PURPOSE: Postplan quality assurance using CT shows considerable interobserver contour variability.
We examined CT postplans of four experienced brachytherapists for comparison with MR-determined prostate volumes.
METHODS AND MATERIALS: Seventy-five patients had CT and MR scans 1 month post-125I prostate brachytherapy. CT scans were contoured by the treating physician and dosimetry calculated. The prostate was contoured independently on MR by one observer with extensive MR experience, the scans were fused and dosimetric parameters compared.
RESULTS: The mean prostate volume on CT was 38.3cc (17.5-78.6cc), on MR 33.3cc (16.3-66.1cc). On average, the volume on CT was 16.1% larger than on MR (range, 8% smaller to 64% larger). Craniocaudal discordance of the CT vs. MR prostate contours ranged from 4mm cranial to 10mm caudal to MR base and from 6mm cranial to 14mm caudal to MR apex. The CT prostate volume not only included an average of 90% of the MR prostate (range, 75-99%) but also included normal tissue (mean, 8.3cc; range, 2.9-17.1cc). The average difference between the calculated D90 from CT contours vs. MR contours was 10.0Gy (standard deviation, 8.8; range, -37.6 to +41.6Gy).
CONCLUSIONS: On average, only 90% of the MR-defined prostate is included in CT contours, while a volume of normal tissue is erroneously designated as prostate. Lack of awareness of this deficiency in planning and/or operative technique gives a false sense of appreciation of the true conformality, delays implementation of corrective measures, and risks unnecessary side effects.
Written by:
Petrik D, Araujo C, Kim D, Halperin R, Crook JM. Are you the author?
Department of Radiation Oncology, British Columbia Cancer Agency, Center for the Southern Interior, Kelowna, BC, Canada.
Reference: Brachytherapy. 2012 Jun 23. Epub ahead of print.
doi: 10.1016/j.brachy.2012.05.001
PubMed Abstract
PMID: 22732323
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