Stereotactic body radiation therapy (SBRT) is increasingly being used to treat lung cancer patients with for whom surgery is not an option. But overweight and diabetic patients have a greater risk of developing chest wall pain, according to a study published in the September issue of the International Journal of Radiation Oncology, Biology, Physics.
Thoracic radiation oncologists and medical physicists at the University of Texas MD Anderson Cancer Center analyzed the toxicities experienced by 265 patients who had pulmonary tumors within 2.5 cm of the chest wall. All received SBRT between August 2004 and August 2008, which consisted of a total radiation dose of 50 Gy in four daily 12.5-Gy fractions (Int J Radiat Oncol Biol Phys, September 2011, Vol. 81:1, pp. 91-96).
The objective of the study was to identify the characteristics that could be associated with chest wall pain and skin toxicities experienced by patients with primary or metastatic lung disease. The median distance between the tumor being treated and the chest wall was 0.59 cm, with a range of 0 to 2.47 cm. The patients were predominantly elderly, with a median age of 73 years, but were as young as 43 years of age. They were followed for a median of 10.3 months.
Assistant professor of radiation oncology Dr. James W. Welsh and colleagues calculated the absolute volumes of the chest wall receiving 10, 20, 30, 40, and 50 Gy, then compared them with the development of chest pain and skin toxicity. They also evaluated whether using immobilization devices during SBRT could contribute to an increased skin dose.
The research team determined that the thickness of a stereotactic immobilization bag affected skin dose, with a 1.5-cm bag increasing the dose by 23% and a 6.0-cm bag increasing the dose by 41%. They also compared an "unspoiled" radiation beam to one delivered through the treatment couch, which caused an increased skin dose up to 49%.
Toxicities experienced
The researchers found that 39% of patients developed skin toxicity. Patients who had a gross tumor volume of 8 mL or more were almost two times more likely to develop a skin reaction, and patients who had a posterior lesion were one and a half times more likely. But patients whose chest wall received at least 30 Gy of radiation dose had the highest likelihood of having a skin reaction, at almost three times more than patients who did not.
One-fourth of patients developed chest wall pain within 11 months of treatment. Eight patients had rib fractures and 14 patients developed acute pain. An additional 45 patients developed chronic pain, almost equally divided between grade 1 and grade 2. Patients whose chest wall received at least 30 Gy of radiation dose were more susceptible, at a rate of 18% compared with those who had received less at 2.7%.
Of the patients with a body mass index of 29 or more, 27% experienced chest wall pain -- more than twice the percentage of thinner patients. More than half of these patients had diabetes mellitus. Based on these findings, the authors suggested that radiation oncologists may wish to be more conservative when treating obese patients, particularly those who also have diabetes.
