Evaluation of the Delta⁴phantom for IMRT and VMAT verification

TLDR

The IMRT and VMAT plans were calculated with Pinnacle3, and the Delta4 phantom— a complex device requiring careful benchmarking—has been introduced into clinical use after successful measurements. The Delta4 diode array phantom was evaluated on an Elekta linear accelerator by testing angular sensitivity across 36 gantry angles, measuring responses to step‑and‑shoot segment doses and dose rates with an ionization chamber, and comparing its results to ion chamber and film for prostate, pelvic, head‑and‑neck, and lung IMRT/VMAT plans. The Delta4 phantom exhibited angular and dose‑rate uniformity better than 0.5 %, measured IMRT/VMAT doses within 2.5 % of an ionization chamber, agreed with film within 3 % and 3 mm over a −2 % to +7 % range, and its successful benchmarking led to clinical implementation.

Abstract

The Delta4 diode array phantom (Scandidos, Uppsala, Sweden) was evaluated for verification of segmental intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) on an Elekta linear accelerator (Crawley UK). The device was tested for angular sensitivity by irradiating it from 36 different gantry angles, and the responses of the device to various step-and-shoot segment doses and dose rates were evaluated using an ionization chamber as a comparison. The phantom was then compared with ionization chamber and film results for two prostate and pelvic nodes IMRT plans, two head and neck IMRT plans and two lung VMAT plans. These plans were calculated using Pinnacle3 (Philips Radiation Oncology Systems, Madison, WI). The uniformity of angular response was better than 0.5% over the range of gantry angles. The uniformity of response of the Delta4 to different segment monitor units and dose rates was better than 0.5%. The assessment of the IMRT and VMAT plans showed that the Delta4 measured a dose within 2.5% of the ionization chamber, and compared to film recorded a slightly larger region (range −2% to +7%) agreeing with the planned dose to within 3% and 3 mm. The Delta4 is a complex device and requires careful benchmarking, but following the successful completion of these measurements, the Delta4 has been introduced into clinical use.