Histopathology-derived modeling of prostate cancer tumor control probability: Implications for the dose to the tumor and the gland

Purpose: To evaluate the impact of GTV-CTV dose differentiation by simulating response of prostate patients to radiotherapy, considering histopathology of prostatectomy specimens.

Material and methods: Tumors' cell numbers (N0) and Gleason Scores (GS) were derived from histopathology of 25 specimens. Index lesions and tumors ⩾0.5cm(3) were considered GTV. Satellites <0.5cm(3) constituted the tumor load in the CTV. Each patient's tumor control probability (TCP) was simulated using the linear quadratic model and considering the N0 while assuming either a constant or GS-dependent α and β.

Results: 19/25 patients had multi-focal disease. In 11 patients the CTV contained GS 4+3 or 4+4 tumors. Compared to the GTV, the CTV pathology was more favorable. For an α=0.140Gy(-1), a GTV dose of 79Gy with a CTV dose of 72Gy achieved an 80% TCP in the population. Varying α between 0.160-0.118Gy(-1) with GS, a GTV and CTV dose of 80Gy and 70Gy also gave an 80% TCP.

Conclusions: Considering only N0, our simulations suggest that a GTV-CTV dose differentiation of 7Gy would not compromise TCP of the patient population. When assuming an increased radiosensitivity with lower GS, a further dose differentiation of 10Gy might be feasible.