EP-1211: Pitfalls in the clinical introduction of the Elekta Agility MLC

R.G.H. van Leeuwen, J.M.A.M. Kusters, D. Martens, R. Monshouwer
2013 Radiotherapy and Oncology  
2nd ESTRO Forum 2013 S455 Conclusions: The source path for ring applicators is dependent on the geometry of the ring. The geometry of the ring causes the source cable to travel along a characteristic path that is different compared to the path of the source and has the effect of introducing significant deviation of the source from its expected position in the lumen along its direction of motion. The observation of significant differences between sets of Ø26 mm ring applicators has shown that,
more » ... some cases, multiple sets of the same applicator size can not be characterized by a single source path. Consequently, care must be taken to ensure that the source path of each ring is measured first. Purpose/Objective: Whilst CP is used in routine clinical practice for DQA purposes prior to HT treatment, practicalities could necessitate the use of OP as a backup measure. This study investigates the validation of OP octagonal QA tool (vol 0.125cc) in contrast to the circular CP (0.057cc). Materials and Methods: Treatment plans of 10 patients were selected and a homogenous high dose PTV area was selected for DQA. The images of Phantoms inserted with the ionisation chambers was imported from the CT scan to theTomotherapy Treatment Planning System (TPS); following which recalculation of the clinical plan was done with the above phantoms for verification purposes. Results of the DQA using the two processes were compared. Results: The standard deviation of the measured doses of A1SL Chamber with cheese Phantom with the TPS calculated dose was 1.24 versus semiflex Chamber with Ocatavius Phantom was 0.979. For Fluence map comparison using Octavius phantom, significant adjustments were made to the beam profile measured by 729 2-d array; but after shifting the coordinates a match was achieved to the TPS calculated fluence. Conclusions: The Deviation of the Point Dose measurements of DQA inTomotherapy with A1SL chamber Cheese Phantom) and semiflex chamber (Ocatavius Phantom) was within the accepted 1.24 and 0.979 were within tolerance limit (3%). Hence the point dose measurement of DQA plan in tomotherapy can be done with the semiflex ion chamber along with the octavius phantom. 2d array was also possible using a manual adjustment to the fluence coordinates using Octavius phantom. Octavius phantom could therefore be used for DQA of HT plans.
doi:10.1016/s0167-8140(15)33517-9 fatcat:bfiqsjc34vdl3baseoleoek5gm