DOI: 10.7910/dvn/13bfhp
title: Replication Data for: A retrospective analysis to compare the dosimetric parameters of two rectum-sparing techniques during intracavitary brachytherapy with tandem-ring applicators for cervical cancer

description: There are many confounding variables that influence the doses to organs at risk during a specific intracavitary brachytherapy (ICB) session on a patient receiving treatment for cancer cervix. For example one of the confounding variable is individual anatomy. Clinical experience suggests that the anatomical variations among patients undergoing ICB play a crucial role in the dosages received by organs at risk during intracavitary brachytherapy procedures. While some patients exhibit anatomy that results in minimal doses to critical organs when specific brachytherapy applicators and organ retraction techniques are utilized, others display higher doses due to inherent anatomical variations, for the same dose prescribed to the tumor utilizing same applicator type, technique and loading pattern. Therefore, when comparing two techniques for rectum separation in terms of OAR doses, it is essential to consider that the individuals in the comparison groups may vary. This variation could potentially influence the positive outcomes observed in a group, leading to uncertainty about whether these outcomes are truly attributed to the technique itself or simply due to a higher number of patients with favorable anatomy in that specific group. To mitigate this confounding factor, it is imperative that both techniques are applied to each patient individually, ensuring that the comparison groups consist of the same individuals. Other confounding variables like size of the ring or ovoids, tandem length, tandem angle, loading pattern, point A definition can also influence the doses to organs at risk. In our study titled: A retrospective analysis to compare the dosimetric parameters of two rectum-sparing techniques during intracavitary brachytherapy with tandem-ring applicators for cervical cancer, in the subset analysis all these variables are matched in both comparison groups by ensuring that both techniques are applied on each patient during two sessions performed repeating the tandem-ring applicators with same physical parameters. Therefore the two sessions done on one patient differ only with regard to rectum separation technique. We want to share in detail the physical parameters that we took into account during each ICB session and help other researchers to critically examine our work. Intention is to make our work transparent for feedback and continued improvement.
description: This data is of locally advanced cervical cancer (LACC) patients with stage
IB2 to IVA as per International Federation of Gynaecology and Obstetrics-
2018 (FIGO-2018), who received treatment with curative intent, between
January 2021 to August 2022, in our institution. Treatment in all patients
began with EBRT in a dose of 45-50.4 Gy @ 1.8- 2 Gy per fraction, to the
whole pelvis with concurrent weekly cisplatin. They were assessed to be fit for
ICB within two weeks of completing EBRT to receive HDR ICB in 3-4 sessions
of 7Gy or 2 sessions of 9Gy each. All ICB procedures were done in the
operation theatre of our department. After the procedure, orthogonal
radiographs were acquired with applicators in place on a conventional
simulator (Varian, Acuity, USA), and the images were transferred to the
treatment planning system (TPS) via a digital imaging and communication in
medicine connection. ICB treatment planning was done on the TPS Oncentra
Brachy v4.6 and was delivered by Nucletron, Microselectron HDR V3 (18-
channel) remote after-loading machine using Ir-192. The orthogonal images
with applicators in place were reconstructed and source positions were loaded
according to standard loading pattern consistently practiced in our
department, to recapitulate the familiar and symmetric pear-shaped dose
distribution typically used in low dose rate (LDR). Point A was taken as 2 cm
superior to the lower most intrauterine source along the axis of the intrauterine
tandem and 2 cm lateral in the plane of the uterus. The dwell times were
equal for all dwell positions. The doses to the ICRU rectal point, bladder point
and point B were taken according to the recommendations of the ICRU-38
and reported and recorded for each ICB session in all cases. The following
parameters were studied for all plans: tandem length, tandem angle and ring
size of the applicator used during a particular session of ICB. The dwell
positions along the central tandem and in the ring were noted for each
individual fraction. The accuracy of the prescribed point A, point B, rectal point
and bladder points was verified. As the absolute dose prescribed to point A is
different in two HDR regimens, it is normalized to 100% to simplify the data
analysis. For the same reason, the absolute doses to point B and the ICRU
rectal and bladder points were also expressed as a percentage of the
prescription dose.
We measured a pear-shaped 100% isodose reference volume (Volref) for
each ICB session and described the volume in terms of its three maximal
dimensions: height (dh) measured in an oblique frontal plane along the
intrauterine sources, width (dw) measured in the same plane perpendicular to
the intrauterine sources and thickness (dt) measured in the oblique sagittal
plane perpendicular to the intrauterine sources. Volref was calculated as the
product of dh ×dw ×dt [2]. Similarly, H, W and T were applied to the same
parameters of a 60 Gy reference volume (Vol60Gy), which was defined as the
60 Gy isodose surface resulting from the additional dose contribution from
whole pelvic irradiation and all intracavitary insertions according to ICRU-38
recommendations. Applying the linear-quadratic model and an alpha/beta
ratio of 10 Gy for the tumor effect, the isodose curve, which encloses the 60
Gy volume for patients who received 50 Gy EBRT followed by two sessions of
9 Gy each, was represented by 3.15 Gy. Similarly, the 60 Gy isodose volume
was enclosed by 2.35 Gy in patients who received 50 Gy EBRT followed by
three sessions of 7 Gy each. The total reference air kerma (TRAK) values for
each ICB session were also recorded. The first uploaded data spreadsheet is

of the subset of 37 patients instead of 41 in the study. We omitted 4 patients
as during all ICB sessions utilizing TR applicators on them, singular rectum
separation technique was applied, which would have prevented us to carry
out an intra patient comparison of two techniques. The second uploaded
spreadsheet contains the data of all the 41 patients in the study. Out of total
141 sessions on 41 patients, 112 were performed utilizing TR applicators and
29 utilizing tandem-ovoid (TO) applicators. The ICB sessions done utilizing
TO applicators were excluded. Out of 112 ICB sessions performed utilizing
TR applicators, one session involving patient number 23, with a tandem
length of 2cm, was excluded from the analysis. This left 111 ICB sessions for
analysis. Out of these 111 sessions, 44 ICB sessions performed using an RR
alone for rectum separation constituted the RR group, and 67 ICB sessions, in
which an RR blade was combined with customized VP, constituted the
RR+VP group.