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ESTRO 36 2017
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same score, 36% had a better final score, and 4.4% had a
worse final score. Patient age, tumor location, tumor size,
number of catheters, V100 (volume receiving 100% of the
prescription dose), V150 (volume receiving 150% of the
prescription dose), DNR (dose non-uniformity ratio), and
skin D
max
(maximum skin dose) were correlated with the
final cosmetic scores and with the change in cosmetic
scores between both photographs. Only lower DNR values
(0.3 vs 0.26; p=0.009) were significantly associated with
improved cosmetic outcome vs same/worse cosmetic
outcome.
Conclusion
APBI using interstitial multicatheter HDR-IMBT adjuvant to
BCS results in acceptable rates of late toxicity and
cosmetic outcome. Deterioration in the breast cosmetic
scores occurs in less than 5% of the patients. The final
breast cosmetic outcome seems to be mainly influenced
by the cosmetic result of the surgery. Lower DNR value is
significantly associated with better cosmetic outcome.
PO-0923 Does catheter entry-exit dosimetry correlate
with grade of skin marks after breast brachytherapy?
T. Wadasadawala
1
, R. Krishnamurthy
1
, U. Gayake
1
, R.
Phurailatpam
1
, S. Paul
1
, R. Sarin
1
1
Actrec-Tata Memorial Centre, Radiation Oncology, Navi
Mumbai, India
Purpose or Objective
Grade of post-implant skin marks after multi-cathetar
interstitial brachytherapy (MIB) is an important factor in
determining cosmesis. This study intends to establish the
correlation if any between catheter entry-exit (E-E)
dosimetry and grade of skin marks at the E-E sites.
Material and Methods
Visibility of the post implant E-E catheter marks was noted
plane-wise for 25 patients (173 planes) with minimum 18
months follow-up post implant. All patients were treated
with 34 Gy in 10 fractions, twice a day at minimum 6 hours
apart. These were graded as 'not visible', 'faint', 'clear' and
'prominent'. Dose received by the skin at the E-E sites was
calculated from the treated plans which were retrieved
from the Oncentra treatment planning system (Figure 1).
Dose maximum (Dmax) for each plane was determined
meticulously. Closest distance of each E-E point in each
plane from the respective first or last dwell position,
clinical target volume (CTV) and the reference isodose
(85%) was measured. Statistical analysis was done in IBM
SPSS version 21. Correlation between quality of implant
marks and dosimetric parameters was analyzed using
Spearman’s co-efficient (single tailed). Chi square test
was done between the quality of marks and plane Dmax as
well as closest distances each from CTV, prescription
isodose and first or last dwell position. ROC curve was used
to determine dose constraints.
Results
The median plane Dmax dose was 1.33 Gy (40% of 3.4Gy,
range 0.24-3.74 Gy) and showed moderate correlation
with grade of skin marks (0.505, p value 0.000). Similarly,
the closest distance of the CTV, prescription isodose
(Figure 2) and first-last dwell position was 1.74 (range
0.32-6.58), 1.09 (range 0.02-5.71) and 1.55 (range 0.25-
4.58) cm respectively all of which also showed moderate
correlation (-0.444, -0.471 and -0.495 respectively, p
value 0.000 for each). 70.1% (61/85) planes with Dmax
<40% of prescribed dose showed invisible or faint marks
and 72.1% (62/88) planes with Dmax >40% of prescribed
dose showed clear or prominent marks (p = 0.001). 86.4%
(19/22) planes with closest distance from CTV <0.7 cm and
91.4% (32/35) planes with closest distance from 85%
Isodose < 0.5 cm showed clear or prominent marks (p =
0.001). There was very high correlation between closest
distance from CTV 0.7 cm and closest distance from
isodose 0.5 cm (0.715). Taking 1.33 Gy (40% of prescription
dose per fraction) as a cut –off value for plane Dmax
resulting in clear-prominent implant marks on ROC curve
resulted in sensitivity 65% and specificity 60%.
Conclusion
This study highlights the need for minimization of dose to
the skin E-E site for reducing the risk of clear or prominent
skin marks which affect cosmesis. Wherever possible it is
advisable to edit the CTV to maintain a safe distance
between the prescription isodose from the skin E-E points.
However, larger sample size needs to be studied to
increase sensitivity and specificity of the E-E dose
constraint.
PO-0924 HDR boost in CT3 breast carcinoma with
neoadjuvant chemotherapy and conserving therapy
F. Romero
1
, J. Guinot
1
, M. Santos
1
, M. Tortajada
1
, P.
Santamaría
1
, L. Oliver
1
, V. Campo
1
, L. Arribas
1
1
Fundación Instituto Valenciano de Oncología, Radiation
Oncology, Valencia, Spain