This work reports on some of the initial tests that were conducted during the commissioning of a commercially available 3D treatment planning system. The system (Pinnacle 3.0d-u1) uses a collapsed cone implementation of the superposition convolution algorithm. Calculated and measured dose in homogeneous media were compared for wedged and unwedged fields for both symmetric and asymmetric collimator settings. Results show agreement of 2% or 2 mm in most cases. Where larger differences were found, further investigation was undertaken to explain these differences. These tests demonstrate the correct behaviour of the collapsed cone implementation of the algorithm in homogeneous media and its ability to characterize the beam.

In intensity modulated radiotherapy (IMRT), the use of small fields where electronic equilibrium does not exist is becoming more common and presents difficulties for both the measurement and calculation of dose to such fields. Pinnacle(3) (Version 6.2b) allows the user to specify a total minimum open area for each IMRT segment, which can result in sub-segments with widths of only a few millimetres. The dose for 6 MV narrow MLC defined fields between 0.1 and 3 cm in width was investigated using Kodak extended dose range film (EDR2), ionization chamber and MOSFET dosimeters and BEAMnrc Monte Carlo calculations, and these results were used to determine the accuracy of Pinnacle(3) dose calculation for narrow MLC segments. The incident fluences calculated by Pinnacle(3) and BEAMnrc were also compared. Results show that if a fluence and dose grid resolution of 0.1 cm is used, Pinnacle(3) dose agrees with the EDR2 and BEAMnrc to within 5% for field widths between 0.5 and 3.0 cm. However, Pinnacle(3) will underestimate the dose by up to 45% for the 0.1 and 0.3 cm wide fields. It is shown that the source size in the Pinnacle(3) beam model and both the fluence and dose grid resolutions have a significant effect on the accuracy of dose calculation for field widths of 1.0 cm and less. For single segment fields, Pinnacle(3) agrees with EDR2 and BEAMnrc to within 0.1 cm at the field edges and underestimates the penumbra width by up to 0.08 cm. Results for multiple segment fields showed that an MLC transmission of 1.7% and a 0.06 cm inward shift of MLCs prior to beam delivery gave the closest agreement between Pinnacle(3) and measurement. The multiple segment fields also revealed a pattern of low dose troughs of up to 7% in the Pinnacle(3) dose profiles.

One feature of the dynamic wedge is the improved flatness of the beam profile in the nonwedged direction when compared to fixed wedges. Profiles in the nonwedged direction for fixed wedges show a fall-off in dose away from the central axis when compared to the open field profile. This study will show that there is no significant difference between open field profiles and nonwedged direction profiles for dynamically wedged beams. The implications are that the dynamic wedge offers an improved dose distribution in the nonwedged direction that can be modelled by approximating the dynamically wedged field to an open field. This is possible as both the profiles and depth doses of the dynamically wedged fields match those of the open fields, if normalized to dmax of the same field size. For treatment planning purposes the effective wedge factor (EWF) provides a normalization factor for the open field depth dose data set. Data will be presented to demonstrate that the EWF shows relatively little variation with depth and can be treated as being independent of field size in the nonwedged direction.

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Purpose: To investigate the suitability of synthetic diamond films as detectors for radiotherapy dosimetry. Method and Materials: A range of commercially available diamond films grown by chemical vapor deposition (CVD) have been studied using spectroscopic, microscopic and electrical characterization techniques, including Raman spectroscopy, optical, secondary electron, and atomic force microscopy. Diamond detectors incorporating Perspex have been fabricated in order to examine various response characteristics, especially transient behavior and priming effects, due to material defects, interface phenomena, etc. Initial dosimetric characterization was performed using a 6 MV photon beam from a Varian 600C linac. Measurements were achieved using a 2570/1 Farmer Dosimeter and a Keithley 6430 SourceMeter. EGSnrc code was used to model simple device structures to assess performance issues that may impede proper measurements e.g. sources of fluence perturbation, absorbed dose distribution, and charge collection efficiency. Results: I–V measurements of polycrystalline diamond films with Ag contacts tested under a ±210 V bias sweep exhibited nonlinear behavior as expected. High leakage currents were a problem for some detectors. Resistivity measurements at 100 V from one manufacturer of films spanned from 1011 to 1012 Ω⋅cm. Dependence on fluence and fluence rates between 50 – 250 MU/min was observed. However, angular dependence appeared to be negligible. Overshoot was also seen during initial exposure, as well as the well‐known priming effect as the signal evolved over time. EGSnrc models have illustrated how electrode thickness alters the dose delivered to the sensitive volume. Conclusion: Experiments will continue to explore the response phenomena of CVD diamond films to evaluate their suitability as detectors for medical applications. The films studied thus far have exhibited typical behavior as seen in previous literature. A thorough characterization of a variety of CVD films and their consequential responses is underway in order to mitigate or ideally eliminate inherent shortcomings.