Dosimetrical and radiobiological approach to manage the dosimetric shift in the transition of dose calculation algorithm in radiation oncology: how to improve high quality treatment and avoid unexpected outcomes?

Table 1 Planning objectives and dose limits for OARs associated with lung treatment when using a new dose calculation algorithm

Structure	TCD₅₀ (Gy)	a	Endpoint	EUDmin (Gy)		Dose limits
Target	50 [35]	−10	Control	EUD = Dpr TCP > 50%		D95% = Dpr V95% > 95% Dpr
OARs	TD₅₀ (Gy)	a [29, 36]	Endpoint	EUDmax (Gy) NTCP ≤1%	EUDmax (Gy) NTCP ≤5%	Dose limits [37, 38] (in 3DCRT)
Lungs	24.5 [30]	1.2	Pneumonitis	13.9	17.1	Dmean< 15–20 Gy
Lungs	30.8* [39]	1.01	Pneumonitis	17.4	21.4	Dmean< 15–20 Gy
Esophagus	68 [30]	18	Perforation	51.1	56.5	Dmean < 34 Gy D2% < 69 Gy
Esophagus	51* [40]	2.27	Acute esophagitis Grade 2–3	38.4	42.4	Dmean < 34 Gy D2% < 69 Gy
Heart	48 [30]	3.1	Pericarditis	32.8	37.5	Dmean < 26 Gy D2% < 30 Gy
Spinal cord	66.5 [30]	20	Necrosis	49.9	< 55.3	D2% < 50 Gy

The EUD values are corresponding to clinical objectives of NTCP ≤1% or 5%. The TCD₅₀ was taken from Okunieff et al. The parameters TD₅₀ and a = 1/n for tissue complications with conventional fractionation were taken from Emami or more recent publications. The symbol (*) indicates the most recent and recommended tolerance dose TD₅₀ for esophagus; and lung with heterogeneity correction using AAA. It can be seen that dose limits as Dmean and D2% depending on OARs (serial or parallel) could be matched with EUD values and the respect of the proposed dose limits might produce NTCP ≤5%. N.B. the Dmean = 20 Gy for healthy lung leads to a NTCP ≈ 15%

ISSN: 1748-717X