SU‐E‐T‐487: TomoTherapy Plan Quality Metrics for Multiple Anatomical Sites

Purpose: TomoTherapy IMRT plans for various anatomical sites were analyzed in order to obtain dosimetric characteristics, and to determine plan quality and deliverability.Methods: Treatment plans for thirty patients treated with TomoTherapy were reviewed and analyzed. The distribution of treatment sites was: abdomen (n=4), brain (n=4), head and neck (HN; n=6), lung (n=6), pelvis (n=5) and prostate (n=5). Prescription dose (PD), D90%, PTV, max, mean and min doses of PTV were extracted from the plans and DVH data. Metrics calculated include: homogeneity index (H.I.=max dose in PTV/ PD), mean dose of PTV over PD, max dose of PTV over min dose in PTV, and D90%/PD were calculated for the different treatment sites. In order to verify plan delivery, absolute and relative dose measurements were performed and analyzed using an ion chamber and GafChromic films. Results: Mean prescription isodose lines were 95.7% (n=30). The PTV ranged from 11.7 to 982.2 cc. For H.I. the prostate site yielded the smallest H.I. of 0.99 while the pelvis site yielded the greatest H.I. of 1.14. The prostate site produced the smallest mean dose over PD (0.97) and HN produced the greatest (1.03). The overall H.I. was 1.06 and the overall ratio of mean dose over PD was 1.02. The overall max dose over min dose was 1.18. The mean difference for absolute point dose measurements was −0.9%. Measured film profiles demonstrated excellent agreement with calculated profiles in plan delivery QA Conclusions: For the treatment sites reviewed prostate had the most homogeneous plans, while lung had the most inhomogeneous plans in this study. The overall mean dose over PD and QA results were excellent in TomoTherapy. TomoTherapy is capable of planning and delivering high quality IMRT treatments for a wide variety of treatment sites.