Dosimetric evaluation of anatomical changes during treatment to identify criteria for adaptive radiotherapy in oesophageal cancer patients

Figures & data

Table I. Patient and tumour characteristics.

Number of patients	29
Number of male/female patients	25/4
Age (years) at beginning of RT, median (range)	66 (48–81)
Tumour positions	1 proximal, 6 central, 6 distal, 1 proximal+ central, 15 central+ distal
GTV-T volume (cm^3), median (range)	45 cm^3 (9–235 cm^3)
GTV-T length (cm), median (range)	6 cm (2–12 cm)
GTV-N volume (cm^3), median (range)	3 cm^3 (0.3–48 cm^3)
Number of pathologic lymph nodes defined by FDG-PET CT and / or biopsies^a, median (range)	3 (1–7)
CTVtotal volume (cm^3), median (range)	280 cm^3 (98–692 cm^3)
CTVtotal superior-inferior extent (cm), median (range)	13 cm (8–20 cm)
Day of additional CT scan, median fraction number (range)	10 (9–14fx)

^aOnly 19 of 29 patients had pathologic lymph nodes.

CTVtotal, clinical target volume of both tumour and lymph node GTVs; fx, fraction number; GTV-T, gross tumour volume of primary tumour; GTV-N, gross tumour volume of lymph node targets; RT, radiotherapy.

Table II. Dosimetric parameters for targets and organs at risk.

	Number of patients with volume included in the CT scan	Treatment plan value, median (range)	Change of value in the dose distribution on the additional CT, median (range)
GTV-T V95%, (%)	29	100 (100)	0 (−54–0)
GTV-N V95%, (%)	19	100 (100)	0 (0)
CTVtotal V95%, (%)	29	100 (100)	0 (−35–0)
PTV V95%, (%)	29	99 (97–100)	−3 (−41–0)
Heart V30Gy, (%)	29	16 (0–24)	0 (−7–5)
Heart V40Gy, (%)	29	9 (3–18)	0 (−6–5)
Mean heart dose, (Gy)	29	16 (0–24)	0 (−4–3)
Lung V20Gy, (%)	29	10 (1–30)	0 (−3–2)
Mean lung dose, (Gy)	29	8 (2–16)	0 (−1–1)
Liver V35Gy^a, (%)	22	3 (0–18)	0 (−3–1)
Mean liver dose, (Gy)	22	9 (0–21)	0 (−3–1)

^aOnly 22 of 29 patients had the full extent of the liver included in the additional CT scan.

Negative change, Decrease of value; Positive change, Increase of value.

CTVtotal, clinical target volume of both tumour and lymph node GTVs; GTV-N, gross tumour volume of lymph node targets; GTV-T, gross tumour volume of primary tumour; n, number of patients for which the given volume was included in the CT scan V95%, percentage of the volume covered by at least 95% of the prescribed dose; VxxGy, Percentage of the volume covered by at least xxGy.

Figure 1. 1a) and 2a), Overlay of planning CT scan (green) and additional CT scan at fraction 11 (magenta); 1b) and 2b), The recalculated dose distribution on the additional CT scan, with 95% of the prescribed dose shown in colour wash; All images, Pink line, CTVtotal on planning CT scan; Blue line, PTV on planning CT scan; Magenta line, CTVtotal on additional CT scan; Cyan line, PTV on additional CT scan. Case 1), Changes in the diaphragmatic base line and the mediastinum shifted the CTVtotal and PTV towards the patient's left side causing underdosage near the top of the diaphragm and to the left in the mediastinum. The CTV and PTV were underdosed, showing decreases in V95% of the CTV of 5% and of the PTV of 12%. Case 2), Changes in the bowel filling and bowel gas shifted the CTVtotal and PTV towards the patient's right side and slightly to the posterior, causing underdosage in the PTV which had a decrease in V95% of 11%.