ABSTRACTS OF THE 21st ANNUAL MEETING OF THE ITALIAN ...

the surgical specimens and 20.2% in the postmortem cases.
Tumors can metastasize to the bladder by direct spreading or
by means of hematogenous or lymphatic spread (2). In one
study, approximately 54% of metastases from bladder cancer
were located near the bladder neck and trigone areas, however,
metastatic colon cancer commonly involves the fundus (3).
The treatment of secondary bladder cancer can be performed
by an open or transurethral resection, and/or by a combination
of chemo- and radiotherapy. However, due to the rarity of
these conditions and to the lack of any large series comparing
the various surgical options, the optimal treatment is unclear.
The possibility of metastasis should be considered in patients
with a history of colonic adenocarcinoma who present with
adenocarcinoma of the bladder. The use of an
immunohistochemical panel is recommended to differentiate
between primary and metastatic tumors (3).
1 Kobayashi T, Kamoto T, Sugino Y, Takeuchi H, Habuchi T
and Ogawa O: High incidence of urinary bladder
involvement in carcinomas of the sigmoid and rectum: a
retrospective review of 580 patients with colorectal
carcinoma. J Surg Oncol 84(4): 209-214, 2003.
2 Bates AW and Baithun SI: Secondary neoplasms of the
bladder are histological mimics of nontransitional cell
primary tumors: clinicopathological and histological features
of 282 cases. Histopathology 36(1): 32-40. 2000.
3 Velcheti V and Govindan R: Metastatic cancer involving
bladder: a review. Can J Urol 14(1): 3443-3448, 2007.
125
SETUP ACCURACY WITH THE USE OF CBCT
IMAGE-GUIDED RADIOTHERAPY IN THE
TREATMENT OF PROSTATE CANCER
Francesco Dionisi, Barbara Bortolato, Francesco Bracco and
Mauro Palazzi
Radioterapia Oncologica, Azienda Ospedaliera Niguarda Ca’
Granda, Milano, Italy
Background: Modern radiotherapy in prostate cancer can be
delivered with sophisticated techniques, such as 3D conformal
radiotherapy, and intensity modulated radiation treatment
(IMRT), which allow for a shaped distribution of dose around
the target with an acceptable toxicity for the nearby healthy
organs (bladder, rectum). There has also been a parallel
advancement in the methods available to verify accuracy of
the patient setup. The aims of the present study were: (i) to
evaluate the effectiveness of cone beam-computed tomography
(CBCT) to determine set-up accuracy in radiotherapy
treatment for prostate cancer; and (ii) to validate an internal
online correction protocol with the goal of reducing systematic
1874
ANTICANCER RESEARCH 31: 1807-1956 (2011)
errors, thus establishing the proper clinical target volume
(CTV) to planning target volume (PTV) margin. Patients and
Methods: The study population consisted of 20 low-
/intermediate-risk prostate cancer patients undergoing
definitive radiotherapy to a total dose of 76 Gy with the use
of an Elekta linear accelerator mounting a CBCT scanner
(Elekta Synergy S, Elekta Oncology Systems Ltd, Crawley,
U.K.). Patients were treated in the supine position with a full
bladder and empty rectum; proper immobilization devices
(Orfit industries, Wijnegem, Belgium) were adopted. The CTV
was identified as the prostate gland and the entire seminal
vesicles plus a 7 mm margin everywhere, except for 5 mm in
the posterior direction and for 1 cm in the superoinferior (SI)
direction. Pre-treatment image registration was performed
using a soft-tissue algorithm applied to a region of interest
including the whole PTV. CBCT was executed for the first
three fractions to detect systematic errors with an action level
of 3 mm; subsequent registrations were performed every seven
fractions. Only translational (no rotational) errors were
considered by the present analysis. The overall mean shift (M),
the SD of the group systematic error (Σ), the root mean square
of the SD of all patients (σ) and the 3D vector of displacement
were calculated. The Van Herk formula (1) (2.5 Σ+ 0.7 σ) was
used to determine CTV to PTV margins. The impact of the
correction protocol was determined by quantifying the set-up
accuracy without the application of systematic adjustments.
Results: A total of 168 CBCT scans (average 8 per patient,
range 6-11), resulting in 504 positional errors along the
mediolateral (ML), SI and anteroposterior (AP) axes, were
analyzed. A systematic correction was requested in 60% of
patients, mostly (66%) in AP direction. The values of M were
−0.2, 1.5 and 0.8 mm in the 3 axes, respectively. The SD of
the group systematic error (Σ) was 1.8, 2.1 and 1.9 mm along
ML, SI and AP directions, respectively; these values rose to
2.5, 2.5 and 4.1 mm in the 3 axes if systematic corrections
were not considered. The values of σ were 2.4, 3.3 and 3.6
mm in the three directions. The mean 3D vector of
displacement was 3.48±1.4 mm. CTV-PTV margins were
6.18, 7.56 and 7.27 mm along the three axes. In the absence of
systematic corrections, a CTV-PTV margin of 7.93, 8.59 and
12.77 mm in ML, SI and AP directions was required,
respectively. Discussion and Conclusion: CBCT image
registration ensures accurate targeting in prostate radiotherapy.
The internal correction protocol allowed for a significant
reduction of CTV-PTV margins, especially in the AP
direction. A PTV margin of 8 mm in all directions seems
appropriate: a margin of 5 mm in the posterior direction to
reduce rectal toxicity could be achievable (i) by the
introduction of a dietary protocol (2) to decrease both
systematic and random errors, and (ii) by increasing the
number of image-guided fractions. The acquisition of posttreatment
CBCT might be helpful in quantifying intrafraction
prostate motion.