Stereotactic ablative radiotherapy with targeted MRI-defined gross tumor dose escalation for prostate cancer: dosimetric feasibility and interfraction robustness

Abstract

Objectives

The purpose of this study was to determine the dosimetric feasibility and reproducibility of stereotactic body radiotherapy (SBRT) with selective dose escalation for gross tumor volume (GTV) in prostate cancer.

Methods

Radiotherapy plans of previously treated patients with dose-escalated radiotherapy multiparametric MRI (mpMRI)-defined prostate and GTV were retrieved. Margins were re-created for prostate planning target volume (PTV) (PTV_36.25) and GTV-PTV (PTV₄₅), and two five-fraction SBRT VMAT plans were generated: (1) standard plan ([Sp], 36.25Gy/5Fx; V36.25 Gy-PTV_36.25 ≥95% and V40 Gy-prostate ≥95%) and (2) dose-escalated plan [DEp] with additional goal V45 Gy-PTV₄₅ ≥95%, while the same organs-at-risk (OAR) constraints. Delivered doses to targets and OAR were calculated from alternate days deformably registered cone beam computed tomography.

Results

In 23 patients (single GTV), all planned and delivered doses to targets and OAR in both Sp and DEp were within the ideal/acceptable criteria. No difference (p > 0.05) was observed in the proportion of Sp and DEp patients achieving ideal criteria either in planned or delivered doses except for prostatic urethra constraint. Differences between planned and delivered doses in DEp were not clinically relevant (i.e., mean differences lesser than 1 Gy).

Conclusion

Selective high-precision (i.e., mpMRI-defined targets, daily volumetric image guidance, intraprostatic fiducials) SBRT with GTV dose escalation seems feasible, without incremental dose to OAR. Prospective studies to determine its clinical benefit are warranted.

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