Isodose surface volumes in cervix cancer brachytherapy: Change of practice from standard (Point A) to individualized image guided adaptive (EMBRACE I) brachytherapy.

Authors Serban M, Kirisits C, Pötter R, de Leeuw A, Nkiwane K, Dumas I, Nesvacil N, Swamidas J, Hudej R, Lowe G, Hellebust TP, Menon G, Oinam A, Bownes P, Oosterveld B, De Brabandere M, Koedooder K, Marthinsen ABL, Lindegaard J, Tanderup K; EMBRACE Collaborative Group
Source Radiother Oncol. 129 (3), pp. 567-574 Publicationdate 19 Sep 2018
Abstract

PURPOSE

To investigate the isodose surface volumes (ISVs) for 85, 75 and 60 Gy EQD2 for locally advanced cervix cancer patients.

MATERIALS AND METHODS

1201 patients accrued in the EMBRACE I study were analysed. External beam radiotherapy (EBRT) with concomitant chemotherapy was followed by MR based image-guided adaptive brachytherapy (MR-IGABT). ISVs were calculated using a predictive model based on Total Reference Air Kerma and compared to Point A-standard loading systems. Influence of fractionation schemes and dose rates was evaluated through comparison of ISVs for α/β 10 Gy and 3 Gy.

RESULTS

Median V85 Gy, V75 Gy and V60 Gy EQD210 were 72 cm3, 100 cm3 and 233 cm3, respectively. Median V85 Gy EQD210 was 23% smaller than in standard 85 Gy prescription to Point A. For small (<25 cm3), intermediate (25-35 cm3) and large (>35 cm3) CTVHRvolumes, the V85 Gy was 57 cm3, 70 cm3 and 89 cm3, respectively. In 38% of EMBRACE patients the V85 Gy was similar to standard plans with 75-85 Gy to Point A. 41% of patients had V85 Gy smaller than standard plans receiving 75 Gy at Point A, while 21% of patients had V85 Gy larger than standard plans receiving 85 Gy at Point A.

CONCLUSIONS

MR-IGABT and individualized dose prescription during EMBRACE I resulted in improved target dose coverage and decreased ISVs compared to standard plans used with classical Point A based brachytherapy. The ISVs depended strongly on CTVHRvolume which demonstrates that dose adaptation was performed per individual tumour size and response during EBRT.