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Sci—Wed PM: Delivery—10: Optical CT‐based Gel Dosimetry in Image Guided Adaptive Radiation Therapy
Author(s) -
Olding T,
Darko J,
Schreiner LJ
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3244102
Subject(s) - dosimetry , dosimeter , imaging phantom , image guided radiation therapy , nuclear medicine , radiation treatment planning , radiation therapy , medical physics , materials science , medicine , biomedical engineering , radiology
Three dimensional gel dosimetry has become more clinically practical with the development of normoxic and less toxic polymer gels and of new accessible imaging techniques for dose readout. In this paper we describe the application of NIPAM polymer and Fricke xylenol (FXG) gels to image‐guided adaptive radiation therapy (IGART). The gel dosimetry was performed with a commercial optical CT imager. The first investigation was the validation of cone‐beam CT (CBCT) based patient localization and repositioning being implemented into our clinic. Gel dosimeters inserted in a phantom mimicking prostate cancer treatment, were processed and irradiated with and without required repositioning, and the dose delivery compared to treatment plans. In the second study, FXG dosimetry was used to determine the dose reduction from a CBCT upgrade on Varian linacs. In both experiments 3D dose data sets were obtained. The IGART repositioning gel experiments clearly showed when the process was followed as intended or when it failed. Without repositioning there were large volumes of disagreement between planned and measured dose distributions, with repositioning a 3D gamma comparison gave good agreement with > 95% of the voxels in agreement. The gel dosimetry of the changes with the upgrade to OBI Advanced confirmed a dose reduction of ∼90%. These results indicate that gel dosimetry provides features for IGART validation not available with conventional dosimeters. In particular, since a gel dosimetry phantom can be put through an IGART process as a patient, the whole process can be tested and validated in a regular quality control program.