Methodologies for localizing loco-regional hypopharyngeal carcinoma recurrences in relation to FDG-PET positive and clinical radiation therapy target volumes

Figures & data

Table I. Target volume definitions.

Target volume	Definition
GTV-PET	The FDG-PET positive volume, delineated by a nuclear medicine physician
GTV	The gross tumour volume, includes all available diagnostic imaging as well as the results of the clinical examination
GTV-oncologist	The GTV with a 1 cm margin to account for delination uncertainty, adjusted for unaffected bone and with a 3 mm margin to the skin
CTVE-h	The high-risk elective clinical target volume, includes areas at high risk of microscopic disease. It is constructed by adding a 1 cm margin to GTV-oncologist and including involved lymph node levels
CTVE-l	The low-risk elective clinical target volume, includes areas at low but still significant risk of microscopic disease. It is constructed by adding a 2 mm margin to CTVE-h and including lymph node levels with low risk of sub clinical disease

The target volumes as they had been delineated on the treatment planning scans (CT_therapy).

Figure 1. Treatment planning scan (CT_therapy) with the contours of the target volumes and the transferred recurrence volume and a point of origin. for this patient, all four POs and the COV were located in the GTV-PET. The recurrence volume is certainly overlapping the GTV-PET, and all the foci of the expert and COV are located therein, but the volumetric approach with a 95% threshold point to the CTVE-l as the likely target volume where the recurrence occurs. With a 50% threshold, the volumetric approach ascribes the site of recurrence to the GTV. Magenta: Point of Origin identified on therapy scan. Orange: GTV-PET. Red: GTV. Turquoise: GTV-oncologist. Pink: CTVE-h. Yellow: CTVE-l. Green: Recurrence volume

Table II. Patient characteristics.

Patient	Gender	Age	TNM	RT	Concomitant medication	Tumour localization	Site of recurrence
1	male	63	T2 N2b M0	2 Gy × 33, 6 F/w	Nimorazol	Left pyriform sinus	T
2	male	62	T3 N2c M0	2 Gy × 34, 6 F/w	Nimorazol Cisplatin	Right pyriform sinus	T and 2 N
3	male	70	T3 N2a Mx	2 Gy × 34, 6 F/w	Nimorazol	Right pyriform sinus	T
4	female	67	T2 N0 M0	2 Gy × 33, 6 F/w	Nimorazol	Posterior hypopharyngeal wall	T
5	male	71	T2 N0 M0	2 Gy × 33, 6 F/w	Nimorazol	Right pyriform sinus	T
6	male	71	T3 N2b M1	2 Gy × 34, 6 F/w	Nimorazol Cisplatin	Left pyriform sinus	N

Demographical data, treatment related data and location of recurrence for the six patients included in the study.

TNM: tumour, node, metastasis classification; F/w: fractions per week.

Table III. Recurrences and target volumes.

		Volume
Scan	Method	GTV-PET	GTV	GTV-oncologist	CTVE-h	CTVE-l
Recurrence CT	Expert PO1	4/8	1/8	3/8	0/8	0/8
	Expert PO2	4/8	2/8	1/8	1/8	0/8
	Centre of volume	4/8	2/8	2/8	0/8	0/8
Treatment	Expert PO3	7/8	0/8	1/8	0/8	0/8
Planning CT	Expert PO4	7/8	0/8	0/8	1/8	0/8
Volume overlaps
50% threshold		3/8	1/8	4/8	0/8	0/8
95% threshold		2/8	1/8	3/8	1/8	1/8
Prescription dose		66–68 Gy	66–68 Gy	66–68 Gy	60 Gy	50 Gy

Table III. Location of points of origin in target volumes as estimated by the expert on the recurrence scan and the treatment planning scan as well as the location estimated with the centre of volume method and the volumetric overlap method. The dose prescribed to the target volume is indicated in the bottom line of the table.

PO1 and PO2: Double determinants of the expert defined point of origin within the recurrence volume.

PO3 and PO4: Double determinants of the expert defined point of origin on the treatment planning CT.

Figure 2. Distances between the repeated expert evaluated PO on the recurrence and therapy scans and the distance between the COV of the recurrence and the expert evaluated POs on the recurrence scan. A trend is seen towards the consistency between expert evaluations being better in the recurrence scan than in the therapy scan. The COV method on the recurrence scan appears to be as consistent with the expert evaluated POs on two consecutive expert evaluations.