Dosimetric comparison of three-dimensional conformal radiotherapy and intensity-modulated radiotherapy for left-sided chest wall and lymphatic irradiation.

INTRODUCTION: The aim of this study was to compare five different techniques for chest wall (CW) and lymphatic irradiation in patients with left-sided breast carcinoma. METHODS: Three-dimensional conformal radiotherapy (3DCRT), forward-planned intensity-modulated radiotherapy (FP-IMRT), inverse-planned IMRT (IP-IMRT; 7- or 9-field), and hybrid IP-/FP-IMRT were compared in 10 patients. Clinical target volume (CTV) included CW and internal mammary (IM), supraclavicular (SC), and axillary nodes. Planning target volumes (PTVs), CTVs, and organs at risks (OARs) doses were analyzed with dose-volume histograms (DVHs). RESULTS: No differences could be observed among the techniques for doses received by 95% of the volume (D95%) of lymphatics. However, the FP-IMRT resulted in a significantly lower D95% dose to the CW-PTV compared to other techniques (P = 0.002). The 9-field IP-IMRT achieved the lowest volumes receiving higher doses (hotspots). Both IP-IMRT techniques provided similar mean doses (Dmean) for the left lung which were smaller than the other techniques. There was no difference between the techniques for maximum dose (Dmax) of right breast. However, FP-IMRT resulted in lower Dmean and volume of right breast receiving at least 5 Gy doses compared to other techniques. CONCLUSION: The dose homogeneity in CW-CTV was better using IMRT techniques compared to 3DCRT. Especially 9-field IP-IMRT provided a more homogeneous dose distribution in IM and axillary CTVs. Moreover, the OARs volumes receiving low radiation doses were larger with IP-IMRT technique, while volumes receiving high radiation doses were larger with FP-IMRT technique. Hybrid IMRT plans were found to have the advantages of both FP- and IP-IMRT techniques.

Evaluation of the effect of changes in dose rate on rat lung cells.

The aim of this study is to evaluate the effect of dose rate (DR) on lung tissue. The rats included in the study were randomly grouped into 3 groups: Group (G) 1 was defined as control group, and in this group rats were sham irradiated. G2 was the group receiving a single dose of 12 Gy in DR of 300 monitor unit (MU)/min. G3 was the group receiving a single dose of 12 Gy in DR of 600 MU/min. Radiotherapy (RT) was applied under general anesthesia with 6-MV photon beams to both lungs. At the 6th and 16th week of the RT, animals from each group were killed for light and electron microscopy evaluation. We evaluated the scores of each group in the 6th and the 16th week and found that in G2, there were significant increases in the perivascular fibrosis (P = .018), interstitial fibrosis (P = .002), total inflammation (P = .040), and total fibrosis (P = .003) scores. In G3, we found statistically significant increases in perivascular fibrosis (P = .001), interstitial fibrosis (P = .002), and total fibrosis scores (P = .029). There was no significant difference in the total inflammation score in G3 (P = .225). When we compare G2 and G3 in the 6th week, we found significant increase in the interstitial thickening (P = .039) and total inflammation (P = .035) scores in G3. Dose rate per fraction may have an impact on normal tissue toxicity. The prominent effect of increased DR in lung tissue is fibrosis which should be kept in mind, especially in cases where higher doses per fraction are used.