25 Oesophageal Cancer

Oesophageal Cancer Brachytherapy

17

THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 10/06/2019

Fig. 27.12: Technique of application by oral intubation for a distal stenotic oesophageal cancer with a guide wire technique (Seldinger) which is introduced via an endoscope or a small diameter tube; 8 mm tube applicator with small open end for the guide wire in place.

Fig. 27.13: Definitions of different lengths and depths around an endo-oesophagal applicator. The Active Source Lentgh (ASL) is defined as number of steps x step spacing. The Reference Dose point is located in the central plane at 5mm depth from the applicator surface. The maximum surface dose point is in the central plane at the surface of the applicator The Treated Length being the length of the oesophagus treated between the crossings of the 90% of the Prescription isodose. In this case prescription was at 5 mm depth (the same as the reference depth).

Fig. 27.15: Axial CT films with bougie applicators in place (diameter 15 mm) and the transverse dimensions of the GTV (arrow heads); the reference isodose is indicated at 5 mm into the oesophageal wall (dotted line) and the luminal/applicator surface.

27.14: Barium swallow (left) with GTL (GTV) and PTL in relation to the carina. X-ray localisation film (right) with bougie applicator in place(outerdiameter15mm)andtube(3.7mm)assourcecarrierwith a marker wire (10 mm distance between the markers). Definition of the different lengths PTL (10.5 cm) and Active Source Length (ASL: 12 cm). The PTL is delineated on the basis of comparison with the diagnostic barium swallow using the tracheal carina as a reference structure. The TL is dependent on the ASL and on the source dwell time loading at the proximal and distal end and should include the PTL as tightly as possible. The Reference Depth (RD, dotted line) is defined in the central plane 5 mm from the applicator surface into the oesophageal wall.

Fig. 27.15 A: T2 oesophageal cancer: limited thickness of the tumour oesophageal wall (5 mm). The prescribed dose of 5 Gy at 5 mm from the applicator surface - 12.5 mm from the source axis (7.5+5) - corresponds to the reference dose at 5 mm. The dose at the luminal surface (white arrow heads) is 8.7 Gy.

Fig.27.15B:T3oesophagealcancer:extensivethicknessoftheanterior- lateral oesophageal wall (up to 12 mm) (white arrow heads). Dose of 5 Gy was prescribed at 7 mm into the oesophageal wall 14.5 mm (7.5+7) fromthesourceaxis.Thereferencedoseat5mm is5.9Gy,themucosa/ tumour surface dose is 9.3 Gy.

Fig. 27.16: Axial, sagittal and coronal CT films with bougie applicator in place (diameter 10 mm) and the corresponding dimensions of the PTV (light blue); the reference isodose of 4 Gy is indicated at 5mm into the oesophageal wall (yellow) and the luminal surface dose of 10 Gy (orange).