Volumetric Modulated Arc Therapy Planning for Primary Prostate Cancer With Selective Intraprostatic Boost Determined by ¹⁸F-Choline PET/CT

Purpose: This study evaluated expected tumor control and normal tissue toxicity for prostate volumetric modulated arc therapy (VMAT) with and without radiation boosts to an intraprostatically dominant lesion (IDL), defined by ¹⁸F-choline positron emission tomography/computed tomography (PET/CT). Methods and Materials: Thirty patients with localized prostate cancer underwent ¹⁸F-choline PET/CT before treatment. Two VMAT plans, plan_{79 Gy} and plan_{100-105 Gy}, were compared for each patient. The whole-prostate planning target volume (PTV_prostate) prescription was 79 Gy in both plans, but plan_{100-105 Gy} added simultaneous boost doses of 100 Gy and 105 Gy to the IDL, defined by 60% and 70% of maximum prostatic uptake on ¹⁸F-choline PET (IDL_suv60% and IDL_suv70%, respectively, with IDL_suv70% nested inside IDL_suv60% to potentially enhance tumor specificity of the maximum point dose). Plan evaluations included histopathological correspondence, isodose distributions, dose-volume histograms, tumor control probability (TCP), and normal tissue complication probability (NTCP). Results: Planning objectives and dose constraints proved feasible in 30 of 30 cases. Prostate sextant histopathology was available for 28 cases, confirming that IDL_suv60% adequately covered all tumor-bearing prostate sextants in 27 cases and provided partial coverage in 1 case. Plan_{100-105 Gy} had significantly higher TCP than plan_{79 Gy} across all prostate regions for α/β ratios ranging from 1.5 Gy to 10 Gy (P<.001 for each case). There were no significant differences in bladder and femoral head NTCP between plans and slightly lower rectal NTCP (endpoint: grade ≥ 2 late toxicity or rectal bleeding) was found for plan_{100-105 Gy}. Conclusions: VMAT can potentially increase the likelihood of tumor control in primary prostate cancer while observing normal tissue tolerances through simultaneous delivery of a steep radiation boost to a ¹⁸F-choline PET-defined IDL