International Journal of Radiation Oncology*Biology*Physics
Clinical investigation: breastTechnical factors associated with radiation pneumonitis after local ± regional radiation therapy for breast cancer
Introduction
External beam radiotherapy (RT) is an important component of post-lumpectomy therapy in patients with breast cancer (BC) desirous of breast conservation. It is also efficacious in the postmastectomy setting by increasing the rate of local-regional control and survival 1, 2, 3, 4, 5, 6. Both local and local-regional RT, i.e., including regional lymph nodes, are generally well tolerated. Nevertheless, morbidity, for example cardiopulmonary toxicity, can arise from incidental irradiation of nontarget tissues in the vicinity of the breast/chest wall or regional lymph nodes 7, 8, 9. Furthermore, symptomatic radiation pneumonitis (RP), i.e., dyspnea, nonproductive cough, and/or low-grade fever, is one of the most common complications in these patients, occurring 1–6 months after RT in approximately 0%–29% of cases 8, 9, 10, 11, 12, 13, 14.
Radiation pneumonitis after RT for BC has been reported to be related to the following factors: the amount of lung irradiated within the tangential fields 13, 14, the use of an additional supraclavicular (SC) field 8, 9, prior exposure to chemotherapy 8, 15, 16, concurrent tamoxifen medication (17), smoking habits 18, 19, 20, age 9, 14, 19, and pre-RT performance status (9).
In patients receiving RT to the breast and/or chest wall, there is longstanding controversy regarding the role of elective regional nodal RT. All trials demonstrating a survival benefit in irradiated high-risk mastectomized patients, compared to patients treated only with systemic therapy, have included internal mammary lymph nodal (IMN) irradiation 5, 6, 21. Because of concern about potential cardiopulmonary toxicity (7), routine irradiation of the IMN has not been widely adopted.
To improve the therapeutic ratio for our patients with BC, since 1994 we have used CT scans to help beam design. This has been done for all patients, whether or not IMN treatment was intended. Individualized cerrobend blocks have been designed for each patient to define the deep border of the tangential fields. For example, in patients with left-sided BC and positive axillary nodes, our conventional technique has been to use partly wide tangential fields (PWTF) designed to selectively irradiate only the superior IMN. For the inferior portion of the field, shaped cerrobend blocks are designed to reduce incidental cardiac and lung irradiation; hence the inferior IMN are excluded (22). Similar lung/heart blocks are used for patients receiving tangential irradiation without IMN treatment. Thus, there is a large intrapatient variability in the height of the lung shadow in the superior and inferior aspect of the tangential fields. Furthermore, because of anatomic differences, there are marked interpatient differences, as well.
Given the unique manner in which our patients were planned and the marked variability in the height of the lung shadow in the tangential fields, we herein review our patients’ incidence of RP. We attempt to relate the rate of RP to the height of the lung shadow seen in both the superior and inferior aspect of the tangential fields. Others factors associated with RP in previous studies are also reexamined.
Section snippets
Study population
A review was made of 710 patients irradiated to the breast/chest wall, with or without comprehensive nodal coverage, at Duke University Medical Center between 1994 and 1998. Patients treated with high-dose carmustine (BCNU)-based chemotherapy and stem cell support were excluded from the analysis because of their high risk of late chemotherapy-induced pulmonary toxicity, i.e., about 40%–50% 23, 24. Patients who did not receive tangential photon fields (e.g., those with multiple electron fields
Results
Overall, 2.4% (15/613) of patients developed RP requiring steroids. The onset of RP ranged from 1 to 9 months (median 3 months) from completion of RT. Twelve of the affected patients have had complete symptom resolution. Three patients have persistent mild shortness of breath.
The results from the univariate analyses for the effect of various factors on the incidence of RP are shown in Table 1. There was an increased incidence of moderate RP among patients treated with local-regional RT
Discussion
Radiation pneumonitis was an uncommon complication after either local (0.9%) or local-regional RT (4.1%) for BC in this review, a finding similar to previous reports where different RT techniques have been used. Local-regional RT techniques employing tangential beams for the breast/chest wall (± IMN) and an SC field were associated with a higher incidence of RP (5.2%) compared to patients treated with only tangents (0.9%). There was no clear statistical association between the incidence of RP
Acknowledgements
Thanks to the University of North Carolina at Chapel Hill for the use of PLUNC (Plan UNC) treatment planning software.
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