16. Cervix cancer - The GEC-ESTRO Handbook of Brachytherapy

Cervix cancer

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

Figure 13. Examples of applicators (Reprinted from Semin. Radiat. Oncol., 29/3, Tan LT, Tanderup K, Kirisits C, et al, Image-guided Adaptive Radiotherapy in Cervical Cancer, 284-298, 2019, with permission from Elsevier).

8. TECHNIQUE

for bladder: bleeding and cystitis and urinary frequency and urinary incontinence). Typical BT-related morbidity, such as telangiectasia, ulceration and fistulae, tend to be related to the dose received in small absolute volumes (e.g., 2 cm 3 , 0.1 cm 3 ). These volumes often have different locations in individual patients depending on vagina and OAR topography and applicator location (Figure 11). For small absolute volumes of 2-3 cm 3 , delineation of the outer contour of the OAR has been shown to be sufficient (Figure 12). Applicator-related and anatomy-based reference points (see 10.1.1) have also been shown to be highly predictive for some OAR morbidity. Consistent protocols for filling status of a hollow OAR is essential for comparison between centres. For bladder filling, various clinical protocols have been suggested, none of which have proven superiority. One suggested protocol is to keep the transurethral catheter on open drainage to provide an “empty” bladder [15]; this is the only practical strategy for PDR. For HDR, another option is to instil a defined volume (e.g. 50 cm 3 ) after emptying the bladder [16]; this should be carried out before the planning MRI/CT and immediately prior to each treatment. For the recto-sigmoid and other bowel, the filling status is similarly important although practice in terms of protocols is even more variable. A suggestion is to use a pre-intervention enema and a rectal tube to achieve an empty recto-sigmoid colon; this is particularly relevant for PDR treatments because of the extended treatment period. Organ motion between imaging and dose delivery may lead to discrepancies between prescribed and delivered absorbed dose. The assumption of static anatomical location of hotspots is recommended for small volumes in fractionated BT to assess the worst-case scenario accumulated high-dose region for a particular treatment.

8.1 Applicator selection Current applicators for cervix BT all have an intrauterine (IU) component (the tandem) and an intravaginal component. The most common intravaginal components are based on classical techniques i.e. ring (Stockholm) or ovoids/colpostats (Manchester, Fletcher). In subsequent developments, a single plane of straight interstitial (IS) needles was incorporated into the ring or ovoid to encompass lateral extension of disease into the parametrium more fully. Latest developments in applicators have incorporated a double plane of IS needles (straight and oblique). Some applicators have also been adapted to allow treatment of disease extension down the vagina, the so-called universal applicator. A few centres create individualised applicators for some patients to accommodate difficult tumour topography – examples include the mould technique [17] and 3D printed templates for transvaginal needle insertion [18]. Examples of some types of applicators are shown in figure 13 [19]. The selection of applicator is based on clinical examination and 3D imaging performed prior to or during the BT application taking into account the definition of the clinical target volume(s). In most centres, the type of intracavitary (IC) applicator (e.g., tandem and ring, tandem and ovoid, or tandem with a vaginal mould) is determined by the preference of the radiation oncologist and availability of equipment. However, if several applicator types are available, the type of vaginal applicator may be selected based on the vaginal geometry. The appropriate size of ring or ovoids is based on clinical examination of the vagina – the largest ovoids, ring, or cylinder that fit comfortably into the vaginal apex abutting the cervix should be chosen. Inserting a vaginal applicator that is too large