World Congress of Brachytherapy 10-12 May, 2012 - Estro-events.org

S136 World Congress of Brachytherapy 2012
PO338
VAGINAL CUFF BRACHYTHERAPY USING OVOIDS: COMPARISON OF
POINT BASED AND TARGET BASED PRESCRIPTION
S. Sharma 1 , D. Manigandan 1 , A.K. Gandhi 1 , D.N. Sharma 1 , V.
Subramani 1 , P.K. Julka 1 , G.K. Rath 1
1
All India Institute of Medical Sciences (AIIMS), Radiation Oncology,
Delhi, India
: To compare the treatment plans with point based
and target dose point based prescription methods for vaginal cuff
brachytherapy with two ovoids.
: Twenty previously treated sessions of post
operative carcinoma uterine cervix patients were studied. For all the
patients, application was done by using two Fletcher ovoids under
sedation. After application, CT scan was done at 3mm slice thickness.
The target volume was contoured and it assumed to be around the
applicator, however, in some cases, modification was done according
to the clinical and planning CT findings. Similarly, organs at risk (OAR)
i.e. bladder and rectum were contoured. The ICRU38 bladder and
rectum points were also marked on CT images. Applicators were
reconstructed using 2.5mm source step size and plans were generated
for Nucletron HDRV2 machine using PLATO planning system. In both
the ovoids, first four dwell positions were activated and dose
prescription was done by using two different prescription methods.
One is conventional point dose (PD) based and the second is target
dose point (TDP) based. For conventional PD method, the dose
prescription point was at 5mm above the superior surface of mid
dwell position of two ovoids. For TDP based method, target dose
points were created 5mm around the target. No optimization was
done after prescription. For comparison purposes, dose was
prescribed at 100cGy. For plan evaluation, following dose volume
indices were used: Volume of target that receive 100% (V100), 95%
(V95), and 90% (V90) of prescription dose, coverage index
(CI=V100/Target volume) and overdose volume index (OI=V200/V100). For
bladder and rectum, doses received by 0.1cc (D0.1cc), 1cc (D1cc), 2cc
(D2cc), 5cc (D5cc), and 10cc (D10cc) of volumes were noted. The ICRU38
bladder and rectum point doses were also noted to correlate with
volumetric doses.
: The plan comparison is summarized in Table.1. Volumetric
evaluation shows that target coverage was lower in PD based plans
than the TDP based plans. However, the OI index shows that high dose
volume was more in TDP based plans compared to PD plans. In
addition, the OAR doses were higher in TDP based method than the PD
based. In the both TDP and PD methods, the bladder doses received
by 0.1cc, 1cc, 2cc and 5cc volumes were higher compared to ICRU38
bladder point doses and doses to 10cc bladder volume were in closer
agreement with the ICRU38 bladder points. Similarly, for rectum, the
doses received by 0.1cc, and 1cc volumes were higher compared to
ICRU38 rectum point doses and doses to 2–5cc volume of rectum were
in closer agreement with the ICRU38 rectum points.
: In the CT guided PD prescription method, lesser target
coverage and lower OAR doses were observed. In TDP based
prescription, target coverage was higher and resulted in higher OAR
doses. Doses received by 10cc of bladder and 2–5cc of rectum were
closer to ICRU38 bladder and rectum points, respectively.
PO339
MRIDUMMY MARKERS OF MRIGUIDED HDR BRACHYTHERAPY FOR
INTERSTITIAL PROSTATE AND INTRACAVITARY GYN CANCERS
J. Schindel 1 , M. Muruganandham 1 , A. Eagle 2 , M. Hewitt 2 , T.
Stockman 2 , C. Pigge 3 , Y. Kim 1
1
University of Iowa, Radiation Oncology, Iowa City, USA
2
University of Iowa, Electrical Computer Engineering, Iowa City, USA
3
University of Iowa, Chemistry, Iowa City, USA
: Compare seven different MRIdummy markers for
interstitial prostate and intracavitary GYN HDR brachytherapy.
: Seven markers were used: Saline, Conray60
(Mallinckrodt medical), CuSO4 (1.5g/L), liquid Vitamin E, fish oil, 1%
Agarose gel (AGEL: 1g Agarose powder/ 100 ml distilled water), and a
cobaltchloride complex contrast (C4) (CoCl2: Glycine=4:1). Interstitial
and intracavitary phantoms were designed. The interstitial phantom
consisted of eight flexi needles (outer/inner diameter of
1.98mm/1.45mm) that were filled with each MRImarker and
embedded in 450 mL of 3% AGEL. The intracavitary phantom consisted
of 4L of 3% AGEL, a plastic tandem and ring applicator (Varian), and
MRIdummy catheters (outer/inner diameter of 2.66mm/1.87mm).
Clinical 3T MRI protocols (both T1weightedMRI (T1MRI:1mm slice
thickness) and T2weightedMRI scans (T2MRI: 3mm slice thickness))
were used. Signal intensities for each marker were characterized as
percentages compared to the 3% AGEL background using ImageJ
software.
: Some interstitial markers, even though small agent volume,
could generate favorable signals (> 100%), implying their feasibility for
MRIguided prostate HDR. The markers of CuSO4, C4, and Vitamin E on
T1MRI and 1% AGEL, Saline, and fish oil on T2MRI showed higher than
100% signals on both phantoms. The volume effect on signals was
found due to different marker volumes in the different dummy
catheters. The markers of CuSO4 and Saline showed highest signals on
T1MRI and T2MRI, respectively. Sourcereconstruction is
recommended on T1MRI, so CuSO4 and C4 markers have great
potentials as a dummy marker for both interstitial and intracavitary
brachytherapy.
: The use of interstitial markers for MRIguided prostate
HDR seems feasible. The markers of CuSO4 and C4 showed
considerably high signals on T1MRI, as did Saline on T2MRI, for
interstitial needles for prostate HDR and for a tandemandring
applicator for GYN.
World Congress of Brachytherapy 2012 S 137
PO340
DOSIMETRIC IMPACT OF NOT CORRECTING FOR THE DISTAL SHIFT
REPORTED IN VARIAN TANDEM AND RING (T&R) APPLICATORS
O. Craciunescu 1 , J. Sánchez Mazón 2 , L. Lan 3 , J. Maurer 1 , B. Steffey 1 ,
J. Cai 1 , J. Adamson 1 , J. Chino 1
1
Duke University Medical Center, Radiation Oncology, Durham NC,
USA
2
Hospital Universitario Marqués de Valdecilla, Servicio de Radiofísica
y Protección Radiológica, Santander, Spain
3
Duke University Medical Center, Department of Biostatistics and
Bioinformatics, Durham NC, USA
: Studies have shown that source stop positions
within Varian’s HDR CT/MR compatible ring applicators can deviate
from the intended positions by several millimeters, and that a
corrective shift has to be applied to limit the effect of these inherent
offsets. The purpose of this study was to investigate the dosimetric
impact of NOT applying this correction.
: Twentyseven HDR T&R clinical plans (cP)
from six different patients treated for cervical cancer in our clinic
were used in this study. Both CT and MR were acquired for each plan.
The dose per fraction was 5.5 Gy. GECESTRO guidelines were
followed for HRCTV and organs at risk (OARs): bladder, rectum,
sigmoid. ICRU 38 points A were also defined. The planning was done in
BrachyVision with a hybrid volume optimization method based on
HRCTV and ABS recommended reference lines. Depending on the
shape of the HRCTV, the posterior ring dwell positions were allowed
in the optimization for 5 patients. For 1 patient, a standard ring
loading that mimicks ovoid placement was used. To show the
dosimetric impact of NOT applying distal corrections, plans were
generated by shifting the dwells in the ring in the opposite direction
incrementally by 1 5 mm. The plans were calculated using the TG43
formalism and ACUROS, a modelbased analytical solver that
accounts for inhomogeneities. To establish clinical significance, the
mean percent difference between all metrics in each of the shifted
plans and the cP were calculated. The Wilcoxon signedrank test was
used to determine if the differences have any statistical significance,
for all cases together, but also separating patients depending on the
ring dwells activated.
: For brevity, only D2cc results for OARs for all 27 plans are
presented. Ring loading strategy did not impact the dosmetric results.
The mean percent differences between the largest shift (5mm) and
the cP for the D2cc bladder, rectum and sigmoid were 1.6, 1.7, 2.5%
for TG43, and 1.2, 1.8 and 1.4 % for ACUROS. The Wilcoxon rank sum
pvalues were > 0.05 for all the OAR metrics, shift amounts, and
method of calculation. For A_RT, A_LT and HRCTV D90, the mean
percent differences were 0.8, 0.5 and 0.6 %, and 0.6, 0.8 and 0.9 %
for TG43 and ACUROS, respectively. However, the Wilcoxon signed
rank pvalues for Point A_RT were < 0.05 for both TG43 and ACUROS,
for all shifts. Only when using ACUROS, the pvalues for HRCTV D90
were < 0.05 for all shifts.
: The dosimetric impact of NOT applying corrective shifts