Room: ePoster Forums
Purpose: To evaluate dosimetric parameters for PTV/OARs and treatment delivery efficiency between Volumetric Inverse Modulated Therapy(VMAT) and Dynamic Conformal Arc Therapy(DCAT) on SBRT planning through statistical analysis.
Methods: A total of 7 patients treated in 2018 in our hospital are included in this study, including 1 adrenal and 6 lung patients with median PTV volume of 15.2cc. Planning was done per protocol BR001/RTOG 0813/RTOG0915. Both DCAT and VMAT plans were generated with 2mm dose grid size in Monaco using non-co-planer beams. Target V100%, V90%, PTV iso-dose line coverage, conformity index, R50, Dmax2cm, OAR DVH parameters (cord/Heart/total lung) and MUs are compared between VMAT and DCAT plans using paired t-test.
Results: For each patient, both VMAT and DCAT plans meet V100%, V90% and conformity index constrains per protocol. Prescription iso-dose line coverage from VMAT is significantly smaller than that from DCAT (p=0.02) indicating DCAT plan creates less hot spot. R50 is significantly smaller for VMAT than DCAT (p=0.001). It is challenging to get R50 in DCAT under protocol constrain for large target (VPTV>50cc). Mean value of Dmax2cm for VMAT and DCAT are comparable (p>0.5). The mean Â± SD values of MU for VMAT and DCAT are 4509 Â± 1553 and 2351 Â± 863 retrospectively indicating MU from DCAT are significantly less than MU from VMAT (p= 0.001). The steep MU reduction leads to significant time drop for DCAT treatment delivery. Overall VMAT offers lower OAR dose than DCAT. For target close to OARs, our study indicates more arcs are needed in DCAT to create comparable plans to VMAT.
Conclusion: Monaco DCAT offers steep reduction of treatment time for SBRT. It offers comparable conformity index, Dmax2cm to VMAT and acceptable R50 for smaller VPTV. For target close to OARs, more arcs are needed in DCAT to create comparable plans to VMAT.
Not Applicable / None Entered.
TH- External beam- photons: VMAT dose optimization algorithms