Testing Continuity between Versions 5.3.9 and 6.3.1 of Plaque Simulator for Planning Eye Plaque Brachytherapy Cases Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2v23vx64v

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  • The purpose of this study is to examine the challenges of accepting and commissioning a new treatment planning system for eye plaque brachytherapy. Currently Oregon Health and Science University (OHSU) utilizes v5.3.9 of the Plaque Simulator software to plan all of its eye plaque brachytherapy cases. However, v5.3.9 is no longer supported by its manufacturer, Eye Physics, LLC. OHSU is upgrading to a supported version of Plaque Simulator, v6.3.1. Prior to planning brachytherapy cases in v6.3.1 an investigation needs to be launched concerning the technical and dosimetric differences between v5.3.9 and v6.3.1. A study investigating the percent difference in doses to the prescription point, sclera, and tumor apex between v5.3.9 and v6.3.1 was created for 28 patients who had undergone eye plaque brachytherapy during 2015 and 2016 at OHSU. The sample size was distributed evenly across five out of seven of the Collaborative Ocular Melanoma Study (COMS) non– notched plaques (n=5 for each plaque size) with a smaller sample size for the notched COMS 20 plaque (n=3). Doses to the prescription point, sclera, and tumor apex were compared to treatment plans created in v5.3.9 and v6.3.1. Acceptance of v6.3.1 requires that the percent difference between its results and v5.3.9 are less than 5%. The prescription point percent differences between v5.3.9 and v6.3.1 were 0% for all (28 out of 28) cases. The sclera doses were between 2–4% lower in v6.3.1 than v5.3.9 for 93% (26 out of 28) cases; the remaining two cases (Trials 24 and 26) had percent differences of –5.21% and –6.22%, respectively. The tumor apex percent differences were less than 1% for 89% (25 out of 28) of cases and less than 1.5% for the remaining three cases. Dosimetric differences between v5.3.9 and v6.3.1 are attributed to the change in the carrier factor correction data set used to calculate the attenuation of radiation via the Silastic insert of the COMS plaque. The percent differences for carrier factor correction between the outer (r=2 mm) and inner (r=3 mm) sclera are –3.36% and – 1.82%, respectively. The carrier factor corrections in v6.3.1 are from Chiu Tsao et al. 1993 for I–125 seed model 6711. It is recommended that the data set from Chiu Tsao et al. 1993 be adopted until a more suitable data set is found. The effect of planning cases based on the true location of the tumor within the eye (3D planning) versus planning to the apex of the tumor (1D planning) were examined in v6.3.1. The same patient data was used as in the comparison between v5.3.9 and v6.3.1, but the tumors locations were moved. A best guess was made as to the location of the tumor based on physician notes and fundus images. The purpose of this study was to establish proof of concept. The doses to the prescription point remained unchanged for 1D versus 3D planning. Doses to the sclera were unchanged for 75% (21 out of 28) of cases. Of the cases where dose changed between 1D and 3D planning, the percent difference was no greater than 0.06% to the sclera. Doses to the tumor apex remained unchanged for 93% (26 out of 28) cases. The cases that saw a change in tumor apex only saw a percent difference of 0.1% and 0.01%, respectively. Doses to the prescription point, sclera, and tumor apex are negligible and do not affect the quality of care. Although 3D planning requires an additional time commitment from the physicist or dosimetrist, proof of concept has been established and is recommended for estimating normal tissue doses.
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