Discrepancies in dose and dose specification in interstitial implants.
The first step in the execution of an interstitial implant is the decision on size and location of the target volume. Several implant systems, e.g. the Paterson-Parker system and the Paris system, give instructions for the optimal arrangement of sources to assure that the planned target volume is adequately covered. They also give guidelines to calculate the reference dose rate encompassing the planned target volume. These systems provide different solutions for the source arrangement for the same planned target volume, and vice versa, resulting in different reference dose rates. The problem of dose specification is discussed. For a number of theoretical implants predicted reference dose rates for the planned target volume were compared with the computer calculated dose rates for that volume. Discrepancies increase when moderate digressions from the adopted implant system rules are allowed, such as could commonly occur clinically. For a number of examples the degree of change in dose rate, if over 10%, and the position where this deviation is likely to occur are described. For optimal results the clinician should be well aware of these variations.
Burgers
J M
JM
Department of Radiotherapy, The Netherlands Cancer Institute (Antoni von Leeuwenhoekhuis), Amsterdam.
Awwad
H K
HK
van der Laarse
R
R
D001918:Brachytherapy / Q000295:instrumentation / Q000592:standards; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted