased by 5 % when dose rate was decreased from 1300 MU/min to 300 MU/min. Output factors agreed within 0.5 % of chamber measurements for 1x1 cm field sizes or greater. Angularity measurements showed good agreement with reference. For measurement of planned clinical doses, gamma pass-rates were 98.5 % ± 2.3 % (treatment planning system reference, 2 %/2mm) and 99.2 % ± 1.0 % (film reference, 2 %,2mm). The detector also showed sensitivity to errors of 1 mm offsets in MLC positioning.

Conclusion

The detector performed well when used for pre-treatment SBRT plan quality assurance, offering a good alternative to radiochromic film.