13 Head and Neck - Oropharynx

Head and Neck - Oropharynx

16

THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 15/02/2021

With stepping source after loaders and current planning systems there are options of geometric and graphical optimization which can be considered (Figure 27 a and b). Plan evaluation Plan evaluation is done by slice by slice evaluation of the target volume coverage and also with the use of dose volume indices. Typically the coverage index of the GTV init and GTV res , CTV-IR and CTV-HR is evaluated. For evaluation the GTV D98 for the GTV init and GTV res are documented. When the dose is prescribed on the CTV-IR, D98, D90 and D50 of the same are documented. The D2cc doses to critical structures such as mandible, parotid and spinal cord should also be documented. In the situationwhere a target volume is not delineated dose volume parameters related to the implant are documented. This includes V100, V150 and V200 for the implant volume. Quality indices such as Dose Homogeneity Index (DHI) described by (V100-V150)/V100 and Dose non-uniformity ratio (DNR) described by V150/V100 should be used where V100 is the volume in cc receiving 100%of the prescribed dose and V150 is the volume in cc receiving 150% of the prescribed dose.

For PDR brachytherapy total doses of 66Gy with pulse sizes of 50 to 60 cGy per hour is recommended in radical cases.

Boost Brachytherapy The majority of patients are considered for boost BT after 46-50Gy EBRT. In such a scenario a BT dose of 20-30Gy LDR equivalent is recommended. A dose per fraction ranging from3-6Gy per fraction has been used in the literature [36], however the recommended fraction size is 3.0-4.5Gy per fraction. The total dose of HDR ranges between 15-30Gy and depends on the EBRT dose which ranges from 45-60Gy. Typically used fractionation after EBRT of 50Gy is 21Gy/7# (EQD2:22.75, BED:27.3Gy). With PDR a total dose of 15-35 Gy with pulse sizes of 50 to 60 cGy per hour has been recommended for a boost after EBRT of 45-60Gy (30). Recurrent BT For BT to recurrent tumours LDR equivalent doses of 60Gy are recommended. Typical HDR doses are 3-4.5Gy per fraction BID for 10-12 fractions (EQD2:50-55Gy, BED:65Gy). For PDR doses of 54-60Gy with pulse sizes of 50 to 60 cGy per hour are recommended (30). Perioperative BT For perioperative brachytherapy a commonly used fractionation is 32Gy: 4Gy x 8 fractions (EQD2:37Gy, BED:44Gy) when there is an R0 resection and 40Gy: 4Gy x10 fractions (EQD2:47Gy, BED:56Gy) when there is an R1 resection. Postoperative BT For postoperative BT doses of 50Gy LDR equivalent are recommended. Typical HDR fractionations used are 4Gy bid delivering 10-11 fractions.

10. DOSE, DOSE RATE, FRACTIONATION

Radical Brachytherapy For radical BT dose per fraction ranging from 2-6 Gy per fraction ( at reference isodose) has been used in the literature. However recommended fractionation ranges between 3.5-4.5Gy per fraction.[6,36–39] Typically two fractions are given each day with a minimum gap of 6 hours. Minimum doses of 60-66Gy LDR equivalent are recommended. A common fractionation is 52Gy/13# (EQD2:60.67Gy, BED: 72.8Gy) .

Figure 27a: Target volume coverage of a base of tongue primary where the plan is optimized using geometrical optimization

Figure 27b: Target volume coverage of a base of tongue cancer where coverage has been improved using graphical optimization