In a phase 2 study, 10 cc of HA was injected between the rectum and prostate. For 16 patients, the same intensity modulated radiation therapy plan (62 Gy in 20 fractions) was optimized on 2 computed tomography scans: CT1 (before injection) and CT2 (after injection). Rectal parameters were compared: dose to 2.5 cc (D2.5), 5 cc (D5), 10 cc (D10), 15 cc (D15), and 20 cc (D20) of rectal wall and volume of rectum covered by the 90 % isodose line (V90), 80 % (V80), 70 % (V70), 60 % (V60), and 50 % (V50).
The mean V90, V80, V70, V60, and V50 values were reduced by 73.8 % (P<.0001), 55.7 % (P=.0003), 43.0 % (P=.007), 34 % (P=.002), and 25 % (P=.036), respectively. The average values of D2.5, D5, D10, D15, and D20 were reduced by 8.5 Gy (P<.0001), 12.3 Gy (P<.0001), 8.4 Gy (P=.005), 3.7 Gy (P=.026), and 1.2 Gy (P=.25), respectively.
The injection of HA significantly limited radiation doses to the rectal wall.