34. Uncommon indications for brachytherapy - The GEC-ESTRO Handbook of Brachytherapy

Uncommon indications for brachytherapy

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THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 30/04/2025

5. DOSE

Guide needles are implanted through the skin 1 to 2 cm away from the surgical incision. The needles may be straight or curved to fit the CTV. The guide needles are then replaced by plastic tubes. Catheters can be placed onto the tumour bed surface and fixed with sutures or tunnelized 2-3 mm under the tumour bed surface for increased stability. The plastic tubes should be implanted parallel and equidistant, along the-axis of the extremity or transverse to the the surgical incision. An intercatheter distance of 1.0 to 1.5 cm allows greater consistency during postoperative changes and allows more meticulous treatment planning due to the increased number of dwell times. To reduce the radiation dose to critical organs (nerves, vessels, bones, etc.), some intraoperative surgical procedures may be considered, e.g. a spacer or layer of muscle or fat can be inserted between the catheters and the structure to be avoided. Spacers must not be thicker than 5mm if the normal tissue to be protected is at risk of harboring microscopic disease. A 5-mm tissue thickness is usually enough to separate the organs at risk away from the high-dose regions around the catheter (Figure 34.1 and 34.2). Finally, CTV needs to be defined intraoperatively. The implant array (surrogate for the tumour bed) and fiducials (surrogates of the CTV boundaries) are needed for a reliable CTV definition in the postoperative setting.

Unirradiated Cases Patients with negative margins may be treated with LDR brachytherapy alone to a total D 90 of 45 Gy at a dose rate of 40 - 60 cGy/hour [5]. Equieffective HDR regimens include a D 90 of 36Gy in 10 fractions b.i.d. [1]. Patients with larger tumours or positive margins usually require a combination of EBRT and brachytherapy. LDR brachytherapy of D 90 of 15-20 Gy combined with 45-50Gy of EBRT is a plausible strategy [9]. If HDR brachytherapy is used instead, a bioequivalent D 90 of 14-16Gy in 4-6 fractions b.i.d. can be used. Previously Irradiated Cases The majority of the cases that require adjuvant reirradiation are usually treated with brachytherapy alone due to the constraints imposed by the prior irradiation course. Reasonable alternatives include HDR brachytherapy alone D 90 32 to 40Gy in 8 to 10 fractions b.i.d. (EQD2 10 of 37.3 to 46.7Gy) with final dose and dose per fraction dependent upon prior DVH parameters to dose-limiting structures.

Figure 34.2: Dose Volume Histogram of the case shown in Figure 34.1. Please note the skin and scar-sparing properties of brachytherapy in deep-seated locations (OAR to CTV ratio of 0.3-0.4). Tumours adjacent to the bone or the neurovascular bundle can also be implanted using special intraoperative techniques to minimize OAR irradiation (OAR to CTV ratio of 0.7-0.85).