Abstract
Purpose: To aid in the selection of a suitable combination of irradiation mode and jaw width in helical tomotherapy (HT) for the treatment of nasopharyngeal carcinoma (NPC).Materials and Methods: Twenty patients with NPC who underwent radiotherapy were retrospectively selected. Four plans using a jaw width of 2.5 or 5-cm in dynamic jaw (DJ) or fix jaw (FJ) modes for irradiation were designed (2.5DJ, 2.5FJ, 5.0DJ, and 5.0FJ). The dose parameters of planning target volume (PTV) and organs at risk (OARs) of the plans were compared and analyzed, as well as the beam on time (BOT) and monitor unit (MU). The plans in each group were ranked by scoring the doses received by the OARs and the superity was assessed in combination with the planned BOT and MU.Results: The prescribed dose coverage of PTV met the clinical requirements for all plans in the four groups. The groups using a 2.5-cm jaw width or a DJ mode provided better protection to most OARs, particularly for those at the longitudinal edges of the PTV (P < 0.05). The 2.5DJ group had the best ranking for OAR-dose, followed by the 2.5FJ and 5.0DJ groups with a same score. The BOT and MU of the groups using a 5.0-cm jaw width reduced nearly 45% comparing to those of the 2.5-cm jaw groups.Conclusion: 2.5DJ has the best dose distribution, while 5.0DJ has satisfactory dose distribution and less BOT and MU that related to the leakage dose. Both 2.5DJ or 5DJ were recommended for HT treatment plan for NPC based on the center workload.
Highlights
Helical tomotherapy (HT) utilizes the opening and closing of a 64-leaf, pneumatically powered, binary multileaf collimator with 51 -spaced beam angles at 360◦ and translational motion of the treatment couch at a constant speed to achieve a high degree of freedom and power in dose optimization [1]
A radiotherapy plan in clinical practice should be selected considering the quality of dose distribution and the delivery time and treatment efficiency, which is related to the patient motion and target displacement during treatment, as well as the total number of monitor units (MUs) associated with leakage dose received by the patient
The use of a narrower jaw width for beam delivery can provide better conformity of dose distribution, which can better protect the aforementioned organs while markedly increasing beam-on time (BOT) and number of MUs
Summary
Helical tomotherapy (HT) utilizes the opening and closing of a 64-leaf, pneumatically powered, binary multileaf collimator with 51 -spaced beam angles at 360◦ and translational motion of the treatment couch at a constant speed to achieve a high degree of freedom and power in dose optimization [1]. A radiotherapy plan in clinical practice should be selected considering the quality of dose distribution and the delivery time and treatment efficiency, which is related to the patient motion and target displacement during treatment, as well as the total number of monitor units (MUs) associated with leakage dose received by the patient. The use of a narrower jaw width for beam delivery can provide better conformity of dose distribution, which can better protect the aforementioned organs while markedly increasing beam-on time (BOT) and number of MUs. when a wider jaw width is used for beam delivery, the BOT and number of MUs are greatly reduced; the conformity of dose distribution may be unsatisfactory. When a wider jaw width is used for beam delivery, the BOT and number of MUs are greatly reduced; the conformity of dose distribution may be unsatisfactory This may increase the doses received by normal organs, such as the hippocampus and temporal lobe. To ensure better protection of OARs, clinical planning of HT for NPC often involves using a jaw width of 2.5cm and partly sacrifices the delivery efficiency when using the conventional fixed jaw mode
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