Dosimetric benefit to organs at risk following margin reductions in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy

Table 4 Comparison of NPC patients not fulfilling dose-volume histogram constraints for plans with pre-correction margins and for plans with post-correction margins

Organ		Objective	Plan with pre-correction margins [ n (%)]	Plan with post-correction margins [ n (%)]	Reduction (%)
Targets	Any PTV	V_93% ≥ 99%	0 (0)	0 (0)	0.0
		V_100% ≥ 95%	0 (0)	0 (0)	0.0
	PTV_7000	V_77Gy ≤ 20%	0 (0)	0 (0)	0.0
		V_80.5Gy ≤ 5%	0 (0)	0 (0)	0.0
OARs	BrainStem	D_max ≤ 54 Gy	23 (57.5)	22 (55.0)	4.3
	BrainStem_PRV	D_1% ≤ 60 Gy	12 (30.0)	8 (20.0)	33.3
	SpinalCord	D_max ≤ 45 Gy	0 (0)	0 (0)	0.0
	SpinalCord_PRV	D_1% ≤ 50 Gy	0 (0)	0 (0)	0.0
	OpticNerve_L	D_max ≤ 50 Gy	21 (52.5)	19 (47.5)	9.5
	OpticNerve_L_PRV	D_1% ≤ 54 Gy	21 (52.5)	17 (42.5)	19.0
	OpticNerve_R	D_max ≤ 50 Gy	22 (55.0)	19 (47.5)	13.6
	OpticNerve_R_PRV	D_1% ≤ 54 Gy	21 (52.5)	19 (47.5)	9.5
	Chiasm	D_max ≤ 50 Gy	26 (65.0)	26 (65.0)	0.0
	Chiasm_PRV	D_1% ≤ 54 Gy	27 (67.5)	27 (67.5)	0.0
	Lens	D_max < 25 Gy	0 (0)	0 (0)	0.0
	Parotids	V_20Gy > 20 cc (both glands)	40 (100)	40 (100)	0.0
		D_50% < 30 Gy (at least one gland)	28 (70.0)	19 (47.5)	32.1
	Parotid_L	D_mean < 26 Gy	40 (100)	40 (100)	0.0
	Parotid_R	D_mean < 26 Gy	40 (100)	40 (100)	0.0
	TemporalLobe_L	D_max ≤ 60 Gy	39 (97.5)	38 (95.0)	2.6
		D_1% ≤ 65 Gy	15 (37.5)	12 (30.0)	20.0
	TemporalLobe_R	D_max ≤ 60 Gy	39 (97.5)	38 (95.0)	2.6
		D_1% ≤ 65 Gy	16 (40.0)	13 (32.5)	18.8
	Mandible/TM joint	D_1cc ≤ 75 Gy	0 (0)	0 (0)	0.0
	Ear_Inner_L	V_55Gy ≤ 5%	30 (75.0)	27 (67.5)	10.0
	Ear_Inner_R	V_55Gy ≤ 5%	34 (85.0)	26 (65.0)	23.5
	Larynx	D_mean < 45 Gy	31 (77.5)	28 (70.0)	9.7

OAR, organ at risk; PTV, planning target volume; PTV_7000, the PTV of gross tumor volume; PRV, planning risk volume; L, left; R, right; TM, temporomandibular; V_93%, percentage volume receiving at least 93% of prescribed dose; V_100%, percentage volume receiving at least 100% of prescribed dose; V_77Gy, percentage volume receiving at least 77 Gy; V_80.5Gy, percentage volume receiving at least 80.5 Gy; D_1%, dose received by 1% of the volume; D_max, maximum dose; V_20Gy, volume receiving less than 20 Gy; cc, cubic centimeter; D_50%, dose received by 50% of the volume; D_mean, mean dose; D_1cc, dose received by 1 cc volume; V_55Gy, percentage volume receiving at least 55 Gy.

ISSN: 2523-3548