Aim: To study the dosimetric advantages of the jaw tracking technique in intensity-modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) for carcinoma of cervix patients.
Materials and Methods: We retrospectively selected ten previously treated cervix patients in this study. All the ten patients underwent CT simulation along with immobilization and positional devices. Targets and organ at risks (OARs) were delineated slice by slice for all the patients. All the patients were planned for IMRT and VMAT with intend to deliver 50 Gy in 25 fractions. All the plans were planned with 6 MV photon beam using millennium-120 multi leaf collimator (MLC) using the TrueBeam linear accelerator. IMRT and VMAT plans were performed with jaw tracking (JT) and with static jaw (SJ) techniques by keeping the same constraints and priorities for the target volumes and critical structures for a particular patient. For standardization, all the plans were normalized to the target mean of the planning target volume. All the plans were accepted with the criteria of bladder mean dose < 40 Gy and rectum mean dose < 40 Gy without compromising the target volumes. Target conformity, dose to the critical structures and low dose volumes were recorded and analyzed for IMRT and VMAT plans with and without jaw tracking for all the patients.
Results: The conformity index average of all patients followed by standard deviation (̄x± σ̄x) for JT-IMRT, SJ-IMRT, JT-VMAT and SJ-VMAT were 1.176 ± 0.139, 1.175 ± 0.139, 1.193 ± 0.220 and 1.228 ± 0.192 and homogeneity index were 0.089 ± 0.022, 0.085 ± 0.024, 0.102 ± 0.016 and 0.101 ± 0.016. In low dose volume J,T-IMRT shows a 5.4% (p-value < 0.001) overall reduction in volume receiving at least 5 Gy (V5) compared to SJ-IMRT, whereas 1.2% reduction was observed in V5 volume in JT-VMAT compared to SJ-VMAT. JT-IMRT showed mean reduction in rectum and bladder of 1.34% (p-value < 0.001) and 1.46% (p-value < 0.001) compared to SJ-IMRT, while only 0.30% and 0.03% reduction were observed between JT-VMAT and SJ-VMAT. JT-IMRT plans also showed considerable dose reduction to inthe testine, right femoral head, left femoral head and cauda compared to the SJ-IMRT plans.
Conclusion: Jaw tracking resulted in decreased dose to critical structures in IMRT and VMAT plans. But significant dose reductions were observed for critical structures in the JT-IMRT compared to SJ-IMRT technique. In JT-VMAT plans dose reduction to the critical structures were not significant compared to the JT-IMRT due to relatively lesser monitor units in the VMAT plans.
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 Mani KR Upadhayaya S Das KJ. Influence of jaw tracking in intensity-modulated and volumetric-modulated arc radiotherapy for head and neck cancers: a dosimetric study. Radiat Oncol J. 2017;35(1):90-100.
 Cadman P McNutt T Bzdusek K. Validation of physics improvements for IMRT with a commercial treatment planning system. J Appl Clin Med Phys. 2005;6(2):74-86.
 Eifel PJ Levenback C Wharton JT Oswald MJ. Time course and incidence of late complications in patients treated with radiation therapy for FIGO stage IB carcinoma of the uterine cervix. Int J Radiat Oncol Biol Phys. 1995;32(5):1289-1300
 Hasselle MD Rose BS Kochanski JD et al. Clinical Outcomes of Intensity-Modulated Pelvic Radiation Therapy for Carcinoma of the Cervix. Int J Radiat Oncol Biol Phys. 2011;80(5):1436-1445.
 Ng J Shuryak I. Minimizing second cancer risk following radiotherapy: current perspectives. Cancer Manag Res 2014; 7 :1-11.
 International Commission on Radiation Units and Measurements. Prescribing recording and reporting photon beam intensity-modulated radiation therapy (IMRT): contents (ICRU Report 83). J ICRU. 2010;10:NP.
 Joy S Starkschall G Kry S et al. Dosimetric effects of jaw tracking in step-and-shoot intensity-modulated radiation therapy. J Appl Clin Med Phys. 2012;13(2):3707.
 Feng Z Wu H Zhang Y et al. Dosimetric comparison between jaw tracking and static jaw techniques in intensity-modulated radiotherapy. Radiat Oncol. 2015;10:28.
 Park BD Cho BC Kim JH et al. Dosimetric Impact of the Jaw-Tracking Technique in Volumetric Modulated Arc Therapy. J Nucl Med Radiat Ther. 2016; 7:301.
 Kim JY Kim SW Choe BY et al. Clinical assessment of the jaw-tracking function in IMRT for a brain tumor. Journal Korean Phys Soc. 2015;66(2):295-300.
 Schmidhalter D Fix MK Niederer P et al. Leaf transmission reduction using moving jaws for dynamic MLC IMRT. Med Phys. 2007;34(9):3674-3687.