International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationSkin-Sparing Radiation Using Intensity-Modulated Radiotherapy After Conservative Surgery in Early-Stage Breast Cancer: A Planning Study
Introduction
Over the last 20 years, therapeutic approaches for early breast cancer have evolved from radical mastectomy toward breast-conserving surgery (BCS) followed by adjuvant external beam radiation (RT). If minimal toxicities and good cosmetic results are achieved, breast preservation has clear advantage over mastectomy, by its strong positive impact on patient quality of life.
For patients with early breast cancer, the standard radiotherapy technique (using two wedged tangential fields and high energy photons) substantially improves local control, decreases the development of distant relapses, and reduces deaths from breast cancer (1). However, it also results in some severe acute and late side effects, including skin desquamation and fibrosis.
Several studies have shown dosimetric advantage of the intensity-modulated radiation therapy (IMRT) over the conventional methods both in terms of dose homogeneity and sparing of critical structures (heart, lung, and contralateral breast) 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. In addition, two phase III randomized control trial comparing breast IMRT to standard wedged radiotherapy have showed a significant decrease of acute moist desquamation (12) and late changes in breast appearance (13) by IMRT. Three recent IMRT studies have suggested that the skin can be contoured and considered an organ-at-risk (OAR) for planning optimization 14, 15, 16. Although the oncologic safety of a radiation skin-sparing approach for women with early breast cancer has not been previously examined, indirect evidence is available from trials of skin-sparing mastectomy with reconstruction 17, 18, 19, 20. Skin-sparing mastectomy is regarded as a major improvement in the surgical treatment of early breast cancer patients. In selected patients with T1 to T2 N0 invasive breast tumors, pathologic invasion of the skin was <10% and the reported local recurrence rate was <6%. The features associated with risk of skin invasion were tumor size >5 cm, multicentric tumor, axillary nodal involvement, periareolar location, nipple retraction, and lymphovascular invasion. Skin-sparing mastectomy was considered safe if these adverse prognostic factors were absent. As patients with T1 to T2 N0 invasive breast cancer undergo breast-conserving surgery plus radiation as per current standards, a skin-sparing approach in radiation delivery may be attempted without compromising local control. Increased detection of breast cancer in very early stages (including ductal carcinoma in situ) provides a significant proportion of patients eligible for this approach.
We hypothesized that restriction of the skin volumes receiving beyond 40 Gy would translate into a significant reduction in the incidence of both acute and late skin toxicity (21) and thereby an improvement in cosmesis. Before applying this concept in a clinical protocol, we did a planning study to evaluate the feasibility of skin-sparing radiation by IMRT. The objective of this study was to compare two IMRT plans generated by helical tomotherapy (HT) with and without skin dose restrictions (skin-sparing and non–skin-sparing plans) in 14 patients of early breast cancer, using dosimetric and dose–volume histogram (DVH) derived parameters for skin, planning target volume (PTV), and other critical organs-at-risk. In this study we showed that HT with skin-sparing approach reduces significantly the dose received by the skin, the volume of skin receiving doses beyond 40 Gy, without compromising the breast coverage. To verify the accuracy of HT, skin dose calculation by the planning system was compared with thermoluminescent dosimeter (TLD) measurements in an anthropomorphic phantom for both skin-sparing and non–skin-sparing plans.
Section snippets
Patients
We obtained archival computed tomography (CT) scan images of 14 patients with left-sided, stage I/II tumors treated with conventional tangential irradiation at our treatment center. Left-sided breast cancer patients were selected to assess whether sparing of skin is possible while the heart is also an organ-at-risk. Institutional board approval for this retrospective dosimetric study was obtained under the category of “minimal risk application.” All CT scans were taken with the patient in the
Characteristics of the cohort
Archival CT images of 14 patients were used in this study. Six patients had a diagnosis of ductal carcinoma in situ (DCIS), whereas the remaining eight had invasive disease (only 1 patient with T2 tumors; 7 patients were staged as T1). Half of the patients underwent an axillary dissection, whereas the other half underwent sentinel node biopsy. Of the patients, 11 had pathologically N0 disease and 3 were staged as pN1. All patients had indications for adjuvant breast irradiation only.
Dose-distribution–based parameters
The volume
Discussion
The cosmetic outcome of patients with early breast cancer depends not only on the quality and type of surgery but also on parameters of adjuvant radiotherapy. There is an intimate relationship between RT-dose fractionation, spatial dose distribution, and the cosmetic outcome. With conventional RT (50 Gy in 25 fractions), areas of large dose inhomogeneities (>10%) may be related to significant radiation-induced, acute skin toxicity, including the presence of breast erythema with patchy
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2021, Radiotherapy and OncologyCitation Excerpt :Our results showed that IMRT with SIB method significantly reduced radiation dermatitis despite higher fractional doses. This was a considerable advantage of IMRT because it could improve the skin toxicity by reducing the dose at 4 mm under the skin without compromising the target coverage of prescribed radiation [21]. The concern with IMRT in breast irradiation is that it might miss the targeted area because of respiratory movement or set-up error with sophisticated radiotherapy plans.
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Presented at the 48th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO), November 5–9, 2006, Philadelphia, PA.
Conflict of interest: none.