Parotid gland mean dose as a xerostomia predictor in low-dose domains

Figures & data

Table 1. Patient and tumor characteristics.

		6 months			12 months
	All patients	Grade 0	Grade 1	Grade 2	Grade 0	Grade 1	Grade 2
Total patients	153	18	93	27	19	68	15
Age [years]
Median	60	62	61	62	60	61	62
Q1–Q3	54–66	55–66	54–66	54–68	55–66	54–67	62–68
Range	29–82	49–78	29–82	43–80	49–79	34–82	43–76
Gender
Female	37	5	21	6	6	16	5
Male	116	13	72	21	13	52	10
Tumor site
Hypopharynx/Larynx	37	9	19	5	5	17	1
Nasopharynx	12	0	9	1	2	4	1
Oropharynx	99	8	63	19	12	46	11
Other	5	1	2	2	0	1	2
Radiation modality
IMRT	37	2	29	4	3	22	4
Tomotherapy	116	16	64	23	16	46	11
Ipsi parotid dose [Gy]
Median	24.3	20.0	25.0	24.4	22.9	24.8	24.1
Q1–Q3	20.6–27.6	17.4–23.4	21.9–28.8	21.5–26.4	17.7–24.8	21.4–30.0	22.4–26.4
Range	0.4–63.4	0.4–34.4	4.6–61.4	11.2–63.4	0.4–27.8	4.6–28.7	17.3–63.3
Contra parotid dose [Gy]
Median	19.9	16.3	21.3	19.9	15.5	20.1	20.3
Q1–Q3	15.4–23.1	11.5–19.6	16.1–24.3	16.8–23.1	7.5–21.4	16.6–23.8	18.0–23.4
Range	0.3–30.9	0.3–22.1	4.1–30.9	5.2–26.2	0.3–27.5	4.1–28.7	12.7–26.1

Q1 is the first quartile demarcating lower 25% of the data, Q3 is the third quartile demarcating upper 25% of the data; Grade 0, Grade 1, and Grade 2 represent xerostomia toxicity grades.

Figure 1. Frequency of the follow-up reports.

Figure 2. Scatterplot of mean doses to parotid glands and corresponding xerostomia grades at 12 months after the treatment.

Table 2. Variability of xerostomia grades.

Time point	Grade 0	Grade 1	Grade 2
6 months	0.0%	3.4%	32.7%
12 months	0.0%	2.6%	30.0%

Figure 3. Comparison of parotid glands mean dose distributions between our (HD) and the PARPSORT (PAR) data sets. Outliers, that is, observations further than 1.5 interquartile range (IQR) from the first or the third quartile, are marked with ‘+’.

Figure 4. NTCP function for G2 + xerostomia at 12 months based on the data from the PARSPORT clinical trial ([19]) with observations from our cohort.

Figure 5. NTCP and performance curves for G1 + xerostomia. (a) NTCP functions at 6 months, (b) NTCP functions at 12 months, (c) ROC curves at 6 months, (d) ROC curves at 12 months, (e) Precision-recall curves at 6 months, (f) Precision-recall curves at 12 months.

Table 3. The parameters and performance of the LKB models with 95% confidence intervals.

Endpoint	Gland	D50 [Gy]	m	AUC	p Value
G1 + 6 months	Contralateral	10.7 (7.5–13.9)	0.61 (0.46–0.75)	0.73 (0.62–0.83)	<.01
G1 + 6 months	Both	12.2 (6.4–18.0)	0.61 (0.37–0.84)	0.76 (0.66–0.87)	<.01
G1 + 12 months	Contralateral	12.0 (7.8–16.1)	0.61 (0.32–0.89)	0.69 (0.54–0.83)	.01
G1 + 12 months	Both	13.6 (5.9–21.3)	0.61 (0.32–0.89)	0.73 (0.60–0.86)	<.01
G2 + 6 months	Contralateral	42.8 (5.7–80.0)	0.60 (0.39–0.82)	0.49 (0.38–0.60)	.43
G2 + 6 months	Both	51.2 (8.0–94.4)	0.60 (0.40–0.81)	0.50 (0.39–0.62)	.53
G2 + 12 months	Contralateral	51.6 (−41.8–145.1)	0.60 (0.20–1.00)	0.56 (0.41–0.70)	.24
G2 + 12 months	Both	64.8 (−31.8–161.3)	0.60 (0.29–0.91)	0.52 (0.38–0.67)	.38

Table A1. Confusion matrix.

	Positive cases	Negative cases
Positive predictions	True positives	False positives	Precision:
Negative predictions	False negatives	True negatives	Negative predictive value:
	Sensitivity^a:	Specificity:

^a also called recall.

Miah AB, Gulliford SL, Clark CH, et al. Dose-response analysis of parotid gland function: What is the best measure of xerostomia?. Radiother Oncol. 2013;106:341–345.

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