Intraoperative ultrasound-based planning can effectively replace postoperative CT-based planning for high-dose-rate brachytherapy for prostate cancer

Abstract

PurposeUltrasound (US)–based planning for high-dose-rate brachytherapy allows prostate patients to be implanted, imaged, planned, and treated without changing position. This is advantageous with respect to accuracy and efficiency of treatment but is only valuable if plan quality relative to CT is maintained. This study evaluates any dosimetric impact of changing from CT- to US-based planning. Methods and MaterialsThirty patients each were randomly selected from CT-planned and US-planned cohorts. All received single fraction high-dose-rate brachytherapy (15 Gy) followed by 37.5 Gy in 15 fractions external beam radiation therapy. Prostate V90, V100, V150, V200, D90, and the dose homogeneity index were compared. For the rectum, Dmax, D0.5cc, D1cc, V10, V50, and V80 were examined. For the urethra, only Dmax and D10 were considered. ResultsUS plans had smaller 200% hot spots, although the dose homogeneity index for both was 0.7 ± 0.1. On average, plans using either modality satisfied planning goals. Although several parameters were significantly different between the two modalities (p < 0.05), the absolute differences were small. Of greatest, clinical relevance was the difference in frequency with which upper dose goals were exceeded. The prostate V200 goal was exceeded in 53% of CT-planned cases, but only 20% of those planned with US. The urethral D10 goal was never exceeded using US but was exceeded in 13% of CT cases. ConclusionsUS planning results in plans that, clinically, are dosimetrically equivalent to CT-based planning. Upper dosimetric goals are, however, exceeded less often with US than with CT.