Brachytherapy in cancer cervix: Time to move ahead from point A?

Abstract

Brachytherapy forms an integral part of the radiation therapy in cancer cervix. The dose prescription for intracavitary brachytherapy (ICBT) in cancer cervix is based on Tod and Meredith's point A and has been in practice since 1938. This was proposed at a time when accessibility to imaging technology and dose computation facilities was limited. The concept has been in practice worldwide for more than half a century and has been the fulcrum of all ICBT treatments, strategies and outcome measures. The method is simple and can be adapted by all centres practicing ICBT in cancer cervix. However, with the widespread availability of imaging techniques, clinical use of different dose-rates, availability of a host of applicators fabricated with image compatible materials, radiobiological implications of dose equivalence and its impact on tumour and organs at risk; more and more weight is being laid down on individualised image based brachytherapy. Thus, computed tomography, magnetic-resonance imaging and even positron emission computerized tomography along with brachytherapy treatment planning system are being increasingly adopted with promising outcomes. The present article reviews the evolution of dose prescription concepts in ICBT in cancer cervix and brings forward the need for image based brachytherapy to evaluate clinical outcomes. As is evident, a gradual transition from "point" based brachytherapy to "profile" based image guided brachytherapy is gaining widespread acceptance for dose prescription, reporting and outcome evaluation in the clinical practice of ICBT in cancer cervix.

Keywords: Cancer cervix; Computed tomography-guided brachytherapy; Image guided brachytherapy; Intracavitary brachytherapy; Magnetic resonance imaging-guided brachytherapy; Point A; Ultrasound guided brachytherapy.

Figure 1

Schematic representation of antero-posterior and lateral radiographs with the applicator for estimation of various applicator components. IUTL: Intrauterine length; VDL: Vertical displacement; ADL: Antero-posterior displacement; ROV: Right ovoid to os; LOV: Left ovoid to os LOV; BP: ICRU bladder point; RP: ICRU rectal point; ICRU: International Commission on Radiation Units and Measurements. Reproduced with permission[18].

Figure 2

Fusion of standard Fletcher-Suit application positions of three insertions in a given patient with respect to the bony pelvis depicted in antero-posterior and lateral projections. Reproduced with permission[21]. LAT: Lateral; AP: Antero-posterior.

Figure 3

Fusion of three 6 Gy International Commission on Radiation Units and Measurements 38 dose distribution in a given patient with respect to the cervical os depicted in antero-posterior and lateral projections. Reproduced with permission[21].

Figure 4

Scatter-plot for tumour volume vs percentage of tumour enclosed within the 6 Gy isodose lines. Reproduced with permission[28].

Figure 5

Tumour well covered within 6 Gy isodose volume (A) and tumour lying outside the 6 Gy isodose volume (B). Reproduced with permission[28].

Figure 6

Positron emission tomography-computed tomography explore for brachytherapy planning in cervical cancers. A and B: Positron emission tomography-computed tomography with the Vienna applicator; C and D: Depiction of the 6 Gy isodose volume. The tumour in relation to the applicator is visualized within the 6 Gy volume.