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

S28 World Congress of Brachytherapy 2012
: Utilities necessary to facilitate routinebased and time
efficient invivo BT dosimetry is presented. The measured 1.5 mm
probe position stability provides a crucial dose rate uncertainty
component during both PDR and HDR BT dosimetry. The thin and light
tight dosimeter probe allows for both easy probe insertion and sub
mm stability measurements.
OC70
A REVOLUTIONARY MULTIPOINT PLASTIC SCINTILLATION DETECTOR
FOR IN VIVO DOSIMETRY IN HDR BRACHYTHERAPY.
F. TherriaultProulx 1 , L. Archambault 2 , S. Beddar 1 , L. Beaulieu 2
1
UT MD Anderson Cancer Center, Department of Radiation Physics,
Houston, USA
2
HotelDieu de Quebec, Departement de RadioOncologie, Quebec,
Canada
: There is a growing interest for in vivo dosimeters
in high dose rate brachytherapy (HDR). If plastic scintillation
detectors (PSDs) have been shown to possess advantageous
characteristics, they require a coupling to an optical guide for each
point of measurement. In brachytherapy the space for dosimeter
insertion is often limited (e.g. in catheters). The necessity of an
optical guide for each scintillating element then often limits the
measurement to a single point per region of interest. The purpose of
our study is to develop a PSD capable of measuring dose at multiple
points along a same optical transmission line for Ir192 HDR/PDR
brachytherapy and to demonstrate additional potential applications
for such a detector.
: A multipoint PSD composed of three
different scintillating elements (2 mm long x 1 mm diameter, 25 mm
apart) and a single collection plastic optical fiber (20 m long x 1 mm
diameter) was built, as depicted in figure 1. Optical spectra (Spec.)
were acquired at the output of the collection optical fiber. The
emission spectra from the scintillating elements were obtained using a
well collimated xray source. The light spectrum of the stem effect
generated in the clear optical fiber was obtained through irradiation
using the Ir192 HDR brachytherapy source. A novel approach allowed
us to calculate the individual contribution (CX) of each lightemitting
component (see equation 1). The dose to a specific scintillating
element can be calculated from equation 2 by using at least one
knowndose condition to this element.
: Dose measurements were performed with the multipoint
detector placed at radial distances (r) of 1.0 cm and 2.0 cm from the
source inside a polystyrene phantom and compared to data from the
treatment planning system (TPS). Figure 1 shows the dose integrated
by the detector by each scintillating element for each source positions
along the z axis together with the expected dose as calculated by the
TPS. There is a (4.6±1.0)% average difference between the measured
dose and the dose from the TPS for individual dwell positions. The
summation of measurements for all dwell positions differs from the
dose calculated across the entire catheter by only (2.1±1.0)%. On top
of their use for simultaneous multipoint dosimetry, we showed that
the scintillating elements were capable of determining the source
position along the zaxis with a (0.8±0.2) mm accuracy.
: This study shows for the first time it is possible to
measure accurately dose at multiple positions in HDR brachytherapy
using a waterequivalent detector with a single line of signal
World Congress of Brachytherapy 2012 S 29
transmission. This will be useful for spatially constrained applications
and will decrease the need for additional catheter implants. Together
with its capacity to determine accurately the source position in space
and all the other advantages known to PSDs, the multipoint PSD has a
bright future and should lead to the development of various
applications in HDR/PDR brachytherapy for both in vivo dosimetry and
pretreatment quality assurance.
OC71
SINGLE NUCLEOTIDE POLYMORPHISMS (SNP'S) ASSOCIATED WITH LATE
RADIATION TOXICITY AFTER PROSTATE BRACHYTHERAPY
N. Leong 1 , M. Parliament 1 , K. Martell 2 , S. Ghosh 3 , N. Pervez 1 , J.
Pedersen 1 , D. Yee 1 , A. Murtha 1 , J. Amanie 1 , N. Usmani 1
1 Cross Cancer Institute, Radiation Oncology, Edmonton, Canada
2 University of Alberta, Faculty of Medicine, Edmonton, Canada
3 University of Alberta, Oncology, Edmonton, Canada
: Excessive toxicity from prostate brachytherapy
treatment may be related to increased radiosensitivity from genetic
polymorphisms. This study was designed to identify particular single
nucleotide polymorphisms (SNP's) that were associated with high
toxicity after therapy in order to determine possible markers for
increased radiation sensitivity
: 349 patients treated with prostate
brachytherapy at the Cross Cancer Institute between 1998 and 2010
provided saliva samples from which DNA was extracted for this
research ethics board approved study. In the cohort of patients with
at least 2 years of followup, 41 patients were identified as having
high late toxicity (≥ RTOG grade 2 GI or GU toxicity), and 110 patients
were identified as controls without high late toxicity. We analyzed 15
SNP's from 13 genes (MSH6, GSTA1, SOD2, NOS3, GSTP1, ATM, LIG4,
XRCC1, XRCC3, RAD51, TP53, TGFβ1, ERCC2) for correlation with
increased late toxicity. Patient factors and dosimetric parameters
were also collected for the analysis.
: All 15 proposed SNP's demonstrated polymorphism within the
study population. We implemented a univariate analysis, with
Bonferroni correction, to examine the correlation between variant
allele SNP's (versus wild type) and the presence of increased toxicity.
This revealed a statistically significant relationship in 3 of the SNP's
(p