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Comparison of Treatment Planning Techniques in Treatment of Carcinoma of Left Breast: Second Cancer Risk Perspective

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V Sakthivel

V Sakthivel1*, (1) Advanced Medical Physics, Houston, Texas

SU-D-137-4 Sunday 2:05PM - 3:00PM Room: 137

Purpose:
To compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Lt.breast patients.

Methods:
Five treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Rapid-Arc (RA) plan (partial arcs) with 6 MV photon beams were generated for a carcinoma of Lt.breast patient of age 40 to a prescription dose of 50.4Gy in 28 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 contralateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (-25.89%, -99.985%, -85.96%) for RA, (-50.12%,-41.94%,-44.57%) for ITF, (-47.78%, -38.43%,-42.05%) for EC and (-32.70%,-26%,-28.31%) for EDW respectively. The relative SCR for heart and Lt-lung were (-89.99% & -89.38%) for RA, (-0.05% & 5.69%) for ITF, (-0.16% & 0.04%) for EC and ( -0.04% & 0.01%)for EDW. In contrast, for skin the relative SCR were 77.68%, -7.71%, -11.11% and -9.04% for RA, ITF, EC and EDW respectively. Also, the 5Gy low dose volume relative to PW for RA was 201.45%, whereas the same for ITF, EC and EDW were -8.41%, -7.33% and -4.2%.

Conclusion:
Compared to all plans, RA plan showed high conformity for CTV and superior heart, contralateral breast and left lung sparing. But SCR for skin and the low dose volume were significantly high in RA. ITF plan showed relatively better sparing for contralateral breast and heart at the same time has the least low dose bath volume. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin. EDW and PW plans were similar but later had high SCR for contralateral breast.

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