Development of a treatment planning protocol for the multi-centre reirradiation CURE Lung trial.

[INTRODUCTION] High-dose lung cancer reirradiation is promising but associated with high toxicity risk. Development of and adherence to consensus guidelines will support safe use.

[MATERIALS AND METHODS] Literature review and live workshops were conducted to develop treatment planning guidelines in preparation for the Scandinavian CURE Lung trial. Relevant OARs, dose metrics, constraints, and priorities were considered. For six high-dose reirradiation lung cancer cases, the physical 3D dose distribution of previous treatment was mapped to current CT. The cases were distributed to eight radiotherapy centres, which optimised plans on current CT respecting equieffective cumulative dose constraints. Mapped previous dose and current dose were rescaled to EQD2Gy (α/β = 3 Gy, spinal cord: α/β = 2 Gy), summed by each centre, and reviewed centrally. After cases 1-4 were completed, prioritisation between OAR constraints and target coverage was clarified.

[RESULTS] Consensus agreement on guidelines for treatment planning, equieffective cumulative dose constraints, and priorities was established. For cases 1-3, centres complied with constraints. For case 4, covering PTV while respecting OAR constraints was difficult, and major variations were identified, underscoring the need for clearer prioritisation guidance. Consensus was reached to prioritise OAR constraints, and centres re-optimised case 4 accordingly. For cases 5 and 6, all centres underdosed PTV, to comply with OAR constraints. Generally, considerable variation in cumulative OAR doses was observed.

[CONCLUSIONS] A treatment planning protocol was developed. The pre-trial multi-centre treatment planning study identified and resolved key missing guidance to facilitate common conception of consensus guidelines. Feasibility and compliance with the proposed equieffective cumulative dose constraints were established.