Room: AAPM ePoster Library
Introducing a novel half beam Volumetric Modulated Arc Therapy (VMAT) technique for treatment of Stereotactic Body Radiation therapy(SBRT) in the retreatment scenario with previously irradiated volumes
VMAT techniques provide highly conformal dose distributions with improved target volume coverage and sparing of normal tissues. Studies have reported that MLC rotation improves target dose distribution and accurate dose prediction as the collimator rotation can minimize inter-leaf radiation leakage. This collimator rotation results in a shallow dose fall off in the longitudinal direction. A novel technique with collimator angle at 90 degrees with the superior/inferior jaw closed to zero is presented here to ensure steep dose fall off and minimize dose overlap with the previously treated irradiation fields. Half beam VMAT arcs were used to optimize the current treatment plan. A traditional VMAT plan with 2 arcs and collimator rotations of 30 and 330 degrees was generated for comparison purposes.
First case with the abutment of retrocrurual LN PTV Volumes with the previously treated paraaortic nodal volume at the L2 vertebral junction showed minimal dose overlap. The composite dose shows that the spinal cord has a maximum dose difference of 1.5 Gy between the half beam VMAT technique while compared to the traditional VMAT plan. Second case was treated to an infraclavicular mass with abutting with a superior previously irradiated volume encompassing base of tongue, larynx and lymph nodes. Half beam block technique was compared with the traditional VMAT planning technique and dose fall off improved by 1 Gy minimizing total dose to brachial plexus, esophagus and the right carotid.
The VMAT technique explained above is an attractive option for retreatment cases with adjoining fields. This is an excellent technique for treatment of spine SBRT lesions and to maintain steep gradients at vertebral body junctions.
Not Applicable / None Entered.