title: An evaluation of the TSE MR sequence for time efficient data acquisition in polymer gel dosimetry of applications involving high doses and steep dose gradients.
abstract: The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to the established Carr-Purcell-Meiboom-Gill (CPMG) multiecho acquisition with regard to providing accurate dosimetric results in significantly reduced imaging times. Polyethylene glycol diacrylate based (PABIG) gels were irradiated and subsequently scanned to obtain R2 relaxation rate measurements, using a CPMG multiecho sequence and a dual echo TSE utilizing an acceleration (turbo) factor of 64. R2 values, plotted against corresponding Monte Carlo dose calculations, provided calibration data of PABIG gels dose response over a wide dose range. A linear R2 versus dose relationship was demonstrated for both sequences with TSE results presenting reduced dose sensitivity. Although TSE data were found to deviate from linearity at lower doses compared to CPMG data, a relatively wide dynamic dose range of response extending up to approximately 100 Gy was observed for both sequences. The TSE and CPMG sequences were evaluated with a brachytherapy irradiation using a high dose rate 192Ir source and a gamma knife stereotactic radiosurgery irradiation with a single 4 mm collimator helmet shot. Dosimetric results obtained with the TSE and CPMG are shown to compare equally well with the expected dose distributions for these irradiations. The 60-fold scan time reduction achieved with TSE implies that this sequence could prove to be a useful tool for the introduction of polymer gel dosimetry in clinical radiation therapy applications involving high doses and steep dose gradients.
authors.affiliation: Philips Hellas Medical Systems, 44 Kifissias Ave., Maroussi 151 25, Athens, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Baras
authors.forename: I
authors.initials: I
authors.lastname: Seimenis
authors.forename: P
authors.initials: P
authors.lastname: Sandilos
authors.forename: L
authors.initials: L
authors.lastname: Vlahos
authors.forename: T
authors.initials: T
authors.lastname: Bieganski
authors.forename: E
authors.initials: E
authors.lastname: Georgiou
authors.forename: E
authors.initials: E
authors.lastname: Pantelis
authors.forename: P
authors.initials: P
authors.lastname: Papagiannis
authors.forename: L
authors.initials: L
authors.lastname: Sakelliou
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D002138:Calibration; D004307:Dose-Response Relationship, Radiation; D005069:Evaluation Studies as Topic; D005782:Gels / Q000737:chemistry*; D007496:Iridium Radioisotopes; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013997:Time Factors
chemical_list: D005782:Gels; D007496:Iridium Radioisotopes; D011108:Polymers; D011092:Polyethylene Glycols