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| | ORIGINAL ARTICLES - CLINICAL | | | | | Year : 2007 | Volume : 3 | Issue : 1 | Page : 8-11 | | | Radiation dose to contra lateral breast during treatment of breast malignancy by radiotherapy
Arun Chougule
Department of Radiotherapy, Incharge Telemedicine, SMS Medical College and Hospital, Jaipur - 302004, India
Correspondence Address:
Arun Chougule
II - 38, Gandhinagar, Jaipur - 302 015
India
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DOI: 10.4103/0973-1482.31964 PMID: 17998712
Aims: External beam radiotherapy is being used regularly to treat the breast malignancy postoperatively. The contribution of collimator leakage and scatter radiation dose to contralateral breast is of concern because of high radio sensitivity of breast tissue for carcinogenesis. This becomes more important when the treated cancer breast patient is younger than 45 years and therefore the contralateral breast must be treated as organ at risk. Quantification of contralateral dose during primary breast irradiation is helpful to estimate the risk of radiation induced secondary breast malignancy.
Materials and Methods: In present study contralateral breast dose was measured in 30 cancer breast patients undergoing external beam therapy by Co-60 teletherapy machine. Postoperative radiotherapy was delivered by medial and lateral tangential fields on alternate days in addition to supraclavicle field daily with 200 cGy/F to a total dose of 5000 cGy in 25 fractions. CaSO4: Dy themoluminescence dosimeter discs were employed for these measurements. Three TLD discs were put on the surface of skin of contra lateral breast, one at the level of nipple and two at 3 cms away from nipple on both side along the midline for each field. At the end treatment of each filed, TLD discs were removed and measured for dose after 24h on Thelmador - 6000 TLD reader.
Results: The dose at the contra lateral breast nipple was to be 152.5 to 254.75 cGy for total primary breast dose of 5000 cGy in 25 equal fractions which amounted to 3.05-6.05% of total dose to diseased breast. Further it was observed that the maximum contribution of contralateral breast dose was due to medical tangential half blocked field.
Conclusion: CaSO4; Dy thermoluminescence dosimetry is quite easy, accurate and convenient method to measure the contra lateral breast dose.
Keywords: Breast malignancy, contralateral breast dose, secondary cancer, thermoluminescence
How to cite this article:
Chougule A. Radiation dose to contra lateral breast during treatment of breast malignancy by radiotherapy. J Can Res Ther 2007;3:8-11 |
| > Introduction | |  |
The age of incidence of breast malignancy is decreasing and because of awareness and availability of treatment options, most women prefer lumpectomy rather than radical mastectomy, which is followed by radiotherapy. During external beam therapy of malignant breast, the contra lateral breast receives radiation due to leakage from collimator and scatter from primary. Breast is highly radiosensitive tissue for radiation induced second malignancy and is of more concern for female younger than 45 years of age receiving radiotherapy for breast malignancy. Boice et al[1] have reported that incidence of radiation induced breast cancer is a linear function of dose received by the contra lateral breast and the latent period is over 10 years. Several investigators[2],[3],[4] have measured the contra lateral breast dose either on Anderson female phantom/ Rando phantom and on actual patients and observed that the scatter dose to contra lateral breast during medial tangential and supra clavicle field is quite high and some times of the order of 500 cGy for 5000 cGy primary breast dose. The quantification of the contralateral breast especially during treatment of diseased breast by cobalt external beam is very important, as the scatter contribution will be more. At our center about 9% of all the cancer patients are cancer breast treated after modified mastectomy of lumpectomy. In present study measurement of contralateral breast dose is done using CaSO4: Dy themoluminescence discs because of small size, very high sensitivity ability to record very small doses and its small size, very high sensitivity, ability to record very small doses and energy independent response for energy of about 150 to 1250 KeV, its many other advantages were reported by author elsewhere.[5],[6]
| > Materials and Methods | | |
Measurement of contralateral breast dose was done in 30 patients undergoing external beam radiotherapy by Co- 60 teletherapy unit at M. B. Govt. Hospital, Udaipur during 1993-1995 with intention to quantify the radiation dose and follow up the patients for late effects. Unfortunately many patients were lost to follow-up and as on date only two patients are traceable; therefore the late effect study could not be completed. In this communication the dose received during various treatment fields is reported.
Precalibrated and standardized CaSO4: Dy TLD discs of size 13 mm dia were put on the surface skin of the contralateral breast, one at the level of nipple and two at 3 cms away from nipple on both side along the midline. For electronic equilibrium 5 mm thick wet cotton bolus was kept on each disc. Patients were treated with supra clavicle field (SCL) daily and medial tangential (MT) and lateral tangential (LT) fields on alternate days with daily dose of 200 cGy/F, 5 F/day to a total dose of 5000 cGy. For medial and lateral tangential field the half blocked breast cone was used. After the treatment each field is over all the TLD discs were removed from patient and another set of TLD disc is put for other fields. This way 3 TLD discs for SCL field and 3 TLD discs for MT/LT fields daily were used. These exposed TLD discs were stored in radiation free area and after 24h the dose was measured by reading the TLD discs on Thelmador - 6000 TLD reader (BARC make). The mean of the three-disc reading is taken as the contralateral breast dose. In each patient the measurement was carried out at least five times during the course of treatment. The precaution is taken to attach the TLD discs at same position during all the measurements. As the response of CaSO4: Dy TL material is almost flat over energy range of 54 KeV - 2 MeV and about 10.9 times[7] higher for the low energy, we assumed the larger contribution of scatter radiation to be over 54 KeV energy. Our dose might be slightly on higher side because of low energy contribution response being higher.
| > Results | | |
The age and stage wise distribution of patients is given in [Table - 1]. It is evident that most of the patients are in age group of 40-49 years. In [Table - 2] the contribution of contralateral breast dose because of various treatment fields is given. It is observed that the contribution to contralateral breast dose due to all the fields varies from 3.05-6.05% of the dose delivered to diseased breast. The contribution due to the medial tangential field is almost twice as that due to lateral tangential field. The lateral tangential fields enters laterally and may be contributing to internal scatter, which is very difficult whereas the medical tangential field is close to the contralateral breast and hence the scatter and the collimator contribution is more.
| > Discussion | | |
According to UNSCEAR[8] report, experimental exposure of animals to radiation and observations on exposed human population have shown that ionising radiations are general carcinogens capable of inducing tumor in almost all tissues of mammals irrespective of species. Dose to the contra lateral breast as a result of radiotherapy of breast should not be ignored in radiotherapy and more so in patients younger than 45 years. The breast tissue is highly sensitive and therefore the contralateral breast must be regarded as organ at risk (sensitive organ) while planning for radiotherapy. Many researchers have reported the contralateral breast dose; some reported results of direct measurement on patient, some reports measurement on phantom and some gave the figures from calculation. Boice et al[9] have conducted case control study in cohort of 41,109 women diagnosed with breast cancer and analyzed the records. They found mean contralateral breast dose to be 282 cGy with maximum of 710 cGy and relative overall increase in risk of contralateral breast malignancy due to treatment of primary by radiation to be 1.19. However the risk of second malignancy in contralateral breast was 1.59, significantly high, in patients who underwent radiotherapy at younger age than 45 years for primary breast malignancy. This indicates high risk for younger patients.
Kelly et al[4] reported a study of evaluation of four different breast treatment techniques with 6 MV linac beam to compare the radiation dose to the contralateral breast. They have done the dose measurement on Rando phantom using TLD and used four different techniques of half beam with custom blocks, half beam using asymmetric collimator jaw, half beam using asymmetric collimator jaws with custom blocks and isocentric technique with non divergent posterior border. They observed higher contra lateral breast dose during medial field with wedge and lowest dose with asymmetric jaws and no medial wedge or block. Bhatnagar et al[10] reported comparison of contralateral breast dose during primary breast irradiation using intensity modulated radiotherapy (IMRT) and conventional tangential field technique. They have treated 36 patients of breast malignancy with IMRT and 8 with 3-D technique using tangential fields with wedge and measured contralateral breast dose during treatment using TLD. They observed the contralateral breast dose of 7.74±2.35% of primary breast dose (5000 cGy) in IMRT treatment planning and 9.74±2.04% of primary breast dose during conventional tangential field technique i.e., about 20% reduction in contralateral breast dose with IMRT as compared to conventional tangential treatment with wedge.
Tercilla et al[11] measured the contralateral breast dose during half beam block and isocentric treatment techniques for patients treated with primary breast irradiation on Cobalt - 60-teletherapy unit. They have measured contralateral breast dose with TLD in 15 patients and the doses were 325-650 cGy during half beam block tangential field treatment and 200-450 cGy for without half beam block tangential field treatment for a total primary breast dose of 5040 cGy in 28 equal fractions. They recommended nonuse of half beam block techniques however it will increase the ipsilateral lung and rib dose. In the present study Cobalt therapy machine was used for treating breast malignancies using medial and lateral tangential half block field on alternate days and SCL field daily.. The doses were measured using TLD and the contralateral breast doses were 153.5 to 254.75 cGy [3.05-6.05%] for a total dose of 5000 cGy in 25 equal fractions. Our doses are on lower side as compared to doses reported by Tercilla et al because we treated the chest wall after mastectomy using smaller fields where very less scattered radiation dose is expected.
Bhatnagar et al[12] have studied the effect of breast size on scatter dose to contralateral breast. They have treated 65 patients of breast cancer using 6 MV photon with IMRT technique and measured contralateral breast dose using TLD. The primary breast size volume was calculated by planning system from CT slices. They found the mean contralateral dose of 7.2% of primary breast dose (5000 cGy) and found that the contribution to contralateral breast dose is strongly dependent on primary breast size of the patient. Therefore it became of more concern in young breast cancer patients with bulky protuberant breast.
Using modern technique of CRT and IMRT the contralateral breast dose can be reduced by 10 - 20 % but still it is about 3.05-6.05% (153-255Gy) of the primary breast dose of 5000 cGy, which cannot be ignored. Muller-Runkel et al[13] have advocated covering of contralateral breast with thin lead sheet to reduce the scattered contribution to contralateral breast skin though little can be done to reduce the dose from the lateral tangential field as the dose is caused by internal body scatter. They used 4 mm thick commercially available vinyl coated flexible lead shield containing lead powder of 1 mm equivalent lead density to cover the contralateral breast and found that the contralateral dose is reduced by 3-fold from 15% to 5%.
| > Conclusions | | |
Themoluminescence dosimetry is very easy, most convenient and reasonably accurate method to measure the dose to contralateral breast. The modern techniques like CRT and IMRT may bring down the contralateral breast dose but still in developing countries where Co - 60 teletherapy is the primary unit of treatment and therefore it is advisable to quantify the contralateral breast dose and all attempts must be made to bring it down.
| > References | | |
| 1. | Boice JD Jr, Land CE, Shore RE, Norman JE, Tokunaga M. Risk of breast cancer following low dose radiation exposure. Radiology 1979;131:589-97.  [PUBMED] | | 2. | Frass BA, Roberson PL, Lichter AS. Dose to the contralateral breast due to primary irradiation. Int J Radiat Oncol Biol Phys 1985;11:485-97. | | 3. | Muller-Runkel R, Kalokhe UP. Scatter dose from tangential breast irradiation to the uninvolved breast. Radiology 1990;175:873-6. [PUBMED] | | 4. | Kelly C, Wang X, Chu J, Hartselle W. Dose to contralateral breast: Comparison of four primary breast irradiation techniques. Int J Radiat Oncol Biol Phys 1996;34:727-32. | | 5. | Chougule AA, Gupta RK, Agarwal GR. Measurement of patient skin exposure by thermoluminescence dosimetry during some radiological examinations. Indian J Radiol Imag 1992;2:193-5. | | 6. | Chougule AA, Hussain S. Radiation dose to the wrist of the radiologists during some fluoroscopic investigations. Indian J Radiol Imag 1993;3:93-5. | | 7. | Pradhan AS, Bhat BC. Response of sensitized CaSO4: Dy phosphor embedded TLD discs to X-rays and gamma rays. Radiat Prot Dosimetry 1982;79:23-6. | | 8. | UNSCEAR: Sources and effects of ionising radiation. United Nations Scientific Committee on Effects of Atomic Radiation E 77 IX I. United Nations: New York; 1977. | | 9. | Boice JD Jr, Harvey EB, Blettner M, Storall M, Flannery JT. Cancer in the contralateral breast after radiotherapy for breast cancer. N Engl J Med 1992;326:781-5. | | 10. | Bhatnagar AK, Brandner E, Sonnik D, Wu A, Kalnicki S, Deutch M, et al . Intensity modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation: Initial report. Cancer Jr 2004;10:381-5. | | 11. | Tarcilla O, Krasin F, Lawn-Tsao L. Comparison of contralateral breast doses from 1/2 beam block and isocentric treatment techniques for patients treated with primary breast irradiation with 60CO. Int J Radiat Oncol Biol Phys 1989;17:205-10. | | 12. | Bhatnagar AK, Heron DE, Deutch M, Brandndner E, Andrew WU, Kalnicki S. Does breast size affect the scatter dose to ipsilateral lung, heart or contralateral breast in primary irradiation using intensity modulated radiotherapy (IMRT)? Am J Clin Oncol 2006;29:80-4. | | 13. | Muller-Runkel R, Kalokhe UP. Methods for reducing scatter radiation dose to the contralateral breast during tangential breast radiation therapy. Radiology 1994;191:853-5. [PUBMED] |
[Table - 1], [Table - 2]
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