988 / 1096
S972
ESTRO 36
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Results
The beam stability is within 3% over 1 hour and the dose
homogeneity at a 40 mm diameter breast applicator
surface is within ± 5% of the central axis dose. The
percentage depth dose at 5 mm is between 35% and 65%
depending on the KVp, FSD and applicator
diameter. Radiation protection to comply with regulation
is easily achieved using a machine mounted shield and the
P+ can be used in a room with only 0.3 mm lead equivalent
shielding or none if room large (> 6 m X 6 m). The P+ can
deliver a high dose to small volume in accessible tumors
such as skin cancer (especially facial and eyelid)
using applicators between 1 and 4 cm, rectum
(endoscopic approach)using applicators 2, 2.5 and 3 cm,
breast (IORT)using a dedicated spherical Nice Breast
Applicator (3 to 5 cm diameter). In the near future it is
proposed that vaginal vault irradiation (stepping source)
and other IORT sites will be possible using P+.
Conclusion
The Papillon +
TM
is a new multipurpose CXB 50 KVp
machine with the advantage of a high dose rate and easy
radioprotection. First clinical results achieved in Nice will
be presented at time of the meeting.
EP-1767 The Dosimetric Consequences Throughout The
Treatment Time In APBI With SAVI Applicators.
S. Chandrasekara
1
, S. Pella
2
, M. Hyyovain
3
, P. Janeil
2
1
Florda Atlantic University, Physics, Boca raton, USA
2
Florida Atlantic university, Physics, Boca Raton, USA
3
Florida Atlantic University, Physics, Boac Raton, USA
Purpose or Objective
To analyze the variation in dose received by the organs at
risk (OARs), that occur during treatment time ( 10
treatments) of early stage breast cancers with APBI using
SAVI applicators.
Material and Methods
A retrospective analysis of 15 patients treated with SAVI
applicators at SFRO Boca Raton were considered for this
study. Treatment plan is made based on the initial CT scan
that is taken post the insertion of the applicator. Then the
patient is treated on outpatient basis on 10 fractions of
3.4 Gy over 5 days.The CT scans of these patients, taken
before each treatment were separately imported in to the
treatment planning system and registered with the initial
CT scan respective to the applicator. Three radio channel
markers of the applicator are used as reference points to
conduct landmark registration on each CT scan. Difference
in Max Dose received by skin, ribs and PTV(Planning target
volume) during each treatment is recorded.
Results
Contours of any of the OARs were not exactly similar when
CT images were fused on each other. Deduction in volumes
of PTV and cavity was noticed. There was always a
difference between received doses by the OARs and PTVs
between treatments. Variations in received dose by Skin
and ribs were statistically significant for 3 treatments and
2 treatments respectively under 5% level. Variations were
statistically significant for 4 more fractions for both organs
under 10% level. Some data indicates, few times patients
received more than 145% of prescribed dose that breach
the specific guidelines of APBI.
Conclusion
The difference recorded in volumes of OARs and iso-doses
near the OARs between treatments indicate that the
received doses to OARs differ from the prescribed dose in
the initial treatment plan. Similarly PTV receiving a lesser
dose than the prescribed dose affects the quality of the
treatment. It appears that taking a CT scan before each
treatment and re-planning is important at this stage to
minimize the risk of delivering different doses than the
prescribed.
Electronic Poster: Brachytherapy: Prostate
EP-1768 What is the proper dose in single fraction
HDR brachytherapy as monotherapy for prostate
cancer?
S. Ruiz Arrebola
1
, A.M. Tornero-López
2
, J.M. De la Vega
3
,
P.J. Prada
1
, D. Guirado
3
1
Hospital Universitario Marqués de Valdecilla,
Department of Radiation Oncology, Santander, Spain
2
Hospital Universitario Dr. Negrín, Unidad de Radiofísica,
Las Palmas de Gran Canaria, Spain
3
Complejo Hospitalario de Granada, Unidad de
Radiofísica, Granada, Spain
Purpose or Objective
High dose rate brachytherapy (HDRBT) as monotherapy for
prostate cancer is applied with several fractionation
schedules. Usually the linear-quadratic (LQ) model is used
to establish their equivalence. However, using the
currently accepted value of α/β for prostate cancer, a
significant discrepancy between the LQ model predictions
and clinical outcomes is found for the only single fraction
schedule in use with long-term results [1].
We aim to determine the value of the absorbed dose for
an extreme hypofractionation regime of one fraction in
HDRBT monotherapy leading to a biochemical failure rate
similar to that of most widely used regimes.
Material and Methods
We used available published data from biochemical
control at 5 years, for prostate cancer patients of low and
intermediate risk treated with exclusive HDRBT: 7 clinical
studies with 9 fractionation schedules, from 1 fraction of
19 Gy to 9 fractions of 6 Gy per fraction.
To compare the different schedules, we used the
equivalent total dose in 2 Gy fractions, and to describe the
biochemical control (BC), we used the LQ model together
with the logistics probability function: