Exhibit Hall | Forum 3
Purpose: Advances have been made to bring pre-clinical irradiation techniques closer to what is used clinically, the latest being small animal intensity-modulated radiation therapy (SA-IMRT). The purpose of this work was to evaluate potential benefits of SA-IMRT by comparing dosimetric plan quality metrics against 3D conformal radiation therapy (3DCRT).
Methods: Treatment plans were generated with SA-IMRT and 3DCRT for fourteen different targets within a mouse phantom using five uniformly spaced co-planar beams. Planning target volumes (PTVs) included: whole heart; each of left, right and both ventricles; left, right and both atria; left, right and both lungs. Plans were also generated to treat the whole heart while sparing each of the four major chambers one at a time. Each plan was normalized such that 95% of the PTV received 24 Gy. Non-target regions of the lung and heart were considered organs-at-risk to demonstrate the potential application of SA-IMRT to study underlying mechanisms of cardiac toxicity or lung pneumonitis. Treatment plans were inversely optimized using an in-house version of the MatRad treatment planning system adapted to use Monte Carlo generated dose kernels for a 225 kVp x-ray beam. Plan quality was evaluated in terms of conformity index (CI= (Rx isodose volume)/(PTV volume)), homogeneity index(HI=(Dmax/Rx)), intermediate dose spill(R50%=(50% isodose volume)/(PTV volume)), and mean dose to the surrounding lung and heart tissues. Statistical significance(p<0.05) was evaluated using two-tailed paired t-tests.
Results: SA-IMRT dose distributions were significantly more conformal (mean CI=1.47) relative to 3DCRT (mean CI=2.35). Dose spill was significantly less for SA-IMRT(R50%=14.7) versus 3DCRT(R50%=20.4). No difference in dose homogeneity was observed with mean HI of 127.7%(SA-IMRT) and 128.7%(3DCRT). Mean doses to non-target lung and heart regions were significantly less for SA-IMRT, 52% and 76% of prescription dose, respectively, versus 62% and 97% for 3DCRT.
Conclusion: SA-IMRT improves target conformity and non-target sparing versus 3DCRT.
Funding Support, Disclosures, and Conflict of Interest: Supported by IRG-19-136-59 from the American Cancer Society and the University of Chicago Medicine Comprehensive Cancer Center.