Optimal gross tumor volume definition in lung-sparing intensity modulated radiotherapy for pleural mesothelioma: an in silico study

Figures & data

Table 1. Patients and tumor characteristics.

Patient and tumor characteristics	Total number
Patient number	16
Age, years
Mean (standard deviation)	60 (9.4)
Median (range)	62 (64–69)
Gender
Male	12 (75%)
Female	4 (25%)
Histological subtype
Epithelioid	14 (88%)
Sarcomatoid	0 (0%)
Biphasic	1 (6%)
Unknown	1 (6%)
Tumor stage (AJCC)
Stage 1 (T1N0M0)	1 (6%)
Stage 2 (T2N0M0)	8 (50%)
Stage 3 (T2N1-2M0/T3N0-1M0)	4 (25%)
Stage 4 (T2N3/any T4/any M+)	3 (19%)
Anatomical location
Left-sided tumors	9 (56%)
Diaphragm	9 (56%)
Parietal pleura	9 (56%)
Mediastinal pleura	9 (56%)
Pericardial pleura	5 (31%)
Fissural pleura	2 (12%)
Chest wall	4 (25%)
Mediastinal fat	1 (6%)
Costo-phrenic sinus	9 (56%)
Right-sided tumors	7 (43%)
Diaphragm	7 (43%)
Parietal pleura	7 (43%)
Mediastinal pleura	7 (43%)
Pericardial pleura	2 (12%)
Fissural pleura	4 (25%)
Chest wall	6 (37%)
Mediastinal fat	3 (19%)
Costo-phrenic sinus	7 (43%)

Figure 1. Images in 69-year-old woman with a newly diagnosed left-sided malignant pleural mesothelioma (epithelioid histology). (a and b): Coronal CT (a) and FDG-PET (b) show a diffuse pleural thickening with diffuse FDG-avid zones, with the exception of a portion of parietal pleura indicated by the arrows (in a and b). (c and d): T2-weighted SPAIR image (c) and contrast-enhanced T1-weighted VIBE image (d) show a possible mesothelioma deposit along the whole lateral pleural surface (arrow in c and d): the region that was negative on the CT (a) and FDG-PET (b) appears to be hyperintense in c and d. Moreover, in c and d the pericardium is hyperintense (arrowhead in c and d), while in a and b is slightly thickened and the FDG-avidity is not clearly visible.

Table 2. Number of patients with additional tumor sites and location details per imaging modality.

	PET/CT vs. CT (A)n (%)	MRI vs. CT (B)n (%)	MRI vs. PET/CT (C)n (%)	χ^2-test p-valueA vs. B	χ^2-test p-valueB vs. C
Number of patients with at least 1 additional tumor site	12 (75)	15 (94)	15 (94)	0.8	0.7
Additional tumor sites: anatomical details
Diaphragm	7 (59)	13 (87)	7 (44)	0.001	0.08
Parietal pleura	3 (25)	11 (73)	9 (56)	0.001	0.6
Mediastinal pleura	1 (8)	3 (20)	3 (19)	0.7	–
Pericardial pleura	1 (8)	2 (13)	2 (12)	0.7	–
Fissural pleura	0	2 (13)	2 (12)	0.4	–
Chest wall	1 (8)	5 (33)	5 (31)	0.07	–
Mediastinal fat	1 (8)	2 (13)	2 (12)	0.9	–
Costo-phrenic sinus	1 (8)	1 (7)	–	0.8	–
No differences	4 (33)	1 (7)	1 (7)	0.07	–

Table 3. Visual assessment of the additional tumor sites identified via PET/CT and MRI compared to CT with IVC per patient.

Patient identifier	PET/CT	MRI
1	Diaphragm	Diaphragm Parietal pleura
2	Diaphragm	Diaphragm Chest wall Parietal pleura
3	No differences	Diaphragm Mediastinal fat Parietal pleura
4	Chest wall Parietal pleura Pericardial pleura	Chest wall Parietal pleura Pericardial pleura Fissural pleura
5	Mediastinal fat Diaphragm	Mediastinal fat Diaphragm Chest wall Parietal pleura
6	Mediastinal pleura	Mediastinal pleura Fissural pleura Chest wall
7	No differences	Parietal pleura Diaphragm
8	Parietal pleura	Parietal pleura Mediastinal pleura Pericardial pleura
9	Costo-phrenic sinus	Costo-phrenic sinus Mediastinal pleura Diaphragm
10	Parietal pleura	Parietal pleura Diaphragm
11	No differences	Parietal pleura Diaphragm
12	Diaphragm	Diaphragm
13	Diaphragm	Diaphragm Chest wall
14	No differences	No differences
15	Diaphragm	Diaphragm Parietal pleura
16	Diaphragm	Diaphragm Parietal pleura

Table 4. GTV Delineation: volume per imaging modality.

				p-Values vs.
GTV	Mean (ml)	SD (ml)	Range (ml)	GTVCT	GTVCT+PET/CT	GTVCT+MRI	COV
GTVCT	630.11	302.81	318.5–1130.8		0.31	0.28	0.49
GTVCT+PET/CT	640.23	302.83	325.41–1142.22			0.30	0.48
GTVCT+MRI	660.8	290.8	335.30–1147.88				0.44

COV: coefficient of variation; GTV: gross tumor volume; SD: standard deviation.