Theoretical assessment of late cardiac complication from endovascular brachytherapy for restenosis prevention.
OBJECTIVE
In this study, a theoretical assessment of late cardiac complication from endovascular brachytherapy is performed using the integrated logistic model.


METHODS
Calculation were performed for various lengths of Ir-192 sources using alpha/beta = 3.2 for the endpoint of chronic ischemia, TD50/5 = 7,000 cGy, and TD5/5 = 5,000 cGy. The dose distribution over a standard heart was divided into volume elements with uniform dose (dose-volume histogram). Using linear-quadratic equation, the dose in each of the volume elements was converted into dose equivalent to standard fractionation external beam irradiation. The normal tissue complication probability (NTCP) for each volume element was calculated and combined together to arrive at the cumulative risk of late cardiac complication. The NTCP was plotted against the dose prescribed at 2-mm radial distance for four treatment lengths.


RESULTS
(1) The overall risk of late cardiac toxicity (chronic ischemia within 5 years) was estimated to be less than 1% for current clinical trials using Ir-192. (2) There is a volume effect with higher risk for larger irradiated volume, which can come from longer treatment time, the same dose prescribed at a greater radial distance, and a longer source train. (3) The NTCP vs. dose demonstrates a sigmoidal relationship. There is a threshold dose (about 500 cGy), below which the risk is minimal; the gradient of the curve is greater for longer treatment length.


CONCLUSIONS
If the prediction from this model is validated with clinical data, it will contribute to guidelines for dose prescription, dose escalation, evaluation of new source design, and multivessel treatment.
Giap
H
H
Division of Radiation Oncology, Scripps Clinic, La Jolla, California 92037, USA. hbgiap@pol.net
Massullo
V
V
Teirstein
P
P
Tripuraneni
P
P
D015906:Angioplasty, Balloon, Coronary; D001918:Brachytherapy / Q000009:adverse effects* / Q000379:methods; D003327:Coronary Disease / Q000517:prevention & control / Q000532:radiotherapy* / Q000628:therapy; D006801:Humans; D016015:Logistic Models; D008954:Models, Biological; D011879:Radiotherapy Dosage; D012008:Recurrence