Inl J. Radiarmn Oncdogy Rid Phys.. Vol. 19, pp. 189-195 Printed in the U.S.A. All rights reserved.

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03603016/90 $3.00 + .Xl 0 1990 Pergamon Press plc

??Technical Innovations and Notes

TECHNIQUE FOR BREAST IRRADIATION USING CUSTOM CONFORMING TO THE CHEST WALL CONTOUR

BLOCKS

WILLIAM F. HARTSELL, M.D., ANANTHA K. MURTHY, M.D., KRYSTYNA D. KIEL, M.D., MARK KAO, PH.D. AND FRANK R. HENDRICKSON, M.D. Department

of Therapeutic Radiology, Rush-Presbyterian-St. Luke’s Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612

A techniquefor the treatment of the breast and regionalnodes is presented.The technique involves the use of tangential fields to treat the breast and chest wall. Customized blocks which conform to the slope of the chest wall are made for each tangent field. Simulation and treatment with this technique requires no special equipment. The setup is simpleand quick.A three-fieldtechniqueis also describedusing the custom half-beam blocks; this technique avoids the use of tangential field corner blocks, thus simplifying simulation and treatment. Breast irradiation, Field matching, Three-field technique.

INTRODUCTION

wall are utilized. Accurate matching of tangent and supraclavicular fields is accomplished without the use of special equipment; a second benefit is that the curved customized block may spare more lung than techniques using a straight edged block.

Breast conservation surgery with irradiation is being used with increasing frequency as an alternative to mastectomy in the treatment of early stage breast cancer (2). One of the potential benefits of primary irradiation is that it allows adequate treatment of the cancer with good to excellent cosmetic results (7). The goal of this therapy is to provide adequate doses of radiation to the tissues at risk while sparing proximate normal tissues. For treatment of the breast, this is often accomplished by the use of medial and lateral tangenting beams. Such beams will treat the breast, overlying skin, and underlying chest wall; of necessity, a portion of the lung will be included in the tangent fields (and for left-sided lesions a portion of the heart may be included as well). Previously reported techniques involve the use of half-blocked techniques (using a beamsplitter to reduce divergence into the lungs from the posterior edge of the field) (2, 14) or techniques in which the divergent posterior edges of the beams are aligned by the use of medial and lateral tangents which have a hinge angle of more than 180” (16). For these techniques, a collimator angle may be necessary to match the slope of the chest wall. If a supraclavicular field is treated, this collimator angle presents matchline problems which make the set-up more complicated ( 13). This report describes a technique of treatment in which customized blocks conforming to the slope of the chest

METHODS AND MATERIALS Two-jield technique The major advantage of this technique is that it does not require any special equipment (such as a breast bridge) for simulation and treatment. In addition, the treatment fields are designed to conform to the chest wall of each patient, potentially sparing lung tissue. This is accomplished by the use of an external marker on the chest wall that can be easily seen under fluoroscopy or on simulation films. The marker that we use is a piece of solder wire which is placed along the chest wall at or near midline and conforms to the slope of the chest wall. The patient lies supine on the treatment couch with her ipsilateral arm extended superiorly out of the field (hand on forehead or behind her head). An immobilization device such as a Styrofoam cast may be used to provide stability and aid in reproducibility. The field borders are then determined and marked on the patient. An attempt may be made to include the ipsilateral internal mammary nodes in the tangent fields; if no attempt is made to include these nodes,

Reprint requests to: William Hartsell, M.D., Department of Therapeutic Radiology, Rush-Presbyterian-St. Luke’s Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612.

Acknowledgements-The authors would like to thank Roger Krueger for his help in preparation of the manuscript. Accepted for publication 24 January 1990. 189

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Fig. 1. Two-field technique for treatment of the breast, showing the setup for (a) medial and (b) lateral tangent fields. A representative transverse section through the center of the field (c)

demonstrates the half-beam blocks. the medial border is placed at midline. Marks are placed on the patient’s skin over the tip of the xiphoid process and in the middle of the suprasternal notch. A straight line is drawn between these points using the longitudinal field alignment laser. A piece of solder wire is then placed over this line and kept in place by paper tape. If the internal mammary nodes are to be included in the tangent fields, we generally perform the same routine except that the line (and solder wire) are placed 3 cm to the contralateral side of midline. The border for the lateral field is marked on the patient’s skin, generally along the midaxillary line. This mark should be parallel to the long axis of the treatment couch but only needs to extend 2 to 3 cm caudal and cephalad to the central axis. A small piece of solder wire is positioned over this mark and held in place by tape. The caudal and cephalad borders of the field are marked as well, leaving an adequate margin around the breast tissue (usually 1.5 to 2 cm). These skin marks may be positioned in the 6 and 12 o’clock positions in relation to the nipple. For patients with large breasts, the cephalad field border is sometimes quite cephalad; in these situations, an angled board or slant board may be helpful. With the gantry in the upright position (AP setup), the center of the field is placed over the midline mark such that it is halfway between the cephalad and caudad field marks; the separation of the chest wall is then measured at the central axis of the field. The treatment depth

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will be one-half of the separation-for example, with a 100 cm SAD machine and a separation of 22 cm, the setup depth would be 1 I cm (one-half of 22 cm) and therefore the SSD would be 89 cm. The gantry is rotated toward the contralateral side 50 to 60” from vertical (Fig. 1A). Using fluoroscopy, the medial and lateral field wires are then made to intersect over the central axis; this will probably require minor adjustments in the gantry angle. The field length is adjusted so that the divergent edges match the upper and lower border marks. The field width is adjusted so that there is at least 1 cm of air gap around the breast. A simulator film is taken in this position (Fig. 2A). The gantry is then rotated 180”; the wires again should be seen crossing at the central axis marker (minor adjustments may be necessary to perfectly align the wires, but this should involve gantry changes of less than lo of rotation). A simulation film is then taken for the lateral field (Fig. 1B and Fig. 2B). If no fluoroscopy is available, an initial film should be taken for the medial tangent with the gantry about 55” from vertical; minor adjustments can be made until a subsequent film shows the wires crossing over the central axis marker. Ideally, there should be 1 to 4 cm of lung visible on the film in the field anterior to the central axis (and the solder wire). If less than 1 cm of lung is in the treatment field, the chest wall and breast may not be adequately covered. In this case, the lateral border may be moved posteriorly (i.e., toward the posterior axillary line) to provide better coverage of the chest wall and breast. Using these films, custom blocks may be made. The borders of the blocks are determined by the solder wire over the anterior chest; the area of lung behind this wire is blocked. The lateral marker used for the setup is usually at the most lateral portion of the breast, but since the blocks are drawn using the medial wire as a guide, the blocks must be checked clinically prior to the first treatment to ensure adequate coverage of the breast tissue in the lateral field. For certain machines (especially those using 80 cm SAD) the blocks on the medial tangent may be too close to the patient. In this situation, an 80 cm SSD setup may be used in a similar manner to that described for the SAD technique. A back-pointer is helpful for the SSD setup to mark the lateral exit point of the medial tangent (which will be the center for the lateral field). If there is no backpointer, the gantry will have to be rotated during the setup to check the exit point.

Three-field technique Supraclavicularjield.

A half-beam block is used on the supraclavicular field to give a non-divergent beam at the matchline. The matchline runs through the central axis of the supraclavicular field along a transverse plane; cephalad to this line will be the supraclavicular area to be treated, and caudal to the line will be shielded with the half-beam block. The patient is placed in the supine position with her arm extended out of the field as in the two-field technique.

Breast technique 0 W. F. HARTSELLet al.

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Fig. 2. Simulation films for (a) medial and (b) lateral tangent fields with the two-field technique. The block has been drawn to conform to the solder wire (which is lying on the skin over the sternum). The breast has been outlined on the medial tangent for clarity. Note that the blocks for the medial and lateral tangents are similar, and both are drawn using the solder wire over the sternum as reference.

The supraclavicular field is set up first. A transverse line is drawn across the patient’s chest above the breast at the level of the inferior border of the medial condyle of the clavicle. The lateral laser is used to obtain this straight line. This line will be at the central axis of the supraclavicular field, but because a half-beam block is used it will actually be the lower border of the treated area. The medial and lateral borders of the supraclavicular field are drawn on the skin; the medial border is usually at or near midline and the lateral border is just medial to the humeral head (Fig. 3A). The cephalad border is marked in the supraclavicular fossa giving enough margin to adequately treat the regional nodes; this will usually spare a strip of skin superiorly and not require a light field “flash.” The field size is then adjusted to match these borders, with the central axis placed over the matchline using a set-up depth of 3 cm. Solder wire is placed along the matchline, and a film is taken of this field. Custom blocks may be made using the wire to designate the superior border of the block, but because this is a straight line the custom blocks are not a necessity (Fig. 4). Tungentjelds. The medial, lateral, and caudal borders of the tangent fields are marked in a similar manner to that used for the two-field technique, with solder wire placed over these borders as well. The field length is estimated by measuring the distance between the supraclavicular wire and the caudal border mark. The separation

of the chest wall is measured, and the depth of treatment is calculated to be one-half of the separation. The center of the field is placed over the medial border wire at depth. The gantry is rotated 50 to 60” from vertical toward the contralateral side. Under fluoroscopy, the medial and lateral wires are made to intersect over the center of the field by rotation of the gantry. To match the cephalad border of the field with the supraclavicular field, both the collimator and the couch must be rotated. The appropriate angles of rotation can be calculated when the field size and gantry angle have been determined (see Appendix) (10). In practice, it is difficult to set the collimator angle with an accuracy of less than half a degree; (10) for that reason, we set the collimator rotation at 4’ for 100 cm SAD machines and 5” for 80 cm SAD machines. The collimator is rotated in the same direction for both the medial and lateral tangents. For treatment of the left breast, the collimator is rotated counterclockwise (from the beam’s eye view, or in other words, the light field on the patient as viewed from the gantry is rotated counterclockwise). For treatment of the right breast, the collimator is rotated clockwise for both the medial and lateral tangents. The cephalad field border of the tangent is matched to the supraclavicular line/wire by rotating the couch. The turntable angle will generally be 4” to 8”. The cephalad field wire and the supraclavicular solder wire should be seen to coincide on fluoroscopy.

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clockwise for the medial tangent, it should be rotated 7” counterclockwise for the lateral). Note that the head of the couch is rotated toward the gantry for both the lateral and medial fields. The collimator angle remains the same as it was for the medial field. With the gantry and couch appropriately rotated, the position of the wires is checked under fluoroscopic guidance. Minor adjustments may be necessary to align the wires and field borders. The center of this field is marked, the SSD noted and recorded, and a film is taken (Figs. 3B and 5B). Blocks are drawn and cut using the same borders as for the medial tangent; the medial (or sternal) solder wire is used as the guide for both the medial and lateral blocks. The blocks should be checked clinically on the treatment machine before the first treatment to ensure adequate coverage of the breast tissue on the lateral field. As discussed in the two-field technique, an SSD set-up may be used for certain machines in which the blocks would be too close to the patient for the tangent fields.

Fig. 3. Three-field technique demonstrating (a) supraclavicular and medial tangent fields, (b) lateral tangent field, and (c) a cross-

section showing the three treatment fields. The center of the supraclavicular field is actually on a more cephalad plane, but entrance angle relative to the tangent angles is presented for clarity.

Additional small adjustments of the gantry angle may be required to re-align the medial and lateral wires over the central axis. The width of the field is adjusted to allow at least 1 cm of air gap around the breast. When the medial and lateral wires align over the center and the cephalad field wire aligns with the supraclavicular wire the field is correctly set (Fig. 3A). The center is marked, the SSD is noted and recorded, and a film is taken (Fig. 5A). The area behind the medial wire is blocked, just as in the twofield technique. The matchline for the three fields is a straight line; as was demonstrated for the medial tangent, this is accomplished by rotating the couch and collimator so that the divergence of the tangent beams matches this line. Therefore, the tangent fields are not parallel opposed. To facilitate the set-up of the lateral field, the couch is first rotated back to the neutral position. With the gantry still rotated to the medial tangent angle, the set-up exit point on the mid-axillary line is marked (using the backpointer). It is also helpful to mark the medial point with the couch in a neutral position, and to use these marks for daily positioning. The gantry is then rotated 180” to be centered on the lateral mark. The couch is rotated the opposite way it was rotated for the medial tangent, and to the same magnitude (i.e., if the couch was rotated 7”

Dosimetry When isodose calculations are performed for the tangential fields, it is important to remember that this is a half-beam technique. At the central axis (which is at the edge of the half-beam block), doses will increase by large amounts over a distance of a few millimeters because of the rapid fall-off of dose at the edge of the block. Because of this rapid gradient, we use a point 1.5 cm from the

Fig. 4. Simulation film for the supraclavicular the central axis is at the edge of the half-beam forms to the solder wire.

field. Notice that block which con-

Breast technique 0 W. F. HARTSELLetal.

Fig. 5. Simulation films for the (a) medial and (b) tangent fields with the three-field technique. More lung is seen in the treatment field (about 2.5 cm vs 1.5 cm at the central axis in Fig. 2); this is because the medial border was 3 cm to the contralateral side of midline to include the internal mammary nodes.

central axis (anterior, as the reference point

or towards the apex of the breast) for isodose calculations.

DISCUSSION The general goal of treatment in radiation therapy is to treat the tissues containing tumor or at risk for harboring tumor, to give an adequate dose to control the tumor without giving an excessive dose to the normal tissues, and to spare as much as possible the surrounding normal tissues. For the definitive treatment of early stage breast cancer, this requires treatment of the breast and chest wall, and may also include treatment of regional lymphatics (which will include the axillary, supraclavicular and/or internal mammary nodes). Multiple techniques have been described for treatment of these areas. Techniques that have been used in randomized trials (some of which involve treatment after mastectomy rather than after lumpectomy) include the use of an en face orthovoltage or supervoltage field to treat the internal mammary nodes (1, 3), or a “hockey stick” field to treat the internal mammary and supraclavicular nodes (17). There is controversy regarding the efficacy of treatment of the internal mammary nodes, and some reports have implicated this field arrangement with a higher rate of cardiac morbidity and mortality (5, 8, 15). For these reasons, Harris and Hellman have recommended that an en face internal mammary photon field not be used routinely.

* Adriamycin,

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(6) The use of electrons to treat a similar portal arrangement has been suggested, using the limited range of electrons to treat the nodes but spare the deeper-lying structures (i.e., the heart) (6). However, the edge of an electron field is not as sharp or easily marked as that of a photon field, which may create problems with field matching (hot or cold spots) (9). Studies using lymphoscintigraphy have shown that in over 80% of patients the ipsilateral internal mammary nodes will be included in tangent fields when the medial entrance point is 3 cm contralateral to midline (11). Such an arrangement will avoid treating the majority of (or all of) the heart and pericardium; this is especially important if the patient will be receiving cardiotoxic chemotherapy such as doxorubicin.* The group from the Joint Center for Radiation Therapy describe a three-field technique for breast treatment which utilizes a supraclavicular field and two tangential fields (13, 14, 16). In the JCRT technique, the tangents are treated with open fields; the posterior edges are aligned geometrically using a hinge angle of greater than 180”. The collimator is rotated to match the curvature of the chest wall, and an additional rotating block is required to avoid overlap with the supraclavicular field. An alignment protractor is also required to set and verify the alignment of the three fields. An Italian group describes a three-field technique for breast irradiation which utilizes individualized blocks for each field (4). The problems with matching of the tangential and supraclavicular fields are avoided

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by using half-beam blocks for all three fields. For the tangential fields, the upper half of the field is blocked and an additional posterior block is attached to shield the lung. Unlike the JCRT technique, our technique does not require any special equipment for simulation or treatment (such as a breast bridge); furthermore, no calculations are required to determine gantry angles. Custom-made blocks are made for each patient to conform to chest wall curvature. This allows treatment of the tangential fields without the use of the rotating tangential field blocks (used in the JCRT technique to avoid overlap of the tangent fields with the supraclavicular field). The chest wall and lung only rarely conform to a straight edge, such as would be obtained from a collimated field; our technique allows the field to conform to the curvature of the chest wall by using customized blocks. The Italian technique, discussed by Conte and colleagues, utilizes half-beam blocks for all three fields. If the length of field to be treated in the tangents is more than, for example, 15 cm, this may result in a large and unwieldy block. If the field to be treated is

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even longer (for example, 2 1 cm), the field size will exceed the maximum field size for many linear accelerators (in this example, a field length of 42 cm would be required with a block covering the cephalad 21 cm). An additional advantage of this technique is that the medial border of the treatment field projects as a straight line on the chest. For patients who require synchronous or metachronous treatment of both breasts, this greatly facilitates matching of fields and avoids field overlaps or gaps.

CONCLUSION There are many techniques described for treatment of the breast ? regional lymphatics. Our technique does not require special equipment for simulation or treatment. Custom-made blocks conform to the curvature of each patient’s chest wall. This technique also offers the advantage of simplicity of simulation and treatment.

REFERENCES I. Atkins, H.; Hayward, J. L.; Klugman, D. J.; Wayte, A. B. Treatment of early breast cancer: a report after ten years of a clinical trial. Br. Med. J. 2:423-429; 1972. 2. Bedwinek, J. M. Treatment of stage I and II adenocarcinoma ofthe breast by tumor excision and irradiation. Int. J. Radiat. Oncol. Biol. Phys. 7: 1553- 1559; 198 1. 3. Cancer Research Campaign. Management of early cancer of the breast: report of an international multicentre trial supported by the Cancer Research Campaign. Br. Med. J. 1:1035-1038; 1976. 4. Conte, G.; Nascimben, 0.: Turcato, G.; Police, R.: Idi, M. B.; Belleri, L. M.; Bergoglio, F.; Simonato, F.; Stea, L.; Bugin, F.; Bortot, N. Three-field technique for breast irradiation using individualized shielding blocks. Int. J. Radiat. Oncol. Biol. Phys. 14:1299-1305; 1988. 5. Cuzick, J.; Stewart, H.; Pete, R.; Baum, M.; Fisher, B.; Host, H.; Lythgoe, J. P.; Ribeiro, G.; Scheurlen, H.; Wallgren, A. Overview of randomized trials of postoperative adjuvant radiotherapy in breast cancer. Cancer Treat. Rep. 7 I( I): 1529; 1987. 6. Harris, J. R.; Hellman, S. Put the “hockey stick” on ice. Int. J. Radiat. Oncol. Biol. Phys. 15:497-499; 1988. 7. Harris, J. R.; Levene, M. B.; Svensson, G.; Hellman, S. Analysis of cosmetic results following primary radiation therapy for Stages I & II carcinoma of the breast. Int. J. Radiat. Oncol. Biol. Phys. 5:257-261; 1979. 8. Host, H.; Brennhovd, I. 0. The effect of post-operative radiotherapy in breast cancer-Iong-term results from the Oslo study. Int. J. Radiat. Oncol. Biol. Phys. 12:727-732; 1986. 9. Khan, F. M. Electron beam therapy. In: Khan, F. M., ed. The physics of radiation therapy. Baltimore: Williams & Wilkins; 1984:299-353.

IO. Lichter, A. S.; Fraass, B. A.; Van de Geijn, J.; Padikal, T. N. A new technique for field matching in primary breast irradiation. Int. J. Radiat. Oncol. Biol. Phys. 9:263-270; 1983. I I. Recht, A.; Siddon, R. L.; Kaplan, W. D.; Andersen, J. W.; Harris, J. R. Three-dimensional internal mammary lymphoscintigraphy: implications for radiation therapy treatment planning for breast carcinoma. Int. J. Radiat. Oncol. Biol. Phys. 14:477-481; 1988. 12. Siddon, R. L. Letter to the editor. Int. J. Radiat. Oncol. Biol. Phys. 10:1817; 1982. 13. Siddon, R. L.; Buck, B. A.; Harris, J. R.; Svensson, G. K.

Three-field technique for breast irradiation using tangential field comer blocks. Int. J. Radiat. Oncol. Biol. Phys. 9:583588; 1983. 14. Siddon, R. L.; Tonnesen, G. L.; Svensson, G. K. Threefield technique for breast treatment using a rotatable halfbeam block. Int. J. Radiat. Oncol. Biol. Phys. 7: 1473-1477: 1981. 15. Strender, L. E.; Lindahl, J.; Larsson, L. E. Incidence of heart disease and functional significance of changes in the electrocardiogram 10 years after radiotherapy for breast cancer. Cancer 57:929-934; 1986. 16. Svensson, G. K.; Bjsrngard, B. E.; Larsen, R. D.; Levene, M. B. A modified three-field technique for breast treatment. Int. J. Radiat. Oncol. Biol. Phys. 6:689-694; 1980. 17. Wallgren, A.; Arner, 0.; Bergstrom, J.; Blomstedt, B.; Grunberg, P.; Raf, L.; Silfversward, C.; Einhom, J. Radiation therapy in operable breast cancer-results from the Stockholm trial in adjuvant radiotherapy. Int. J. Radiat. Oncol. Biol. Phys. 12:533-537; 1986.

APPENDIX Several authors have described the problems of matching an anterior supraclavicular field with tangential fields. The use of a couch (turntable) angle reduces the matching problem, but there is still an overlap (medial tangent) or

gap (lateral tangent) at depth. Siddon described a simple demonstration which shows that turntable angle alone cannot eliminate the mismatch. (12) Lichter et al. derived an equation for the calculation

Breast technique 0 W. F.HARTSELLetal.

of the turntable angle (T) and collimator angle (p) when the gantry angle (0) SAD (F) and field length (L) are known: L tan p = ~ 2F cos f3 where tan 7 = &

(IO).

These equations are based on the assumptions that the

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angles T and p cannot be set with an accuracy of greater than half a degree. Because of the difficulty in setting the collimator and turntable angle, we empirically use a collimator angle of 5” for 80 cm SAD setups and 4” for 100 cm SAD setups. The turntable angle is then determined using fluoroscopy, matching the supraclavicular line with the cephalad field wire of the tangent. Using this method, the fields can be made to match on the skin with a minimal overlap or gap. We have measured the gap and overlap at a depth of 10 cm for various field sizes using this technique (empiric collimator angle and visual alignment for couch angles) and the gap or overlap at that depth does not exceed 2 mm, and is usually less than 1 mm.

Technique for breast irradiation using custom blocks conforming to the chest wall contour.

A technique for the treatment of the breast and regional nodes is presented. The technique involves the use of tangential fields to treat the breast a...
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