Page 83 - ARNM-3-2

Advances in Radiotherapy
& Nuclear Medicine Radiotherapy in node-positive bladder cancer

was recommended. Due to the retrospective nature of the The above dose modeling generated a dose fractionation
study, obtaining consent for participation from the study of 57.5 Gy in 23 fractions with BED of 71.88 Gy, which
10
subjects was not feasible. was similar to BED of 70.13 Gy observed with 55 Gy in
10
The following parameters were identified and assessed 20 fractions.
through a review of the patients’ clinical records: 2.3. Treatment simulation
i. Patient characteristics, including age, sex,
comorbidities, and the reason for not proceeding with All patients were scanned supine with an empty bladder
surgery and rectum. Ankle and knee support were used to
ii. Features of the disease – histology, stage (tumor [T] immobilize and achieve set-up reproducibility. A 100 mL
and node [N]), and date of diagnosis Omnipaque intravenous contrast was administered with a
iii. Treatment characteristics and toxicity – information 70 sec delay. No oral contrast was used for these patients.
about concomitant chemotherapy, early toxicity (less 2.4. Target delineation
than 3 months), late toxicity (more than 3 months),
and RT (number of completed fractions) The primary clinical target volume (CTVp) included the
iv. Treatment response following chemoradiotherapy bladder and any extravesical extension, with a 5 mm margin
(CRT) completion – complete response was defined applied mainly at the tumor site. The inclusion of prostatic
as complete tumor response on both CT scan and urethra in the volume was at a clinician’s discretion, and
cystoscopy performed 3 months after treatment the whole prostate was included in patients with tumors
completion; stable disease was characterized by located at the base or invading the prostate. In addition, the
persistent tumor at cystoscopy, but no progression clinical target volume for the elective nodes (CTVn) started
evident on staging CT scan; progressive disease was at the lower border of L5, using a 7 mm margin around
defined as unequivocal evidence of progression on the vessels, including common iliac, internal and external
cystoscopy or CT scan iliac, pre-sacral (from S1 to S3), and pelvic lymph nodes
v. Survival outcomes – overall survival (OS) and down to the level of obturators (top of pubic symphysis).
progression-free survival (PFS) estimated from The bowel, bladder, bone, and muscle were excluded from
the date of diagnosis, as well as the type (local vs. the CTVn. The primary PTV (PTVp) was produced using
metastatic) and site of progression. a 15 – 20 mm superiorly and 15 mm posteriorly, anteriorly,
inferiorly, and laterally from the CTVp. The node PTV was
2.2. Development of VMAT clinical protocol produced using 10 mm in all directions from the CTVn.
The standard RT dose is 55 Gy in 20 fractions for localized
bladder cancer and 46 Gy in 23 fractions for pelvic nodes. 2.5. Treatment planning
The dose to the nodes was predefined at 46 Gy in 23 All patients were treated with VMAT using either Halcyon
fractions. Radiobiological modeling was employed to (Varian, United States) or TrueBeam (Varian, US) linear
estimate the biologically effective dose (BED) – equivalent accelerators. The doses were calculated using the Acuros
to 55 Gy in 20 fractions delivered over 23 fractions as a (dose to medium) algorithm (version 16, Varian, US). The
synchronous integrated boost to the bladder. The BED was treatment plans were optimized to achieve PTV coverage
calculated using an α/β value of 10 for the tumor, and the of V95% ≥99% (i.e., the volume of PTV receiving 95% of
aim was to keep BED for the primary tumor similar to the the prescription dose should be ≥99%) and V105% ≤2%.
bladder-only clinical protocol (i.e., equivalent to 55 Gy In addition to the target and OAR volumes, optimization
in 20 fractions), without increasing the dose or the dose structures were produced around the PTVp and node
per fraction to the pelvic nodes, which was maintained at PTVs using an inner margin of 0.5 cm and outer margin of
46 Gy in 23 fractions. 1.5 cm to enhance target conformity. Upper objectives were
The BED calculations were performed to calculate used on these structures during optimization (Figure 1).
the dose per fraction to the primary tumor (i.e., bladder 2.6. Treatment delivery
planning target volume [PTV]) for 23 fractions using
Equation 1. Before treatment delivery, all patients underwent daily
cone beam CT imaging, and the setup differences were
d corrected for all fractions.
BED = nd [1 + ] (1)
( ) 2.7. Statistical analysis
α
β
Note: d is the dose per fraction, and n is the number of Descriptive statistics, such as the frequency (percentage)
fractions. for categorical variables, were used to summarize the

Volume 3 Issue 2 (2025) 75 doi: 10.36922/ARNM025090009