(Tuesday, 7/16/2019) 3:45 PM - 4:15 PM
Room: Exhibit Hall | Forum 1
Purpose: To evaluate the dose delivery to a moving lung tumor when planned by using Acuros compared with that of using AAA.
Methods: A moving phantom with a lung tumor insert was imaged four-dimensionally, and its images of maximum intensity projection (MIP) was generated. The phantom was additionally imaged using a slow scan protocol. Based on our departmental protocol, the internal target volume (ITV) of the tumor was contoured in the MIP images, and copied into the slow images in which a treatment plan was created using the dynamic conformal arc (DCA) technique and AAA. A dose of 60 Gy was prescribed to 95% of PTV (ITV+0.5cm). In order to find out the delivered dose to the tumor, a four-dimensional plan (4D plan) was produced by copying the plan to each of ten-phase sorted 4D images after overriding the density of PTV-ITV with that of ITV and calculating with Acuros (for accuracy), and summing the phase-specific plans through organ/dose registration. The density overriding was to generate a realistic delivered dose. The AAA-based plan was altered by changing AAA with Acuros and overriding the density in PTV-ITV (clinical choice), keeping the other conditions the same. The 4D plan was similarly produced.
Results: The Acuros-based plan delivered a smaller true (4D) dose to PTV by 6.7% of the prescribed dose than that the AAA-based plan delivered (63.8Gy vs 67.7Gy) at 95% of PTV. V60Gy of the former and the latter were 99.3% and 100%, respectively, when it was set as 95% in planning on the slow images. This implies that the motion of the tumor allowed colder PTV areas near beam edges from planning to receive more central doses.
Conclusion: The more accurate Accuros provided planned dose delivery. Modeling breathing irregularity and study on patient images will follow this study.
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