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Objective To evaluate the dosimetric penumbra and delivery accuracy of dynamic jaw delivery in tomotberapy.Methods The jaw positioning hardware and the beam model were updated.Mechanical alignments were verified after the upgrade of the jaw positioning hardware.PDDs and beam profiles were measured by a two-dimensional water tank and compared with the new beam model.Dose penumbras in the longitudinal direction were compared between the dynamic and fixed jaw plans for different field width.Delivery accuracy was evaluated by point dose measurements with A1SL chamber and gamma analysis on the dose distribution measured by ArcCheck detector array.Results Mechanical alignments were in tolerance and beam characteristics were tuned to match the dynamic jaw beam model.Differences in the field width between the measured results and reference data were ＜ 0.3％ for both symmetric and asymmetric profiles in the longitudinal direction.The dose penumbra in dynamic jaw delivery was reduced from 17.92 mm to 7.51 mm for 2.5 cm jaw,and from 33.73 mm to 6.97 mm for 5.0 cm jaw,close to the penumbra of the traditional 1.0 cm jaw.IMRT verification of clinical cases was performed by A1SL ion chamber and ArcCheck detector array.The mean point dose difference was 0.33％ ± 0.73％ between the calculated and meassured data.Gamma analysis of dose distributions revealed that approximately 99.8％ of the points satisfied the gamma criteria of 3％ dose difference and 3 mm distance-to-agreement and the mean passing rates remained 97.9％ even with tightest criteria of 2％/2 mm,and 100.0％ with the criteria of 4％/4 mm,respectively.Conclusions Dosimetric penumbra in the longitudinal direction is significantly improved by the dynamic jaw delivery.Both the mechanical alignment and treatment delivery are qualified,suggesting that this new treatment is accurate and reliable.
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Objective To evaluate the feasibility of replacing the fixed jaw 2.5 cm mode with dynamic jaw 5.0 cm for mid-esophageal cancer after the upgrade of helical tomotherapy (TOMO).Methods A total of 10 patients with locally advanced esophageal cancer were planned with radical intent using 2.5 cm fixed jaw (FJ2.5),2.5 cm dynamic jaw (DJ2.5) and 5.0 cm dynamic jaw (DJ 5.0) modes respectively on TOMO.Dose conformity index (CI),dose homogeneity index (HI) and dose to OARs were analyzed to evaluate the plan quality.Treatment time and monitor units were used to assess efficiency.Results CI and HI met clinical requirement for all plans.D J5.0 plans showed significant improvement over FJ2.5 plans in terms of V5 and mean dose to lungs,the V5,V10 and mean dose to normal tissues (t =9.751,4.163,11.840,10.321,3.745,P＜0.05).DJ2.5 plans were superior to DJ5.0 plans in the aspects of the V30,V40 and mean dose to heart,the V20 and mean dose to normal tissues (-2.454,-3.275,-4.192,-6.435,-4.139,-6.431,P＜0.05).Compared with DJ2.5 plans,the V5,V20,V30 and mean dose to lungs,the V4 0and mean dose to heart,maximum dose to cord and cord PRV,the V5,V10,V20 and mean dose to normal tissues of FJ2.5 plans were worse (t=8.289,6.142,3.137,8.895,3.597,4.565,3.782,5.429,16.421,12.496,8.286,11.933,P＜0.05).The beam-on time of DJ5.0 plans was significantly reduced by 43.9％ and 42.8％ compared with FJ2.5 and DJ2.5 plans respectively,and the machine monitor unit was reduced by 42.8％ and 43.8％ respectively.Conclusions The dynamic jaw of 5.0 cm technique is recommended for treatment of mid-esophageal cancer for sake of plan quality and efficiency.It does not only shorten the treatment time and improve radiation efficiency compared with fixed and dynamic jaw of 2.5 cm technique,but also provides a dosimetric advantage in terms of lung and normal tissue sparing in comparison with fixed jaw of 2.5 cm.When only improving plan quality is concerned,the dynamic jaw of 2.5 cm technique is more recommendable.
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Objective To investigate the influences of loading time and loading angle on the stress, displacement of human periodontal ligament in dynamic jaw. Methods The three-dimensional assembly model of the mandible front teeth, periodontal ligament and alveolar bone was reconstructed by using the reverse engineering technology. The thickness of periodontal membranes was 0.2 mm. The stress, displacement at different positions of the periodontal ligaments during different jaw cycles were analyzed under dynamic load in the direction from bucca to tongue side with 0°, 15°, 30°, 45°, 60°, 75°, 90° angle to the long axis of the tooth. Results During one jaw cycle, the ratio of the maximum to minimum value of the maximum residual stress due to different loading angles was 5.5, and the ratio of the maximum to minimum value of the maximum displacement was 8.1. The ratio of the maximum to minimum value of the maximum displacement which was caused by five jaw cycles was increased in the range from 1.02 to 1.35 with the increase of loading angles. The ratio of the maximum to minimum value of the maximum residual stress which was caused by different loading angles was increased in the range from 1.86 to 3.00 with the increase of jaw cycles. The location of the maximum stress was at the tongue side of the cervical margin at different loading angles, and the location of the maximum residual stress was distributed at different positions of the cervical margin. Most stress was accumulated at the root of the periodontal ligament under the 0° dynamic load. Conclusions The situation of the accumulated residual stresses and the uncertainties in the distribution of the maximum residual stresses should be observed in the clinical choice of mandible incisors fixed by bridge abutments; large angle force applied to the tooth was harmful to the periodontal ligament and rapid succession of chewing hard food should be avoided as much as possible during the clinical treatment.