Cervical To ensure consistency in the reporting of ICBT

Cervical cancer is one of the most common cancers in
the women in developing countries (1). Except for early stage cervical cancer who are  treated by only surgery, radiation therapy is
the major curative treatment options for this disease. Intracavitary
brachytherapy is a component in the curative management of carcinoma of the
cervix,which significantly improves survival(6,7) . The current treatment of choice includes external beam
megavoltage radiation (EBRT) with weekly cisplatin along with intracavitary
brachytherapy (2,3). The rapid dose fall-off around the radioactive source during
brachytherapy allows the delivery of high radiation doses to the tumour with
relative sparing of the rectum and bladder 26.      

 The probability of
local control and development of normal tissue toxicity is related to the dose
of radiation delivered.  The dose prescription for
intracavitary brachytherapy (ICBT) in cancer cervix was 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.

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 Classically, doses to the
rectum and bladder are calculated and reported using the rectum and bladder
reference points, as defined by the International Commission on Radiation Units
and Measurements (ICRU) in Report No. 38 12. The simplicity and cost-effectiveness
of radiograph-based planning has ensured its continued applicability for dose
reporting in brachytherapy 28.

 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. Recently, recommendations were given for target and organs at
risk (OAR) delineation and dose prescription on magnetic resonance imaging
(MRI) for image-based brachytherapy in cervical cancer by the GEC-ESTRO (4,5) In
absence of MRI, CT scans alone when used for brachytherapy planning can ensure
OAR doses to be kept within acceptable limits. However, CT based target volumes
have been overestimated as compared to MRI volumes17,18

  To
ensure consistency in the reporting of ICBT applications in cervical cancer,
the International Commission on Radiation Units and Measurement (ICRU)
recommended a number of parameters for doses and volumes to be considered.
These include points A and B, representing the doses in the parametria and the
pelvic wall, and the rectal and bladder points representing the organs at risk
(OARs), respectively 12. Physicians have used these reference point doses to
report treatment intensity and to estimate the maximal dose to normal tissues,
which can predict late complications. A modern approach in treatment planning
for cervical carcinoma is based on computed tomography (CT) sections and on a
3D dose distribution. This allows better assessment of dose distributions in
different volumes, such as the gross tumor volume (GTV), clinical target volume
(CTV), and OARs (rectum, bladder, and intestines). Ling et al. published the
first report describing the volumetric dose distributions from ICBT 16. In
2004, guidelines were published for proposing image-based BRT for cervical
cancer 11.

In a systematic comparison of MRI and radiograph-based planning,
Kirisits et al 14 have shown that there is a

good correlation between point doses and minimum dose to the most exposed
2 cc volume (D2cc) for both bladder

and rectum. Good correlation has  also previously been described for D2cc and
ICRU dose points, more so for rectum than bladder(22). In this study, we aimed to
compare  the 0.1-, 1.0-, 2.0-cc doses to
the bladder and the rectum with the corresponding ICRU point doses using
computed tomography (CT)-based planning in the intracavitary brachytherapy of
carcinoma of the cervix.

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