RESUMEN
PURPOSE: To investigate enlargement of prostate volume by edema during brachytherapy seed implantation and develop a nomogram model to calculate air-kerma strength (AKS) required for implantation of the enlarged transient prostatic volume. MATERIALS AND METHODS: The prostate volume was measured prior and after seed implantation using trans-rectal ultrasound imaging in the operating room to obtain volume enlargement. A nomogram model was developed that calculates AKS required for implantation of the enlarged transient prostate volume with optimal dose coverage. RESULTS: The measured prostate enlargement in this study was up to 60% of the initial volume. The effective prostatic volume enlargement was calculated for three isotopes: 125I, 103Pd and 131Cs. The effective volume enlargement for 125I implants was relatively small (< 10%) because of its long half-life. For 103Pd and 131Cs with short half-lives, additional AKS up to 20% and 30%, respectively, might be required to provide appropriate dose coverage of possible enlarged prostatic volumes. CONCLUSIONS: Prostate volume enlargement should be considered to obtain optimal dose coverage particularly for short half-life isotopes such as 131Cs and 103Pd. The nomogram model developed in this work provides the AKS required for implants with a wide range of prostatic volume enlargements (5-100%) for three isotopes. KEYWORDS: prostate brachytherapy, nomogram, airkerma strength, edema, volume enlargement.