Influence of jaw tracking in intensity-modulated and volumetric-modulated arc radiotherapy for head and neck cancers: a dosimetric study

PURPOSE: To Study the dosimetric advantage of the Jaw tracking technique in intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) for Head and Neck Cancers. MATERIALS AND METHODS: We retrospectively selected 10 previously treated head and neck cancer patients stage (T1/T2, N1, M0) in this study. All the patients were planned for IMRT and VMAT with simultaneous integrated boost technique. IMRT and VMAT plans were performed with jaw tracking (JT) and with static jaw (SJ) technique by keeping the same constraints and priorities for a particular patient. Target conformity, dose to the critical structures and low dose volumes were recorded and analyzed for IMRT and VMAT plans with and without JT for all the patients. RESULTS: The conformity index average of all patients followed by standard deviation (x¯±σ(x¯)) of the JT-IMRT, SJ-IMRT, JT-VMAT, and SJ-VMAT were 1.72 ± 0.56, 1.67 ± 0.57, 1.83 ± 0.65, and 1.85 ± 0.64, and homogeneity index were 0.059 ± 0.05, 0.064 ± 0.05, 0.064 ± 0.04, and 0.064 ± 0.05. JT-IMRT shows significant mean reduction in right parotid and left parotid shows of 7.64% (p < 0.001) and 7.45% (p < 0.001) compare to SJ-IMRT. JT-IMRT plans also shows considerable dose reduction to thyroid, inferior constrictors, spinal cord and brainstem compared to the SJ-IMRT plans. CONCLUSION: Significant dose reductions were observed for critical structure in the JT-IMRT compared to SJ-IMRT technique. In JT-VMAT plans dose reduction to the critical structure were not significant compared to the SJ-IMRT due to relatively lesser monitor units.

Application of Jaw-tracking function in VMAT for upper thoracic esophageal cancer / 重庆医学

Objective To explore the effect of the Jaw‐tracking with RapidArc(JT‐RapidArc) plans for upper thoracic e‐sophageal cancer .Methods Treatment planning was designed by using RapidArc and JT‐RapidArc techniques for 11 consecutive patients .The dose‐volume histogram parameters of PTV and the organs at risk ,conformity index(CI) ,heterogeneity index(HI) , low dose volume of normal tissue (B‐P ) and monitor units (MU ) were compared between the different techniques . Results Compared with the RapidArc plan ,JT‐RapidArc had increased coverage of PTV1(64) D98 and HI(P0 .05) .Plans with JT‐RapidArc had lower Lung(V5 ,V10 , V13 ,V20 ,V30 ,Dmean ,P0 .05) .JT‐RapidArc plans increaseed the MU by 1% (349 ± 29 vs .345 ± 16 ,P>0 .05) as compared with RapidArc plans .Conclusion All of the plans had met the requirements of clinical dosime‐try .JT‐RapidArc plans as compared with RapidArc plans ,showing better part of target coverage ,part of lung and heart and B‐P sparing ,which MU was slightly increased .

Effects of jaw tracking technique on the absorb dose of PTV and OARs in intensity-modulated radiation therapy for nasopharyngeal carcinoma / 国际生物医学工程杂志

Objective To study the effects of using jaw tracking technique with Smart LMC algorithm on the absorbing dose of planning target volume (PTV) and organs at risk (OARs) in dynamic intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC).Methods Field fluencies of 10 cases of NPC patients were optimized using DVO algorithm on Eclipse TPS (11.0),and according to the same optimal fluence,MLC operation files were calculated using jaw tracking technique and jaw fixing technique respectively,dose distribution was calculated with AAA algorithm and jaw tracking IMRT plan (JT-IMRT) and jaw fixing IMRT plan (JF-IMRT) were generated respectively.Collimators' position at the plan implementation was observed,and the total number of plans' monitor units (MU),the dose of PTV,the absorb dose of OARs,and the actual fluence verification pass rate were compared.Results The collimators' opening gap distances in 166 control points of the JT-IMRT reduced in both X and Y directions in the field,compared to that of the JF-IMRT.Total number of the JT-IMRT's MU increased by 3.59％-11.63％.There was no statistical significant difference between the doses of the PTV.Statistical significance was found in the differences between maximum dose (Dmax) of brainstem,spinal cord,crystal,optic nerve,the mean dose (Dmean) and D50％ of parotid and their decreased values after therapy (t=5.70-8.66,P＜0.05).The actual fluence verification pass rate of the JT-IMRT was higher than that of the JF-IMRT.There was a significant difference between the results (t=5.18,P＜0.05).Conclusions The JT-IMRT plan of the smart LMC algorithm is more tolerant to the radiation leakage between inter-and intra-leaf.The dose of OARs is lower,while the dose calculation precision and the verification pass rate are higher,the actual radiation dose is more accurate and reliable.Therefore it is more suitable for clinical applications.

Dosimetric comparison of jaw tracking technique with static jaw technique in intensity-modulated radiotherapy for preoperative radiotherapy of rectal cancer / 中华放射医学与防护杂志

Objective To compare the dosimetric difference between jaw tracking technique (JTT) and static jaw technique (SJT) in dynamic intensity-modulated radiotherapy (IMRT) for preoperative radiotherapy of rectal cancer patients.Methods Jaw tracking and static jaw were used to develope the intensity-modulated plans for 10 patients respectively.For all the patients,the dose to surrounding tissues was minimized as low as possible,the 95％ volume of the planning target volume (PTV) and planning gross target volume (PGTV) satisfy the prescribed dose.The doses of the planning target volumes,organs at risk and normal tissue were detected by dose-volume histogram.Two groups of treatment plan dose were verified by ionization chamber array 2D-Array 729 and OCTAVIUS (PTW) phantom.Results The treatment plans of two groups could satisfy the clinical requirements.There was no significant difference between the maximum and the mean dose of target.The volumes of jaw tracking dynamic intensity-modulated radiotherapy were lower,including the V5,V10,V20,V30,V40 (volumes receiving 5,10,20,30 and 40 Gy,respectively),mean dose(D) for body and V10,V20,V30,D for bilateral femoral head,bladder,and small intestine.There was significant difference for the results (t =-2.32-12.24,P ＜0.05).The verification results showed that the treatment plans were all passed the dosimetric verification.Conclusions Jaw tracking intensity-modulated radiotherapy and jaw fixed IMRT plan could achieve equal dose coverage in patients with rectal cancer,while jaw tracking techniques could reduce normal tissue dose and organs at risk dose.