25 Oesophageal Cancer

Oesophageal Cancer Brachytherapy

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

displacement (PTL) (fig. 27.14). The Treated Length (TL) should include the PTL at the depth of the prescription point (intersection with the 90% isodose) (fig. 27.13, take into account also fig. 27.5 and 27.10). 3D planning The residualGTVafter external beamradiotherapy+/- chemotherapy has to be delineated and if possible, High-Risk CTV, should be delineated by including residual grey zones as visible on MRI as well as residual pathological tissue as visible through endoscopy. If no MRI is available, the endoscopy data should be used or the initial GTV can be projected into the planning CT. This procedure leads to an over-estimation of the HR-CTV, but can be considered as safe. An intermediate risk CTV can be delineated by extending the High-Risk CTV into the surrounding oesophageal wall. Again, a PTVmargin of 1 cm is taken in both longitudinal directions only. 9.B. Palliative treatment In palliative situations 2D planning is usually performed. Without cross sectional image-based information, the dose prescription point is usually taken at a distance the radiation oncologist considers as an adequate distance. This distance is related to the applicator surface (e.g. 5 to 8 mm) but can be additionally related to the source axis (at 10 mm) in the case of small diameter applicators (fig. 27.6, 27.11, 27.15). This chosen distance should respect as much as possible the goal of treatment, which is prevention of obliteration of the lumen in palliative treatments, where some distance into the obliterating part of the tumour will be sufficient. The dose may be prescribed at a single point at a certain depth in the central plane, or for a stepping source afterloader at several points at distances along the source tract. The dose distribution around a line source with constant linear activity over the source length results in a cigar shaped treated volume, which is narrowing towards the proximal and distal end of the applicator. With the stepping source, dwell times can be optimised to treat a completely cylindrical volume, or (when using 3D planning on sectional imaging) can even be adapted to differences in target depth along the active source length (e.g. more dose in the area of the thicker stenotic tumour, less dose in the proximal and distal adjacent tissue). 9.C. Dose prescribing, recording and reporting There is no common language in the literature describing how dose should be recorded and reported. Most often, when small diameter applicators are used, doses are prescribed and reported at a reference point of 10 mm from the source axis. Another practice of dose prescription and reporting which reflects more the individual situation in a patient is related to the applicator and to the oesophageal lumen. A reference point at 5 mm from the applicator surface or at 5 mm tissue depth is chosen. Taking these different reference points, the reported reference doses and the dose gradients including the applicator and lumen surface doses vary significantly, in particular when considering the different diameters of the applicators used (2 - 20 mm: e.g. 5-10 Gy as reference dose and 10-30 Gy as luminal surface dose per fraction). We recommend recording and reporting the dose at 5 mm tissue depth (reference depth) from the applicator surface (lumen or applicator radius + 5 mm) and at the lumen or applicator surface, indicating the dose gradient in the tumour and the normal tissue. Reporting at 5 mm tissue depth is independent of the prescription

strategy chosen (e.g. at 10 mm from the source axis in palliative indications or at x mm as Minimum Target Dose in 3D planning in curative or selected palliative indications). (fig. 27.16)

10. DOSE, DOSE RATE, FRACTIONATION

Radiotherapy total dose, fractionation and overall treatment time depend on the intent of treatment (see also chapter 6). Different dose rates have been used and are in principle applicable. However, because of the discomfort for the patient from a long treatment time with MDR, LDR or PDR brachytherapy, nowadays HDR brachytherapy is regarded as the preferred method of treatment. For treatment with curative intent, a dose of 50 - 60 Gy (2 Gy per fraction) by external beam radiotherapy is followed by 1 or 2 brachytherapy applications with 4 to 6Gy (HDR).The brachytherapy is delivered using the largest possible applicator diameter (at least 10 mm, preferably 15-20 mm) and the reference dose is specified at 5 mm tissue depth (e.g. at 5 mm tissue depth with a 10 mm applicator). Special attention should be payed to avoiding high mucosal doses >6-10 Gy per brachytherapy fraction and >65- 70 Gy EQD2 3 total prescribed dose considering the additional preirradiated dose by external beam radiotherapy. [Yorozu A and Dokiya T, Yorozu et al.]. Exceptionally, higher doses may be considered for special curative indications: squamous cell carcinoma with 5 cm or less tumour length, no deep invasion (T1 or T2), and good response after external radiotherapy (complete or partial remission). [Okawa et al.]. The value of brachytherapy combined with chemotherapy (cis- Platinum, 5 FU, MMC) and external beam radiotherapy is controversial. Specific studies have shown that this combination may be associated with a high incidence of strictures, fistulae and treatment-related death under certain technical conditions [Gaspar et al]. Should chemo-radiation be considered, it seems to be necessary to avoid high doses at the lumen surface by using large diameter applicators, to limit the radiation dose and keep the overdosage volume small [Calais et al.]. There is no consensus or clear evidence for an ideal interval between external radiation and brachytherapy boost. When chemotherapy is added to external radiotherapy, however, a larger interval (2-3 weeks) before the brachytherapy procedure may be left. In other situations, a shorter interval of 1-2 weeks for normal tissue recovery between EBT and BT seems to be sufficient. In palliative indications, slightly higher fraction doses of 3 x 7 Gy HDR endoluminal brachytherapy plus 50 Gy external irradiation [Bergquist et al, Fuccio et al.] or self-expandingmetal stent (SEMS) placement followed by 3 x 8 Gy HDR endoluminal brachytherapy can be safely used [Amdal et al.]. The total dose for brachytherapy alone in a palliative setting (obstructive disease) usually based on a small diameter applicator is 15-25 Gy at 10mm from the source axis given in 3-4 brachytherapy applications (4-6Gy per fraction). Using a 6mmdiameter applicator with 6 Gy at 10 mm from the source axis the respective dose at 5 mm tissue depth is 7.8 Gy and at the lumen surface 22.2 Gy per fraction [Sur et al.]. Time interval varies between 1-2 days and one week.