ESTRO 36 Abstract Book

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S164 ESTRO 36
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Acknowledgement: BVO was supported by The Danish
Cancer Society and CIRRO
OC-0316 Single dose external beam preoperative
radiotherapy in breast cancer: experience and
guidelines
K.R. Charaghvandi1, S. Yoo2, B. Van Asselen1, M.D. Den
Hartogh 1, H.J.G.D. Van den Bongard1, J.K. Horton2
1 University Medical Center Utrrecht, Radiation Oncology
Department, Utrecht, The Netherlands
2 Duke Cancer Center, Department of Radiation Oncology,
Durham, USA
Purpose or Objective
In patients treated with breast-conserving surgery,
suboptimal cosmetic results have been reported following
post-operative 3D-conformal accelerated partial breast
irradiation (APBI) [1]. The delivery of radiation (RT)
preoperatively to the intact tumor enables better target
visualization and reduction in treatment volumes, and
thus, the potential for less normal tissue toxicity [2]. We
compiled our clinical experience and dosimetric data to
develop practical guidelines for this new treatment
approach.
Material and Methods
Dosimetry and toxicity data were pooled from 2
preoperative single dose APBI cohorts and 1 planning-study
[table 1]. In an American dose escalation trial, patients
≥55 years, with non-lobular cT1N0Mx or DCIS received a
single dose of 15, 18 or 21Gy (1.5cm CTV margin) using
IMRT in the prone position (n=32) followed by lumpectomy
within 10 days [fig 1A]. In the Netherlands, the feasibility
of VMAT-based supine APBI (20 Gy to tumor, 15Gy to 20mm
clinical target volume(CTV)) was evaluated initially in a
planning study (n=20) and is currently ongoing in women
≥50 years with cT1-2(max. 3 cm)N0Mx non-lobular
carcinoma (n=10) [fig. 1]. In this trial, lumpectomy is
planned 6 months after RT. Acute toxicity was scored
according to CTCAE version 4.03. Single dose APBI
constraints were derived from pooled OAR estimates. The
limit for optimal OAR dosimetry was set at the 75 th
percentile, whereas the 90 th percentile represented non-
optimal but acceptable dosimetry. Replanning of the US
cohort was performed to check the adherence of these
constraints for uniform single dose 21Gy APBI with a 20mm
CTV margin (n=32).
Results
In the dose escalation cohort (n=32), grade 1 local
radiation dermatitis, fibrosis and fatigue developed in
39%, 23% and 6% of the cases within 90 days after RT. At a
median follow-up of 57 days in the 15/20Gy simultaneous
boost cohort (n=10) grade 1 fatigue and local fibrosis was
encountered in 90% and 80% of patients, without any
radiation dermatitis. In both cohorts no acute ≥grade 3
toxicity developed. Based on pooled OAR estimates,
optimal dosimetry was defined as a maximum value of
0.7Gy for the mean heart dose, 1.5Gy Dmax for
contralateral breast, 1.3Gy for mean ipsilateral lung dose,
and 12.3Gy as D20cc dose to chest wall [table 1]. All
replanning plans adhered to these constraints. At least
acceptable mean ipsilateral breast dose (max. 5.5Gy) was
achieved in 97% of cases. Optimal skin dosimetry was set
at Dmax ≤100% prescription dose, D1cc ≤13.2Gy and D10cc
≤10.0Gy.
Conclusion
Acute toxicity following single dose IMRT-based
preoperative APBI appears to be mild. Clinically feasible
optimal and acceptable OAR constraints were developed
for future studies. Long-term follow-up is required for
validation and the skin dosimetry constraints, in
particular, may need additional modification based on
long-term outcomes. Chronic toxicity will be available at
the 36th ESTRO conference.
[1] Olivotto et al. 2013 [2] van der Leij et al. 2014
OC-0317 MR radiomics and fractal dimension in
cervical cancer predicting pathological complete
response
N. Dinapoli1, A.L. Valentini2, A. Pesce1, R . Gatta1, C.
Masciocchi1, V. Ninivaggi2, B. Gui2, G. Matt ana1, M.A.