(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Dose falloff in stereotactic body radiotherapy (SBRT) of lung tumors is known to correlate with normal tissue toxicity. Dynamic conformal arc (DCA) techniques, relative to other methods, produce highly conformal dose distributions while eliminating the interplay between gantry angle and both dynamic MLC and target motion. They also expedite treatment delivery time in many cases. In this study, we utilize a non-coplanar, multiple-arc arrangement to increase intermediate dose falloff.
Methods: Lung SBRT patients were simulated using a free-breathing CT, 4DCT was also acquired to determine internal target volumes. Treatment plans using two non-coplanar DCAs were created on the free-breath CT and normalized all plans to D(95%)=100%. Planned table angles were ±15 degree from coplanar, providing a 30 degree spread between each DCA. Coplanar DCA plans were also created for control purpose. Changes in dose metrics, such as conformal index (CI), maximum dose (Dmax), and ratio of 50% prescription isodose volume to the PTV (R50%), were quantified for each patient to evaluate the effect on plan quality.
Results: Seven lung SBRT patients were treated with non-coplanar DCA. All plans met RTOG SBRT lung dose criteria. Compared with the coplanar plans, the use of non-coplanar DCAs on average improved CI by 4.12% and R50% by 8.5%. The non-coplanar approach also reduces the Dmax by an average of 1.64%. Our experience using non-coplanar field arrangement does not increase the complexity in the planning process. Moreover, it only slightly increases treatment time compared with the coplanar DCA.
Conclusion: Using a non-coplanar field arrangement, we have improved the dose conformity and intermediate dose falloff in lung SBRT. Non-coplanar DCA could be a viable approach to reduce normal tissue toxicity risk in lung SBRT.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External beam- photons: extracranial stereotactic/SBRT
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