Evaluation of the ability of a 2D ionisation chamber array and an EPID to detect systematic delivery errors in IMRT plans

Two clinical intensity modulated radiotherapy plans were selected. Eleven plan variations were created with systematic errors introduced: Multi-Leaf Collimator (MLC) positional errors with all leaf pairs shifted in the same or the opposite direction, and collimator rotation offsets. Plans were measured using an Electronic Portal Imaging Device (EPID) and an ionisation chamber array. The plans were evaluated using gamma analysis with different criteria. The gamma pass rates remained around 95% or higher for most cases with MLC positional errors of 1 mm and 2 mm with 3%/3mm criteria. The ability of both devices to detect delivery errors was similar

Evaluation of the ability of three commercially available dosimeters to detect systematic delivery errors in Step-and-Shoot IMRT plans

Background: There is limited data on error detectability for step-and-shoot intensity modulated radiotherapy (sIMRT) plans, despite significant work on dynamic methods. However, sIMRT treatments have an ongoing role in clinical practice. This study aimed to evaluate variations in the sensitivity of three patient-specific quality assurance (QA) devices to systematic delivery errors in sIMRT plans. Materials and methods: Four clinical sIMRT plans (prostate and head and neck) were edited to introduce errors in: Multi-Leaf Collimator (MLC) position (increasing field size, leaf pairs offset (1–3 mm) in opposite directions; and field shift, all leaves offset (1–3 mm) in one direction); collimator rotation (1–3 degrees) and gantry rotation (0.5–2 degrees). The total dose for each plan was measured using an ArcCHECK diode array. Each field, excluding those with gantry offsets, was also measured using an Electronic Portal Imager and a MatriXX Evolution 2D ionisation chamber array. 132 plans (858 fields) were delivered, producing 572 measured dose distributions. Measured doses were compared to calculated doses for the no-error plan using Gamma analysis with 3%/3 mm, 3%/2 mm, and 2%/2 mm criteria (1716 analyses). Results: Generally, pass rates decreased with increasing errors and/or stricter gamma criteria. Pass rate variations with detector and plan type were also observed. For a 3%/3 mm gamma criteria, none of the devices could reliably detect 1 mm MLC position errors or 1 degree collimator rotation errors.  Conclusions: This work has highlighted the need to adapt QA based on treatment plan type and the need for detector specific assessment criteria to detect clinically significant errors

Evaluation of the ability of a 2D ionisation chamber array and an EPID to detect systematic delivery errors in IMRT plans

Two clinical intensity modulated radiotherapy plans were selected. Eleven plan variations were created with systematic errors introduced: Multi-Leaf Collimator (MLC) positional errors with all leaf pairs shifted in the same or the opposite direction, and collimator rotation offsets. Plans were measured using an Electronic Portal Imaging Device (EPID) and an ionisation chamber array. The plans were evaluated using gamma analysis with different criteria. The gamma pass rates remained around 95% or higher for most cases with MLC positional errors of 1 mm and 2 mm with 3%/3mm criteria. The ability of both devices to detect delivery errors was similar

Investigation of barium sulphate shielding during panoramic radiography

Abstract Background Radiation shielding in radiology has historically been achieved with lead; however, there has been an increasing demand for radiation shielding to be more environmentally friendly. Barium has shown promise as a substitute in many radiology applications. This study aims to investigate a barium sulphate shield in protecting the thyroid and the eye lens during panoramic radiography. Methods During a simulated panoramic examination, an anthropomorphic phantom and a solid-state detector measured the radiation dose to the surface thyroid and the eye lens. The measurements were taken using no shield and a barium sulphate shield. A Welch's T-test was employed to compute the shield's effect on radiation. Two radiologists assessed the image quality with and without the thyroid shields. Results The dose reduction was between 66 and 75% for the barium shield at the thyroid. The dose reduction ranged between 15 and 61% in the eye region. Images using a barium shield were deemed adequate for diagnostic interpretation. Conclusions Barium shields effectively reduce the radiation dose in the thyroid region during panoramic radiography without degrading image quality. The dose reduction depends on the tube voltage and the area of interest