29 Skin Cancer

Skin Cancer

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 30/04/2017

5. WORK UP

implant patients. Moreover, it allows control of the active source length making the treatment volume conformal to the target volume and respecting the healthy surrounding tissue, with dose optimization. The short irradiation time allows for some extra shielding on critical structures such as the eyes. With regard to the more conventional orthovoltage photons and electrons, the dose distribution on the skin surface with contact HDR-BT shows a sharp gradient, similar to the conventional low- energy X-ray, in contrast to the electron dose distribution. This gradient allows a relatively higher dose to the first mm and a lower one to the deeper tissues. Moreover, the multicatheter applicator in moulds allows us to conform the isodose to irregular surfaces, which is not possible using orthovoltage photons or electrons. Electron beam therapy often requires cut-outs, in most cases the cut-out sizes are small and then specific dosimetry needs to be evaluated. Moreover, if collimation is done at a distance from the skin, then larger penumbra should be considered. Typically, additional collimation at skin with lead inserts is required to improve penumbra. Full-scalp irradiation with brachytherapy may have a lower risk of excessive brain irradiation than external beam irradiation because the intensity of surface-mould brachytherapy drops off rapidly away from the source [7]. A study on the technical considerations and dosimetry of HDR surface applicators shows that the availability of optimization techniques results in superior dose uniformity at the prescription depth [8].

All suspected lesions should have a biopsy to confirm the diagnosis. Local tumour extension should be carefully documented. Exact measurements (in mm) are required. Photographs may help to document local tumour extension. Suspected deep infiltration into the orbit, ear or other structures, should be studied byCTor other investigations. Agood collaboration with dermatologists is very helpful in order to define the real extension of the tumour, especially in basal cell carcinomas where a subdermal extension is not easily evaluated. Examination under direct vision with a dermatoscope can help to delineate better the margins. High-resolution ultrasound with frequencies higher than 18MHz (30MHz) is a good tool to document the widespread and depth of small lesions [6].

6. INDICATIONS, CONTRA-INDICATIONS

6.1 Indications • Basal cell as well as squamous cell carcinoma is radiosensitive, andmost of these lesions are detected at an early stage, when the chance for cure by radiation is high. Both external radiotherapy (low energy X-ray or electron beam) and brachytherapy can be used, but brachytherapy is preferred to X-rays or to electron beams when these are difficult to apply, for example on curved surfaces. • Exclusive brachytherapy: the main indications are epidermal skin cancers T1 - T2 N0 on the face for which curative surgery with adequate margins cannot be offered without mutilation or without the need for extensive reconstructive surgery under general anaesthesia. • As a boost in larger T2 - T3 or in N+ cases after external beam radiotherapy to the primary tumour and lymph nodes. • As a postoperative procedure when there are close or positive margins, or in some cases of nerve involvement. • Upper eyelid lesions for LDR or PDR BT, but not for HDR • Where the anatomical situation makes the source positioning needed to provide adequate covering of the target volume impossible: Pinna tumours involving both the concha and the external auditory canal, ear conduct or any other site, unless special devices can be delivered to get adequate dosimetry. 6.3 Comparison of HDR Brachytherapy with LDR and external beam therapy Contact BT with HDR has some relative advantages compared to LDR interstitial BT with fewer radioprotection issues; the treatment is administered on an outpatient basis, in fast sessions, and isolation is not required, a very important issue whenmanaging elder patients. The moulds, flaps and surface applicators are easy to place and patients do not report discomfort, unlike interstitial 6.2 Contraindications • Malignant melanoma of the skin. • Skin cancers invading bony structures.

7. TUMOUR AND TARGET VOLUME

The clinical target volume for well-delineated squamous cell or basal cell carcinomas is the palpable or visible tumour with a safety margin of 3-5 mm for skin cancers and 5 mm for lip cancers. For poorly defined lesions, such as morphea like basal cell carcinomas, a wider safety margin is taken (7-10 mm). The depth of the tumour can be evaluated by clinical assessment or by means of high frequency ultrasound.

8. TECHNIQUE

Two different techniques are useful for skin cancers: contact (plesiotherapy) and interstitial brachytherapy. Contact brachytherapy can be used with the three modalities (LDR, PDR or HDR) through flaps, moulds or contact surface applicators that are applied on the skin area to be treated; no anaesthesia required. Interstitial implants have been used in several ways with low dose rate (LDR) by means of hypodermic needles, silk wires, and inner nylon tubes with flexible 192-Ir wires. Nowadays, high dose rate (HDR) or pulsed brachytherapy (PDR) use afterloading rigid needles or plastic tubes.