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. 2023 Dec;15(6):448-452.
doi: 10.5114/jcb.2023.134173. Epub 2023 Dec 29.

Dosimetric impact of applying a model-based dose calculation algorithm for skin cancer brachytherapy (interventional radiotherapy)

Elisa Placidi  1 , Bruno Fionda  2 , Enrico Rosa  3 , Valentina Lancellotta  2 , Antonio Napolitano  4 , Martina De Angeli  2 , Francesco Pastore  2 , Maria Antonietta Gambacorta  2   5 , Luca Indovina  1 , Luca Tagliaferri  2 , Marco De Spirito  1   3
Affiliations

Dosimetric impact of applying a model-based dose calculation algorithm for skin cancer brachytherapy (interventional radiotherapy)

Elisa Placidi et al. J Contemp Brachytherapy. 2023 Dec.

Abstract

Purpose: Brachytherapy (BT, interventional radiotherapy) is a well-established radiotherapy technique capable of delivering high doses to tumors while sparing organs at risk (OARs). Currently, the clinically accepted dose calculation algorithm used is TG-43. In the TG-186 report, new model-based dose calculation algorithms (MBDCA), such as Elekta's advanced collapsed cone engine (ACE), have been introduced, although their clinical application is yet to be fully realized. This study aimed to investigate two aspects of TG-186: firstly, a comparison of dose distributions calculated with TG-43 and TG-186 for skin tumors; and secondly, an exploration of the impact of using a water bolus on the coverage of clinical target volume (CTV) and OARs.

Material and methods: Ten treatment plans for high-dose-rate IRT were developed. All plans were initially calculated using the TG-43 algorithm, and were subsequently re-calculated with TG-186. In addition, one of the treatment plans was assessed with both TG-43 and TG-186, using 10 different water bolus thicknesses ranging from 0 to 5 cm. To assess dose variations, the following dose-volume histogram (DVH) parameters were compared: D2cc and D0.01cc for OARs, and V150, V100, V95 and V90 for CTV coverage.

Results and conclusions: The average dosimetric results for CTV and OARs, as calculated by both algorithms, revealed statistically significant lower values for TG-186 when compared with TG-43. The presence of a bolus was observed to enhance CTV coverage for the TG-186 algorithm, with a bolus thickness of 2 cm being the point at which ACE calculations matched those of TG-43. This study identified significant differences in dosimetric parameters for skin tumors when comparing the TG-43 and TG-186 algorithms. Moreover, it was demonstrated that the inclusion of a water bolus increased CTV coverage in TG-186 calculations.

Keywords: TG-186; TG-43; brachytherapy; interventional radiotherapy; non-melanoma skin cancer.

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Conflict of interest statement

The authors report no conflict of interest.

Figures

Fig. 1
Fig. 1
A) The CT slice of a NMSC patient with CTV and OARs contoured. A 3 cm layer of air, shown in cyan, was added externally with a mass density of 0.001 g/ml, while 0 cm bolus was considered. B-J) The same CT slice, with an addition of bolus with varying thicknesses from 0.25 to 5 cm. This electronic bolus, shown in orange, was considered as water with a mass density of 1 g/ml
Fig. 2
Fig. 2
V95CTV (%) coverage as a function of the bolus thickness for an eye lid patient calculated with the TG-43 (•) and TG-186 (Δ) algorithms. With a water bolus of 2 cm, differences between TG-43 and TG-186 are reduced under 0.5%
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