Purpose: Accurate beam parameters (percent depth dose-PDD and profiles) are essential for treatment planning and dose calculations that are acquired during machine commissioning. However, these are dependent on the selection of a detector. The suitability of modern detectors for a wide range of field sizes and beam energies are investigated.
Methods: : Beam parameters are measured using IBA blue phantom scanning water tank on a Varian TrueBeam machine with 6, 10, 18MV, 6FFF and 10FFF energies for field sizes ranging from 1x1 cm² to 30x30 cm². Modern detectors such as IBA CC-01, CC-04, Scanditronix SFD, PFD, microDiamond (PTW-60017), microSilicon (PTW-60023) and Standard imaging-W2 plastic scintillator detector (PSD) were used with recommended bias (300V and 0V). IBA Stealth chamber and Scanditronix RFD were used as the reference chambers for small to intermediate and large fields, respectively. IBA CC-04 was treated as a reference detector for 5x5cm² to 30x30cm² and W2 for 1x1cm² for PDD and profile analysis and comparisons.
Results: The PDD and profiles varies significantly among the detectors, field size and beam energies. The average variation in PDD beyond buildup region, among detector was ±1%, ±2% and ±5% for 1x1cm², 10x10 cm² and 30x30 cm², respectively but nearly independent (±2%) on beam energy. The variation in profiles at 10 cm depth was ±5%, ±4.5% and ±3% for 1x1cm², 10x10cm² and 30x30cm² for 6MV and slightly larger (±1%) for 18MV but mainly in penumbral region. Differences are pronounced with beam energy and field sizes due to μen/ρ variation associated with photon spectrum.
Conclusion: Selection of detector is critical for acquiring accurate PDD and profile for various energies and field sizes. It is concluded that PSD W2 and small volume ion chamber are preferred for field sizes from 1x1-5x5cm² and 3x3-30x30cm² respectively.