Abstract
Hypofractionated stereotactic body radiotherapy(SBRT) in the treatment of lung tumors delivers high dose fractions with radioablative potential. Consequenlty, accurate dosimetric representation is crucial in treatment planning. To evaluate the treatment uncertainties introduced due to homogeneous dose calculation and manual beam aperture design for lung cancer patients treated with SBRT. Twenty-one manually designed, homogeneously-calculated SBRT plans(PLAN1), with coplanar and noncoplanar beam arrangements, were generated from CT planning data sets of clinical stage I non-small cell lung cancer patients. If those plans met all dosimetric parameters described in RTOG 0236, three additional plans with identical beam arrangements were designed. PLAN2 had identical beam design as PLAN1, but was recalculated with heterogeneity correction. PLAN3 and PLAN4 were designed using heterogeneity correction from the start, allowing changes in beam characteristics to achieve adequate target volume coverage. Beam weights and aperture were optimized manually(PLAN3) or automatically(PLAN4) by using the Dynamic Machine Parameter Optimization(DMPO) algorithm in Pinnacle. PLAN1 and PLAN4 served as the bases of comparison for PLAN2 and PLAN3, respectively. Dosimetric parameters of the four plans were evaluated and compared. Six cases failed to meet all dosimetric criteria and were excluded from further planning. Of the remaining 15 cases that passed, only 3 retained adequate PTV V60/V54 coverage (mean absolute reduction: 10.6%/5.6%, respectively) when recalculated with heterogeneity correction(PLAN2). One homogeneously-calculated case that passed all critical normal tissue constraints failed after it was recalculated with heterogeneity correction. All manually(PLAN3) and DMPO(PLAN4)-designed, heterogeneity-corrected plans met all dosimetric criteria. DMPO-designed plans exhibited the best PTV coverage without compromising critical normal tissue constraints. The active time for planning was significantly shorter using DMPO, compared to manual planning. Failing to apply heterogeneity correction to hypofractionated SBRT treatment plans results in reduced target volume coverage with the potential for overdosing critical normal tissues. Heterogeneity-corrected plans displayed superior PTV coverage with only minor increases in lung dose-volume parameters. The automated beam weighting/aperture optimization (DMPO) algorithm with heterogeneity correction resulted in the most optimal plans and the shortest planning time.
Published Version
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