Comparison of treatment planning techniques in treatment of carcinoma of left breast: Second cancer perspective

Aim: To compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Left-Breast patient. Materials and methods: Five treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Volumetric modulated arc (VMAT) plan (partial arcs) with 6 MV photon beams were generated for a carcinoma of Left breast patient of age 40 to a prescription dose of 50Gy in 25 fractions. The SCR was estimated using the organ equivalent dose (OED) concept with a linear-exponential, a plateau, and a linear dose-response model for OARs. Also, the low dose-bath volume (5Gy) was calculated for all the plans. Results: For contra lateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (−26.0%, −35.0%, −39.0%) for VMAT, (−50.0%,−50.0%,−51.0%) for ITF, (−48.0%, −49.0%,−49.0%) for EC and (−33.0%, −24% , −25.0%) for EDW respectively. The relative SCR (plateau) for heart and left lung were (−66.0% & −73.0%) for VMAT, (−20.0% & −6.0%) for ITF, (−24.0% & −18.0%) for EC and ( −17.0% & −14.0%)for EDW. In contrast, for skin the relative SCR (linear - exponential) were 78.0%, −8.0%, −13.0% and −10.0% for VMAT, ITF, EC and EDW respectively. The 5Gy low dose volume relative to PW for VMAT was 201.45%, whereas the same for ITF, EC and EDW were 17.0%, −7.33% and −4.3%. Conclusion: Compared to all plans, VMAT plan showed high conformity for CTV and superior heart and left lung sparing. But SCR for skin and the low dose bath volume were significantly high in VMAT. ITF plan showed relatively better sparing for contra lateral breast and heart. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin next to EDW. EDW and PW plans were similar but later had high SCR for contra lateral-breast. Planning techniques like ITF and VMAT can be strongly considered for left breast, provided better skin sparing techniques and less dose spillage can be achieved. - Highlights: • Five treatment plans using PW, EDW, EC, ITF and VMAT plan were generated. • SCR estimated using OED - linear-exponential, plateau, linear dose response model. • VMAT - better SCR for organs closer to the treatment field than those are away it. • The low dose bath volume (5Gy) relative to PW for VMAT was very significant. • Further studies, intend to provide more emphasis to age and time dependencies.