Fabrication and development of a thorax phantom to evaluate 3D CRT treatment planning techniques for post-mastectomy chest wall radiotherapy.

The aim of this study was to design and fabricate a thorax phantom to quantify the radiation doses to the region of the chest wall (with 3 ionization chambers), the organ at risk (OAR) (lung), and the surface using radiochromic films (EBT3) for three different 3D CRT treatment planning techniques. Anthropomorphic phantoms are one of the best tools for verifying the quality of the radiotherapy treatment plans generated by treatment planning systems since they can provide equivalent human tissue densities. Thirty acrylic plates were cut into ellipses 21 cm in height and 31 cm in width, and slots were created to insert lung equivalent cork material and bone equivalent Teflon material. Three treatment planning techniques were designed: (A) tangential pair beams, (B) tangential pair beams with wedges and (C) tangential beams followed by an anterior oblique beam. The percentage difference between the measured point doses and the calculated doses (measured with three CC13 ionization chambers) ranged from - 3.2 to 1.6%, with a mean deviation of - 1.04 ± 1.3%. The measured mean percentage doses on the target surface with EBT3 film were 90.3% and 95.1% of the prescribed dose with 5-mm and 10-mm boluses, respectively. Finally, the average absolute dose difference between the measured and calculated surface doses was within 10 cGy in all three planning techniques. The developed thorax phantom is suitable for point dose measurements using ionization chambers and for surface dose measurements using EBT3 Gafchromic films in post-mastectomy chest wall radiotherapy.