Influence of MLC leaf width on biologically adapted IMRT plans

Figures & data

Figure 1. Coronal CT images through the central part of the tumour, with dose distribution as overlay for the seven fields and seven step-and-shoot intensity levels dose plan. Top image: 2.5 mm MLC. Middle image: 5 mm MLC. Bottom image: 10 mm MLC. Contour colours, with prescribed dose in brackets: Compartment 1: green (48.1 Gy), Compartment 2: yellow (53.8 Gy), Compartment 3: blue (63.4 Gy), Compartment 4: red (70.3 Gy).

Table I. Dosimetric and radiobiological parameters for three different MLC types¹.

MLC leaf width, [mm]	Compartment	Prescribed dose, [Gy]	Mean dose, [Gy] ± SD, [%]	EUD, [Gy]	TCP^2	TCP^3
2.5	1	48.1	49.1 ± 4.9	47.5	0.96	0.56
	2	53.8	54.1 ± 6.7	51.4	0.86
	3	63.4	61.6 ± 6.4	58.3	0.68
	4	70.3	66.0 ± 4.5	63.8	0.59
5.0	1	48.1	49.1 ± 5.1	47.3	0.95	0.51
	2	53.8	54.2 ± 7.7	51.0	0.85
	3	63.4	61.5 ± 7.0	57.4	0.65
	4	70.3	64.8 ± 5.1	62.5	0.55
10.0	1	48.1	50.1 ± 6.0	47.5	0.96	0.41
	2	53.8	54.3 ± 7.4	50.8	0.85
	3	63.4	60.0 ± 6.8	56.0	0.60
	4	70.3	62.1 ± 5.1	59.4	0.44

¹The data shown are for an IMRT plan of seven fields and seven step-and-shoot intensity levels.

²TCP for each compartment.

³TCP for the whole tumour.

Figure 2. Differential DVHs from the seven fields and seven step-and-shoot intensity levels dose plan. Each panel represents one compartment, and shows data for the 2.5 mm MLC (solid lines), 5 mm MLC (dashed lines) and 10 mm MLC (dotted lines).

Figure 3. TCP values for the whole tumour for the three MLC types. Each panel shows one field setup with four different step-and-shoot intensity levels.

Figure 4. TCP calculations resulting from shifting the tumour relative to the dose matrix in the coronal plane. Data shown are for the seven fields and seven step-and-shoot intensity levels dose plan, with redistributed and uniform dose distributions. The abscissa for the random displacement panel (top) represents one standard deviation.