14 Nasopharynx Cancer

Nasopharynx Cancer

13

THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 10/09/2019

Table 5. Brachytherapy boost protocols for primary disease Levendag, 1997

BCI protocol

Dose (EQD2, αβ =10)

Dose (EQD2, αβ =10)

T-stage

EBRT

BT

SEQD2

EBRT

BT

SEQD2

60Gy/30F (60.0Gy 10 ) 70Gy/35F (70.0Gy 10 )

18Gy/6F (19.5Gy 10 ) 12Gy/4F (13.0Gy 10 )

66Gy/33F (66.0Gy 10 ) 70Gy/33F (70.7Gy 10 )

12-14Gy/4F (13.0-15.8Gy 10 ) 12-14Gy/4F (13.0-15.8Gy 10 )

T1

79.5Gy

79.0-81.8Gy

10

10

T2

83.0Gy

83.7-86.5Gy

10

10

F, fractions; EQD2, dose equivalent in 2Gy; Σ, cumulative

Table 6. Brachytherapy monotherapy regimens for persistent and recurrent disease Previous EBRT GEC-ESTRO (Mazeron, 2009)

BCI protocol

EQD2, αβ =10

Dose (EQD2, αβ =10)

Dose (EQD2, αβ =10)

BT

ΣEQD2

BT

ΣEQD2

12-18Gy/4-6F (13.0-19.5Gy 10 ) ≥60Gy LDR-PDR (≥60.0Gy 10 )

12Gy-14/4F (13.0-15.8Gy 10 ) 50/10F; 56/14-16F

Persistence

66.0-70.0Gy

73.0-79.5Gy

79.0-86.5Gy

10

10

10

0.0Gy 10 (Ignored)

Recurrence

≥60.0Gy

62.4-65.8Gy

(62.6Gy

; 62.4-65.8Gy

)

10

10

10

10

Persistent disease would pertain to that treated to 66-70Gy, completed within the last 2-3 months. Recurrent disease would pertain to that with previ- ously documented complete response to definitive radiotherapy, now with documented recurrence. Recurrent disease considered for full brachytherapy monotherapy dose shall ideally be at least 6 months from previous radiotherapy course. F, fractions; EQD2, dose equivalent in 2Gy; Σ, cumulative

10. DOSE, DOSE RATE, FRACTIONATION

Dosimetric outcomes The following parameters are monitored and noted: HR-CTV D95%, D90% and D85%; IR-CTV D95%, D90% and D85%; D2cc of the brainstem, spinal cord, pituitary, optic chiasm, and retina; and D2cc and mean dose of the clivus, atlanto-axial joint and soft palate. Sample Case Table 4 summarises the comparison of the classic Levendag target andOAR point doses with dose-volume parameters on 3Dplanning for a rT2 case.The Na and BOS point doses correlate poorly with the HR-CTVD90. Specifically, the former overestimates the HR-CTV D90 by 9-14%, which could lead to clinically significant HR-CTV underdosage. The C points overestimate the D2cc for the spinal cord, which receive negligible doses. Similarly, the pituitary and optic chiasm receive negligible doses.The retina D2cc is significant but is underestimated by the Re point dose; routine monitoring of the retina D2cc is recommended. Significant volumes of the soft palate receive important doses (bothD2cc andDmean >3Gy) which are underestimated by the Pa point. Similarly, significant volumes of the clivus and the atlanto-axial joint receive significant doses (D2cc and Dmean in the 1.3-2.3 Gy range), but are not monitored in OARs in the Levendag system. For these OARs that are in close proximity to the applicator, routine D2cc and Dmeanmonitoring and optimizing to keep the doses to minimum are recommended. In cases of re-irradiation, routine monitoring and minimization of doses to all of the above OARs are recommended.

Some literature data are strongly suggestive for the existence of a dose-response relationship above 65 Gy in NPC. However, dose escalation is limited by OAR tolerances. Brachytherapy can be used to deliver an additional dose to a small volume after a full course of EBRT. Wang delivers with LDR afterloading intracavitary implant 7-12 Gy at 5 mm below the mucosa [Wang, 1997]. When brachytherapy is carried out for a recurrent NPC in a previously irradiated area, 60 Gy are delivered in roughly 6 days with a LDR or PDR technique. Early HDR brachytherapy regimens, which entailed delivery of 5-8 Gy fractions, were associated with acceptable toxicity rates. Levendag et al. deliver after a rest period of 1-2 weeks, a boost dose to the primary site with HDR brachytherapy, with two 3-Gy fractions daily with a 6-hour interfraction interval. Total of fractions is 6 (after 60 Gy EBRT) for T1 - 3 tumours, and 4 (after 70 Gy EBRT) for T4 tumours. In order to further risks of late toxicity, especially with re-irradiation, it is now recommended to give HDR treatments in 3.0-4.0 Gy twice-daily fractions with at least a 6-hour interfraction interval [Mazeron, 2009; Kovacs, 2017]. With the emergence of cross-sectional imaging and 3D brachytherapy planning techniques, combined with the use of stepping-source techniques, better evaluation of dose-volume parameters and thus optimization are now possible. Improvement of intracavitary applicator designs and combination with interstitial techniques can potentially improve dosimetry and outcomes.