68Ga-PSMA PET/CT–Based Atlas for Prostate Bed Recurrence After Radical Prostatectomy: Clinical Implications for Salvage Radiation Therapy Contouring Guidelines

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FIGURE 1.
Flowchart of screening process.
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FIGURE 2.
Definition of location of ⁶⁸Ga-PSMA PET lesion exceeding CTV borders. ⁶⁸Ga-PSMA PET contours are in light blue, and CTV contours are in pink. ⁶⁸Ga-PSMA PET lesion extended beyond CTV at posterior (A), inferior (B), lateral (C), superior (D), anterior (E), posteroinferior (F), and posterolateral (G) borders.
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FIGURE 3.
Heat map of distribution of prostate bed ⁶⁸Ga-PSMA PET recurrences in miTrN0Mo cohort (127 patients), mapped on template patient’s anatomy (green contour represents CTV).
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FIGURE 4.
Three-dimensional rendering of all PB recurrences in relation to RTOG-based CTV (light green), rectum (brown), and urinary bladder (pink) of template patient. PSMA recurrences are in solid colors: green = completely covered, yellow = partially covered, and red = not covered.
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FIGURE 5.
Results of coverage analysis and detailed description of location of ⁶⁸Ga-PSMA PET recurrences exceeding CTV. Two central pie charts show full cohort divided into main cohort (miTrN0M0; purple) and all subcohorts (gray). Full pie charts on sides show location of ⁶⁸Ga-PSMA PET recurrences exceeding CTV.

TABLE 1.

Clinical and Demographic Characteristics of All Patients and All Cohorts^*

Characteristic	Full cohort (miTrNxMx)	miTrN0M0 cohort	miTrN1M0 cohort	miTrN0M1 cohort	miTrN1M1 cohort	P
No. of patients	226	127	30	32	37
Median age (y)^†	69.5 (64–73)	70 (47–89)	68.5 (63.3–76.3)	65 (61–74.5)	72 (68–76)	0.47^‡
Median serum PSA level (ng/mL)^†	1.21 (0.3–0.6)	1.02 (0.5–2.18)	1.49 (1–2.25)	1.5 (0.52–4.21)	2.8 (1–9.24)	0.3^‡
Median tumor volume (mL)^†	0.88 (0.38–1.35)	0.72 (0.04–15)	0.89 (0.44–1.73)	0. 91 (0.39–1.34)	1.55 (0.46–4.6)	0.16^‡
NCCN risk group^§						<0.001^∥
Low risk	9 (5)	8 (6)	0 (0)	1 (3)	0
Intermediate risk	82 (44)	54 (43)	9 (38)	132 (41)	7 (26)
High risk	52 (28)	28 (22)	7 (29)	10 (34)	7 (26)
Very high risk	43 (23)	16 (13)	8 (33)	6 (21)	13 (48)
Not available	40	21	6	3	10
Surgical margin involvement^§						0.08^¶
No	99 (63)	58 (46)	16 (84)	12 (48)	13 (57)
Yes	57 (37)	31 (24)	3 (16)	13 (52)	10 (43)
Not available	70	38	11	7	14
Outcome^§						0.35^¶
Completely covered by CTV	107 (46)	68 (53)	14 (47)	11 (34)	14 (38)
Partially covered by CTV	91 (41)	43 (34)	12 (40)	17 (53)	19 (51)
Not covered by CTV	28 (13)	16 (13)	4 (13)	4 (13)	4 (11)
Location of recurrence partially or completely exceeding CTV^§						Not applicable
Total no.	119 (100)	59 (100)	16 (100)	21 (100)	23 (100)
Posterior	57 (48)	30 (51)	5 (31)	10 (48)	12 (55)
Posterolateral	34 (29)	14 (24)	8 (50)	8 (38)	4 (17)
Posteroinferior	8 (7)	3 (5)	2 (13)	0	3 (13)
Anterior	1 (1)	1 (2)	0	0	0
Superior	4 (3)	1 (2)	0	2 (10)	1 (4)
Inferior	13 (11)	10 (17)	1 (6)	0	2 (9)
Lateral	2 (2)	0	0	1 (5)	1 (4)
Lesion extension^§						0.23^¶
Rectal wall involvement	19 (8)	12 (9)	2 (7)	1 (3)	4 (10)
Bladder wall involvement	10 (4)	4 (3)	1 (3)	0	5 (13)

↵* Location and extension of tumor recurrence on ⁶⁸Ga-PSMA PET for full cohort and subcohorts. Age and PSA level are at time of PET. Percentages were calculated on basis of total number of patients with data available in selected category.
↵† Values in parentheses are interquartile ranges.
↵‡ One-way ANOVA.
↵§ Reported as number of patients, with percentages in parentheses. NCCN = National Comprehensive Cancer Network.
↵∥ Spearman (ρ) correlation matrix.
↵¶ χ² test.

TABLE 2.

Clinical Characteristics and Outcome Analysis for miTrN0M0 Cohort^*

Characteristic	miTrN0M0 cohort (n = 127)	Completely covered by CTV (n = 68)	Partially covered by CTV (n = 43)	Not covered by CTV (n = 16)	P
No. of patients^†	127 (100)	68 (54)	43 (34)	16 (13)	Not applicable
Median age (y)^‡	70 (64–73)	69.5 (62–72)	70 (67–75)	68.5 (66.3–75.3)	0.14^§
Median serum PSA level (ng/mL)^‡	1.02 (0.5–2.18)	1.11 (0.5–2.2)	1.09 (0.46–2.63)	0.84 (0.62–1.11)	0.26^§
Median tumor volume (mL)^‡	0.72 (0.38–1.35)	0.57 (0.36–1.13)	1.01 (0.49–67)	0.68 (0.37–0.96)	0.12^§
NCCN risk group^∥					0.38^¶
Low risk	8 (8)	7 (10)	0 (0)	1 (6)
Intermediate risk	54 (51)	26 (38)	19 (44)	8 (50)
High risk	28 (26)	12 (18)	12 (28)	4 (25)
Very high risk	16 (15)	9 (13)	5 (12)	2 (13)
Not available	21	14	7	1
Surgical margin involvement^∥					0.04^#
No	58 (65)	21 (45)	20 (69)	12 (92)
Yes	31 (35)	26 (55)	9 (31)	1 (8)
Not available	38	21	16	4
Location of recurrence partially or completely exceeding CTV^∥		Not applicable			Not applicable
Total no.	59 (100)		43 (100)	16 (100)
Posterior	30 (52)		25 (58)	5 (31)
Posterolateral	14 (24)		10 (23)	4 (25)
Posteroinferior	3 (5)		1	2 (13)
Anterior	1 (2)		1 (2)	0
Superior	1 (2)		1 (2)	0
Inferior	10 (14)		5 (10)	5 (31)
Local extension^∥					0.002^#
Rectal wall involvement	12 (9)	1 (1)	5 (12)	6 (38)
Bladder wall involvement	4 (3)	4 (6)	0	0

↵* Age and PSA level are at time of PET. Percentages were calculated on basis of total number of patients with data available in selected category.
↵† Values in parentheses are percentages of total number of patients.
↵‡ Values in parentheses are interquartile ranges.
↵§ One-way ANOVA.
↵∥ Reported as number of patients, with percentages in parentheses. NCCN = National Comprehensive Cancer Network.
↵¶ Spearman (ρ) correlation matrix.
↵# χ² test.