Evaluation on dosimetric plan quality and treatment delivery time of dynamic jaw mode in TomoTherapy® for left-side breast cancer patients

Background: Few studies claimed that dynamic jaw (DJ) mode in Helical TomoTherapy (R) (HT ) could improve the crania-caudal dose distribution without prolonging the treatment time in treating different types of cancer. Also, studies suggested that DJ with a wider 5 cm field width (FW) could replace fixed jaws (FJ) with 2.5 cm FW to reduce the delivery time with the sustainable plan quality. Yet, the study on breast cancer with supraclavicular fossa (SCF) nodal involvement using DJ mode in HT is limited. This study aims to evaluate the DJ mode retrospectively by comparing their dosimetric quality with normal tissue complication probability (NTCP) of organs at risk and treatment delivery time with FJ mode on treating left-side breast with SCF nodal involvement. Materials and methods: All post-mastectomy patients, who had been irradiated for left-side breast with SCF nodal involvement were selected retrospectively in this study. With the same dose constraint and prescription as the treated DJ2.5 plan, two extra plans using DJ mode with 5 cm FW(DJ5.0) and FJ mode with 2.5 cm FW (FJ2.5) were computed for plan comparison. Results: No statistical significance was found in all the parameters of PTV and OARs, except for V-20 of whole lung. DJ5.0 received V-20 in ipsilateral left lung than FJ2.5 and DJ2.5. However, the average delivery time of DJ5.0 was significantly lower than that of DJ2.5 and FJ2.5 by almost 40%. Conclusions: No statistical significance was found in those dosimetric and radiobiological parameters among three modes while the delivery time has greatly reduced by using DJ5.0. A shorter treatment time can minimise intra-fractional error and better the patient's experience during treatment.