Treatment planningClinical implications of the anisotropic analytical algorithm for IMRT treatment planning and verification
Section snippets
Treatment planning
Twenty prostate treatment plans were produced, using a fixed beam arrangement with fields at gantry angles 180°, 100°, 45°, 315° and 260° (IEC1217). The prescribed dose was 60 Gy in 20 fractions. The organs at risk (OARs) considered in the inverse planning process were the rectum, the bladder and the femoral heads. The tolerance doses were for no more than 50% of the bladder or rectum to receive 57 Gy and no more than 2.0 cm3 of the femoral heads to receive 55 Gy.
Eighteen head and neck plans were
Treatment planning
Example DVHs for a prostate plan, a nasopharynx plan and a lung plan are shown in Fig. 1. The results of the comparison of the IMRT treatment plans as calculated by the two algorithms are shown in Table 1.
In the prostate plans, the AAA predicted lower doses than the PBC algorithm, including slightly lower coverage by the 95% isodose. However, of those differences that were statistically significant, only the reduction of 0.6% in the minimum PTV dose was of any clinical significance. A similar
Discussion
If the AAA is taken to provide a more accurate representation of the dose distribution from a given treatment, the comparisons between the AAA and PBC dose distributions in Table 1 provide an indication of the difference between the dose predicted by the PBC algorithm and that actually delivered.
In the prostate plans, the distributions were found to be very similar, with no differences between the OAR doses that were considered clinically significant. In all but three patients, the AAA
Conclusions
The AAA was, in general, not found to significantly alter the quality of IMRT treatment plans for the prostate, parotid or nasopharynx compared to the PBC algorithm. However, some small differences were seen and the importance of evaluating treatment plans on an individual basis cannot be overemphasised. The PBC algorithm overestimated the PTV coverage in IMRT plans for NSCLC, the AAA’s more accurate modelling of lateral electron transport demonstrating significant increases in the volume of
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