Using a thermoluminescent dosimeter to evaluate the location reliability of the highest–skin dose area detected by treatment planning in radiotherapy for breast cancer
Introduction
Breast cancer has been the most common type of cancer diagnosed among women in Taiwan since 1996. According to statistics of Department of Health, Executive Yuan, R.O.C., its incidence rate increased by 19.6% from 2008 to 2011.1 The age-adjusted incidence rate has increased steadily, and in 2011, it reached 74.63 new cases per 100,000 people.2 Because of the relative success of cancer screening programs, early detection and timely and appropriate treatment yield a more favorable prognosis for patients with breast cancer than for patients with most other types of cancer. Breast cancer is the fourth leading cause of deaths due to cancer in Taiwanese women, with a mortality rate of 11.45 per 100,000 people in 2011.2
Postoperative adjuvant radiotherapy (RT) plays a crucial part in the locoregional management of breast cancer. Nowadays, breast-conservation therapy is preferred for T1, T2, and selected T3 tumors3, 4 involving breast-conserving surgery, followed by 6 to 7 weeks of daily radiation treatments for the entire breast. RT is an essential component of breast-conservation therapy. However, it is inevitable that the skin receives a high radiation dose in the RT field. The skin is relatively radiosensitive and tends to exhibit various degrees of damage after certain radiation doses.5 Therefore, the appearance of radiation dermatitis in the RT field of breast cancer is expected. Maintaining radiation-induced skin toxicities as low as possible, while providing the intended dose to the underlying breast, remains a challenge.6 Accurately estimating skin doses provides a guide for predicting the location and severity of RT-induced skin reactions in patients with breast cancer.
Little information is available regarding accurate skin doses because of its uncertainty.7, 8 The skin irradiated dose is observable on the isodose curve distribution by using the RT treatment planning system (TPS), the results of which enable approximation of the location of the highest–skin dose area. Nevertheless, estimating a skin dose accurately is difficult because megavoltage x-ray beams exhibit the well-known phenomenon of dose buildup within the first few millimeters of the incident body surface, which is the skin. However, appropriately measuring a skin dose during radiation may overcome this problem, and thermoluminescent dosimeter (TLD) measurement has been reported to be a suitable method for providing reliable dose data.9 In a previous study, we suggested that the location of the highest–skin dose area predicted using the TPS may adequately reflect the severe skin reaction area in some treatment areas.10 We designed the current study to measure skin doses using the TLD and to locate the highest–skin dose area in each patient. We compared the results with the highest-dose area located using the TPS to ascertain the consistency between the 2 methods and to determine whether the skin dose shown using the TPS is an alternative, reliable approach for estimating the highest–skin dose area.
Section snippets
Patients
Between January 2013 and October 2013, 80 consecutive patients with breast cancer who had received breast-conserving surgery and were referred to our department for postoperative adjuvant RT were evaluated. The eligibility criteria were patients with pathologically proven primary breast carcinoma, curative intent for RT, and the ability of the patients to raise their arms steadily when immobilized during daily RT. There was no age limitation. This study was approved by the Institutional Review
Results
Table 1 shows the characteristics of 80 patients. Their age ranged from 22 to 80 years, and the median age was 52 years. Because of a relatively young population, the median BMI was 22.8. Among the patients, 55% had a bra cup size of B or smaller. Cancers in the left breast were more common. Most of the patients (57%) were at Stage I or earlier stages. Only 12 (15%) patients had the treatment field extended to cover the SCLNs.
The distribution of the highest-dose areas measured by the TLD were
Discussion
The 2 methods yielded consistent results when the highest-dose spots were located in the axillary and breast areas but not in the inframammary fold. Additional stratified analyses showed that the pattern of consistency varied according to different patient characteristics.
A young woman who was 22 years old with breast carcinoma in situ was among our patient group. Breast cancer in Taiwan is characterized by a striking recent increase of incidence and a relatively young median age (45 to 49
Conclusions
Based on dose verification by using the TLD, it is suggested that the TPS can be used as a reference to predict the skin dose in some areas of the body during RT for breast cancer. If the highest skin dose estimated using the TPS is located in the breast area or axillary area, it is likely to have the highest dose over there. However, a TPS result is less reliable if it shows that the highest skin dose is located in the inframammary area.
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Evaluating the consistency of location of the most severe acute skin reaction and highest skin dose measured by thermoluminescent dosimeter during radiotherapy for breast cancer
2016, Medical DosimetryCitation Excerpt :We further published an article recently to evaluate the location consistency of the highest skin dose area detected by TPS and TLD in RT for breast cancer. We suggested that skin doses shown on the treatment planning might be a reliable and simple alternative method for estimating the highest skin doses in some areas.28 In the current study, we tried to determine if the clinical skin reaction matches to skin dose measurement of TLDs.
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These authors contributed equally to this work.