Postoperative irradiation for the prevention of heterotopic bone: analysis of different dose schedules and shielding considerations.
Ninety-seven high risk hips were irradiated postoperatively for prevention of heterotopic bone (HTB) in the UCLA Department of Radiation Oncology from 1980 to 1988. Ninety-two hips in 82 patients were eligible for analysis with a minimum follow-up of 2 months and a median follow-up of 10 months. Forty-nine of the hips had porous coated ingrowth prostheses. From 1980 to 1986, 2 Gy fractions were used to deliver 20 Gy (8 hips), 12 Gy (1 hip), and 10 Gy (27 hips). Since December of 1986, 38 hips received 8 Gy in two increments and 18 hips received a single 7 Gy fraction. All porous ingrowth components were shielded with custom blocks. Six out of 92 hips developed clinically significant (Brooker grade 3 or 4 heterotopic bone). There was one clinically significant failure in 78 hips (1.3%) when irradiation was initiated before post-operative day (POD) #6 and shielding was properly placed. One clinical failure occurred in 38 hips which received 8 Gy in two increments. One clinical failure occurred out of the 18 hips treated with 7 Gy in one fraction. This failure could be related to block malposition. There were four clinical failures in the 36 hips treated with 2 Gy fractions to total doses of 10 Gy, 12 Gy, or 20 Gy. Three of these failures were associated with initiation of treatment after POD #5, and the fourth was related to block malposition. Unshielded trochanteric osteotomies resulted in five migrations and seven fibrous unions for a total non-osseous union rate of 12/36 (33%). Shielding of the remaining 28 trochanteric osteotomies resulted in a non-osseous union rate of 7% (0 migrations and 2 fibrous unions). There were no failures of union of components, and the only side effects noted in the series were the five trochanteric migrations. In conclusion, the use of 8 Gy in two increments or 7 Gy in one fraction was found to be as efficacious as conventional 2 Gy fractionation schemes with no increase in side effects. For optimal results, treatment should be implemented prior to POD #5 with shielding of the trochanteric osteotomy. Postoperative irradiation to prevent HTB can be used in hips with porous components using properly placed blocks to shield the porous region.
Department of Radiation Oncology, UCLA School of Medicine, Jonsson Comprehensive Cancer Center.
L H
LH
Blount
B J
BJ
Thomas
L
L
Tran
M T
MT
Selch
J E
JE
Sylvester
R G
RG
Parker
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001842:Bone and Bones; D002828:Choristoma / Q000517:prevention & control*; D005260:Female; D006615:Hip / Q000528:radiation effects*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000517:prevention & control*; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D012983:Soft Tissue Neoplasms / Q000517:prevention & control*