Tolerances for the accuracy of photon beam dose calculations of treatment planning systems

Background and purpose: To design a consistent set of criteria for acceptab ility of photon beam dose calculations of treatment planning systems. The s et should be applicable in combination with a test package used for evaluat ion of a treatment planning system, such as the ones proposed by the AAPM T ask Group 23 or by the Netherlands Commission on Radiation Dosimetry. Results: Tolerances have been defined for the accuracy with which a treatme nt planning system should be able to calculate the dose in different parts of a photon beam: the central beam axis and regions with large and small do se gradients. For increasing complexity of the geometry, wider tolerances a re allowed, varying between 2 and 5%. For the evaluation of a large number of data points an additional quantity, the confidence limit, has been intro duced, which combines the influence of systematic and random deviations. Th e proposed tolerances have been compared with other recommendations for a n umber of clinically relevant examples, showing considerable differences, wh ich are partly due to the way the complexity of the geometry is taken into account. Furthermore differences occur if criteria for acceptability of dos e calculations are related either to the local dose value or to a normalize d dose value. Conclusions: Although it is acknowledged that the general aim must be to ha ve good agreement between dose calculation and the actual dose value, e.g. within 2% or 2 mm, current day algorithms and their implementation into com mercial treatment planning systems result often in larger deviations. A hig h accuracy can at present only be achieved in relatively simple cases. The new set of tolerances and the quantity confidence limit have proven to be u seful tools for the acceptance of photon beam dose calculation algorithms o f treatment planning systems. (C) 2001 Elsevier Science Ireland Ltd. All ri ghts reserved.