Purpose In this study we present a novel method for re‐calculating a treatment plan on different respiratory phases by accurately modeling the panning and tilting beam motion during DTT (the “rotation method”). This method is used to re‐calculate the dose distribution of a plan on multiple breathing phases to accurately assess the dosimetry. Methods sIMRT plans were optimized on a breath hold computed tomography (CT) image taken at exhale (BHexhale) for 10 previous liver stereotactic ablative radiotherapy patients. Our method was used to re‐calculate the plan on the inhale (0%) and exhale (50%) phases of the four‐dimensional CT (4DCT) image set. The dose distributions were deformed to the BHexhale CT and summed together with proper weighting calculated from the patient’s breathing trace. Subsequently, the plan was re‐calculated on all ten phases using our method and the dose distributions were deformed to the BHexhale CT and accumulated together. The maximum dose for certain organs at risk (OARs) was compared between calculating on two phases and all ten phases. Results In total, 26 OARs were examined from 10 patients. When the dose was calculated on the inhale and exhale phases six OARs exceeded their dose limit, and when all 10 phases were used five OARs exceeded their limit. Conclusion Dynamic tumor tracking plans optimized for a single respiratory phase leave an OAR vulnerable to exceeding its dose constraint during other respiratory phases. The rotation method accurately models the beam’s geometry. Using deformable image registration to accumulate dose from all 10 breathing phases provides the most accurate results, however it is a time consuming procedure. Accumulating the dose from two extreme breathing phases (exhale and inhale) and weighting them properly provides accurate results while requiring less time. This approach should be used to confirm the safety of a DTT treatment plan prior to delivery.

Reduction in doses to organs at risk and normal tissue during breast radiotherapy with a Carbon-fibre Adjustable Reusable Accessory (CARA),

Abstract.A radiochromic silicone based dosimeter has been fabricated that allows for threedimensional (3D) dose verification. This paper characterizes the silicone dosimeter and verifies previous results found by other research groups. Using a recipe found to be dose rate independent, we identify the spectra of the dosimeter irradiated to different doses and verify that the response from different dose rate deliveries is constant within uncertainty. The reproducibility of a response from identically irradiated and stored cuvettes is also investigated. A noticeable difference in response indicates that there is an inhomogeneous distribution of active ingredients due to the viscous nature of the dosimeter during fabrication. Irradiating multiple cuvettes to the same dose in different fractions shows that the response decreases as the number of fractions increases. Introduction3D dosimetry has been of much interest to the radiation oncology community [1]. Deformable 3D radiochromic dosimeters have recently been developed that use silicone to spatially fixate dose information [2][3][4][5]. Silicone dosimeters are deformable and may be formed to any clinically relevant shape, allowing for assessment of new features, such as deformable image registration algorithms in radiation delivery planning [6]. DeDeene et al [2,3] and Høye et al [4] have collectively identified many properties of silicone dosimeters containing leucomalachite green (LMG) as a dose indicator and chloroform as a sensitizer, such as the absorption spectra when exposed to UV light [3], dose rate dependence [2-4], effects due to fractionation of dose delivery [4], short term and long term sensitivity stability [3,4], independence of response from photon energy [2], and the effect cuvette temperature during irradiation has on the final sensitivity [3].Recently, Høye et al. identified an optimal concentration of ingredients that eliminates dose rate dependence using 0.26% w/w LMG and 1% w/w chloroform, creating a dose rate independent dosimeter [5]. In this paper, the results of further investigations into these silicone radiochromic systems are reported to reproduce and confirm the results found in these previous studies, as well as further characterize the dosimetric properties of silicone dosimeters.

No abstract