The beam and performance characteristics of a new orthovoltage X-ray unit, the Pantak DXT-300 have been evaluated. Data were collated for four qualities: 3.27 mmAl, 7.15 mmAl, 1.65 mmCu and 3.51 mmCu half value layer (HVL) (SE = 0.04 mm). Parameters which were investigated included beam quality, central axis depth dose, relative output, backscatter factors, field uniformity, peripheral dose and head leakage. The calibration procedure and the performance of the dosimetry system have also been described.

Radiotherapy treatments are becoming more complex, often requiring the dose to be calculated in three dimensions and sometimes involving the application of non-coplanar beams. The ability of treatment planning systems to accurately calculate dose under a range of these and other irradiation conditions requires evaluation. Practical assessment of such arrangements can be problematical, especially when a heterogeneous medium is used. This work describes the use of Monte Carlo computation as a benchmarking tool to assess the dose distribution of external photon beam plans obtained in a simple heterogeneous phantom by several commercially available 3D and 2D treatment planning system algorithms. For comparison, practical measurements were undertaken using film dosimetry. The dose distributions were calculated for a variety of irradiation conditions designed to show the effects of surface obliquity, inhomogeneities and missing tissue above tangential beams. The results show maximum dose differences of 47% between some planning algorithms and film at a point 1 mm below a tangentially irradiated surface. Overall, the dose distribution obtained from film was most faithfully reproduced by the Monte Carlo N-Particle results illustrating the potential of Monte Carlo computation in evaluating treatment planning system algorithms.

For a linear accelerator the direction and orientation of a beam is specified uniquely by a set of gantry, turntable and collimator angles. Sometimes, particularly for 3D planning, it is very difficult for the planner or plan checker to visualize the set-up of the treatment machine from the angles specified for each beam. This note describes a simple line-of-sight model that can be used for planning and checking the radiotherapy geometry prior to simulator verification.

This note describes the design of a multiblock semi-anatomic phantom, which lends itself to a variety of radiotherapy dosimetry applications, in particular, the audit of external beam treatment planning and delivery. The basic building blocks of the phantom were formed from a variety of tissue substitute materials and could be assembled in many ways to model different cross-sections through the body.

This technical note describes a hinged lead alloy shielding block that could be used, in certain circumstances, for shaping a megavoltage X-ray field. The construction of the shield is described and the results of transmission and penumbra measurements are given.