Delta4 Discover transmission detector: A comprehensive characterization for in-vivo VMAT monitoring

Edoardo Petrucci; Lorenzo Radici; Valeria Casanova Borca; Silvia Ferrario; Marina Paolini; Massimo Pasquino

doi:10.1016/j.ejmp.2021.04.017

Delta⁴ Discover transmission detector: A comprehensive characterization for in-vivo VMAT monitoring

Phys Med. 2021 May:85:15-23. doi: 10.1016/j.ejmp.2021.04.017. Epub 2021 May 1.

Authors

Edoardo Petrucci¹, Lorenzo Radici¹, Valeria Casanova Borca¹, Silvia Ferrario², Marina Paolini², Massimo Pasquino³

Affiliations

¹ Medical Physics Department, A.S.L. TO4, 10015 Ivrea, TO, Italy.
² Radiotherapy Department, A.S.L. TO4, 10015 Ivrea, TO, Italy.
³ Medical Physics Department, A.S.L. TO4, 10015 Ivrea, TO, Italy. Electronic address: mpasquino@aslto4.piemonte.it.

PMID: 33945949
DOI: 10.1016/j.ejmp.2021.04.017

Abstract

Objective: To investigate the dosimetric behaviour, influence on photon beam fluence and error detection capability of Delta⁴ Discover transmission detector.

Methods: The transmission detector (TRD) was characterized on a TrueBeam linear accelerator with 6 MV beams. Linearity, reproducibility and dose rate dependence were investigated. The effect on photon beam fluence was evaluated in terms of beam profiles, percentage depth dose, transmission factor and surface dose for different open field sizes. The transmission factor of the 10x10 cm² field was entered in the TPS's configuration and its correct use in the dose calculation was verified recalculating 17 clinical IMRT/VMAT plans. Surface dose was measured for 20 IMRT fields. The capability to detect different delivery errors was investigated evaluating dose gamma index, MLC gamma index and leaf position of 15 manually modified VMAT plans.

Results: TRD showed a linear dependence on MU. No dose rate dependence was observed. Short-term and long-term reproducibility were within 0.1% and 0.5%. The presence of the TRD did not significantly affect PDDs and profiles. The transmission factor of the 10x10 cm² field size was 0.985 and 0.983, for FF and FFF beams respectively. The 17 recalculated plans met our clinical gamma-index passing rate, confirming the correct use of the transmission factor by the TPS. The surface dose differences for the open fields increase for shorter SSDs and greater field size. Differences in surface dose for the IMRT beams were less than 2%. Output variation ≥2%, collimator angle variations within 0.3°, gantry angle errors of 1°, jaw tracking and leaf position errors were detected.

Conclusions: Delta⁴ Discover shows good linearity and reproducibility, is not dependent on dose rate and does not affect beam quality and dose profiles. It is also capable to detect dosimetric and geometric errors and therefore it is suitable for monitoring VMAT delivery.

Keywords: IMRT quality assurance; In-vivo delivery monitoring; Transmission detector.

MeSH terms

Particle Accelerators
Radiometry
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted
Radiotherapy, Intensity-Modulated*
Reproducibility of Results