SU-E-T-534: Beam and MLC Commissioning and Assessment of Three Commercial Treatment Planning Systems

Abstract

Purpose: To assess and compare the open beam and multi-leaf collimator modeling of Pinnacle, Ecilpse (AAA and Acuros) and RayStation planning systems.

Method and materials: The 6MV photon beam of a Varian TrueBeam with Millennium 120 MLC was used for this study. Measurements made with combinations of ion chamber, radiochromic film, and diodes in water and plastic phantoms. Depth and crossplane profiles of open square fields shaped by jaws or MLC ranged from 3×3 to 40×40cm² and from 0 to 20 cm depth. Depth dose, flatness (80% of FWHM), and penumbra (20-80%) of calculated and measured profiles were compared. Various MLC test patterns were calculated and compared with measurements to assess the modeling of the round leaf edge, tongue-and-groove, and interleaf transmissions.

Results: Calculated depth doses are within 1.0% and flatness is within 2% for all field sizes and depths. Jaw penumbrae are within 2mm and 3mm for 20×20 and 30×30cm² at 10cm depth respectively. MLC penumbrae (20-80%) of the three systems are within 0.3mm and 1.0mm for a 3×3cm² and 10×10cm² MLC apertures. Notably, to match the measured MLC round-edge transmission, the half thickness (10% transmission) leaf-tip width of the current RayStation MLC model has to be broadened to 10mm. All three systems appear to adequately model the tongue-and-groove. Pinnacle explicitly models the interleaf transmission while Eclipse and RayStation simply use average MLC transmission.

Conclusions: All three systems are capable of generating clinically acceptable beam models for open fields. Based upon the round-edge profile, Eclipse and Pinnacle provide better MLC models than RayStation. Among the three systems, Eclipse took the least time and effort to commission these features.

Keywords: Collimators; Electric measurements; Field size; Ionization chambers; Medical treatment planning; Multileaf collimators; Photons; Transmission measurement.