Dosimetric validation of a redundant independent calculation software for VMAT fields

A redundant independent dosimetric calculation (RIDC) prior to treatment has become a basic part of the QA process for 3D conventional radiotherapy, and is strongly recommended in several international publications. On the other hand, the rapid growth in the number of intensity modulated treatments has led to a significant increase in the workflow associated with QA treatments. Diamond ("K&S Associates") is RIDC software which is capable of calculating VMAT (Volumetric Modulated Arc Therapy) fields. Modeling, validation and commissioning are necessary steps thereby making it a useful tool for VMAT QA. In this paper, a procedure for the validation of the calculation algorithm is demonstrated. A set 3D conventional field was verified in two ways: firstly, a comparison was made between Diamond calculations and experimental measures obtaining an average deviation of -0.1 ± 0.7%(1SD), and secondly, a comparison made between Diamond and the treatment planning system (TPS) Eclipse, obtaining an average deviation of 0.4 ± 0.8%(1SD). For both steps, a plastic slab phantom was used. VMAT validation was carried out by analyzing 59 VMAT plans in two ways: first, Diamond calculation versus experimental measurement with an average deviation of -0.2 ± 1.7%(1SD), and second, Diamond calculation versus TPS calculation with an average deviation of 0.0 ± 1.6%(1SD). In this phase a homogeneous cylindrical phantom was used. These results led us to consider this calculation algorithm validated for use in VMAT verifications.