Can radiographic plain film be used to determine the depth of the tumour bed in the absence of surgical clips for breast boost planning?
1 Department of Radiology, Faculty of Medicine, Chiang Mai University, Thailand
2 Department of Surgery, Faculty of Medicine, Chiang Mai University, Thailand
Purpose: A number of studies have demonstrated the
importance of using surgical clips to define the tumour bed in breast boost
radiotherapy. In the absence of such clips, other techniques suggested to
improve boost location have included CT and ultrasound (US). Determination of the depth of the tumour bed is important in the selection of electron
energy. This study was conducted to prospectively compare the depth of the
lumpectomy cavity as defined by ultrasound to radiographic plain film
evaluation of the anterior border of the pectoralis muscle.
Materials and Methods: Forty-one breast-cancer
patients treated at the Division of Therapeutic Radiology and Oncology, Department
of Radiology, Faculty of Medicine, Chiang Mai University between December 2004
and December 2006 were prospectively identified as having no surgical clips
within the lumpectomy cavity. All patients underwent both US evaluation of the depth of tumour bed (D1) and radiographic evaluation of the depth of
the anterior border of the pectoralis muscle (D2). These depth dimensions (D1
and D2) were compared using a paired t-test. The correlation of both methods
was analyzed by Pearson correlation test.
Results: Depth dimensions by US were shorter than
the radiographic film method in 85% of patients. The absolute mean difference
of the depth (radiographic films minus US) was 0.129 cm. A paired t-test
demonstrated that the difference between these two methods to be not statistically
significant (p= 0.27). The absolute difference of depth between the two methods
ranged from 0 to 0.5 cm. A significant correlation was found between US and
radiographic film measurements (p<0.01).
Conclusion: Plane radiographic film evaluation of
the anterior border of the pectoralis muscle can be used to define the depth of
the tumour bed in patients who have no surgical clips. However, the plane
radiographic film method determines only the depth, not the transverse and
longitudinal dimensions of the tumour bed. Additional information from US is
needed to delineate the target volume for the tumour bed boost. In the absence
of surgical clips, the authors recommend integration of both methods in breast
boost planning process. � 2009 Biomedical Imaging and Intervention
Journal. All rights reserved.
Keywords: absence of surgical clips, breast boost,
Breast conserving surgery followed by external beam
radiotherapy is one standard treatment of early breast cancer. An additional
radiation boost dose to the tumour bed or lumpectomy cavity is required after
breast conserving surgery to reduce the risk of local recurrence. There are
many ways to design the boost fields but no standard technique has been
established. In a recent Patterns of Care Study on early stage breast cancer,
the breast volume was determined by CT in 11.7%, a clinical fluoroscopic
simulator in 43.9%, and clinically alone in 37.2% .
One of the most common planning employs clinical
information and surgical scars. However, many reports have demonstrated the
unreliability of this boost technique with geographic miss rate ranging from 43‑68%
[2-4]. The gold standard tool to guide the design of boost field is
radiographic evaluation of intra-operatively placed surgical clips. However,
placement of surgical clips is not routinely performed by all surgeons.
In the absence of surgical clips, other techniques
suggested to improve boost location include computed tomography (CT) planning
and ultrasound (US) [5-7]. Several studies of boost fields using US to identify
the location and dimensions of the lumpectomy cavity found the fields were
acceptable in size and that accuracy compared favourably to other techniques
for boost planning [3-10]. However, Rabinovitch et al. recommended against
using US for breast boost planning as it could result in inappropriate
selection of low electron energies and small field sizes compared to the
radiographic evaluation of surgical clips . Similarly, CT can be used to
target the tumour bed with cavity visualization similar to US , but CT is
not available in all radiation centres.
The authors are seeking ways to shorten the process of
defining the radiation boost plan in order to improve working practice at the
Division of Therapeutic Radiology and Oncology where 200 patients were treated
daily. Focusing on patients who had no clip placement, the authors conducted
this study to compare the depth of the lumpectomy cavity as defined by
ultrasound technique to radiographic plain film evaluation of the anterior
border of the pectoralis muscle. The authors wished also to explore these
relatively easy techniques of delineating the surgical bed for the benefit of
institutions where other advanced techniques are not feasible. This study was
approved by the Institutional Review Board of the Faculty of Medicine, Chiang Mai University.
Materials and Methods
Between December 2004 and December 2006, 54 patients
underwent excisional biopsy and axillary lymph node dissection followed by
irradiation at the Division of Therapeutic Radiology and Oncology, Department
of Radiology, Faculty of Medicine, Chiang Mai University. The major inclusion
criteria were 1) stage I and II breast cancer, 2) negative resection
margins and 3) no surgical clip placement in the tumour bed. Nine patients with
surgical clips and four patients with positive surgical margins were excluded.
Thus, 41 patients were included in this study.
Before the day of initial simulation, all patients
underwent US evaluation of the lumpectomy cavity to define all dimensions of
the cavity. Dimensions of the cavity included transverse measurement (T)
(medial to lateral), longitudinal measurement (L) (superior to inferior) and
depth (D1) (skin to the posterior portion of the cavity). The extent
of the lumpectomy cavity was marked on the patient�s skin at the time of US to
determine the field borders. US was performed using ATL 5000 (Bothell, Washington) with a 5-10 MHz bandwidth transducer by a radiologist. Radiotherapy consisted
of treatment to the entire breast with medial and lateral tangential fields to
a total dose of 50 Gy in 2 Gy per fraction with a 6MV linear accelerator.
The boost field was irradiated by electrons between 10 and 16 Gy.
At the time of initial radiation therapy simulation of
tangential fields, a lead wire was placed over the lumpectomy scar and further
films were undertaken for boost planning. The techniques used were as described
by Rabinovitch et al. . Orthogonal films were taken with the isocentre at
the middle of the scar. The first film was taken with the beam perpendicular to
the skin surface at the surgical scar (treatment direction) (Figure 1A,
2A). By using SSD (source-skin distance) technique, the second film was taken
90 degrees from the first, with the beam tangential to the skin surface (Figure 1B,
2B). These films required a couch, gantry and collimator rotation to achieve
the desired beam angles. The depth (D2) from the skin to the
anterior border of the chest wall muscle was measured from the second film. In
the absence of clip placement, we could not measure the transverse and
longitudinal distances using the radiographic film. Electron energy was chosen
by defining �treated depth� (TD) as the higher value between the depth to
pectoralis muscle from radiographic film (D2), and ultrasound cavity
The depth measurements from US and radiographic film were
compared using paired t-test. Correlation with the depth measurements from US
and radiographic film were determined by the Pearson�s test.
Forty-one patients were treated in this study. Patients
and tumour characteristics are listed in Table 1. The median age was 45 years
(range: 27-58). The majority of tumours were between 2.1 and 3.0 cm in
diameter. Most patients (87.8%) received chemotherapy before RT. The median
interval between surgery and US was 24 weeks (range: 1 - 48). Table 2 gives the
mean of the measured depth results for D1 and D2 and the
mean of the absolute difference in depths (i.e. absolute mean of D2 �
D1). The absolute mean difference of the depth (radiographic films
minus US) was 0.129 cm. The absolute depth discrepancy between the two methods
ranged from 0 to 0.5 cm. A paired t-test demonstrated no statistically
significant difference between US and plain film measurements (p=0.27). The
Pearson�s correlation coefficients between depth dimensions estimated by US and
by radiographic film was 0.98 (n = 41). (repeated)
For this study, the chosen electron energy was based on
the deepest extent (regardless of method of measurement: US or orthogonal film)
and the field borders were defined by marking the extent of the lumpectomy
cavity on the patient�s skin at the time of US: i.e. information from both the
plane radiographic film and US was used in the planning of the radiation boost
treatment. In two patients whose intervals from surgery to US were more than 40
weeks, US evaluation was of no value due to lack of identifiable cavity. Median
follow-up time was 47 months (range: 30- 52). Two of the 41 patients (4.9%)
developed a local recurrence of the breast cancer outside the boost area at 25
months and 27 months, respectively, after completion of radiotherapy. One of
them also developed lung metastases and eventually died. At the time of
analysis, 40 patients were still alive with no evidence of disease.
Although CT-based planning with surgical clips remains the
most accurate method to delineate the tumour bed, this is not possible with all
patients: some do not have surgical clips placed, and some radiation facilities
do not have access to CT for this planning. In the absence of surgical clips,
Rabinovitch et al.  recommended using CT-guided treatment planning. Smitt
et al.  published information on the use of CT in the absence of surgical
clips to visualize the lumpectomy cavity and found results similar to those
obtained with US. Conversely where equipment is limited, several studies have
found that fluoroscopy of surgical clips is a fairly precise method of
delineating the surgical cavity [2, 4, 8, 11, 13].
This study considered the options for patients without
surgical clips and where CT is not available. Previous studies [13, 14] have
demonstrated successful results of using US to localize the lumpectomy cavity
and facilitate boost field placement in patients treated with lumpectomy and
radiation therapy but issues can arise with US planning alone. The optimal time
to perform US is not known. It should not be performed too early following
lumpectomy because significant seroma fluid or haematoma may exist within the
cavity, distorting the volume. And it should not be performed too late, such as
after the end of chemotherapy cycles, because a long gap post operatively can
cause near complete absorption of seroma and lumpectomy cavity and US may not
be able to estimate the dimensions of the surgical bed or even discern any
cavity. Almost all the patients received chemotherapy before RT except for 5 patients
with tumours of ≤ 1 cm. The common chemotherapy regimens were FAC or FEC
and half of the patients had cycles delayed due to grade 3 or 4 neutropenia,
accounting for the long median time between surgery and RT. Two patients (4.8%)
had no identifiable cavity and both of them had a long interval from surgery to
US procedure (40 and 48 weeks, respectively). Because of this obscuration of
the lumpectomy cavity with time, an increasing gap between surgery and
radiotherapy simulation can lead to underestimation of the tumour bed and
margins by US [6,11].
In this study, no patients had surgical clips, so
radiography could only be used to estimate the depth of the surgical tumour bed
(by measuring the depth from the surface to the anterior border of the chest
wall) and not the transverse and longitudinal dimensions of the tumour bed.
Radiography alone is therefore inadequate for patients without surgical clips.
However, as discussed above, it is not clear that the cavity identified by US
will still be accurate, or even visualisable, if several months pass before
radiation therapy is commenced.
In this study, depth measurements were obtained both from
the plane radiograph and from the US. A paired t-test demonstrated no
statistically significant difference between the two methods. Neither was
consistently deeper than the other. In figure 3, the correlation between both
measurements was shown that there are correlation coefficients between them. To
avoid geographical miss, the safest approach is therefore to integrate both
methods and use the deepest of the two depth measurements to define the
electron energy and the US to delineate the radiation field margins.
Although CT-based planning with surgical clips remains the
most accurate method to delineate tumour bed, fluoroscopy in combination with
US is also a fairly acceptable technique for boost field delineation. The
authors would encourage breast surgeons to place surgical clips in the walls of
the lumpectomy cavity, so that further studies can be undertaken to compare the
transverse and longitudinal dimensions as determined by fluoroscopy and US, and
to confirm the effectiveness of this integrated technique.
Figure 1 Diagram of electron beam direction (A) Treated direction, (B) 90 degree from treated direction.
Figure 2 Orthogonal radiographic film of (A) Treated direction, (B) 90 degree from treated direction.
Figure 3 Correlation coefficients between the two measurement methods.
Table 1 Patients and tumor characteristics.
Table 2 Comparison of the depth by two methods.
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|Received 5 May 2009; accepted 25 May 2009
Correspondence: Division of Therapeutic Radiology and Oncology, Department of Radiology, Faculty of Medicine, Chiang Mai University, Thailand 50200. Tel.: +66-53-945456; Fax: +66-53-945491; E-mail: email@example.com (Imjai Chitapanarux).
Please cite as: Chitapanarux I, Muttarak M, Na-Chiangmai W, Trakultivakorn H, Somwangprasert A, Kamnerdsupaphon P, Tharavichitkul E, Sukthomya V, Lorvidhaya V, Watcharawipha A,
Can radiographic plain film be used to determine the depth of the tumour bed in the absence of surgical clips for breast boost planning?, Biomed Imaging Interv J 2009; 5(3):e11