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SU‐GG‐T‐219: Monitoring and Quality Assurance of the Tomotherapy Hi‐Art Using the Build‐in MVCT Detector
Author(s) -
Althof V,
Kramer D,
Westendorp H,
Wispelweij M,
Haaren P van,
Minken A
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2961971
Subject(s) - tomotherapy , quality assurance , detector , imaging phantom , dosimetry , nuclear medicine , energy (signal processing) , physics , computer science , medical physics , optics , radiation therapy , medicine , external quality assessment , pathology , quantum mechanics
Purpose: Monitoring the Helical Tomotherapy (HT) machine using the signals from the systems' built‐in Megavoltage CT‐detector (MVCT), leading to a filmless Quality Assurance (QA) program. Method and Materials: Four monitoring tools are developed in the RISO which are in use for both HT machines, since May 2007: ‐‘Tomo Output’ for daily measurement of output and energy. ‐‘Tomo Scope’ provides a 30 Hz graphical presentation of the operational state of the machine, while radiating. ‐‘Tomo Physics’ provides both a pulse‐by‐pulse analysis and a trend‐analysis of the transversal profile and of 18 different machine parameters and combinations from that. ‐‘Tomo QA’ automates QA, using an Al‐stepwedge phantom. Results: A number of parameters are monitored daily, like water‐flows, air‐pressure, water‐temperature, CT‐channels and monitor‐chambers. The transversal profile is tuned within typically 2%. Drift indicates target degradation. Output shows a variation of 0.8%. Drift in dose rate is 0.9%/200sec for one HT and 0.3%/200sec for the other. Geometric stability as function of gantry position is excellent: top‐top 0.5 CT‐channel. The QA tool results (sept'07–feb.'08): The longitudinal profile FWHM 10mm varies 0.05mm (1σ). Energy varies 0.2% (1σ). Synchronization of MLC‐gantry varies 0.2deg (1σ). Couch speed varies 0.2% (1σ). A restarted procedure should closely align the interrupted one. Small mismatches of 0.2 mm are measured (1σ). Stability of the sagittal and transversal lasers is good (σ=0.4mm). Conclusions: The monitoring tools have increased our understanding of the behaviour of this emerging treatment modality. The QA tool is time efficient because the analysis is filmless and addresses several items simultaneous. We aim to run the procedure on a daily basis. A new QA program is implemented based on these tools and experiences. This program is in use since September 2007. Future functionality will incorporate gantry behaviour and MLC dynamics.