Greater Postimplant Swelling in Small-Volume Prostate Glands: Implications for Dosimetry, Treatment Planning, and Operating Room Technique

Journal Article · Sun Apr 01 04:00:00 EDT 2012 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/J.IJROBP.2011.03.024· OSTI ID:22056256

Chung, Eugene; Stenmark, Matthew H ^[1]; Evans, Cheryl ^[2]; Narayana, Vrinda ^[1]

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1. Department of Radiation Oncology, University of Michigan, Ann Arbor, MI (United States)
2. Department of Radiation Oncology, Providence Cancer Center, Novi, MI (United States)

Purpose: Postimplant prostatic edema has been implicated in suboptimal permanent implants, and smaller prostates have been reported to have worse dosimetric coverage. In this study we compare the degree of postimplant edema between larger and smaller prostates and examine the effects of prostate size on the dose delivered to 90% of the prostate (D90). Methods and Materials: From September 2003 to February 2006, 105 hormone-naive patients underwent permanent prostate brachytherapy with {sup 125}I Rapid Strand (Oncura Inc., Arlington Heights, IL). All patients underwent pelvic magnetic resonance imaging (MRI) within 3 weeks before implant, transrectal ultrasound at the time of implant, and both computed tomography and MRI 2.5 to 3 weeks after implant. Prostates were divided into 5 subgroups based on preimplant MRI volumes: less than 25 mL, 25 to 35 mL, 35 to 45 mL, 45 to 55 mL, and greater than 55 mL. Prostate swelling was assessed by use of preimplant and postimplant MRI volumes. Postimplant dosimetry was determined by MRI and compared between the subgroups. Results: All prostates showed postimplant swelling on MRI when compared with preimplant MRI, with a mean increase of 31% {+-} 31% (p < 0.0001). The greatest swelling was noted in small prostates (volume less than 25 mL), with a mean increase of 70% {+-} 36%. The degree of swelling in the group with a volume less than 25 mL was significantly larger than the degree of swelling in all other prostate subgroups (p < 0.003). Transrectal ultrasound significantly overestimates the prostate volume when compared with MRI by a mean of 15% {+-} 25% (p = 0.0006) and is more pronounced for smaller prostates. Although prostates with volumes less than 25 mL did not have significantly worse D90 compared with larger prostates, they had the largest percent of suboptimal implants by the standard ratio of D90 divided by the prescription dose. Conclusions: Although small prostates have the greatest postimplant edema, planning ultrasound at the time of implant overestimates the volumes of smaller prostates to a greater degree than larger prostates, which may minimize the effects of edema on postimplant dosimetry.

• OSTI ID: 22056256
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 5 Vol. 82; ISSN IOBPD3; ISSN 0360-3016
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
BRACHYTHERAPY
COMPUTERIZED TOMOGRAPHY
DOSIMETRY
EDEMA
IMPLANTS
IODINE 125
NMR IMAGING
PATIENTS
PLANNING
PROSTATE
RADIATION DOSES
SWELLING