STABILIZATION DEVICE FOR PATIENTS UNDERGOING RADIATION THERAPY FOR CARCINOMA OF THE BREAST
Gunilla C. Bentel, RN, RTT
Duke University Medical Center
Durham, North Carolina

INTRODUCTION
Improved imaging modalities, primarily Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI), and three-dimensional treatment planning capabilities has resulted in increased confidence in the target localization. This increased confidence, along with sharply defined penumbra of linear accelerator beams and the capability to customize the field shape to target, has led to the use of smaller margins around the target, thus the volume of normal tissues within the irradiated field is reduced. The smaller margins also increase the risks for geographic miss, therefore, improved immobilization methods are crucial.
ALPHA CRADLE® brand Patient Repositioning Systems have been used for immobilization of patients receiving breast irradiation in our department for approximately 15 years. Ongoing efforts to improve the reproducibility of the set-up of these patients has lead to two major modifications. The addition of a handle to the breast ALPHA CRADLE® form has been described in an earlier report. This modification improved the repositioning but not to our satisfaction. Recently, another modification has been made which is described in this report.

TREATMENT
The goal of breast irradiation is to treat the chestwall and regional lymph nodes and, in an increasing number of patients, also the breast. Irradiating this very irregularly shaped target while minimizing the dose to adjacent normal tissues requires a complex arrangement of multiple fields angled in different directions across the patient’s chest. Reproducibility of the set-up is difficult since the skin surface in this area often moves with respect to deep-laying tissues. Set-up marks made on the skin surface in this region are therefore unreliable. In obese patients or patients with large breasts, the skin marks can move several centimeters with respect to underlying bony anatomy. The degree of arm elevation on the involved side also plays a role in the position of the skin marks with respect to deeper, fixed tissues. Reproducible patient positioning and the ability to make set-up marks peripheral to the breast itself as well as on a positioning device is crucial to successful radiation therapy of these patients.
In our breast treatment technique, the breast and/or the chestwall are treated through opposed tangential fields. The internal mammary nodes are sometimes treated in a separate anterior field or, alternatively, are included in the tangential fields. The ipsilateral supraclavicular nodes are treated via an anterior oblique field angled to avoid inclusion of the larynx, the spinal cord, and the esophagus. Since the cephalad margins of the two tangential fields are diverging in opposite directions into the superclavicular area, the couch is angled such that these margins form a common border and the caudal half of the field is blocked to form a vertical match line. The internal mammary field is 5 to 6 cm wide and covers the ipsilateral internal mammary nodes. The deep margin of the tangential fields is blocked to match the internal mammary field. Since the position of either one of these breast fields is depending on the position of its neighbor, misalignment of one field frequently but not always results in misalignment of all fields.
Traditionally, in all radiation therapy treatments, attempts are made to position the patient “straight” on the couch. However, in order to treat the same volume as the simulation or “prescription” radiograph indicates, it is crucial to reposition the patient exactly as during the simulation procedure. In order to deliver the “prescription treatment”, the patient must be in the “prescription position”, therefore, whether the patient is straight or not is irrelevant.
The use of a positioning device and an alignment system aids in reproducing the set-up from day-to-day. A small misalignment of the patient with the sagittal alignment line will cause the internal mammary field to be misaligned with the sternum (Fig. 1) and hence, the tangential and supraclavicular fields are also misaligned. A small rotation of the patient’s body with the lateral or horizontal alignment lines causes the deep borders of the tangential fields to be at different depth (Fig. 2). This type of misalignment can occur even when the field edges correctly match the skin marks for the internal mammary and supraclavicular fields. In an effort to reduce this type of misalignments, we use a hemibody immobilization device which the patients feel is comfortable and the technologists like because it is easier to position and treat the patients and the request for field shifts and repeat port films is reduces.

Fig. 1 The patient is aligned with the alignment system and four points (M) are marked on the Alpha Cradle® form (left). To reproduce the “prescribed” treatment portals in the treatment room, the patient must be re-aligned with the alignment system. The internal mammary node field is aligned with the sagittal alignment line. On the right, the patient and the Alpha Cradle® form are misaligned 5° with the alignment lines. The internal mammary node field is now rotated 5° with respect to the patient.

Fig. 2 When the patient is rotated only 5° around the sagittal axis (the long axis of the patient’s body), the depth of the tangential fields is different even when the medial field margin is unchanged.

POSITIONING DEVICE
ALPHA CRADLE® brand Patient Repositioning Systems have been used routinely for positioning patients undergoing radiation therapy for breast cancer in our institution for approximately 15 years. During the late 1980s, a modification was made to include a support for the arm position.1 The modification consisted of the addition of a handle which the patient can hold onto during the treatment. This modification offers the patient a comfortable resting place for the hand and the elevated arm and also fixes the orientation of the hand during treatment. A reduction in the number of requested treatment field adjustments was noted when the modified ALPHA CRADLE® form was used but further improvements were desired.
In patients where a separate internal mammary field was used, the field position with respect to bony anatomic landmarks, primarily the spinal column, was often found to be different from the simulated field when port films were reviewed. It was attributed to the fact that the sagittal alignment line was marked only within the treated segment, i.e., on the chest. It appeared that the entire torso needed to be aligned with the sagittal alignment line in order to correctly reposition the patient (Fig.1). The deep margin of the tangential fields was also frequently different from that which was simulated. This problem was thought to be caused by failure to reproduce the patient’s body rotation around the sagittal axis. The gantry angle was fixed while the patient’s body was rotated differently causing the depth to vary even when the medial beam entry point remained unchanged (Fig. 2). A more aggressive immobilization system was therefore designed in an effort to reduce these errors.
In most areas of the human body, skin moves over underlying rigid anatomy, causing skin marks to change position with respect to target. This is particularly evident in the breast region where the soft tissues can move several centimeters with respect to the underlying rib cage. We found in other treatment sites, that repositioning the patient in a rigid position device and setting up the treatment to set-up marks on the device, is more reproducible than setting up to skin marks. We therefore designed an ALPHA CRADLE® form which extends from above the head to the knees, allowing all alignment lines to be marked on the immobilization device.

FABRICATION OF THE DEVICE
The ALPHA CRADLE® brand Patient Repositioning System consists of a Styrofoam®* piece, roughly shaped to the part of the patient’s body for which it is intended, glued to an extruded polystyrene base, and a set of bottles containing the foam which, when prepared as directed by the manufacturer, foams up around the patient and forms and mold which tightly fits the shape of the patient’s body (Fig. 3). The ALPHA CRADLE® form is placed inside a protective polyvinyl bag before the foam is poured inside the form. The patient is then positioned on the bag and the foam expands and fills the space between the patient and the walls of the form.

Fig. 3 The finished Alpha Cradle® form fits tightly to the shape of the patient’s body.

All breast patients receiving radiation therapy in our department have a CT scan as part of the treatment planning process. For immobilization we therefore use the ALPHA CRADLE® BREAST FORM labeled BF4 which has been designed to fit through the tunnel of most CT units. The previously described modification of the ALPHA CRADLE® form has been extended such that the base is 54” long reaching to just below the knees in most patients (Fig. 4). With the patient in the form, several pieces of Styrofoam® are placed on the base where appropriate for each individual patient. Marks are made where these pieces need to be fastened and, with the patient removed, they are taped in place (Fig. 5).

* Registered by Dow Chemical

Fig. 4 The extended breast Alpha Cradle® form extends from above the head to below the knees. Alignment marks are made on the Alpha Cradle® form (arrows).

Fig. 5 Several pieces of Styrofoam® are taped in place before the foam is poured. A handle for the patient’s raised arm is in a separate small bag above the head.

A small triangular-shaped piece of Styrofoam® is taped to the base of the ALPHA CRADLE® form under each knee. When the patient’s knees are slightly bent, the lumbar region of the spine becomes relaxed and the patient feels more comfortable. Another piece of Styrofoam®, approximately 5” x 2” x 1”, is placed between the patient’s knees. This piece increases the height of the foam between the knees where the sagittal alignment line is marked and also helps in making the foam raise up on the medial side of each leg. A 6” high and 1” wide piece of Styrofoam® is taped to each side of the base to form a barrier for the foam.
The handle is added by placing a Styrofoam® cylinder, approximately 3” long and 1” in diameter, into a separate bag which is taped in place under the position of the elevated arm. Several small holes are made in this bag on the side which is toward the ALPHA CRADLE® BF4-E form so that excess foam can leak out and form a glue which fixes this separate support to the rest of the immobilization device.
The entire device is then placed inside a protective polyvinyl bag, which is approximately 1’ wider and 1’ longer than the form. The bag is taped down near the chestwall where the lateral tangential field is anticipated to prevent foam from raising more than a couple of inches on the treated side. The absence of foam in this area makes it possible to mark the lateral tangential field on the patient skin surface as well as on the ALPHA CRADLE® BF4-E form. It also prevents the lateral tangential beam from being intercepted by the foam, which could reduce the skin-sparing effect otherwise observed with high energy beams. Radiation beams entering the skin surface at a steep incline or tangentially provides less skin sparing than a beam entering perpendicular to the surface. Further reduction of the skin sparing by the ALPHA CRADLE® BF4-E form could, in some cases, cause undesirable skin reaction (SMP always recommends cutting ports in forms. See our attenuation report.).
One set of AC660 of foaming agents* are prepared as directed by the manufacturer. Approximately 50cc of the foam is poured in to the arm support bag and the remainder is distributed evenly within the form. After approximately 60 seconds, during which time air is allowed to circulate inside the bag, the air is squeezed out, the bag is sealed, and the patient is returned to the form. The patients enter the form by first sitting on the couch near the caudal edge of the ALPHA CRADLE® BF4-E form and then gradually lift and move the buttocks over the knee supports and into the form. A visual check is

* In some cases, another 250 or 375cc of foam may be needed.

made to see that the patient appears straight on the mold and they are asked to adjust the chest and hips until they feel straight. The patient’s arm is elevated to desired position and the Styrofoam® handle is moved into the patient’s hand. The foam is pushed up around the hand and the arm. Masking tape, fastened to the sides of the ALPHA CRADLE® BF4-E form, is placed across the patient’s body to force the two sides in toward the patient’s body to force the two sides in toward the patient’s body to form a tight-fitting mold. Foam is also forced up between the patient’s knees where the sagittal alignment line is later marked.
A board, which is wider and longer than the ALPHA CRADLE®
BF4-E form, is placed on top of the couch before the ALPHA CRADLE® bf4-E form fabrication is initiated to prevent the foam from leaking and forming a lip under the ALPHA CRADLE® BF4-E form. Such lip or other irregular surface under the ALPHA CRADLE® BF4-E form could cause a tilt of the ALPHA CRADLE® BF4-E form and consequently of the patient, giving rise to field misalignments.
The foam stops swelling after approximately 7-10 minutes but requires approximately 10 additional minutes to become firm. During this time, the patient is asked to think about how it feels to lay in the mold so that when they are repositioned, they can adjust their body until it feels the same.
To produce a tight-fitting mold, it is important that the patient wears minimal clothing during the fabrication of ALPHA CRADLE® brand forms. Since patients usually wear different clothing each day during the course of treatment, the mold may be too large some days and too tight on other days. Both situations could compromise the ability to reposition the patient correctly. In patients where the simulation procedure is preceding the CT, the ALPHA CRADLE® BF4-E form is made in the simulation room, otherwise it is made in the CT room.

PATIENT-BEAM ALIGNMENT
Prior to the simulation procedure it is necessary to have all machine settings (gantry, collimator and couch angles) set to zero degrees. During the simulation procedure, the position of the ALPHA CRADLE® BF4-E form with respect to the couch is adjusted until the patient’s midline is parallel with the sagittal alignment line. This is determined under fluoroscopy by viewing the position of the patient’s spinal column with respect to the central axis of the beam as the couch is moved along its longitudinal axis. The sagittal line is then marked on the patient’s chest and on the ALPHA CRADLE® BF4-E form both above the head and between the knees. Since alignment lines frequently are not accurate away from the isocenter, these lines are marked as close to the isocenter as possible by moving the couch along the longitudinal axis.
The simulation procedure is then carried out in the usual fashion with as much of the set-up marks as possible made on the ALPHA CRADLE® BF4-E form. Experience from other treatment sites has indicated that these marks are more reliable than skin marks. The internal mammary and supraclavicular fields are usually marked only on the skin surface. The tangential fields are marked on the skin surface while the transverse, sagittal, and coronal alignment lines, indicating the isocenter of the tangential fields, are marked on the ALPHA CRADLE® form as well as on the patient’s skin surface.

PORT FILM REVIEW
The reproducibility of patient-beam alignment is assessed through weekly port films. Port films are always taken of each field during the first treatment. If no misalignment is noted, the port films are repeated on a weekly basis. If a misalignment is noted, a correction is made and the port film is repeated during the following treatment. To assess the effectiveness of the extended breast form BF4-E, a retrospective review of port films was made. In the review, port films taken of both tangential fields on the same day were recorded as one port film day since it represented only one set-up. Only the physicians’ routine review of port films was used to determine the frequency of misalignments. Small discrepancies between alignment systems in the simulator room and the treatment room and varying amount of sag between the two couches may be the cause of small errors in patient alignment observed on the first set of port films,27 however, in evaluation of the effect of the extended breast (BF4-E) described in this report, all port films were included in the review.

PATIENT CHARACTERISTICS
Thirty-two patients using the extended breast ALPHA CRADLE® BF4-E forms were treated between 1/93 and 7/93 and have completed treatment. To assess the effect on the set-up reproducibility when the extended breast ALPHA CRADLE®
BF4E form was used, the number of misalignments observed on port films were compared with that of a group of 29 patients treated between 1/92 and 7/92. The earlier group were treated using an ALPHA CRADLE® BF4-E form which also had a handle for the patient to hold onto during treatment but is extended only to the waist.
All patients were treated to the breast and/or chestwall using tangential fields. There were 132 port film days in the earlier group and 145 in the group with the extended breast ALPHA CRADLE®
BF4-E form.
In the earlier group of patients, 16 had supraclavicular field with 63 port film days while in the group using the extended breast ALPHA CRADLE® BF4-E form, 13 had supraclavicular field with 57 port film days.
Fourteen patients in the earlier group, had a separate internal mammary node field with 51 port film days while in the later group only 5 had separate internal mammary node fields in these two groups of patients, it was difficult to make a true comparison of the effect of the modified ALPHA CRADLE® BF4-E form.

RESULTS
The rate of tangential field misalignments in the earlier group using a short ALPHA CRADLE®
BF4-E form was 21.2% (28in 132 port film days) while in the more recent group using the extended breast ALPHA CRADLE® BF4-E form the rate was 10.3% (15 in 145 port film days). The magnitude of the needed adjustment was difficult to assess because the problem appeared to be a combination of translation and rotation errors in most cases. There was no noticeable difference between the two groups.
Port film review of the supraclavicular field showed that in the earlier group, the error rate was 17.5% (11 in 63 port film days). This increase in misalignments with the long modified ALPHA CRADLE® BF4-E form is due to 4 misalignments observed in one patient where an anterior supraclavicular field was simulated and initially treated using and SSD technique. This field was later changed to an isocentric technique and an opposing posterior field was added without re-simulation. When these 4 misalignments that are not related to patient positioning are excluded, the error rate is comparable to that found in the earlier group or 14% (8/57).
A review of the reproducibility of the internal mammary node fields was made but the results are not reliable because of the large difference in number of port film days. In the earlier group of patients, there were 25 misalignments in 51 port film days for an error rate of 49% (25/51) while in the latter group there was only one error in 16 port film days for an error rate of 6.3% (1/16). The results of the internal mammary port film review are very difficult to interpret. One can only surmise that the modified long ALPHA CRADLE® BF4-E form is superior to the earlier type of breast immobilization since the entire torso of the patient now is immobilized.
In addition to a reduction in misalignments observed on port films, the patients express a feeling of security and comfort while laying in the ALPHA CRADLE® form. The arm support and the handle which they hold onto during the treatment prevent straining and thus tiredness. The technologists find it easier and faster to position and to set up the treatment. The reduction in the number of port films is also saving both time and cost.

DISCUSSION
Precision in radiation therapy is critical to the effectiveness of the treatment both in terms of delivery of dose and the coverage of the target. Uncertainties resulting from mechanical machine problems, patient alignment errors, and involuntary motions account for much of the difficulties with reproducing the treatment fields from day-to-day. Increased awareness of these problems has led to the development of the immobilization device described in the report.
From this retrospective review of port films of these two groups of patients it is clear that the extended breast ALPHA CRADLE® form improves the accuracy of the set-up although there is room for further improvements. It is difficult to assess the affect on the repositioning of breast patients because of the number of factors that play a role. A field placement error observed on a port film may be due to patient positioning, machine settings, block cutting and mounting, as well as to the compulsion with which the technologists set up the treatment and the physicians review the port films. Some misalignment is more easily observed than others and as a result some misalignments may go undetected. For example, a misalignment on an internal mammary node port film, where bony landmarks (spinal column) can be used for comparison, is easier to detect than an error on a tangential port film.
The modification of the ALPHA CRADLE® form described in this report represent only one refinement in the radiotherapy techniques which may have a role in the final outcome of the treatment for patients with breast carcinoma.