Validation and application of polymer gel dosimetry for the dose verification of an intensity-modulated arc therapy (IMAT) treatment

Abstract

Polymer gel dosimetry was used to assess an intensity-modulated arc therapy (IMAT) treatment for whole abdominopelvic radiotherapy. Prior to the actual dosimetry experiment, a uniformity study on an unirradiated anthropomorphic phantom was carried out. A correction was performed to minimize deviations in the R2 maps due to radiofrequency non-uniformities. In addition, compensation strategies were implemented to limit R2 deviations caused by temperature drift during scanning. Inter- and intra-slice R2 deviations in the phantom were thereby significantly reduced. This was verified in an investigative study where the same phantom was irradiated with two rectangular superimposed beams: structural deviations between gel measurements and computational results remained below 3% outside high dose gradient regions; the spatial shift in those regions was within 2.5 mm. When comparing gel measurements with computational results for the IMAT treatment, dose deviations were noted in the liver and right kidney, but the dose-volume constraints were met. Root-mean-square differences between both dose distributions were within 5% with spatial deviations not more than 2.5 mm. Dose fluctuations due to gantry angle discretization in the dose computation algorithm were particularly noticeable in the low-dose region.

Polymer gel dosimetry

“…Compensation of all these error contributions has resulted in far better outcomes. Further optimization of imaging sequence parameters has also aided in acquiring 3D dose distributions within a feasible time span (Vergote et al 2003, 2004a, Duthoy et al 2003, 2004, Gustavsson et al 2003, Sandilos et al 2004, Papagiannis et al 2005, Karaiskos et al 2005). An example of a large volume dose verification gel dosimetry experiment is shown in figure 24.…”

“…It was established that significant issues relating to the accuracy of this dosimetry technique were a result of oxygen inhibition in the polymer gel and MRI imaging artifacts. Authors continued to investigate clinical aspects of polymer gel dosimetry using MRI including conformal therapy, IMRT and IMAT (Cosgrove et al 2000, De Deene et al 2000c, Vergote et al 2003, Duthoy et al 2003, 2004, Love et al 2003, Vergote et al 2004a, Sandilos et al 2004), stereotactic radiosurgery (Ertl et al 2000, Grebe et al 2001, Pappas et al 2001, Audet et al 2002, Novotny et al 2002, Scheib and Gianolini 2002,Watanabe et al 2002, Papagiannis et al 2005, Karaiskos et al 2005), brachytherapy (Farajollahi et al 1999, Wuu et al 2003), low-energy x-rays (Boudou et al 2004), high-LET and proton therapy (Ramm et al 2000, Jirasek and Duzenli 2002, Heufelder et al 2003, Gustavsson et al 2004), boron capture neutron therapy (Farajollahi et al 2000, Gambarini et al 2004) and tissue inhomogeneities (Love et al 2003, Vergote et al 2003). …”

A retrospective analysis for patient-specific quality assurance of volumetric-modulated arc therapy plans

“…1 However, owing to the completely dynamic implementation and the complexity of treatment delivery, patient-specific dosimetric verifications for VMAT plans are required before clinical treatments. 8 Many types of dosimeters have been used for patientspecific quality assurance (QA), such as ion chamber, film, 9,10 2-dimensional (2D) diode or ion chamber matrix detectors, [10][11][12][13][14] electronic portal imaging devices, 15 gel dosimetry, 16 and 3D diode arrays. 17,18 3D diode arrays are easy to use and provide 3D dose distributions and QA results, while measurements are being performed.…”

Intensity-Modulated Arc Therapy with Simultaneous Integrated Boost in the Treatment of Primary Irresectable Cervical Cancer

“…Three-dimensional polymer gel dosimetry as validation method was described elsewhere [8,49]. Following the strate- gy outlined in [8] (pages 117-128 by De Wagter), further quality assurance (QA) was streamlined into patient-specific QA by delivering the clinical treatment plan to "CarPet", an anthropomorphic pelvic phantom [18], transversally loaded with one or more radiochromic energy-independent EBT films (International Specialty Products Corporation, Wayne, NJ, USA) [38] and by comparing the measured dose distributions to the ones that were computed for CarPet using the Pinnacle treatment planning system.…”