Dosimetric Importance of Implementing Jaw Tracking Technique in Radiotherapy Treatment Plan Execution

To study the dosimetric importance of Jaw tracking technique in reducing the doses to organs at risk (OAR) while achieving the optimal dose coverage for the target.

We retrospectively selected ten Glioblastoma cases and for each patient, two plans were created namely Static Jaw Technique Dynamic Intensity Modulated Radiotherapy plan and Jaw Tracking Technique D-IMRT plan with 6 MV for Varian Truebeam™ STx machine using Eclipse Treatment planning system. Both plans were analyzed and compared based on various dosimetric parameters for Planning Target Volume (PTV) and OARs. The dose agreement between the Portal dose image prediction and the portal dosimetry measurement was also analysed  using gamma analysis criteria of 3%/3mm, 2%/2mm and 1%/1mm of dose distance/distance-to-agreement.

The dosimetric parameters evaluated for both plans showed that most of the parameters gave significant P values, where D50% of PTV showed a mean difference (Δ) of 0.45 with significant P value, 0.0104. Similarly mean dose, D2%, D98%, D80% to PTV, Conformity Index and Conformation number showed Δ values of 0.45, 0.51, 0.41, 0.40, 0.02 and 0.01 with their significant P values as 0.0138, 0.0172, 0.0313, 0.0466, 0.0279, 0.0561 respectively. The Δ values and significant P values obtained among OARs are 0.54;0.0224 for brainstem, 0.54;0.0017 for RT optic nerve, 0.52;0.0001 for LT optic nerve, 0.59;0.0040 for optic chiasm and for the healthy tissues it showed the values with their mean dose, V5 and V30 parameters as 0.19;0.0115, 0.59;0.0067 and 0.25;0.0125 respectively. The JTT plans showed better passing results of gamma analysis criteria when compared to SJT plans.

The findings in the studies emphasize the importance of using JTT technique in the radiotherapy treatment plans as it lowers the risk of acute or late toxicity and secondary radiogenic cancers in patients by reducing the OAR doses and achieves better tumor control.