23. Anal Cancer - The GEC-ESTRO Handbook of Brachytherapy

Anal Cancer

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 01/03/2023

Figure 10: Example of follow-up by MRI (T2, sagittal and axial cross-sections) a. Imaging before treatment - b. Follow-up 3 months after treatment: persistence of residual tumour - c. Follow-up 6 months after treatment: complete regression of the tumour

and Mitomycin, followed by a 15 Gy EQD2 (α/β ratio = 10 Gy) brachytherapy boost with no gap or, if not possible, with a gap limited to 2 to 3 weeks [36]. The exact dose of the brachytherapy boost, depending on the stage of the tumour and its response to treatment, is still debated [17,24]. Some studies suggest that in case of residual disease after concurrent chemoradiation, a brachytherapy boost dose ≥ 20 Gy EQD2 should be prescribed. If complete clinical response is observed after concurrent chemoradiation, the brachytherapy dose should be ≤ 16 Gy EQD2 [37], but an overall dose of at least 54 Gy EQD2 is needed [38,39]. Dose escalation for poor responders using a brachytherapy boost seems to improve the clinical outcome, without an increase in late side effects [38]. Brachytherapy boost can be delivered by pulsed-dose-rate (PDR) brachytherapy or high-dose-rate (HDR) brachytherapy. LDR brachytherapy has been the first and the most utilized technique with excellent rates of local control and relatively low toxicity [27,40]. The end of the commercialisation of iridiumwires in some countries entailed the need to develop other brachytherapy techniques [41]. PDR and HDR brachytherapy provide similar rates of disease control and toxicity (1) with safer irradiation than LDR techniques in terms of radioprotection of the medical staff. Optimization of dose distribution used with PDR/HDR brachytherapy represents in general a real advantage compared to LDR brachytherapy [42]. For PDR brachytherapy, the recommended average dose rate is 0.5 to 1 Gy/hour [8], to mimic the biological effect of the historical LDR technique.

For HDR brachytherapy, there is lack of consensus on doses and fractionation schedules.There is still limited literature on dosimetric and clinical results of HDR brachytherapy in anal cancer. Doses and dose fractionation thus vary according to local protocols, but overall refer to the biological equivalent of 15Gy of LDR/PDR techniques. Published series typically consist of 2-7 fractions of 3-7 Gy. In one study [43], patients with complete clinical response received a total dose of 12 Gy in three fractions over 24 h (one fraction delivered the day of implant and two fractions at least 6 h apart the day after). Patients with partial response received a total dose of 16 Gy in four fractions over 48 h with a similar interval between fractions. In a retrospective review [44], anHDR dose of 14 Gy in 7 fractions over 3 days gave equivalent control to an EBRT boost. In another study [45], the dose per fraction was 3 Gy delivered twice daily with an interfraction interval of 6-8 hours. Two brachytherapy dose schedules were used: 21 Gy in seven fractions and 18 Gy in six fractions depending on response to EBRT. Another study [9] delivered two to three fractions of 5Gy over 1 to 2 days.

11. MONITORING

Patient follow-up and tumour evaluation (clinical and imaging) are not specific to brachytherapy. It is usual to perform an evaluation at two months, then at least every four months for two years and then every six months until five years after the end of treatment. It is important that the brachytherapist participates in this evaluation.