Dose-adapted salvage radiotherapy after radical prostatectomy based on an erMRI target definition model: Toxicity analysis

Figures & data

Table I. Patient demographics, disease and erMRI work-up characteristics (n = 171).

	N	%
Age at SRT (years)
Median (range)	66 (41-82)
RP to SRT interval (months)
Median (range)	32.1 (4–144)
pT-Stage status (n = 171)
T2a	8	4.7
T2b	14	8.2
T2c	48	28.1
T3a	59	34.5
T3b	37	21.6
T4	3	1.7
Unknown	2	1.2
PSA at RP (ng/mL) (n = 171)
Median (range)	8 (2.1–50)
Gleason Score (n = 171)
≤ 3 + 4	114	66.7
≥ 4 + 3	54	31.6
Unknown	3	1.7
Lymphadenectomy (n = 171)
Yes	109	63.8
No	62	36.2
Surgical Margins (n = 171)
Positive	103	60.3
Negative	56	32.7
Unknown	12	7.0
PSA at salvage (ng/mL)
Mean ± SD all pts (n = 169)	1.89 ± 2.8
Mean ± SD erMRI + pts (n = 131)	2.08 ± 3.0
Mean ± SD erMRI – pts (n = 38)	1.26 ± 1.8
Relapse erMRI location (n = 131)
Anastomosis	47	35.9
Penile bulb	25	19.0
Seminal vesicles	5	3.8
Prostatic bed/bladder neck	44	33.6
Anastomosis and prostatic bed	1	0.8
Unknown	9	6.9

erMRI, endorectal magnetic resonance imaging; SRT, salvage radiotherapy; RP, radical prostatectomy; PSA, prostate-specific antigen.

Table II. Radiotherapy treatment characteristics (n = 171).

	n	%
RT
Boost	131	76.6
No boost	40	23.4
Median RT dose (range, Gy)
Boost group	74 (72–78)
No boost group	64 (64–64.4)
WPRT
Yes	34^a	19.9
No	137	80.1
Median dose (range, Gy)	50.4 (48–50.4)
CTV definition
CTVstandard	80	46.8
CTVnew	91	53.2
RT technique for PB (n = 171)
3D-CRT	152^b	89
IMRT	19	11
RT technique for boost (n = 131)
3D-CRT	106	81
IMRT/Dynamic Arc RT	25	19

CTV, clinical target volume; IMRT, intensity-modulated RT; PB, prostatic bed; RT, radiotherapy; WPRT, whole pelvic RT; 3D-CRT, three-dimensional conformal RT.

^aWith a four-field 3D-CRT technique; ^bA four-, six- and three-field 3D-CRT beam arrangement was used in 106 (62%), 43 (25%) and 3 (2%) patients, respectively

Table III. Late genitourinary and gastrointestinal toxicities (RTOG scale): maximum score and toxicity at time of last follow-up (n = 109).

Grade	Late RTOG toxicity, n (% of patients)
	GU		GI
	Worst score	At last follow-up	Worst score	At last follow-up
0	71 (65.1)	86 (78.9)	71 (65.1)	81 (74.3)
1	23 (21.1)	16 (14.7)	29 (26.6)	26 (23.9)
2	7 (6.4)	5 (4.6)	7 (6.4)	2 (1.8)
3	7 (6.4)	1 (0.9)	2 (1.8)	–
4	1 (0.9)	1 (0.9)	–	–

GI, gastrointestinal; GU, genitourinary; RTOG, Radiation Therapy Oncology Group.

Figure 1. Overall grade ≥ 2 (1a) and ≥ 3 (1b) late genitourinary toxicity-free survival.

Table IV. Univariate and multivariate analysis of clinical, pathologic and treatment factors predicting for grade ≥ 2 late GU toxicity after SRT (n = 109).

Variable	Univariate	p^a	Multivariate	p^b
	4yr-grade ≥ 2 toxicity-free survival		HR (95% CI)
SRT group
Boost (n = 82)	79.4 ± 5.9	0.06	0.115 (0.13–0.980)	0.048
No boost (n = 27)	100
WPRT
Yes (n = 24)	100	0.077	–	0.097
No (n = 85)	79.3 ± 5.9
CTV definition
CTVstandard (n = 59)	88.4 ± 5.5	0.031	–	0.181
CTVnew (n = 50)	80.8 ± 6.6
ADT use
Yes (n = 22)	88.7 ± 7.6	0.585	–	0.524
No (n = 87)	82.8 ± 5.5
Acute GU toxicity grade ≥ 2
Yes (n = 17)	67.1 ± 13.5	0.023	0.215 (0.070–0.666)	0.008
No (n = 92)	86.5 ± 5.0

ADT, androgen deprivation therapy; CI, confidence interval; CTV, clinical target volume; GU, genitourinary; HR, hazards ratio; SRT, salvage radiotherapy; WPRT, whole pelvic radiotherapy.

^a Kaplan-Meier analysis log-rank p-value; ^b Cox proportional hazards model p-value.

Figure 2. Overall grade ≥ 2 (2a) and 3 (2b) late gastrointestinal toxicity-free survival.