Comparison of forward intensity modulated radiation therapy and two field tangential wedged beam techniques in radiotherapy of breast cancer: dosimetric and radiobiologic study

Introduction: This study aims to compare the dose delivery parameters and radiobiologic model prediction of Tumor Control Probability (TCP) of the FIMRT technique compared with rectangular two tangential wedged fields (2FW) in the treatment of breast cancer. Furthermore, reduction of the heart and lung dose in the FIMRT was studied via dosimetric parameters and radiobiologic model prediction of Normal Tissue Complication Probability (NTCP). Materials and Methods: 25 left-sided breast cancer patients were selected. The planning target volume (PTV) and organs at risk (heart ad ipsilateral lung) were countered. The tangential technique of treatment planning consists of two optimized wedged beam (2FW) were compared to FIMRT plans for same patients. The FIMRT and 2FW was planned for delivery of 50Gy dose to the target for 25 fractions. The minimum dose, maximum dose, mean dose and homogeneity index (HI) of the dose for the PTV were obtained for both techniques.  Moreover, maximum and mean dose for the lung and heart tissues were obtained. The monitor unit (MUs) and the PTV97% were recorded. Paired samples t-test was used for statistical analysis and p<0.05 was considered as significant level. TCP and NTCP for radiation pneumonitis and late heart mortality was calculated with the Lyman model for organs at risk using dose-volume histogram (DVH). Results: the homogeneity index between the two techniques was significant (p>0.05), HI= 1.32 vs 1.10 for 2FW and FIF, respectively. Mean dose to the breast PTV as mean±standard deviation value was 46.6±0.5 Gy for FIMRT vs. 46.8±1.3 Gy for 2FW plans. The PTV97% was 92.5%± 3.2%, and 91.1%± 3.7 for the FIMRT and 2FW. The MUs of the 2FW plans and FIMRT plans were 326.4±11.2 and 212±10.3, respectively. With the FIMRT, the mean dose of the heart and the lung was (2.9Gy vs. 1.9Gy) and (12.1Gy vs. 8.3Gy) respectively; the maximum doses in the heart and lung were decreased significantly from (3.5Gy to 2.1Gy) and (15.8Gy to 10.2Gy) in favor of the FIMRT plans. TCP was 72.3% for FIMRT and 72.1% for 2FW plans. The NTCP for radiation pneumonitis was (0.4%±0.1%) and (0.6%±0.5%) for the FIMRT and 2FW techniques, respectively. The NTCP for late heart was (6.1%±2.1%) for the 2FW technique. However, it was reduced to (3.8%±1.9%) in the FIMRT technique. Differences of the NTCP values were statistically significant for both lung and heart (p<0.05). Conclusion: the treatment MUs were significantly reduced by the FIF-RT technique (p<0.05). For all organs, mean NTCP were lower for FIMRT than for the 2FW plans. The FIMRT delivered more homogenous dose to the target while maintaining or increasing the TCP. The FIMRT technique can be considered as a straightforward and fast technique to use clinically particularly in clinics that have not inverse IMRT.