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Hypofractionated Whole Breast Radiation Therapy: Does Size Matter?

2010; Elsevier BV; Volume: 78; Issue: 3 Linguagem: Inglês

10.1016/j.ijrobp.2010.07.529

1879-355X

Reid F. Thompson, M. Spierer, Raquibul Hannan, Y. Chen, Rafi Kabarriti, William Skinner, C. Chen, Eirwen M. Miller, Hong Liang, Shalom Kalnicki,

Advances in Oncology and Radiotherapy

Concerns of suboptimal dose distribution and toxicity in large-breasted patients have led to their exclusion in hypofractionation (HfRT) trials. However, with the use of IMRT, HfRT in large-breasted patients may be both appropriate and advantageous. In this IRB-approved study, we looked at the relationship of dose distribution and toxicity in this patient population. We reviewed 94 patients treated at our institution between 2005 and 2009 with chest wall separation >25 cm or PTV >1500 cc and who received radiation of 42.4 Gy in 16 fractions using IMRT, with a boost of 9.6 Gy in 4 fractions. 74 patients were treated prone and 20 supine. All patients had early stage invasive breast cancer or DCIS treated with lumpectomy. DVH data were collected from Varian's ARIA 8.6 treatment planning software. Patient charts were reviewed for acute and late toxicity measured using RTOG radiation morbidity scale. Data were analyzed using R (v. 2.9) by Pearson correlation, Fisher's exact test, and t test, as appropriate. Median chest wall separation was 24.33 cm (SD 2.87 cm), and the median PTV was 1974 cc (SD 622.6 cc). DVH analysis showed the mean PTV V95 was 90.3% and mean V105 was 3.73% with no dose >107%. The mean D05 for heart was 4.3Gy and mean V10Gy was 1.42%. The mean D05 for total lung and ipsilateral lung was 6.06Gy and 10.31Gy respectively, while the V20 Gy was 1.44% and 2.95% respectively. 64% and 24% of patients experienced acute RTOG grade 1 and 2 skin toxicity, respectively. At a median follow-up of 6 months, the RTOG late skin toxicity grade was 0 in 21.3% and 1 in 35.1% of patients. There were no local recurrences. Acute toxicity correlated weakly with body mass index (BMI) (R = 0.34, p = 0.002), with late skin toxicity also demonstrating a direct correlation (R = 0.41, p = 0.002). An inverse relationship was observed between BMI and heart dose (V10 Gy; R = -0.3, p = 0.006). Comparison of prone and supine showed no significant differences in acute toxicity, however, there was significantly more late grade 1 skin toxicity in prone (40.5%) compared to supine (15%) (p = 0.006). Chest wall separation distance was higher in the supine cohort by a mean of 3.5 cm, with a consequent 10-fold increase in lung V20 Gy (p = 6.6 x 10-7). Adequate PTV coverage with acceptable hot spots and excellent sparing of organs at risk was achieved using IMRT in a population of large-breasted patients. Acute and late toxicities were comparable to those reported in the literature. Interestingly, prone positioning resulted in better lung sparing as compared to supine positioning, whereas supine positioning minimized the relative prevalence of late grade 1 skin toxicity. Taken together, these data suggest that HfRT IMRT in either the prone or supine positions is a viable and appropriate therapeutic modality for large-breasted patients.