Optimization of the prescription isodose line for Gamma Knife radiosurgery using the shot within shot technique

Radiation Oncology

Table 2 Comparison between the actual treated plan (prescribed almost exclusively at the 50% IDL), a re-plan using the shot within shot technique prescribed at the 50% IDL (SS_50%), and a re-plan using the shot within shot technique prescribed at the optimal IDL (SS_opt)

Case	Vol (cc)	RX (Gy)	IDL (%)	Selectivity			Gradient index			Brain V_12Gy (cc)			ΔT1 (%)		ΔT2 (%)
			SS_opt	Plan	SS_50%	SS_opt	Plan	SS_50%	SS_opt	Plan	SS_50%	SS_opt	Plan - SS_50%	Plan - SS_opt	SS_50% - SS_opt
1A	0.21	21	65	0.67	0.51	0.50	3.50	2.62	2.63	0.68	0.69	0.71	35	53	28
2A	0.09	21	52	0.51	0.61	0.61	3.53	3.39	3.50	0.40	0.31	0.33	0	4	4
2A	0.10	21	51	0.31	0.58	0.58	2.78	3.42	3.45	0.64	0.37	0.38	0	0	0
2B	0.16	21	74	0.47	0.47	0.48	2.87	3.03	3.07	0.59	0.58	0.59	1	39	38
2C	1.13	18	65	0.72	0.72	0.67	3.20	3.10	2.96	2.00	1.99	2.16	48	61	25
3A	1.58	21	67	0.67	0.73	0.72	3.06	2.60	2.56	4.26	3.03	3.00	14	37	27
3B	0.16	21	58	0.67	0.74	0.73	3.17	3.22	3.31	0.45	0.41	0.44	1	15	16
3C	0.05	21	50	0.45	0.45	0.45	2.85	2.84	2.84	0.19	0.19	0.19	0	0	0
4A	0.18	21	76	0.64	0.58	0.67	3.63	2.84	3.08	0.62	0.52	0.50	29	56	38
4B	0.18	21	74	0.64	0.55	0.59	3.46	2.80	2.89	0.60	0.55	0.56	24	51	36
4C	0.11	21	63	0.71	0.50	0.52	3.58	3.17	3.39	0.34	0.46	0.49	16	35	23
4D	2.22	18	60	0.81	0.79	0.77	2.50	2.61	2.62	2.56	2.76	2.78	17	29	14
5A	1.40	20	75	0.74	0.60	0.61	3.17	2.55	2.52	3.20	3.18	3.03	62	76	37
5B	0.61	20	52	0.63	0.56	0.56	3.52	3.42	3.48	1.86	2.20	2.28	15	18	4
5C	0.04	20	57	0.37	0.22	0.22	3.17	3.26	3.40	0.25	0.46	0.44	19	30	14
6A	0.48	21	50	0.63	0.60	0.60	3.24	3.37	3.37	1.51	1.72	1.72	0	0	0
6B	0.83	21	56	0.68	0.54	0.56	2.99	2.95	3.08	2.20	2.94	2.92	46	52	11
6C	0.16	21	74	0.67	0.67	0.65	3.11	3.11	3.22	0.45	0.45	0.49	0	36	36
6D	0.11	21	77	0.40	0.40	0.38	2.91	2.91	2.89	0.58	0.58	0.61	0	40	40
7A	0.83	20	71	0.54	0.37	0.40	3.89	2.57	2.58	3.60	3.58	3.34	19	45	32

Reduction in beam-on times are shown in a comparison between the re-plans and the treated plan (ΔT1), and in comparison between the SS_50% plan and optimized plan (ΔT2)

ISSN: 1748-717X