Homogeneous and heterogeneous boosting in prostate radiotherapy: Treatment planning and target dosimetry comparison

Delivering a homogeneous dominant intra-prostatic lesion (DIL) boost enables improved tumour control in prostate radiotherapy. Opportunities for further escalation of tumour control probability (TCP) may be presented by heterogeneously boosting the DIL according to the known spatially-varying characteristics of the disease.

To investigate the practical limits and robustness of treatment planning for both homogeneous and heterogeneous DIL boost.

The tumour cell distribution maps, representing voxel-wise distributions of estimated prostate tumour cell numbers, of three high-risk patients with various DIL volumes in a cohort of 63 patients were selected. Heterogeneous, structure-based prescriptions, which maximize TCP, were derived for DIL boosts for each patient. Treatment plans were generated for all patients for seven treatment modalities. The resulting homogeneous DIL boost plans and heterogeneous DIL boost plans were evaluated and compared.

In total, 42 plans were generated, including 21 plans produced for a homogeneous DIL boost and for a heterogeneous DIL boost, respectively, without violating any dose constraints. For more than 50% of heterogeneous DIL boost plans, a TCP increase could be achieved relative to plans produced for a homogeneous DIL boost. Compared to a homogeneous DIL boost, intensity modulated proton therapy (IMPT) has the potential to maximize the likelihood of effective toxicity-free treatment by implementing heterogeneous DIL boost.

Heterogeneous DIL boost implemented by structure-based prescriptions enabled higher TCP improvements for the majority of plans produced for a homogeneous DIL boost.