Effects of four‐dimensional simulation of boost radiation after breast conservation surgery: A prospective dosimetric and volumetric analysis

Objective Breast conservation therapy is the standard of care for early breast cancer. After whole breast irradiation, lumpectomy cavity boost increases local control and survival. However, accurate identification of the tumor bed and internal displacement caused by respiratory movements poses major challenges in achieving the optimal therapeutic index. Although surgical clips are considered accurate surrogates for localization of the tumor bed, no consensus has been reached regarding the use of motion management during treatment delivery. The purpose of the present study was to evaluate the dosimetric and volumetric effects of respiratory motion on the delivery of boost radiation using 4‐D computed tomography simulation. Methods A total of 25 patients undergoing tumor bed boost radiation were recruited prospectively. Dosimetric and volumetric comparisons were made between conformal plans formed with 3‐D and 4‐D datasets obtained from each patient. Results No significant differences were observed in target volumes, degrees of inclusion, conformity indices, or homogeneity indices between the plans formed with the two datasets ( P  < 0.05). The magnitude of internal movement of the tumor bed was insignificant compared with the margin for setup errors. Conclusion Displacement of the tumor bed caused by respiratory motion was minimal with insignificant dosimetric or volumetric effects, and does not warrant the routine use of 4‐D simulation or the generation of internal target volumes.