Purpose: To analyze the dosimetric and radiobiological metrics of breast conformal radiotherapy (CRT) with sequential boost to tumor bed against intensity-modulated radiation therapy (IMRT) with simultaneously integrated boost to tumor bed.
Methods: This study includes 20 primary left-sided breast cancer patients (10 with super clavicular node involvement (SCV) and 10 without SCV). In total 20 CRT plans and 20 IMRT plans were created. In the CRT plans the whole breast with or without super clavicle irradiation receives a dose of 50Gy in 25 fractions with a sequential boost to the tumour bed of 10Gy in 5 fractions. In the IMRT plans the whole breast receives 50Gy and the tumor bed 60Gy in 25 fractions. Each plan was evaluated in terms of PTV coverage, primary tumour conformity index, maximum plan dose, ipsilateral lung dose (Dmean, V20Gy, V10Gy, V5Gy), heart dose (Dmean, Dmax, V15Gy), contralateral lung dose (V5Gy) contralateral breast dose (max, D5%) and spinal cord dose (D0.03cc). The tumor control and normal tissues complication probabilities (TCP and NTCP) were calculated for each plan.
Results: IMRT created more conformal plans in all cases, (conformity index: CRT=0.35, IMRT=0.75 with SCV and CRT=0.33, IMRT=0.76 without SCV). CRT plans delivered higher heart V15Gy (CRT=6.5%, IMRT=5.2% with SCV and CRT=1.6%, IMRT=0.7% without SCV). CRT plans delivered higher V20Gy ipsilateral lung doses with SCV (CRT=15.0%, IMRT=12.8%). Also, IMRT plans delivered lower D0.3cc spinal cord doses (CRT=17.3Gy, IMRT=7.1Gy with SCV and CRT=2.6Gy, IMRT=0.5Gy without SCV). The NTCP values of heart and ipsilateral lung were lower for IMRT (0.03% and 1.87%) than CRT (1.10% and 4.70%) with SCV, respectively.
Conclusion: IMRT produced plans of superior dose conformity, lower NTCP values and shorter treatment duration. Especially, when there is SCV node involvement, it should be considered as the treatment of choice.
TH- External Beam- Photons: treatment planning/virtual clinical studies