Dosimetric Study of Breast Scar Marker in Different Radiotherapy Dose Calculation Algorithms

The purpose to this work is to validate and benchmark the delivered dose accuracy during radiotherapy treatment (without marker at scar site) to the dose calculated by treatment planning that included a marker on scar site. Dose distributions in breast cancer 3-dimensional conformal treatment planning (3D CRT) calculated with Pencil Beam (PB) and Collapsed Cone (CC) algorithms of commercial treatment planning system (Monaco and Oncentra MasterPlan) was compared as photon beam through homogenous and heterogenous media (by placing marker on phantom surface) to evaluate the perturbation of photon beam. Radiochromic film dose distribution value was compared to the dose calculated by CC algorithm of Monaco and Oncentra MasterPlan (OMP) Treatment Planning Systems (TPS) and PB algorithm of OMP TPS. During Computed Tomography (CT) simulation procedure for breast case, a metal-based scar marker (wire) was used to localize the tumour bed during treatment planning procedure which the phantom was considered as heterogeneous medium. In homogenous medium, PB algorithm gave smaller dose deviation compared to CC algorithm. When wire was introduced to the surface of phantom, PB algorithm (6.0 cGy) gave higher dose deviation compared to CC algorithm (2.0 cGy). However, CC algorithm (plasticine: 7.0 cGy and cable: 7.3 cGy) shows higher dose deviation compared to PB algorithm (plasticine: 6.3 cGy and cable: 6.6 cGy) when Plasticine and Cable marker were introduced. The placement of marker in lateral orientation gave smaller perturbation to megavoltage photon beam compared to axial orientation in overall case. Moreover, wire and plasticine are suitable as a scar marker due to its tissue equivalent density with less perturbation to photon beam.