Purpose: Clinical implementation of knowledge-based treatment planning for Volumetric Modulated Arc Radiotherapy for post-mastectomy loco-regional radiotherapy.
Methods: A knowledge-based treatment planning (KBP) model was built (Rapid-Plan v13.5.35, Eclipse v13.5, Varian Medical System) using 73 left-sided patients who had undergone irradiation of the ipsilateral chest wall with internal mammary nodes (IMN) and supra-clavicular fossa (SCF) with prescribed dose of 26 Gy/5 fractions. All the clinical were generated using 6MV photon beams with two tangential partial arcs with isocentre located in the centre of PTV chest wall (Eclipse v13.5). For the validation, automatic plans(KBP) were generated for 13 patient datasets in a single optimization step without any manual intervention. Various dose volume parameters were compared and analysed using paired t-test and Wilcoxon signed rank test. P<0.05 was considered significant.
Results: Mean ± Standard deviation (SD) between clinical plans and KBP for various DVH parameters have been analysed and comparisons are given as :D 95[%] of PTV for CW, IMN and SCF were 93.2±2.4vs 93.2±3.1 (p=0.95), 89.48±2.94 vs 91.21±2.49 (p=0.17) and 94.95±1.4 vs 97.27±1.7 (p=0.00) respectively. For OARs, mean dose (Gy) ± SD to heart, contralateral breast, ipsilateral lung was 2.92±0.54 vs 2.79±0.55 (p=0.06), 2.14±034 vs 2.27±0.24 (p=0.162) and 6.67±0.71vs 7.48±0.39 (p<0.001) respectively. For contralateral lung, mean dose (Gy) with (IQR) was 2.46 (2.21,2.51) vs 2.2 (1.97,2.28) with (p =0.012). Maximum dose to left anterior descending artery (LAD) was 15.1±3.1 vs 13.16±2.43 (p=0.001). Homogeneity index (HI) and Conformation Number (CN) of total PTV for clinical and KBP were 0.12±0.02 vs 0.12±0.02 (p=0.39) and 0.93±0.02vs 0.93±0.03 (p=0.47). Mean ± SD of MU for clinical and rapid plan were 1994±275.3 vs 1704±315.3 (p=0.002).
Conclusion: The KBP were either better or comparable to the clinically acceptable plans generated by experienced physicist for various Dosimetric parameters analysed. Hence KBP can be used for clinical implementation.
Funding Support, Disclosures, and Conflict of Interest: Varian Medical Systems,Palo Alto, California, United States for providing licence to use Knowledge base planning (Rapid Plan) module