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Background: The development of pulmonary complications after breast radiotherapy is still controversial. These complications might result in temporary or permanent damage to the lung. The aim of this study was to evaluate changes in the lung volume parameters (LVP) and to assess their relation with mean dose and the percentage of the lung receiving 20 Gy (V20) in the upper and lower lobes of the lung. Methods: Twenty three patients with breast cancer who underwent locoregional radiotherapy were selected. Six thermoluminescence dosimeters (TLDs) were distributed uniformly throughout the chest phantom to assess the accuracy of lung dose was calculated using treatment planning system (TPS). Body plethysmography was performed before, and 3 and 6 months after radiotherapy. Findings: Changes in LVP showed a decrease 3 months, and a slight improvement 6 months after radiotherapy. The mean percentage decrease in LVP was 0.64% and 0.34%for each Gy increase in mean lung dose (MLD) and for each percentage increase of V20, respectively. There was no significant correlation between changes in LVP with respect to age and concurrent hormonal therapy. The minimum and maximum calculation errors of the TPS were 1.8% and 4.2%, respectively. Conclusion: This study showed that changes in LVP, 3 and 6 months after radiotherapy did not cause pulmonary disease, and the TPS dose distribution was reasonably accurate.