Assessment of testicular dose during preoperative radiotherapy for rectal cancer

Figures & data

Table I. Characteristics of the study participants treated with preoperative radiotherapy and surgery.

	Short course RT	Long course RT
Number of patients	76	25
Median age at baseline (years)	64 (32–84)	61 (41–73)
Median tumour distance from anal verge (cm)	7 (0–15)	10 (4–15)
	Count data
Tumour distance from anal verge
0–5 cm  6–10 cm  11–15 cm	24 40 12	6 11 8
Type of operation
Anterior resection  Extralevator abdominoperineal excision  Intersphincteric abdominoperineal excision  Hartmann	40 30 3 1	18 7

RT, preoperative radiotherapy, range in brackets.

Table II. Stratified analysis of the planned testicular dose.

	Short course RT	p-Value	Long course RT	p-Value
Number of men	76		25
mTD minTD maxTD	0.57 (0.06–14.37) 0.33 (0.0–7.73) 1.08 (0.18–25.91)		0.81 (0.36–10.80) 0.48 (0.21–1.73) 1.87 (0.56–42.74)
mTD by distance testes-PTV
0–1 cm  1–5 cm  >5 cm	4.32 (2.21–14.37) 0.78 (0.33–2.35) 0.27 (0.06–0.51)	<0.001[a]	6.09 (5.40–10.80) 1.31 (0.99–2.97) 0.58 (0.36–0.81)	<0.001[a]
mTD by tumour distance from anal verge
0–5 cm  6–10 cm  11–15 cm	1.35 (0.18–14.37) 0.50 (0.15–14.19) 0.29 (0.06–1.92)	<0.001[a]	1.16 (0.43–10.80) 0.81 (0.47–6.09) 0.70 (0.36–1.67)	0.52[a]
mTD by relation of anal canal to PTV
Anal canal included in PTV  Anal canal not in PTV	0.91 (0.15–14.37) 0.34 (0.06–0.77)	<0.001[b]	1.33 (0.43–10.80) 0.69 (0.36–2.59)	0.08[b]
mTD by type of surgery
Pelvic floor resected  Pelvic floor preserved	1.34 (0.18–14.37) 0.37 (0.06–4.32)	<0.001[b]	1.37 (0.43–10.80) 0.70 (0.36–6.09)	0.10[b]

Doses reported in Gy as median (range).

^aKruskal-Wallis test,

^bWilcoxon ranksum test.

maxTD, maximal testicular dose; minTD, minimal testicular dose; mTD, mean testicular dose; PTV, planning target volume; RT, preoperative RT for rectal cancer.

Figure 1. Spaghetti plot of planned and delivered testicular dose for 32 men treated with short course radiotherapy (25 Gy). CT = computed tomography, CBCT = cone beam computed tomography.

Figure 2. Scatter plot of planned and in average delivered testicular dose for 32 men treated with short course radiotherapy (25 Gy).

Figure 3. Estimated 25^th, 50^th, 75^th and 90^th percentiles of the absolute difference between planned and delivered mean testicular dose for a given planned mean testicular dose. TD = testicular dose.

Table III. Longitudinal quantile regression analysis with the inverse of the mean testicular dose based on planning and repeated cone beam CT as outcome.

Predictor		Longitudinal change of inverse mTD
Time-point of TD assessment  (planning CT, CBCT 1–5)	p25 p50 p75	0.01 (−0.31–0.33) 0.01 (−0.48–0.49) −0.08 (−0.87–0.71)
Distance testes-PTV (Distance testes-PTV)^2	p25 p50 p75 p25 p50 p75	0.18 (−0.12–0.48) 0.29* (0.01–0.56) 0.21 (−0.07–0.49) 0.02 (−0.01–0.06) 0.02 (−0.01–0.05) 0.04* (0.01–0.07)

CBCT, cone beam computed tomography; CT, computed tomography; mTD, mean testicular dose; PTV, planning target volume; p25, 25th percentile; p50, 50th percentile (median); p75, 75th percentile; TD, testicular dose.

*p < 0.05; 95% confidence interval in brackets.