Purpose: The purpose of this study is to compare the dosimetric and radiobiological differences between conformal radiotherapy (CRT) to the whole breast with sequential boost to the primary tumor and intensity-modulated radiation therapy (IMRT) to the whole breast with simultaneously integrated boost to the primary tumor.
Methods: This study included 5 primary left-sided breast cancer patients. In total 5 CRT plans and 5 IMRT plans were created. In the CRT plans the whole breast receives a dose of 50Gy in 25 fractions with a sequential boost to the primary tumour of 10Gy in 5 fractions. In the IMRT plans the whole breast receives 50Gy and the primary tumor 60Gy in 25 fractions. Each plan was evaluated in terms of PTV coverage, primary tumour conformity index, maximum plan dose, ipsilateral lung dose (mean, V20), heart dose (mean, V5), contralateral breast doses and spinal cord dose. The doses of the respective plans were compared between each other and against the clinical goals. Furthermore, the respective tumor control and normal tissues complication probabilities (TCP and NTCP) were calculated.
Results: IMRT created more conformal plans in all cases, (conformity index: average CRT = 0.33, IMRT = 0.76). CRT plans delivered lower mean heart doses in all cases (average CRT = 2.2Gy, IMRT = 2.8Gy). CRT plans delivered higher mean ipsilateral lung doses in 4 of 5 cases (average CRT = 6.8Gy, IMRT = 6.3Gy) and V20Gy in 4 of 5 cases (average CRT = 11.0%, IMRT = 10.1%). The NTCP values of ipsilateral lung and heart were lower for IMRT than CRT (0.02% and 0.0% vs. 0.04% and 0.23%, respectively).
Conclusion: IMRT produced plans of superior dose conformity, lower NTCP values and shorter treatment duration at the expense of slightly higher maximum doses to contralateral breast and spinal cord.