|Year : 2020 | Volume
| Issue : 4 | Page : 393-397
Should we consider thyroid gland as an organ at risk in carcinoma breast patients receiving adjuvant radiation by conformal technique? A single institute dosimetric study
Adilakshmi Madisetty1, Aparna Suryadevara1, Sanjeeva K Chinta1, Srinivas Vuppu2, Venkata R R Marella2
1 Department of Radiation Oncology, Mehdi Nawaz Jung Institute of Oncology and Regional Cancer Centre, Hyderabad, Telangana, India
2 Department of Medical Physics, Mehdi Nawaz Jung Institute of Oncology and Regional Cancer Centre, Hyderabad, Telangana, India
|Date of Submission||14-Sep-2017|
|Date of Decision||24-Jun-2019|
|Date of Acceptance||12-Jul-2019|
|Date of Web Publication||02-Oct-2020|
Department of Radiation Oncology, Mehdi Nawaz Jung Institute of Oncology and Regional Cancer Centre, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
Background: The most common malignancy among Indian women is carcinoma of the breast. In the management of breast cancer (BC), radiation therapy (RT) is given to breast or chest wall and supraclavicular lymph nodal (SCLN) area, with at least part of the thyroid receiving RT dose.There is an increased incidence of hypothyroidism (HT) among BC patients after RT involving the SCLN area. Moreover, the incidence of HT in India is higher than in the West. The aim of our study is to dosimetrically evaluate the thyroid doses during RT for BC.
Methods: This is a single institute prospective study (n = 131). Radiation was planned by three-dimensional conformal radiation therapy (3D-CRT) technique and dose-volume parameters for thyroid gland were noted.
Results: The median thyroid gland volume was 7.4 cc. The median of the mean dose to thyroid gland was 2068 cGy, V10 was 42%, and V40 was 33%. In other studies, BC patients with smaller thyroid gland were more prone to HT (volume <8 cc). In our study, we have seen that the median thyroid volume was 7.4 cc.
Conclusion: Our study showed a lower mean dose to the thyroid gland and smaller volume thyroid glands than in the literature. As the incidence of HT is higher in India, compared to the west and our patients had small volume thyroid glands, they could be at higher risk of developing HT RT. So BC patients should be monitored for HT and should be given a dose constraint while planning RT.
Keywords: Breast cancer, carcinoma, conformal, organ at risk, radiation dose, thyroid
|How to cite this article:|
Madisetty A, Suryadevara A, Chinta SK, Vuppu S, R Marella VR. Should we consider thyroid gland as an organ at risk in carcinoma breast patients receiving adjuvant radiation by conformal technique? A single institute dosimetric study. Indian J Cancer 2020;57:393-7
|How to cite this URL:|
Madisetty A, Suryadevara A, Chinta SK, Vuppu S, R Marella VR. Should we consider thyroid gland as an organ at risk in carcinoma breast patients receiving adjuvant radiation by conformal technique? A single institute dosimetric study. Indian J Cancer [serial online] 2020 [cited 2020 Oct 23];57:393-7. Available from: https://www.indianjcancer.com/text.asp?2020/57/4/393/297026
| » Introduction|| |
Carcinoma of the breast (CB) is the most common malignancy among Indian women and at present, the most common stage in India is stage II and III. In the management of stage III breast cancer, radiation therapy (RT) is used in most cases requiring RT to the breast or chest wall and supraclavicular lymphnodal (SCLN) area with at least part of the thyroid receiving RT dose. The thyroid gland is usually not contoured as an organ at risk (OAR) in breast cancer patients in the planning of RT. In general, the incidence of hypothyroidism is much higher in Indian population than the western population., The literature on thyroid as an OAR in RT of CB is sparse in Indian patients. The aim of our study was to evaluate thyroid doses while planning RT for breast cancer at our institute which is a regional cancer center in South India.
| » Materials and Methods|| |
This is a single institute prospective study including 131 female breast cancer patients in the age group of 20–80 years. Institutional ethics committee approval was taken for this study. We included all patients from stage IIA to stage IIIB postoperative cases of CB, either after breast-conserving surgery (BCS) or modified radical mastectomy, who received SCLN area irradiation as an adjuvant RT from September 2014 to November 2015. Patients who had bilateral breast cancer, thyroid surgery, thyroid disorder, prior radiation to the chest, or history of any other malignancy were excluded from the study.
The study patients had a thermoplastic immobilization device in a supine position with an armrest on an all in one board and planning CT scan was done in the treatment position. A CT scan with 3 mm slice thickness was taken and then images were transferred to the Eclipse version 15.6 planning system for further contouring and planning.
All patients were contoured according to the radiation therapy oncology group (RTOG) contouring guidelines and atlas for carcinoma of the breast or chest wall. Radiation was planned by three-dimensional conformal radiation therapy (3D-CRT) technique to intact breast or chest wall along with SCLN area. They received axillary nodal irradiation as per the stage of the disease. All the study patients received 50 Gy of external beam radiation in 25 fractions, 5 days/week. All plans were done by one physicist and reviewed by another physicist to avoid variations in planning. Furthermore, to avoid bias during the planning of radiation, RT planning was done and approved at first by the radiation oncologist. Later, the thyroid gland was contoured and dose-volume parameters such as the volume of the thyroid gland and dose to thyroid gland were noted from the dose-volume histogram (DVH). Contouring of breast or chest wall and SCLN area and the thyroid gland was done by the same radiation oncologist and confirmed by the second radiation oncologist.
| » Results|| |
A total of 131 patients in the age group of 20–80 years (median age of 47 years) were included in the study. Out of 131, there were 51 patients with stage II disease (39%) and 80 patients with stage III disease (61%). The total thyroid gland volume was noted and dose to the thyroid was calculated from the DVH. The median thyroid gland volume in the study was 7.4 cc (+/- 7.97 cc).
The median of the thyroid dose values was calculated from the DVH. The median of the mean thyroid dose received by the entire thyroid gland was 2068 cGy with a standard deviation of 901 cGy. The median of minimum thyroid dose was 113.5 cGy with a standard deviation of 136 cGy and the median of the maximum dose received by the entire gland was 5358 cGy with a standard deviation of 608 cGy.
The DVH dose parameters were analyzed; the median of V10 was found to be 42% with a standard deviation of 17% while that of V40 was 33% with a standard deviation of 19%.
The details of the results are summarized in [Table 1]. SD is the standard deviation for the parameter measured. V10 is the volume of the thyroid gland receiving 10 Gy and V40 is the volume of thyroid gland receiving 40 Gy. Both V10 and V40 are measured as percentages in the table.
|Table 1: The DVH parameters analyzed in the study with the median value and standard deviation (SD)|
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The planning images are shown in [Figure 1] and DVH with thyroid doses are shown in [Figure 2] and [Figure 3].
|Figure 1: Planning images of a study patient planned for radiation to the left chest wall and left supraclavicular lymph nodal area by 3D-CRT technique by Eclipse version 13.6 planning system. The images are showing the thyroid gland contoured in magenta colour in the axial, sagittal and coronal view. The radiation dose is displayed as a colour wash|
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|Figure 2: Showing the DVH image of a study patient showing the V10 (Volume of the thyroid gland receiving 10 Gy) and mean dose received by entire gland and total thyroid gland volume|
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|Figure 3: DVH image of a study patient showing the V40 (Volume of the thyroid gland receiving 40 Gy) and mean dose received by entire gland and total thyroid gland volume|
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| » Discussion|| |
There is an increased incidence of hypothyroidism among breast cancer patients, after chemotherapy and RT involving the SCLN area, with an incidence of about 18 to 21% in studies done in breast cancer patients at Norway compared to 8% in their general population., Studies were done on irradiated breast cancer patients with SCF LN area RT showed that a dose of >30 Gy and patients with small thyroid glands were associated with a higher risk of developing hypothyroidism while another study showed a dose of >26 Gy as a high dose with increased risk of hypothyroidism.,
However, a study by Smith et al. from MD Anderson Cancer Center, USA showed an increased risk of hypothyroidism (about 14%) in all the patients treated for breast cancer irrespective of whether they received RT or not. But in this study, they evaluated only elderly women (>65 years) which may not be applicable for breast cancer patients in general. Moreover, the radiosensitivity of the thyroid gland is believed to be lower for elderly patients.,
The incidence of hypothyroidism in developed countries like UK and USA is about 2 to 5%, while it is much higher in adult Indian population (about 11%)., Given the higher rate of hypothyroidism, we need further studies looking at thyroid gland as an OAR and also the incidence of hypothyroidism in Indian breast cancer patients post-RT.
Studies from other countries like Turkey, (though a small number of patients), showed similar results of higher incidence (21%) of hypothyroidism in carcinoma of breast patients who had SCF LN area RT. In this Turkish study by Akyurek et al, the volume of the thyroid gland and mean thyroid RT dose of >36 Gy were independent risk factors for the development of hypothyroidism.
Due to high incidence of thyroid disorders in Indian population and less data available for hypothyroidism in carcinoma of the breast patients in India, we need more dosimetric and clinical studies on our patients to make any recommendations.
In our study, we have seen that the median of the mean dose to thyroid gland was 20.68 Gy which was much lower than the OAR dose constraints reported by Emami et al. whereina dose of 45 Gy would result in hypothyroidism in 8% patients at 5 years after completion of radiation. The studies from literature also showed a mean thyroid dose of 26 Gy to 36 Gy as associated with increased risk of hypothyroidism, which was much higher than our study (20.68 Gy).,,
According to the normal tissue constraint guidelines, the dose to entire thyroid gland should be limited to <45 Gy or V26 <20%. The dose-volume constraint in our study showed a V10 of 42% and V40 of 33% which was higher than the constraint.
The size or volume of the thyroid gland was also found to be a significant factor in studies done on breast cancer patient's post-radiation. It is seen that patients with smaller thyroid gland were more prone for hypothyroidism (median value of 7 cc versus 16 cc) or a volume <8 cc., Thyroid glands in our patients were smaller in size (7.4 cc) than studies from other ethnicity patients. The mean volume of the thyroid gland was 16.7 cc and 32 cc, 11.5 cc, 8.1 cc in studies from Turkey, Norway, and Japan, respectively. Thus, the thyroid gland volume was smaller compared to Asians like Japanese but lower in Western patients. There is also variation among studies conducted within the same country for e.g., from Turkey it was 16 cc in one study and 32 cc in another study done in the same population.
In our study, we have seen that the median thyroid volume was 7.4 cc which warrants further studies in our patients for considering thyroid as an OAR.
The merit of our study lies in the fact that this the first prospective study done on a large number of Indian breast cancer patients. The limitation of our study is that it is only a dosimetric study and needs to be correlated clinically with measurement of clinical hypothyroidism in these patients on follow-up.
| » Conclusion|| |
Our study showed a lower mean dose to thyroid gland considering that our patients had smaller volume thyroid glands than the studies in the literature. As the incidence of hypothyroidism is higher in Indian population compared to the western population in general and our patients had small volume thyroid glands, they could be at increased risk of developing hypothyroidism post RT.
So monitoring of carcinoma breast patients who had RT to breast or chest wall with SCLN RT should be evaluated for hypothyroidism during follow up. Also, all thyroid patients should have thyroid gland contoured and given a dose constraint while planning RT until further studies on hypothyroidism post-irradiation in Indian breast cancer patients are available.
Parameshwar Marati, MSc, Dip RT, Medical physicist, Department of Medical Physics, Mehdi Nawaz Jung Institute of Oncology and Regional cancer center, Hyderabad, Telangana, India.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]