Comparison of Prostate Volume and Shape Determined by Magnetic Resonance and Transrectal Ultrasound Imaging

Abstract

time or pre-plan accordingly, post implant prostate volume (CT-based), D90, V100 and V200 from post implant dosimetry. Since dosimetric parameters were compared, only patients receiving a prescription dose of 145 Gy were included in this review.Patients were split into three groups based on pre-implant prostate volumes: !20cc, 20e50cc, and O50cc. Average, minimum and maximum values for the dosimetry parameters listed above were compared. Plan and implant quality were assessed through differences in planned versus post implant dosimetry using parameters of D90 and V100. V200 data was compared for all volumes to assess the potential for hot spots specifically in smaller prostate volumes. Results: Implant quality varied between pre-plan and real-time planning across all sub-groups based on prostate volume. Differences in D90 (plan postimplant) prevs. real-time (O50 cc: 21%, 11%;!20cc: 28%, 13%; 20e50cc: 24%, 11%) support the idea that real-time planning achieves similar implant quality across all volumes and offers greater consistency. Average postimplant D90 values were 160.8 Gy (!20 cc), 165.0 Gy (20e50 cc), and 163.3 Gy (O50 cc). Differences in V100 values follow the same trend for prevs. real time planning for all volumes. However, post implant values for V200 using prevs. real-time planning show a trend for hotter implants (O50 cc: 26%, 29.7%;!20cc: 21.5%, 29.3%; 20e50cc: 21.3%, 31.6%) with real-time planning. On the other hand, the average V200 for volumes !20cc was lower than the prostate volumes within 20e50cc. Conclusions: Patients with prostate volumes outside of the normal clinical range of 20e50 cc may be candidates for LDR prostate seed implantation. Real-time planning results in smaller differences between planned and delivered prostate dosimetry, including D90 and V100. Although not addressed in this analysis, careful consideration must be given to urethral doses when faced with smaller prostate volumes and pubic arch interference with respect to large prostate volumes.