Dosimetric comparison of jaw tracking in intensity modulated and volumetric modulated arc radiotherapy for carcinoma of cervix

Abstract

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.

The use of collimator angle optimization and jaw tracking for VMAT‐based single‐isocenter multiple‐target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system

“…This contributes to low‐dose levels without having a large impact upon intermediate dose levels. These results are consistent with findings from previous studies of the impact of jaw tracking upon treatment at various locations in the body 9–15 …”

“…These results are consistent with findings from previous studies of the impact of jaw tracking upon treatment at various locations in the body. 9 , 10 , 11 , 12 , 13 , 14 , 15 …”

“…This is a recently developed method involving the secondary collimator jaws moving dynamically throughout treatment to match the MLC apertures as closely as possible, therefore, providing additional shielding 10,11 . There have been many studies that confirm the improvement in low‐dose parameters via the addition of jaw tracking to VMAT treatment plans, though very few of these focus on treatment of brain cancer or the use of SRS 9–12,14,15 . These studies found all plans with jaw tracking to be deliverable, 10,12,15 however, a study by Wu et al 15 reported some variation in quality assurance (QA) pass rates for VMAT plans with jaw tracking compared to fixed jaws while still remaining clinically acceptable.…”

“… 10 , 11 There have been many studies that confirm the improvement in low‐dose parameters via the addition of jaw tracking to VMAT treatment plans, though very few of these focus on treatment of brain cancer or the use of SRS. 9 , 10 , 11 , 12 , 14 , 15 These studies found all plans with jaw tracking to be deliverable, 10 , 12 , 15 however, a study by Wu et al 15 reported some variation in quality assurance (QA) pass rates for VMAT plans with jaw tracking compared to fixed jaws while still remaining clinically acceptable. Though current literature in general agrees that jaw tracking results in improved low dose to normal tissue, 9 , 10 , 11 , 12 , 14 , 15 the limited investigations into deliverability of SRS plans implies that further research is required.…”

“…[9][10][11][12]14,15 These studies found all plans with jaw tracking to be deliverable, 10,12,15 however, a study by Wu et al 15 reported some variation in quality assurance (QA) pass rates for VMAT plans with jaw tracking compared to fixed jaws while still remaining clinically acceptable. Though current literature in general agrees that jaw tracking results in improved low dose to normal tissue, [9][10][11][12]14,15 the limited investigations into deliverability of SRS plans implies that further research is required.…”