ESTRO 36 Abstract Book

S298

ESTRO 36 2017

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5,6

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Symposium with Proffered Papers: Selection of patients

and radiotherapy technique for APBI in the light of new

phase III trial data

SP-0565 Target coverage and dose to organs at risk

using different techniques of APBI (EBI, IORT, BT)

L. Marrazzo

Azienda Ospedaliera Universitaria Careggi, Medical

Radiation Physics, Firenze, Italy

The evidence that most breast cancer local recurrences

develop in close proximity to tumour bed paved the way

to the introduction of APBI, an approach in which only the

lumpectomy bed plus a 1-2 cm margin is treated, rather

than the whole breast. Because of the small volume of

irradiation, a higher dose can be delivered in a shorter

period of time. Various approaches have been proposed

for APBI: multi-catheter interstitial or balloon catheter

brachytherapy (BT), intraoperative radiation therapy

(IORT) and external beam irradiation (EBI). These

techniques are intrinsically different in terms of both

radiation delivery and obtainable dose distributions thus

leading to different target coverage, dose conformality,

and OARs sparing. A number of papers aims at exploring

the differences between APBI planning with different

techniques. Starting from these comparison studies, we'll

go through the main differences between the treatment

modalities, trying to identify subgroups of patients who

would benefit from a specific approach and to see whether

different results are due no only to the technique that was

used but also the way it was implemented (e.g. use of non-

coplanar beams, partial arcs, blocked regions). In BT no

margin is applied around the CTV, which allows reducing

the breast normal tissue irradiated with high doses, which

seems to correlate with some adverse cosmetic

effects. Moreover BT can provide highly conformal dose

distribution and steep dose gradients, which allow optimal

sparing of critical structures. Nevertheless, due to the

shape of the dose distribution, the OARs sparing is strongly

dependent on the location of the PTV. IORT could

minimize some potential side effects since skin and the

subcutaneous tissue can be displaced during radiation

delivery. The dose distribution is characterized by a sharp

dose fall-off but possibilities to shape the dose distribution

are very limited. EBI is attractive since no specific manual

skills are required. Several strategies have been used: 3D

conformal radiotherapy (3D-CRT), static field intensity

modulated radiation therapy (IMRT), volume modulated

arc therapy (VMAT), helical Tomotherapy and proton

therapy. At the current state, the chosen approach mostly

depends on the technical availability. A general result is

that intensity modulation techniques are characterized by

a better dose conformity when compared to 3DCRT. Non-

coplanar beams may be used to reduce the proportion of

ipsilateral breast receiving high doses. Proton beams

generally show the best performances, allowing the

smallest volume of ipsilateral breast to be exposed to low

dose, even though scattered beam techniques may be

associated to higher skin doses. Not only the planning

technique, but also the delivery could affect the dose to

OARs:

- image guidance could allow for margin reduction thus

further reducing dose to uninvolved breast;

- left sided lesion could benefit from using a deep

inspiration breath-hold technique, which reduces heart

dose;

- real-time tracking could allow further margin reduction.

Currently, we are far from being able to understand

whether the dosimetric differences between the different

treatment techniques are clinically relevant.

SP-0566 External beam partial breast irradiation:

changing patient selection based on current evidence

I. Meattini

Azienda Ospedaliero Universitaria Careggi - University

of Florence, Radiation Oncology Unit - Oncology

Department, Florence, Italy

Accelerated partial breast irradiation (APBI) has been

introduced as an alternative treatment method for

patients with early stage breast cancer (BC). APBI

advantages includes shorter treatment time, decreased

volume in the breast tissue treated, and cost reduction

compared with the standard whole breast irradiation

(WBI). The concept of APBI was introduced basing on the

results of several large prospective randomized trials

comparing postoperative WBI and exclusive surgery, that

evidenced the majority of recurrences for patients who

did not receive radiation at or in the region of the surgical

cavity. The first 5-year results of the IMPORT-LOW trial

were presented at the European Breast Cancer Conference

(EBCC) 2016 and showed non-inferiority of PBI when

compared to WBI in women with low risk early BC, with a

5-year local recurrence (LR) rate of 0.5%. The role of APBI

has been investigated in large-scale prospective phase 3

clinical trials using different techniques. Main published

results showed conflicting results in terms of local control

of disease, while demonstrated equivalent impact in terms

of survival when compared with WBI. The Cochrane

Database Systematic Review on PBI for early BC published

in 2016 showed an increased LR rate with PBI/APBI (small

difference), but no evidence of detriment to other

oncological outcomes (overall survival, distant

metastases). Published data evidenced the crucial role of

patient’s selection in clinical outcome. Two trials have

reported results of intra-operative radiotherapy (IORT)

compared to WBI: the TARGIT-A trial, and the ELIOT trial.

In both cases a significant higher rate of LR was observed

using APBI, mainly due to high-risk BC patient’s selection

for treatment. Conversely, the GEC-ESTRO and the

Florence trials, enrolling low risk early BC, obtained an

equivalent local control. To note, patient’s population of

the Florence trial had a high proportion of luminal-A

patients (79% in the APBI, and 73% in the WBI arm)

compared to the ELIOT trial (40% and 37% in the IORT and

WBI arm, respectively). In the ELIOT trial, the 5-year risk

of LR was substantially higher in selected subgroups of

patients including those with grade 3 tumors (15.6%), ER-

negative disease (14.4%), and triple-negative BC (18.1%).

The Florence trial, using a 30 Gy in 5 fractions with IMRT

technique, showed an equivalent 1.5% rate of LR at a

median 5-year follow-up time. Also age could play an

important role in a multifactorial patient’s selection; the