Dosimetric Evaluation of PSMA PET-Delineated Dominant Intraprostatic Lesion Simultaneous Infield Boosts

Abstract

Prostate cancer is multifocal. However, there often exists a single dominant focus in the gland responsible for driving the biology of the disease. Dose escalation to the dominant lesion is a proposed strategy to increase tumor control. We applied radiobiological modeling to evaluate the dosimetric feasibility and benefit of dominant intraprostatic lesion simultaneous in-field boosts (DIL-SIB) to the gross tumor volume (GTV), defined using a novel molecular positron emission tomography (PET) probe (18F-DCFPyL) directed against prostate specific membrane antigen (PSMA). Methods and Materials: Patients with clinically localized, biopsy-proven prostate cancer underwent preoperative [ 18 F]-DCFPyL PET/computed tomography (CT). DIL-SIB plans were generated by importing the PET/CT into the RayStation treatment planning system. GTV-PET for the DIL-SIB was defined by the highest %SUVmax (percentage of maximum standardized uptake value) that generated a biologically plausible volume. Volumetric arcebased plans incorporating prostate plus DIL-SIB treatment were generated. Tumor control probability (TCP) and normal tissue complication probability (NTCP) with fractionation schemes and boost doses specified in the FLAME (Investigate the Benefit of a Focal Lesion Ablative Microboost in Prostate Cancer; NCT01168479), PROFIT (Prostate Fractionated Irradiation Trial; NCT00304759), PACE (Prostate Advances in Comparative Evidence; NCT01584258), and hypoFLAME (Hypofractionated Focal Lesion Ablative Microboost in prostatE Cancer 2.0; NCT02853110) protocols were compared. Results: Comparative DIL-SIB plans for 6 men were generated from preoperative [ 18 F]-DCFPyL PET/CT. Median boost GTV volume was 1.015 cm 3 (0.42-1.83 cm 3 ). Median minimum (D99%) DIL-SIB dose for F35 BS , F20 BS , F5 BS , and F5 BSH were 97.3 Gy, 80.8 Gy, 46.5 Gy, and 51.5Gy. TCP within the GTV ranged from 84% to 88% for the standard plan and 95% to 96% for the DIL-SIB plans. Within the rest of the prostate, TCP ranged from 89% to 91% for the standard plans and 90% to 92% for the DIL-SIB plans. NTCP for the rectum NTCP was similar for the DIL-SIB plans (0.3%-2.7%) compared with standard plans (0.7%-2.6%). Overall, DIL-SIB plans yielded higher uncomplicated TCP (NTCP, 90%-94%) versus standard plans (NTCP, 83%-85%). Conclusions: PSMA PET provides a novel approach to define GTV for SIB-DIL dose escalation. Work is ongoing to validate PSMA PET-delineated GTV through correlation to coregistered postprostatectomy digitized histopathology.

Automated Planning for Prostate Stereotactic Body Radiation Therapy on the 1.5 T MR-Linac

“…Autoplanning is a current hot topic of development to reduce interplanner variability while generally improving plan quality. 3 For PC-SBRT, the feasibility of autoplanning for even complex techniques as simultaneous integrated boost to the dominant intraprostatic lesion has been reported 20 , and as shown in Figure 2S Fig. 1 Box-and-whisker plots of the metrics computed from the 50 manual plans (left) and mCycle plans (right).…”

Value of 18F-fluorocholine PET/CT in predicting response to radical radiotherapy in patients with localized prostate cancer

“…They found that the mean dose to the tumor tissue – defined as the pathological volume established from the 68 Ga-PSMA positive volumes – can be increased significantly without any significant increase in the mean dose to rectum and bladder. In 6 patients who underwent 18F-DCFPyL PET/CT, Goodman et al [37] likewise found that PSMA PET can be used as a novel approach to defining the gross tumor volumes for the purposes of dominant intraprostatic lesion simultaneous in-field boost (DIL-SIB) dose escalation. No data on the effect of PSMA PET on patient prognosis in this setting have become available as yet, however.…”

Comparison of Manual and Semi-Automatic [18F]PSMA-1007 PET Based Contouring Techniques for Intraprostatic Tumor Delineation in Patients With Primary Prostate Cancer and Validation With Histopathology as Standard of Reference

“…In case intraprostatic SUVmax is close to the applied SUVmax for manual scaling, adjustment of the range, for instance SUVmin-max 0–5, might be considered as an appropriate alternative. Our results suggest, that the use [ 18 F]PSMA-1007 for contouring of lesions for focal therapy planning is likely to be as effective as other tracers, who’s performance was evaluated in radiotherapy planning studies and showed promising results in terms of tumor control and normal tissue toxicities ( 14 , 32 ).…”