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

Figure 2. Example of treatment of a vaginal rhabdomyosarcoma Fig. 2a, sagittal magnetic resonance imaging (T2-weighted) showing a bulky vaginal tumour. Fig. 2b, vaginal mould applicator in situ, inserted for treatment of residual disease after 6 cycles of chemotherapy. Fig. 2c, dose distribution for a treatment delivering 60 Gy through 143 hourly pulses of 0.42 Gy per pulse. In yellow: isodose 100%, in purple: isodose 90%, in blue: isodose 50%. The target volume is indicated as a red broken line structure, encompassed by the 90% isodose.

the young child. All BT procedures are performed under general anaesthesia. The following examples for BT techniques are described according to major locations which have been treated: cervix/ vagina/vulva, bladder prostate, limbs and trunks, head and neck, anus-rectum. These examples include different methods of BT (interstitial, endocavitary). Some procedures are or can be performed intraoperatively (bladder, prostate, trunk, limbs). Only a short description is given here; for detailed description we refer to the respective chapters in this book. Gynaecological RMS For vaginal and cervical RMS, treatment is usually based on an intracavitary procedure, with a vaginal applicator being inserted under general anaesthesia. It is recommended that a personalized mould applicator or a small cylindric applicator (the vaginal diameter is usually less than 15-20 mm) is used, following the same procedure as described in adults. Nevertheless, in children the cervical-vaginal impression is made under general anaesthesia often using a condom introduced into the vaginal cavity for easy removal of the impression from the vagina, which is too small to receive liquid paste and strips. The following steps are identical to making a mould in adult patients: impression into plaster, rough mould, positioning of the catheters according to the anatomy and the CTV, making appropriate perforations including four small holes to suture the applicator with silk thread to the inferior lateral parts of the vagina A washing catheter is also fixed to the vaginal mould applicator, to allow vaginal irrigation during treatment. The mould applicator is inserted under general anaesthesia, together with a Foley urinary catheter (Figure 2). Gold fiducial markers may be placed to mark the tumour landmarks. For patients with significant residual disease, a conservative tumour debulking is performed, without resection of the vaginal wall, to allow vaginal mould insertion. Para-vaginal interstitial catheters are rarely useful in vaginal RMS but may be required when there is significant residual para-vaginal disease (> 5mm thickness), following a free-hand technique. For tumours involving the upper part of the vagina and/or the cervix, an intrauterine catheter may be inserted and sutured to the vaginal mould applicator.

considering pre-treatment description of the tumour site, as per clinical and radiological evaluation. Specific points: In vaginal RMS, it has been shown that inclusion of the initial sites (extent) of disease was associated with more complications, without any benefit in terms of local control [37, 42, 43]. Therefore, only residual disease at time of BT should be included in the target volume. For a gynaecological implant, e.g., considering the CTV to be treated, MRI should be performed before and during the implant with the moulded vaginal applicator in place [41]. Tumour thickness and the exact topography of the residual disease can be evaluated and can be compared to the initial findings including the vaginal imprint. In BP RMS, it is recommended to systematically include both the prostate and the bladder neck as parts of the CTV when tumours extended to both organs at diagnosis, even if residual tumour only involves the prostate or the bladder. The prostate and bladder neck have the same embryogenesis and only very selected cases of patients with prostate only disease, and no initial extension to the bladder neck can be treated with prostate only BT. For multimodal strategies combining macroscopic tumour resection and intracavitary BT such as in the AMORE protocol (orbits, head, and neck tumours), the CTV encompasses the microscopically residual tumour volume and is defined as being 5 mm of tissue as measured from the surface of the mould.

8. TECHNIQUE

The details for the techniques to be applied in paediatric RMS are mainly derived from the techniques developed for adult BT as outlined in the respective chapters in this book for adult BT, but adaptation is required because of the small dimensions of