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The use of ultrasound to measure breast thickness to select electron energies for breast boost radiotherapy
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E;IDNCO,OGV
ELSEVIER
Radiotherapy and Oncology 32 (1994) 265-267
Technical note
The use of ultrasound to measure breast thickness to select electron energies for breast boost radiotherapy D. Gilligan*, J.A. Hendry, J.R. Yarnold Department of Radiotherapy, Royal Marsden Hospital. Downs Road, Sutton. Surrey, UK Received 9 February 1994; revision received l0 May 1994; accepted 3 June 1994
Abstract
Ultrasound has been used in 30 patients to measure breast thickness as a means of selecting the most appropriate electron energy for the boost in breast conservation radiotherapy. When compared with electron energies selected on the basis of clinical examination, the target volume was underdosed in 21/30 patients. A major problem in the placement of an electron boost is the demarcation of the target volume.
Keywords: Ultrasound; Target volume; Electron energy
1. Introduction
2. Methods
A boost field given as part of radiotherapy for breast conservation is aimed at delivering an increased dose to the area most at risk of local relapse. The boost is given to the region around the excised tumour generally as part of a course of radiation to the whole breast, although the use of a boost in this situation is controversial [6]. Arguments in favour of such a treatment are based upon studies of the pathological distribution of tumour within the breast [3]. Following local excision alone it has been reported that 80-90% of relapses occur close to the primary site [5]. When radiotherapy is given to the whole breast the risk of relapse is reduced, but for the first 5 - I0 years most relapses occur close to the primary site [2]. Where there is microscopic clearance of the excised tumour, a boost may be unnecessary and could be responsible for an increased risk of late normal tissue damage. Various studies have been undertaken to assess both the site and depth of an electron boost in breast conservation using orthogonal films external markers [9l, ultrasound [41 and CT scanning [7l. This paper describes a study which was designed to audit our conventional practice of determining breast thickness by clinical examination compared with a simple ultrasound technique.
Thirty patients undergoing radiotherapy to the whole breast for early breast cancer ( T I - 2 N0-1 M0) and in whom an electron boost was planned, gave informed consent. The target volume for the boost was defined using a combination of clinical examination and pre-operative Polaroid photographs. The usual surface dimensions were 8-10-cm diameter circles. The deep border was defined at the pectoralis fascia; this was chosen because it was not possible to visualise the inferior margin of the tumour bed by ultrasound in every case, particularly as marker clips were not used. The area to receive an electron boost was delineated on the skin with a marker and the electron energy selected in the conventional manner by the prescribing radiotherapist. This involved an estimation of average breast thickness across the boost volume from clinical, pathological and operative details. When the area had been marked each patient was scanned in the position for which the boost treatment was to be given using a 5 MHz Hitachi B ultrasound scanner. Measurements were taken across the boost area from the skin surface to the pectoralis fascia overlying the anterior ribs. Breast thickness was recorded at the maximum and minimum depths and at the centre of the boost site. Hard copies were reviewed by a consultant in diagnostic imaging experienced in breast imaging with ultrasound. Conventional and ultrasound measurements were then converted into electron energies such that the target depth was covered by the
* Corresponding author, Radiotherapy Research Unit. Institute of Cancer Research, Cotswold Road, Sutton, Surrey, UK SM2 5NG.
0167-8140/94/$07.00 © 1994 Elsevier Science Ireland Ltd. All rights reserved SSD! 0167-8140(94)01418-3
266
D. Gilligan et at/Radiother. Oncol. 32 (1994) 265-267
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Fig. 1. Conventional versus ultrasound measurements at (a) centre, (b) maximum, and (c) minimum depths across the boost volume. The dashed line represents what would be a perfect correlation (r = i) between the two forms of measurement.
90% isodose of the electron beam. The 90% isodose depths used in this study range from 1.8 cm for 6 MeV to 5.4 crn for 18 MeV electrons for a 10-cm circle. 3. Results
The conventionally estimated depths were compared with the ultrasound derived depths at the centre, minimum and maximum depths across the boost target volume, as shown in Fig. 1. In 24 patients the ultrasound depth at the centre of the boost was greater than the conventionally measured depth, in only 4 patients was the depth less. The difference between the measurements at the centre of the boost field is significant (p < 0.001) (Wiicoxon's signed rank test). When these measurements at the boost centres are converted into the actual electron energies which would have been used for treatment, 21/30 would require an increase in electron energy to adequately cover the depth of the target volume had the ultrasound depth been used for prescribing the electron energy. In 8/30 patients the energy would have been increased by more than 2 MeV and in 3 this would have been greater than 4 MeV.
4. Discussion These results show that there is a significant discrepancy betwcen the two forms of measurement used. There is a tendency for the prescribing radiotherapist to underestimate the breast thickness and therefore underdose the tumour bed by selecting too low an electron energy. This has implications for audit, in that measurements using ultrasound have revealed a disagreement and discussion is now required as to whether there should be a change in practice. At present the definition of the target volume is somewhat arbitrary and it may not be essential to define the target volume as deep as the pectoral fascia when the tumour is superficial. In addition, because of the curvature of the chest wail, the depth varies. In this study we have taken the depth at the centre of the boost field for comparison. During the study it became apparent that it is frequently hard to localise the tumour bed accurately, and that this problem exists for
other imaging modalities too. Precise operative and pathological details are essential, preoperative photography may also be helpful, but Iocalisation can be difficult without the aid of a physical marker. One means of improving target volume definition is to demarcate the tumour bed at surgery with marker clips. A number of workers have reported geographical misses when conventional demarcation of the boost volume was compared with that using surgical clips. Bedwinek [1] reported a 54% (19/35) geographical miss rate when the target volume was measured in medio-lateral and cranio-caudal dimensions, but no comment was made on the measurement of the depth of the turnout bed. Radiotherapists may err towards lower electron energies because they fear overdosing underlying structures, particularly as electrons have increased transmission across air-filled cavities. The contribution of the boost to non-target structures would become more significant if higher doses confined to the excision site are to be considered such as those investigated by the Manchester trial [8]. Our findings compliment those of others in that the placement of the electron boost with respect to the target volume can frequently be inaccurate. Therefore, in order to optimise the delivery of radiotherapy to areas most at risk of relapse it is essential that the target volume is defined properly. Ultrasound measurement is a feasible technique for measuring chest wall thickness. The depth of the target volume ultrasound would probably be best combined with the use of marker clips placed at the time of surgery. This would be especially important if there is a move towards more localised treatments. Acknowledgements
We would like to thank Dr Jeff Bamber for his help with the ultrasound equipment and Dr David Cosgrove for reviewing the ultrasound scans. Re~reunces
Bedwinek, J. Breast conserving surgery and irradiation: the importance of demarcating the excision cavity with surgical clips. Int. J. Radiat. Oncol., Biol. Phys. 26: 675-679, 1993.
D. Gilligan et al. / Radiother. Oncol. 32 (1994) 265-267
2
Fowble, B., Solin, L.J., Schultz, D.J., Rubenstein, J. and Goodman, R.L. Breast recurrence following conservative surgery and radiation: patterns of failure, prognosis and pathologic findings from mastectomy specimens with implications for treatment. Int. J. Radiat. Oncol., Biol. Phys. 19: 833-842, 1990. 3 Holland, R., Veling, S.H.J., Mravunac, M. and Hendricks, J.H.C.L. Histologic multifocality of Tis, T I - 2 breast carcinomas. Cancer 56: 979-990, 1985. 4 Leonard, C., Harlow, C.L., Coffin, C., Drose, J., Norton, L. and Kinzie, J. Use of ultrasound to guide radiation boost planning following lumpectomy for carcinoma of the breast. Int. J. Radiat. Oncol., Biol. Phys. 27: 1193-1197, 1993. 5 Price, P., Walsh, G., McKinna, A.J., Ashley, S. and Yarnold, J.R. Patterns of relapse local excision ± radiotherapy for early stage breast cancer. Radiother. Oncol. 13: 53-60, 1988.
6 7
8
9
267
Recht, A. and Harris, J.R. To boost or not to boost, and how to do it. Int. J. Radiat. Oncol., Biol. Phys. 20: 177-178, 1991. Regine, R.F., Ayyangar, K.M., Komarnicky, L.T., Bhandare, N. and Mansfield, C.M. Computer CT planning of the electron boost in definitive breast irradiation. Int. J. Radiat. Oncol., Biol. Phys. 20: 121-125, 1991. Ribeiro, G.G., Magee, B.. Swindell, R., Harris, M. and Banerjee, S.S. The Christie Hospital breast conservation trial: An update at 8 years from inception. Clin. Oncol. 5: 278-283, 1993. Solin, L.J., Chu, J.C., Larsen, R., Fowble, B., Galvin, J.M. and Goodman R.L. Determination of depth for electron breast boost. Int. J. Radiat. Oncol., Biol. Phys. 13: 1915-1919, 1987.
E;IDNCO,OGV
ELSEVIER
Radiotherapy and Oncology 32 (1994) 265-267
Technical note
The use of ultrasound to measure breast thickness to select electron energies for breast boost radiotherapy D. Gilligan*, J.A. Hendry, J.R. Yarnold Department of Radiotherapy, Royal Marsden Hospital. Downs Road, Sutton. Surrey, UK Received 9 February 1994; revision received l0 May 1994; accepted 3 June 1994
Abstract
Ultrasound has been used in 30 patients to measure breast thickness as a means of selecting the most appropriate electron energy for the boost in breast conservation radiotherapy. When compared with electron energies selected on the basis of clinical examination, the target volume was underdosed in 21/30 patients. A major problem in the placement of an electron boost is the demarcation of the target volume.
Keywords: Ultrasound; Target volume; Electron energy
1. Introduction
2. Methods
A boost field given as part of radiotherapy for breast conservation is aimed at delivering an increased dose to the area most at risk of local relapse. The boost is given to the region around the excised tumour generally as part of a course of radiation to the whole breast, although the use of a boost in this situation is controversial [6]. Arguments in favour of such a treatment are based upon studies of the pathological distribution of tumour within the breast [3]. Following local excision alone it has been reported that 80-90% of relapses occur close to the primary site [5]. When radiotherapy is given to the whole breast the risk of relapse is reduced, but for the first 5 - I0 years most relapses occur close to the primary site [2]. Where there is microscopic clearance of the excised tumour, a boost may be unnecessary and could be responsible for an increased risk of late normal tissue damage. Various studies have been undertaken to assess both the site and depth of an electron boost in breast conservation using orthogonal films external markers [9l, ultrasound [41 and CT scanning [7l. This paper describes a study which was designed to audit our conventional practice of determining breast thickness by clinical examination compared with a simple ultrasound technique.
Thirty patients undergoing radiotherapy to the whole breast for early breast cancer ( T I - 2 N0-1 M0) and in whom an electron boost was planned, gave informed consent. The target volume for the boost was defined using a combination of clinical examination and pre-operative Polaroid photographs. The usual surface dimensions were 8-10-cm diameter circles. The deep border was defined at the pectoralis fascia; this was chosen because it was not possible to visualise the inferior margin of the tumour bed by ultrasound in every case, particularly as marker clips were not used. The area to receive an electron boost was delineated on the skin with a marker and the electron energy selected in the conventional manner by the prescribing radiotherapist. This involved an estimation of average breast thickness across the boost volume from clinical, pathological and operative details. When the area had been marked each patient was scanned in the position for which the boost treatment was to be given using a 5 MHz Hitachi B ultrasound scanner. Measurements were taken across the boost area from the skin surface to the pectoralis fascia overlying the anterior ribs. Breast thickness was recorded at the maximum and minimum depths and at the centre of the boost site. Hard copies were reviewed by a consultant in diagnostic imaging experienced in breast imaging with ultrasound. Conventional and ultrasound measurements were then converted into electron energies such that the target depth was covered by the
* Corresponding author, Radiotherapy Research Unit. Institute of Cancer Research, Cotswold Road, Sutton, Surrey, UK SM2 5NG.
0167-8140/94/$07.00 © 1994 Elsevier Science Ireland Ltd. All rights reserved SSD! 0167-8140(94)01418-3
266
D. Gilligan et at/Radiother. Oncol. 32 (1994) 265-267
r
•
a)
correlation
,," s j
coefficient
b)
i
r=0.54
:z: t~ L~
=
c)
/
r=0.32 , "
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,
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//
9~'
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........ ., ......................... 3 4 5 ULTRASOUND D E P T H ( c m )
6
2
3 4 5 ULTRASOUND D E P T H (cm)
6
Fig. 1. Conventional versus ultrasound measurements at (a) centre, (b) maximum, and (c) minimum depths across the boost volume. The dashed line represents what would be a perfect correlation (r = i) between the two forms of measurement.
90% isodose of the electron beam. The 90% isodose depths used in this study range from 1.8 cm for 6 MeV to 5.4 crn for 18 MeV electrons for a 10-cm circle. 3. Results
The conventionally estimated depths were compared with the ultrasound derived depths at the centre, minimum and maximum depths across the boost target volume, as shown in Fig. 1. In 24 patients the ultrasound depth at the centre of the boost was greater than the conventionally measured depth, in only 4 patients was the depth less. The difference between the measurements at the centre of the boost field is significant (p < 0.001) (Wiicoxon's signed rank test). When these measurements at the boost centres are converted into the actual electron energies which would have been used for treatment, 21/30 would require an increase in electron energy to adequately cover the depth of the target volume had the ultrasound depth been used for prescribing the electron energy. In 8/30 patients the energy would have been increased by more than 2 MeV and in 3 this would have been greater than 4 MeV.
4. Discussion These results show that there is a significant discrepancy betwcen the two forms of measurement used. There is a tendency for the prescribing radiotherapist to underestimate the breast thickness and therefore underdose the tumour bed by selecting too low an electron energy. This has implications for audit, in that measurements using ultrasound have revealed a disagreement and discussion is now required as to whether there should be a change in practice. At present the definition of the target volume is somewhat arbitrary and it may not be essential to define the target volume as deep as the pectoral fascia when the tumour is superficial. In addition, because of the curvature of the chest wail, the depth varies. In this study we have taken the depth at the centre of the boost field for comparison. During the study it became apparent that it is frequently hard to localise the tumour bed accurately, and that this problem exists for
other imaging modalities too. Precise operative and pathological details are essential, preoperative photography may also be helpful, but Iocalisation can be difficult without the aid of a physical marker. One means of improving target volume definition is to demarcate the tumour bed at surgery with marker clips. A number of workers have reported geographical misses when conventional demarcation of the boost volume was compared with that using surgical clips. Bedwinek [1] reported a 54% (19/35) geographical miss rate when the target volume was measured in medio-lateral and cranio-caudal dimensions, but no comment was made on the measurement of the depth of the turnout bed. Radiotherapists may err towards lower electron energies because they fear overdosing underlying structures, particularly as electrons have increased transmission across air-filled cavities. The contribution of the boost to non-target structures would become more significant if higher doses confined to the excision site are to be considered such as those investigated by the Manchester trial [8]. Our findings compliment those of others in that the placement of the electron boost with respect to the target volume can frequently be inaccurate. Therefore, in order to optimise the delivery of radiotherapy to areas most at risk of relapse it is essential that the target volume is defined properly. Ultrasound measurement is a feasible technique for measuring chest wall thickness. The depth of the target volume ultrasound would probably be best combined with the use of marker clips placed at the time of surgery. This would be especially important if there is a move towards more localised treatments. Acknowledgements
We would like to thank Dr Jeff Bamber for his help with the ultrasound equipment and Dr David Cosgrove for reviewing the ultrasound scans. Re~reunces
Bedwinek, J. Breast conserving surgery and irradiation: the importance of demarcating the excision cavity with surgical clips. Int. J. Radiat. Oncol., Biol. Phys. 26: 675-679, 1993.
D. Gilligan et al. / Radiother. Oncol. 32 (1994) 265-267
2
Fowble, B., Solin, L.J., Schultz, D.J., Rubenstein, J. and Goodman, R.L. Breast recurrence following conservative surgery and radiation: patterns of failure, prognosis and pathologic findings from mastectomy specimens with implications for treatment. Int. J. Radiat. Oncol., Biol. Phys. 19: 833-842, 1990. 3 Holland, R., Veling, S.H.J., Mravunac, M. and Hendricks, J.H.C.L. Histologic multifocality of Tis, T I - 2 breast carcinomas. Cancer 56: 979-990, 1985. 4 Leonard, C., Harlow, C.L., Coffin, C., Drose, J., Norton, L. and Kinzie, J. Use of ultrasound to guide radiation boost planning following lumpectomy for carcinoma of the breast. Int. J. Radiat. Oncol., Biol. Phys. 27: 1193-1197, 1993. 5 Price, P., Walsh, G., McKinna, A.J., Ashley, S. and Yarnold, J.R. Patterns of relapse local excision ± radiotherapy for early stage breast cancer. Radiother. Oncol. 13: 53-60, 1988.
6 7
8
9
267
Recht, A. and Harris, J.R. To boost or not to boost, and how to do it. Int. J. Radiat. Oncol., Biol. Phys. 20: 177-178, 1991. Regine, R.F., Ayyangar, K.M., Komarnicky, L.T., Bhandare, N. and Mansfield, C.M. Computer CT planning of the electron boost in definitive breast irradiation. Int. J. Radiat. Oncol., Biol. Phys. 20: 121-125, 1991. Ribeiro, G.G., Magee, B.. Swindell, R., Harris, M. and Banerjee, S.S. The Christie Hospital breast conservation trial: An update at 8 years from inception. Clin. Oncol. 5: 278-283, 1993. Solin, L.J., Chu, J.C., Larsen, R., Fowble, B., Galvin, J.M. and Goodman R.L. Determination of depth for electron breast boost. Int. J. Radiat. Oncol., Biol. Phys. 13: 1915-1919, 1987.