The implementation of an advanced treatment planning algorithm in the treatment of lung cancer with conventional radiotherapy

Recent improvements in planning systems have made use of sophisticated dose calculation algorithms such as collapsed cone, a realistic possibility for routine lung radiotherapy treatment planning. However, it is more difficult to achieve ICRU 50/62 compliant plans (i.e. a minimum of 95% of the prescribed dose to the planning target volume) with the collapsed cone algorithm, due to the more accurate modelling of dose in heterogeneous media. The aim of this study was to determine planning guidance for the implementation of the collapsed cone algorithm for conventional radiotherapy treatment planning.

Ten pencil beam lung plans were recalculated using the collapsed cone algorithm. Then, beam weights were optimised on the recalculated collapsed cone plan, without altering field sizes. Finally, both field sizes and beam weights were optimised on the same plan in an attempt to deliver a minimum of either 90 or 95% of the prescribed dose to the planning target volume. Thus, four sets of plans were available for comparison.

Compared with pencil beam plans recalculated with the collapsed cone algorithm, all collapsed cone plans had improved dose coverage of the planning target volume. For two of the beam weight optimised plans, less than 80% of the planning target volume received 90% of the prescribed dose. For the field size, beam weight optimised plans, nearly 100% of the planning target volume attained 90% of the prescribed dose, with the clinical target volume generally reaching 95%. Compared with the original pencil beam plans, the volume of lung receiving greater than 20 Gy (V(20)) increased by 3.1 and 6.8%, respectively, for those plans optimised to deliver a minimum of 90 or 95% of the prescribed dose to the planning target volume.

We suggest that the collapsed cone algorithm might reasonably be implemented for conventional radiotherapy treatment planning with the aim of delivering a minimum of 90% of the prescribed dose to the planning target volume and 95% of the prescribed dose to the clinical target volume. This guidance offers consistent prescription of dose to target volumes.