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

Abstract

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 ⩾0.5 cm³ were considered GTV. Satellites <0.5 cm³ 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 = 0.140 Gy⁻¹, a GTV dose of 79 Gy with a CTV dose of 72 Gy achieved an 80% TCP in the population. Varying α between 0.160–0.118 Gy⁻¹ with GS, a GTV and CTV dose of 80 Gy and 70 Gy also gave an 80% TCP.

Conclusions

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