Analysis of relations between treatment parameters and the verification results in VMAT

Abstract

Objective: to identify the relations between treatment and verification Volumetric Arc Therapy (VMAT)  variables: accelerator, treatment area, number of volumes, delivered dose, monitor units (UM), arc geometry,  gamma index and the number of measurement points used for the verification.

Materials and methods: 308 prostate and head and neck patients have been analyzed. The treatment plan is  calculated using the Eclipse system, version 13.0 (Varian Medical Sytems, Palo alto, CA). Plans are verified with  the Sun Nuclear Archeck phantom and the SNC Patient software, version 6.6.2 (Sun Nuclear corporation,  Melbourne, FL).

Eleven variables related to the geometry and complexity and the treatment areas were analyzed. This  statistical analysis was done using the predictive analytics software PSPP, version 0.10.4-g50f7b7 (Free  Software Foundation, Boston, MA).

Results: correlations between the studied variables are obtained. The more remarkable ones are the relations  between the field modulation, the gamma index γ_{1%-1 mm} and the treatment pathology, which show up the actual relation between a decrease in the gamma index value for the highly modulated plans and increase in the treatment modulation according to the treatment pathology.

Conclusions: a correlation has been found between the treatment complexity and the dose agreement (or the planned dose and verified dose agreement). This might allow to anticipate tendencies in future verifications, being able to change the treatment plan or verification schemes depending on treatment complexity.