Dose-volumetric Parameters for Predicting Severe Radiation Pneumonitis and Skin Toxicity in Breast Cancer Patients Treated with Three Dimensional Conformal Radiation Therapy and Paclitaxel

Abstract

Delaying the initiation of adjuvant radiation therapy (RT) adversely affects local-regional control and RT given concomitantly with chemotherapy may increase rates of radiation pneumonitis (RP) and skin toxicity (ST). For this reason, it is important to identify dosimetric parameters that would permit the safe administration of this treatment. Our aim was to identify potential clinical factors and dosimetric factors for RP and ST following concomitant paclitaxel and RT. Records of 57 patients treated with weekly paclitaxel at 80 mg/m2 for 12 cycles and 50 Gy RT plus a boost to the surgical bed of 16-20 Gy between January 2005 and December 2007 were reviewed. All patients had either node positive or high risk node negative breast cancer. RP and ST were graded according to the RTOG criteria. Factors including performance status, comorbidities, smoking status, tamoxifen use, body mass index (BMI), plastic cup (PC) use, breast volume (BV), dose-volume parameters (V5, V20, V25, V30), MLD (mean lung dose), and radiation fields were analyzed and correlated with clinical toxicity. Median follow-up was 30 months (range, 7.87-56 months). Twenty-six and 31 patients, respectively, received two-field radiotherapy (2FRT) and three-field radiotherapy (3FRT). In no case was the internal mammary chain irradiated. Grade ≥2 RP was observed in 14% of cases. All cases of RP resolved without any clinical sequelae. The mean time to develop RP after RT was 50 days. The mean ipsilateral V5, V20, V25, V30, MLD were 22.55%, 8.9%, 8.07%, 7.3%, and 6.35 Gy, respectively, for patients with 2FRT group and 41.7%, 21.6%, 19.64%, 17.8%, 11.97 Gy, respectively, for patients with 3FRT group. These values were significantly correlated. There was no significant association between specific RT fields and RP. By univariate analyses, MLD (p = 0.03), V5 (p = 0.003), V20 (p = 0.03), V25 (p = 0.04), V30 (p = 0.04), V25 cc (p = 0.03), and V30 cc (p = 0.04) were found to be significantly associated with RP. By multivariate analysis, only V20 (p = 0.01) and V30 (p = 0.001) were significant factors. There was a significant trend for increasing RP with V20 values ≥17% (p = 0.05) and V30 ≥14% (p = 0.043). Using ST scoring criteria, 21 patients (37%) experienced grade 3-4 toxicity. By univariate analysis, mean BMI (p = 0.01), BV (p = 0.009) and use of PC (p = 0.011) were predictors of grade 3-4 ST. Multivariate analysis revealed the BMI (p = 0.004) and BV (p = 0.002) to be significant predictors of ST. Given the high rate of RP observed with concomitant paclitaxel and RT, the V20 and V30 ipsilateral constraints should be adhered to closely in order to decrease the risk of RP. BMI and BV are the main predictors of ST in these patients.