SU‐GG‐T‐306: Can Single Dataset in Treatment Planning System Represent Several Beam‐Matched Accelerators?

Abstract

Purpose: Beam matched accelerators can provide the flexibility within the radiotherapy department. Furthermore, the accelerators could be represented by single beam data set in the treatment planning system (TPS). The aim of this study was to evaluate the match between dosimetrical characteristics of Elekta accelerators. Method and Materials: The data from three accelerators was used in analysis. Three photon and six electron beams were matched according to the vendor specification. The first accelerator data served as reference. Subset of commissioning measurements for second and third accelerators was performed. The comparison was done in absolute terms, i.e. that PDDs and profiles were used with corresponding accelerator output factors. Results: The average difference between the sets of open field PDDs was −0.7%, −0.1% and −0.1% for 6, 10 and 15MV, respectively. Difference up to −2.2% was observed for 60° motorized wedge PDDs. Aligned profiles showed good agreement, with differences generally less than 1% at dmax and 10 cm for field sizes up to 30×30 cm2. For 40×40 cm2 diagonal profiles at dmax the maximum differences of 2.4% was observed. The difference of up to 4.5% between output factors for small fields have been observed which may result in larger discrepancies in IMRT fields. Conclusion: Beam match for photon beams showed a satisfactory agreement for open fields and support the use of a single data set for TPS. However, vendor's beam matching criteria is not strict enough and better beam matching could be achieved if instead of single value the subset of dosimetrical data is used together with corresponding output factors for both open and wedged fields. Although, scanned data for electron beams showed good agreement larger differences (up to 5%) in electron cone output factors does not support the use of a single dataset in TPS.

Golden beam data provided by linear accelerator manufacturers should be used in the commissioning of treatment planning systems

“…It is not enough to rely only on the vendor beam-matching criteria, and very strict criteria needs to be implemented to obtain a satisfactory match. This has been shown by several authors [ 15 – 17 ].…”

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study

“…For a department that wishes to beam match their linear accelerator fleet to a degree beyond VMAT that allows for distributive QA and delivery of SBRT, the following items are recommended: Profiles and PDDs should be matched to criteria that is stricter than vendor guidelines . For example, the linacs in this study were matched at commissioning with PDD 20,10 matching <0.5% and all points in the PDD within 0.5% of the reference curve.…”

“…The study showed that matching a new linac to a reference linac does not guarantee that it is matched to the established treatment planning model. Similarly, Gersgjevitsh et al . demonstrated that a single TPS model could not be supported by their three Elekta linacs which were matched according to the vendor's beam matching criteria, calling for stricter criteria and an additional subset of dosimetric data to be matched to if a single model was to be used.…”

Delivery accuracy of VMAT on two beam‐matched linacs provided by accelerated go live service

“…It was reported that the gamma analysis with vendor‐provided criteria were insufficient for the purpose of beam matching, and stricter gamma criteria were recommended. 4 , 6 , 7 , 8 To ensure clinically sufficient beam matching, it was insisted that the beam data of each linac should not be matched to that of the reference linac, but the TPS calculation should be used as the reference. 4 Furthermore, it was recommended that the calculation by TPS beam model may be employed as the reference.…”