2129 - Retrospective Assessment of Model-Based Dose Calculation Algorithm and AAPM TG-43 Formalism in HDR Brachytherapy with H.A.M. Applicators

Purpose/Objective(s):

The accuracy of dose calculation algorithms in high-dose-rate (HDR) brachytherapy significantly impacts treatment quality, particularly in complex anatomical regions like the head and neck. This study evaluates differences in dose distributions between calculations using the AAPM TG-43 formalism and AcurosBV (v16.1), a model-based dose calculation algorithm, in patients treated with H.A.M. applicators. The hypothesis is that model base dose calculation algorithm will provide systematically lower reported dose.

Materials/Methods:

A retrospective analysis was performed on 20 patients treated with H.A.M. applicators in head and neck region (17 nasal, 1 cheek, 1 posterior neck, 1 right temple). All received 40 Gy in 8 fractions. Original HDR brachytherapy plans were created using TG-43 formalism and subsequently recalculated with AcurosBV in treatment planning system, incorporating Hounsfield Unit (HU)-based inhomogeneity corrections with dose-to-medium reporting. Physician-defined planning target volumes (PTVs) and automatically segmented OARs (brain, eyes, lenses, optic nerves, and body) were analyzed. Dose-volume histogram (DVH) metrics (mean, D90, V100, V150, V200, D0.1cc, D0.2cc, D1cc, and D2cc) were compared between the algorithms. Statistical significance was assessed using a paired Student’s t-test (p < 0.05 considered significant).

Results:

AcurosBV consistently reported lower doses than TG-43. The largest discrepancy was observed in PTV V100, with a mean reduction of 6.43±0.95% (p < 1×10?5). PTV mean dose, D90, V100, V150, and V200 were 48.65±1.22 Gy, 86.47±2.97%, 72.33±2.44%, 16.35±2.62%, and 3.38±1.41%, respectively, for AcurosBV, compared to 50.78±1.40 Gy, 90.21±3.07%, 78.76±2.09%, 19.65±2.69%, and 3.95±1.49%, respectively, for TG-43 (all p < 0.003). Isodose line comparisons demonstrated cooler, less conformal dose distributions with AcurosBV, attributed to the presence of air cavities. Differences in OAR doses were minimal, with mean variations of ~1.5% for brain, lenses, optic nerves, and eyes, and 5% for the skin.

Conclusion:

Model-based dose calculation with AcurosBV results in systematically lower dose estimates than TG-43 in HDR brachytherapy with H.A.M. applicators, particularly within the PTV, due to inhomogeneity corrections. These findings underscore the importance of adopting model-based algorithms for accurate dosimetry, particularly in anatomically complex treatment sites.

Abstract 2129 - Table 1: Comparison of PTV DVH metrics Between TG-43 and AcurosBV for Head and Neck HDR treatments using H.A.M. applicators

Parameters	TG-43 (Mean ± SE)	ACUROS (Mean ± SE)	Mean Difference (AcurosBV – TG-43)	p-value
D90 % (%)	90.21±3.07	86.47±2.97	-3.75 ± 0.25	< 1×10?¹¹
V100 % (%)	78.76±2.09	72.33±2.44	-6.43±0.95	< 1×10?5
V150 % (%)	19.65±2.69	16.35±2.62	-3.30±0.43	< 1×10?6
V200 % (%)	3.95±1.49	3.38±1.41	-0.57±0.17	< 0.003