Dosimetric comparison of Acuros^TM BV and AAPM TG-43 formalism for interstitial iridium-192 high-dose-rate...

The aim of this study was a retrospective dosimetric comparison of iridium-192 (¹⁹²Ir) high-dose-rate (HDR) interstitial brachytherapy plans using model-based dose calculation algorithm (MBDCA) following TG-186 recommendations and TG-43 dosimetry protocol for breast, head-and-neck, and lung patient cohorts, with various treatment concepts and prescriptions.

In this study, 59 interstitial ¹⁹²Ir HDR brachytherapy cases treated in our center (22 breast, 22 head and neck, and 15 lung) were retrospectively selected and re-calculated with TG-43 dosimetry protocol as well as with Acuros^TM BV dose calculation algorithm, with dose to medium option based on computed tomography images. Treatment planning dose volume parameter differences were determined and their significance was assessed.

For the breast planning target volume (PTV), TG-43 formalism calculated higher D_90%, V_95%, V_100%, and V_150% values than Acuros^TM BV, ranging from 2.2% to 5.4% (mean differences), as it did for the head and neck cases, ranging from 2.5% to 4.7% and for the interstitial lung cases, ranging from 2.2% to 4.4%, showing statistical significance (p < 0.001). For the skin D_0.1cm3, D_0.2cm3, and D_1cm3, the values were overestimated by TG-43, with a mean absolute differences of 1.4, 1.8, and 2.0 Gy, respectively for the breast, and 1.0 Gy for all DVH statistics for the head and neck cases compared with Acuros^TM BV (p < 0.001). Ipsilateral lung V_5Gy was also higher in TG-43-calculated plans, with a mean difference of 1.0% and 1.1% in the breast and lung implants, respectively. For the chest wall TG-43, the respective overestimation in D_0.1cm3 and D_1cm3 was 0.8 and 0.8 Gy for the breast, and 0.4 and 0.3 Gy for the interstitial lung cases, respectively.

The TG-43 algorithm significantly overestimates the dose to PTVs and surrounding organs at risk (OARs) for breast, head and neck, and lung interstitial implants. TG-43 overestimation is in accordance with previous findings for breast and head and neck. To our knowledge, this is also exhibited for Acuros^TM BV for the first time in interstitial lung HDR brachytherapy.