Dosimetric Comparison between Intensity Modulated Radiation Therapy and 3-Dimensional Conformal Radiation Therapy in Both Semi-Lateral Decubitus and Supine Positions for Left Breast Cancer Radiation Therapy in Egypt.

Prior studies in our institute in Alexandria, Egypt, have proved the efficacy of Semi-lateral decubitus position (SLDP) using Alexandria Left Breast Board-16 (ALB-16) in reducing radiation dose to the heart and Left Anterior Descending Artery (LAD)without compromising the dose to the target volumes. Hence it represents a good alternative technique in developing countries to overcome Linear Accelerators (LINAC) lacking Respiratory Gating and Deep Inspiration Breath Hold (DIBH) techniques. This study aims to compare the dosimetric outcomes between intensity-modulated radiation therapy (IMRT) and 3DCRT in both SLDP and supine position (SP) for adjuvant radiation therapy in left breast cancer (BC). 20 female patients with node negative left BC post breast conservative surgery underwent CT simulation on both ALB-16 and SP boards. Treatment plans were created for each patient using both 3DCRT and IMRT techniques in both positions and their dosimetric parameters were compared for both IMRT and 3DCRT plans in both positions. IMRT plans were done using the same optimization parameters. Our results showed a significantly lower mean heart dose (MHD) in 3DCRT vs. IMRT in both SLDP and SP positions (195cGy, 228cGy vs. 448cGy, 476cGy) (p<0.001) respectively. MHD was also significantly lower using IMRT in SLDP vs. IMRT in SP (448cGy vs. 476cGy) (p<0.04). Regarding the LAD mean dose our data showed no significant difference between IMRT and 3DCRT in SLDP (533cGy vs. 596cGy, p = 0.18) and between IMRT in both positions (596cGy vs. 632cGy, p = 0.13), while mean LAD dose was significantly lower in IMRT vs. 3DCRT in SP (632cGy vs. 759cGy, p = 0.03). The mean lung dose was statistically lower in 3DCRT vs. IMRT in both positions (3DCRT 669cGy in SLDP, 603cGy in SP) vs. (IMRT 1139cGy in SLDP, 1112cGy in SP) respectively (p<0.001). However, there was no significant difference between mean lung dose in SLDP vs. SP by IMRT (1139cGy vs.1112cGy, p = 0.24). Regarding the mean dose to the contralateral breast the results showed a statistically lower dose in 3DCRT vs. IMRT in both positions (3DCRT 17cGy in SLDP, 20cGy in SP) vs. (IMRT 157cGy in SLDP, 170Gy in SP) respectively (p<0.001). On the contrary there was no significant difference between mean doses in SLDP vs. SP by IMRT (157cGy vs.150cGy, p = 0.37). Meanwhile for the WB coverage, IMRT plans were superior to the 3DCRT in all treatment positions. Using IMRT in left BC irradiation in either SLDP or SP showed no significant differences in the mean WB dose or OARs apart from the mean heart dose still shows a significant lower dose in SLDP in both IMRT and 3DCRT techniques. OARs received higher doses in IMRT compared to 3DCRT irrespective of the positioning yet did not exceed their tolerance thresholds. [ABSTRACT FROM AUTHOR]