Clinical characteristics
Final analyses were conducted on 30 patients, and the baseline clinical features and initial treatments are summarized in Table 1. The median age was 55 years (range: 19–79 years) and 60% patients were male. At initial diagnosis, extranodal involvement was present in 76.7% patients, bulky disease (≥10 cm) was present in 30%, and the majority had advanced-stage disease (stage III/IV, 63.3%). The distribution of medical histology is as follows: diffuse large B-cell lymphoma not otherwise specified (DLBCL-NOS, n=20); primary mediastinal large B-cell lymphoma (PMBL, n=6); transformed DLBCL (n=2); primary breast DLBCL (n=1); and high-grade B-cell lymphoma (MYC, BCL2, and BCL6 rearrangement, n=1).
Table 1. Patient characteristics and treatment at initial presentation.
Characteristics
|
Patients
|
Number
|
Percent
|
Age, median (range)
|
55.5 (19-79)
|
Sex
|
|
Female
|
18
|
60%
|
Male
|
12
|
40%
|
Ann Arbor Stage
|
|
I/II
|
11
|
36.7%
|
III/IV
|
19
|
63.3%
|
Extranodal involvement
|
|
Yes
|
23
|
76.7%
|
No
|
7
|
23.3%
|
Bulky disease, cm
|
|
|
≥10
|
9
|
30%
|
<10
|
21
|
70%
|
Histology
|
|
DLBCL-NOS
|
20
|
66.7%
|
Primary mediastinal B-cell lymphoma
|
6
|
20%
|
Transformed DLBCL
|
2
|
6.7%
|
High-grade B-cell lymphoma
|
1
|
3.3%
|
Primary breast B-cell lymphoma
|
1
|
3.3%
|
Initial systemic regimen
|
|
|
R-CHOP
|
26
|
86.7%
|
DA-EPOCH-R
|
4
|
13.3%
|
Abbreviations: DLBCL-NOS, diffuse large B-cell lymphoma not otherwise specified; R-CHOP, rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone; DA-EPOCH-R, dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, rituximab; RT, radiotherapy.
Radiotherapy outcomes
Baseline patient characteristics at the time of RT are listed in Table 2. Prior to RT, most patients experienced PR after initial therapy (86.7%), and the remaining 4 (13.3%) patients had progressive disease (PD) after chemotherapy. Second-line chemotherapy was used in 7 (23.3%) patients, and 1 (3.3%) patient received third-line treatment before RT. Three-quarters of RT patients exhibited localized disease (76.7%), with a total of 45 treated sites. The median maximum diameter of residual lesions was 4.5 cm, and the median volumes of GTV and CTV were 53 mL and 372 mL, respectively.
Table 2: RT characteristics and treatment response (n=30).
Characteristics
|
Patients
|
Number
|
Percent
|
Refractory/relapsed
|
|
Refractory
|
27
|
90%
|
Relapsed
|
3
|
10%
|
Numbers of residual sites
|
|
1
|
23
|
76.7%
|
≥2
|
7
|
23.3%
|
Extranodal involvement
|
|
Yes
|
18
|
60%
|
No
|
12
|
40%
|
Maximum diameter of residual tumor, median (range)
|
4.5 cm (1-9 cm)
|
Lines of chemotherapy before RT
|
|
|
1
|
22
|
73.3%
|
2
|
7
|
23.3%
|
3
|
1
|
3.3%
|
RT dose and fractionation
|
|
|
36 Gy/12f
|
23
|
76.7%
|
30 Gy/6f
|
3
|
10%
|
39.1 Gy/17f
|
3
|
10%
|
30 Gy/10f
|
1
|
3.3%
|
Numbers of treated sites
|
45
|
100%
|
1
|
22
|
73.3%
|
2
|
5
|
16.7%
|
3
|
1
|
3.3%
|
4
|
1
|
3.3%
|
6
|
1
|
3.3%
|
RT modality
|
|
|
IMRT
|
9
|
30%
|
VMAT
|
21
|
70%
|
Response to RT
|
|
|
CR
|
24
|
80%
|
PR
|
3
|
10%
|
PD
|
3
|
10%
|
Abbreviations: RT, radiotherapy; IMRT, intensity-modulated radiation therapy; VMAT, volumetric-modulated arc therapy; CR, complete response; PR, partial response; PD, progressive disease.
All patients received either intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT). Subsequently, 19 patients received salvage chemotherapy. After the completion of RT, the objective response rate (ORR), CR, and PR rates were 90%, 80%, and 10%, respectively. 39 of 45 (86.7%) treated sites achieved CR, for 8 patients who had multiple lesions at the time of RT with a total 23 treated sites, the CR rate was 87% (20/23). With a median follow-up of 10 months (range, 2–27), 10 of the 30 (33.3%) patients experienced disease progression, and three patients died. The 1-year OS and PFS rates for all patients were 81.8% and 66.3%, respectively (Figure 1). The corresponding 1-year OS and PFS rates for patients who obtained CR after RT were 95.8% and 83.1%, respectively, and 0% (P=0.001, Figure 2A) and 0% (P=0.001, Figure 2B) for patients who had not. The 1-year PFS rate was 82.4% for patients who had a single lesion at the time of RT compared with a 1-year PFS rate of 14.3% for patients who had multiple lesions (P<0.001); there was no statistically significant difference in OS (P=0.132) (Figure 3).
Failure patterns and associated factors
For the entire cohort, failure analysis showed that the majority of post-RT progressions involved out-field relapses (Table 3). After RT, 2 (6.7%) relapses were completely in-field, 3 (10%) were a combination of in- and out-of-field relapses, and 5 (16.6%) were completely out-of-field relapses (Figure 4). All out-of-field relapse patients (n=8) had extranodal involvement; 7 patients had initial stage III/IV disease; and in 5 patients with only out-of-field relapse, all occurred at new sites only after RT. According to univariate analysis, four factors have a significant impact on the incidence of out-of-field relapses: refractory/relapsed (refractory [18.5%] vs. relapsed [100%], P=0.002); response to systemic therapy before RT (yes [19.2%] vs. no [75%]. P=0.019); number of residual sites (single lesion [8.7%] vs. multiple lesions [85.7%], P<0.001); and response to RT (CR [16.7%] vs. no-CR [66.7%], P=0.013).
Table 3: Pattern of failure analysis after RT.
Characteristics
|
Patients
|
Number
|
Percent
|
Progression
|
|
No
|
21
|
70%
|
Yes
|
9
|
30%
|
Site of progression
|
|
Pre-existing sites only
|
2
|
6.7%
|
New sites only
|
5
|
16.6%
|
Both
|
2
|
6.7%
|
Site of progression in relation to RT field
|
|
|
In-field only
|
2
|
6.7%
|
Out-of-field only
|
5
|
16.6%
|
Both
|
2
|
6.7%
|
Abbreviations: RT, radiotherapy.
RT toxicity and dose to normal tissues
No serious non-hematological adverse effects (≥ grade 3) associated with RT were reported. Radiation-related adverse events included leukocytopenia in three patients (grade 2: two patients, grade 4: one patient) and oral mucositis (grade 2); radiation dermatitis (grade 1); asymptomatic pneumonia (grade 1); and nausea (grade 2) in one patient each, respectively.
Owing to the heterogeneity of RT schemes, we present the DVH statistics for the critical normal tissues of the 23 patients with 36 radiated sites treated with 36 Gy in 12 fractions (Table 4). For five RT sites in the head and neck, the median mean dose (Dmean) to the parotid gland and larynx was 13.2 Gy and 9.7 Gy, respectively, and the median maximal dose (Dmax) to the spinal cord was 14.2 Gy. For 15 RT sites in the thorax (mediastinum and axilla dominate the list), the median lung irradiated by 20 Gy or more (V20) was 4.7%, the median Dmean to the heart was 1.1 Gy, and the median Dmax to the spinal cord was 16.8 Gy. For 10 RT sites in the abdomen, the median V20 of the kidney was 7.47%, and the median Dmax to the small intestine and spinal cord was 33.4 Gy and 15.6 Gy, respectively. For six RT sites in the pelvis, the Dmean to the bladder and rectum was 5.52 Gy and 3.65 Gy, respectively, and the median Dmax to the head of the femur was 16.6 Gy.
Table 4: RT characteristics of the 23 patients with 36 sites treated with hypofractionated schemes of 36 Gy in 12 fractions.
RT target site (patient ID)
|
Volume, cm3
|
OARs
|
GTV
|
CTV
|
Head and neck
|
|
Parotid gland, Dmean, Gy
|
Larynx, Dmean, Gy
|
Spinal cord, Dmax, Gy
|
Cervical lymph node (P4)
|
NA
|
10.9
|
4.0
|
2.7
|
7.4
|
Cervical lymph node (P11)
|
2.3
|
216.9
|
17.8
|
15.7
|
14.4
|
Nasal cavity (P8)
|
128.3
|
331.9
|
13.2
|
9.7
|
16.7
|
Maxillary sinus (P5)
|
5.5
|
85.5
|
5.8
|
17.4
|
9.9
|
Masseter (P18)
|
29.6
|
88.5
|
30.4
|
6.5
|
14.2
|
Thorax
|
Lung, V20, %
|
Heart, Dmean, Gy
|
Spinal cord, Dmax, Gy
|
Axilla (P2)
|
19.8
|
118.9
|
0.7
|
0.2
|
4.2
|
Axilla (P6)
|
6.6
|
164.5
|
2.4
|
0.2
|
6.4
|
Axilla (P20)
|
NA
|
95.8
|
0.2
|
0.3
|
0.5
|
Axilla (P20)
|
NA
|
93.6
|
0.1
|
0.1
|
0.5
|
Mediastinum (P3)
|
24.6
|
283.3
|
2.2
|
9.5
|
14.7
|
Mediastinum (P4)
|
NA
|
65.1
|
0.2
|
0.3
|
16.8
|
Mediastinum (P12)
|
18.6
|
157.2
|
14.2
|
5.2
|
17.3
|
Mediastinum (P12)
|
80.1
|
258.1
|
6.6
|
14.4
|
21.3
|
Mediastinum (P15)
|
151.3
|
253.9
|
7.6
|
5.3
|
17.3
|
Mediastinum (P19)
|
13.5
|
343.7
|
27.8
|
16.6
|
19.6
|
Mediastinum (P20)
|
172.3
|
463.9
|
22.5
|
17.0
|
33.4
|
Mediastinum (P21)
|
2.8
|
51.4
|
2.9
|
0.3
|
15.1
|
Mediastinum (P22)
|
62.8
|
337.1
|
13.0
|
8.7
|
18.5
|
Arm (P4)
|
2.7
|
119.9
|
NA
|
1.1
|
2.5
|
Breast (P17)
|
191.5
|
781.4
|
6.9
|
1.1
|
18.7
|
Abdomen
|
Kidney, V20, %
|
Small intestine, Dmax, Gy
|
Spinal cord, Dmax, Gy
|
Spleen (P4)
|
12
|
172.4
|
4.3
|
6.5
|
9.8
|
Psoas major (P4)
|
26.7
|
137.4
|
NA
|
35.8
|
7.7
|
Buttock (P4)
|
9.6
|
233.3
|
NA
|
24.8
|
7.5
|
Back (P9)
|
191.9
|
692.6
|
23.3
|
30.9
|
24.0
|
Mesentery (P10)
|
86.7
|
258.8
|
2.2
|
38.9
|
15.1
|
Stomach (P16)
|
20.6
|
287.5
|
8.5
|
27.1
|
18.4
|
Retroperitoneum (P7)
|
95.7
|
685.6
|
18.6
|
37.7
|
19.5
|
Retroperitoneum (P13)
|
38.4
|
461.0
|
7.5
|
39.6
|
23.1
|
Retroperitoneum (P18)
|
116.3
|
225.0
|
NA
|
22.0
|
1.5
|
Retroperitoneum (P18)
|
8.0
|
155.8
|
6.2
|
39.2
|
15.9
|
Pelvic
|
Bladder, Dmean, Gy/V30, %
|
Head of femur, Dmax, Gy
|
Rectum, Dmean, Gy/V30, %
|
Prostate and bladder (P1)
|
134.7
|
512.6
|
29.1/24.1
|
19.3
|
23.6/23.6
|
Rectum and prostate (P14)
|
55.1
|
NA
|
16.2/5.2
|
13.8
|
23.5/32.6
|
Testicle (P7)
|
NA
|
145.1
|
5.9/NA
|
21.0
|
4.0/NA
|
Uterus (P11)
|
12.6
|
NA
|
5.1/1.9
|
8.7
|
3.30/NA
|
Groin lymph node (P8)
|
19.5
|
99.9
|
0.4/NA
|
1.5
|
0.7/NA
|
Groin lymph node (P18)
|
6.5
|
54.0
|
0.8/NA
|
20.0
|
1.8/NA
|
Abbreviations: RT, radiotherapy, Dmean, mean dose; Dmax, maximal dose; V20, percentage volumes receiving 20 Gy; V30, percentage volumes receiving 30 Gy.