Effect of selection of statistical uncertainty of control points in Monaco planning system on dose calculation in nasopharyngeal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective:To explore the influence of the selection of statistical uncertainty of control points in Monaco planning system on the dose distribution of nasopharyngeal carcinoma (NPC), aiming to provide the statistical uncertainty of single control point in Monte Carlo calculation which satisfies clinical needs.Methods:First, nine 10 cm×10 cm square fields with an equal interval of gantry angle were designed and five cases of 9-field intensity-modulated radiotherapy (IMRT) and five cases of single-arc volumetric-modulated arc therapy (VMAT) plans were randomly selected, Then, quality assurance (QA) verification plan using patient CT as QA phantom was created. Second, the grid spacing was selected as 3 mm during the calculation of dose distribution of QA plan. The statistical uncertainties of single control point were selected as 1%, 2%, 3%, 4% and 5%, respectively. Last, the deviation of dose distribution between different statistical uncertainties and 1% statistical uncertainty was analyzed.Results:For a square field and single IMRT field, the dose deviation of center point was almost 7% while the statistical uncertainty was selected 4%. For 9-field IMRT and single-arc VMAT, the dose deviation of center point was ≤ 1.5% and the average dose deviation of PTV was ≤ 0.3% when the statistical uncertainty of control points was changed from 1% to 5%. The percentage of the point dose deviation of the coronary plane of ≤ 1% was greater than 99% when the statistical uncertainty was ≤ 3% for 9-filed IMRT and 4% for single-arc VMAT.Conclusions:For the Monaco treatment planning system based on Monte Carlo calculation, the changes in the statistical uncertainty of control point from 1% to 5% exert significant effect upon the single field. In clinical application, the statistical uncertainty of control point should be ≤ 3% for 9-field IMRT and ≤ 4% for single-arc VMAT.