The radiation doses to erectile tissues defined with magnetic resonance imaging after intensity-modulated radiation therapy or iodine-125 brachytherapy

Abstract

Purpose To report penile bulb (PB) and corporal bodies (CB) doses during intensity-modulated radiation therapy (IMRT) and permanent 125I prostate implant alone (BT) for favorable, early stage, clinically localized prostate cancer using computed tomography (CT) and magnetic resonance imaging (MRI) to provide a basis for comparison as the initial report of a comprehensive project to develop erectile tissues sparing techniques. Methods and material Prostate, PB and CB volumes were defined by a fused CT/MRI simulation study performed before treatment in 29 IMRT patients and verification study performed 30 days postimplant in 15 BT patients. The median prescribed prostate dose for the IMRT and BT groups was 74 Gy and 145 Gy, respectively. Dose volume histograms (DVHs) were generated to determine the dose characteristics for the PB, CB, and prostate for each patient. D 90, V 100, and V 50 were used, where D i was defined as the dose that covers i% of the prostate volume and V i is the fractional volume of the prostate that receives i% of the prescribed dose. The Wilcoxon rank sum test was used to evaluate significance between the groups. Results The median PB D 90, V 100, and V 50 values were 17.5 Gy, 0%, and 31.9% for the IMRT group; and 52.5 Gy, 21.5%, and 89.7% for the BT group. The median CB D 90, V 100, and V 50 values were 7.3 Gy, 0%, and 0.9% for the IMRT group; and 26.9 Gy, 2.4%, and 20.1% for the BT group. The differences between the IMRT vs. BT V 100 values, but not V 50, were statistically significant for the PB ( p = 0.001) and CB ( p = 0.001). Conclusions Radiation dose to the PB and CB is low with IMRT or BT. Magnetic resonance imaging is superior to CT for the imaging of erectile tissues. Intensity-modulated radiation therapy may offer further reductions in the doses received by the PB and CB; however, at what cost to prostate coverage and normal tissue sparing will be the subject of a follow-up study.