30. Paediatric malignancies - The GEC-ESTRO Handbook of Brachytherapy

Paediatric malignancies

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THE GEC ESTRO HANDBOOK OF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 01/09/2023

buttons. Additional interstitial catheters may be required, especially for patients with bulky residual tumour (> 3-4 cm), or involving the perineum. The patient is transferred to the brachytherapy department a few days after the implant procedure (usually 5 days later), to allow for the management of postoperative pain and of any early postoperative complication by a specialized team of anaesthesiologists and paediatric surgeons. Anus, rectum RMS For ano-rectal tumours, the BT technique follows the principles used in the adult patient. However, the dimensions of the applicator must be especially adapted. One layer of plastic or steel needles (3 - 5) is implanted depending on the target volume. Specific care must be taken to keep the contralateral side of the rectal wall as far away from the needles as possible with a rectal cylinder. Perineal RMS For perineal tumours, the prognosis is poorer than for urogenital RMS and achieving good local control may warrant combining conservative surgery and BT. When BT is associated with surgery, catheters are usually placed postoperatively, after complete surgical healing. Catheters are placed through a transperineal approach, which may involve intraoperative imaging procedures, such as ultrasound. The catheters should be fixed to the skin, possibly by means of buttons or through a perineal template. Soft tissue sarcoma of the extremities and the trunk The technique applied for paediatric soft tissue sarcoma of the extremities and the trunk is schematically the same as for adults. The most common technique is the intraoperative placing of flexible catheters, with buttons at the level of the skin and a template to keep the implant geometry. Usually, this treatment is associated with gross tumour resection, and an interstitial single-plane implant with catheters placed according to Paris system rules (parallel and equidistant) which allows an adequate dose distribution to treat the tumour bed. In cases of unresectable tumours, deeply seated tumour, large operative cavity, or microscopic residual disease, it may be necessary to use a multiple plane implant. Catheters are usually inserted orthogonal to the axis of surgical incision (Figure 4). In some cases, with wide excision, placement can be done parallel to the surgical bed. Attention should be paid at the time of surgery to avoid placing the catheters close to the nerves and vascular structures. Close collaboration between surgeons and the brachytherapist is therefore mandatory. Orbits BT has a place as local treatment for orbital RMS. It may be proposed as part of primary treatment in patients who have a residual disease after induction chemotherapy or as part of a salvage treatment after initial radiotherapy (external beam radiotherapy or brachytherapy). As described in detail by Blank and colleagues, the BT procedure is part of a multimodal approach to treat the operative bed after macroscopic tumour resection. The technique relies on an individual mould of silicone material that fits into the surgical defect, with flexible catheters inserted into the mould and adapted for remote afterloading treatment (Figure 5). The wound is closed over the mould, with only the catheters protruding through the closed incision [4]. A contraindication is deeply seated tumours close or in the orbital apex. These tumours cannot be reached for macroscopic radical excision and the chance of permanent damage with BT to the optic nerve is very high. Only in the case of radiorecurrent disease a mutilating orbital exenteration is an option followed by BT of the whole orbital surface (Figure 6).

For vulval sites, catheters are implanted according to the Paris system rules (parallelism and equidistance of the catheters). The same interstitial-BT technique used in adult patients can be

employed for children. Bladder prostate RMS

BT implant for BP RMS is usually performed at the time of open surgery, and most data are derived from the Institut Gustave Roussy (IGR) experience [12, 13, 46, 45]. The possibility for a conservative procedure is determined according to the response after chemotherapy, based on imaging (MRI with full bladder) with or without cystoscopy. A conservative procedure is not indicated in patients who would require irradiation of the whole bladder height. In IGR experience, the main criterion to allow the conservative procedure is the absence of tumour extension more than 1 cm above the level of the trigone in the posterior bladder wall. When tumour response is insufficient, additional chemotherapy courses can be delivered to increase tumour shrinkage. For tumours located in the anterior part of the bladder wall, a partial cystectomy is usually performed with free upper margins, respecting the muscular layer of the bladder neck. When the trigone is involved, a conservative tumour resection is performed. A bilateral ureteral transposition may be indicated to avoid stenosis of the ureteral orifices. For bulky residual tumours involving the prostate, partial prostatectomy with urethral preservation is considered. As this is a conservative approach, the surgery never aims at being microscopically complete at the level of the prostate and/or bladder neck, as BT will treat residual tumour cells. Usually, the implantation is carried out during the surgical procedure. Plastic catheters are inserted through a transperineal approach, to encompass the prostate/urethra and the bladder neck (Figure 3). Catheters are sutured to the bladder wall to avoid topographical modification and to the perineum through

Figure 3. Example of treatment of a bladder prostate rhabdomyosarcoma Four catheters were placed through transperineal approach to encompass the prostate and bladded neck for a pulse dose rate treatment delivering 60 Gy in pulses of 0.42 Gy per pulse. The 100% isodose is shown in yellow. The target volume is indicated as a red broken line structure.