Validation of new transmission detector transmission factors for online dosimetry: an experimental study

Abstract

BackgroundThe demand for dose verification during treatment has risen with the increasing use of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in modern radiation therapy. This study aims to validate the transmission factors of a new transmission detector, the Dolphin online monitoring system (IBA Dosimetry, Schwarzenbruck, Germany), for clinical use.MethodsThe transmission factors of the Dolphin detector were evaluated using 6 MV, 6 flattening filter free (FFF), 10 MV, and 10 FFF clinical beams from a TrueBeam STx linear accelerator system. Two-dimensional (2D) dose distributions were measured through portal dosimetry with and without Dolphin to derive the transmission factors. The measurements were performed using 10 IMRT and 10 VMAT treatment plans. The transmission factors were calculated using a non-negative least squares problem solver for the 2D dose matrix. Normalized plans were generated using the derived transmission factors. Patient-specific quality assurance with normalized plans was performed using portal dosimetry and an ArcCheck detector to verify the transmission factors. The gamma passing rates were calculated for the 2%/2 mm and 1%/1 mm criteria.ResultsThe transmission factors for the 6 MV, 6 FFF, 10 MV, and 10 FFF beams, were 0.878, 0.824, 0.913, and 0.883, respectively. The average dose difference between the original plan without Dolphin and the normalized plan with Dolphin was less than 1.8% for all measurements. The mean passing rates of the gamma evaluation were 98.1 ± 2.1 and 82.9 ± 12.6 for the 2%/2 mm and 1%/1 mm criteria, respectively, for portal dosimetry of the original plan. In the case of the portal dosimetry of the normalized plan, the mean passing rates of the gamma evaluation were 97.2 ± 2.8 and 79.1 ± 14.8 for the 2%/2 mm and 1%/1 mm criteria, respectively.ConclusionsThe Dolphin detector can be used for online dosimetry when valid transmission factors are applied to the clinical plan.

Evaluation of the effects of implementing a diode transmission device into the clinical workflow

“…Attenuation of 6 MV beams along the central axis for the various detectors they compared ranged from 1.0% to 7.2%, with ion-chamberbased devices typically having higher attenuation (ranging from 3.3% to 7.2%) and diode transmission devices typically having lower attenuation (~1%). Another available transmission detector not included in the comparison by Li et al [13] is the Dolphin detector (IBA Dosimetry, Schwarzenbuck, Germany) [18,20,21]. The Dolphin is a 2D array of 1513 plane-parallel ion chambers.…”

Technical Note: Alternating clinical usage of the integral quality monitor transmission detector

“…This small variation could be the result of the simple homogeneous design of the IQM detector. For the dolphin transmission detector, the ratio of the TF of the 5 cm × 5 cm and the 20 cm × 20 cm field was reported to be 7.6% …”

“…A very similar approach has been used by Park et al for the dolphin transmission detector. Furthermore, the obtained dTF was compared to the TF of regular open fields.…”

Verification of Extended Source-To-Imager Distance (SID) Correction for Portal Dosimetry

“…[10][11][12] PD has been established utilizing EPID for pretreatment verification. 13,14) 138 www.ksmp.or.kr Modern radiotherapy has increased the need for online dose verification owing to the complexity and accuracy of the new delivery techniques. (e.g., VMAT or Stereotactic ablative radiotherapy (SABR)).…”