Background and purpose: Dose calculations in trachea HDR brachytherapy treatment planning systems are greatly based on TG-43 protocol in which, all materials including air inside trachea are treated the same as water. The aim of this study was to survey the effect of air on dose calculations of Flexiplan treatment planning system in trachea HDR brachytherapy. Materials and methods: To evaluate the effect of air inhomogeneity, a neck-equivalent plexiglass cylindrical phantom was used. Dose measurement was carried out by EDR2 film. Treatment planning and irradiation were performed using Flexiplan software and Flexitron brachytherapy system, respectively. Results: The results showed that considering the air inside trachea as water increases the absorbed dose by 12% which can lead to increment of patient dose. Conclusion: A significant difference was seen between dosimetry results in the two conditions. Therefore, taking the air similar to water has a considerable effect on dose calculations of trachea HDR brachytherapy and accuracy of treatment plan performed.

Evaluating the Effect of Air Inhomogeneity on Dose Calculations of Trachea HDR Brachytherapy Using EDR2 Film

Introduction Interaluminal brachytherapy is one of the important methods of esophageal cancer treatment. The effect of applicator attenuation is not considered in dose calculation method released by AAPM-TG43. In this study, the effect of High-Dose Rate (HDR) brachytherapy esophageal applicator on dose distribution was surveyed in HDR brachytherapy. Materials and Methods A cylindrical PMMA phantom was built in order to be inserted by various sizes of esophageal applicators. EDR2 films were placed at 33 mm from Ir-192 source and irradiated with 1.5 Gy after planning using treatment planning system for all applicators. Results The results of film dosimetry in reference point for 6, 8, 10, and 20 mm applicators were 1.54, 1.53, 1.48, and 1.50 Gy, respectively. The difference between practical and treatment planning system results was 0.023 Gy (<2.7%), on average. Conclusion Due to the similar practical results for different esophageal applicators, it can be concluded that attenuation properties of applicator wall doesn't have a significant difference with water and therefore the Flexiplan treatment planning system accuracy is further confirmed.

http://ijmp.mums.ac.ir/article_326_fd89a1ed50fd3124b1bbd41bbb2cc3b1.pdf

Applicator Attenuation Effect on Dose Calculations of Esophageal High-Dose Rate Brachytherapy Using EDR2 Film

Introduction In order to treat uveal Melanoma , first, radioactive seeds are laid on a silicone- made substance which is called Silastic after that they are inserted in the plaque, and finally, this plaque containing silicone-made substance is stitched to the sclera surface. The dose gradient within the tumor and healthy tissues can be varied due to changing the Silastic thickness between sclera surface and radioactive seeds. In turn, this leads to difference in the amount of absorbed dose of tumor and healthy tissues. Present study is to investigate the optimum Silastic thickness in uveal Melanoma brachytherapy.  Materials and Methods To measure changes of depth dose of the plaque in a sphere with a radius of 12 mm, MCNP4C code was applied. Exact specifications of a 20-mm Collaborative Ocular Melanoma Study (COMS) plaque, Silastic and three I-125 seed sources, 6711 model were integrated in simulation. Dose calculations were performed using F6 tally in spheres with a radius of 0.2 mm. Results By measuring the changes of dose rate of plaque in distances of 0.2 to 18 mm from the sclera surface and having the prescribed dose for the absolute treatment of eye melanoma, final absorbed doses by tumor and healthy tissues for each different Silastic thicknesses of 0, 0.5, 1, 1.5, and 2 were calculated. Conclusion Considering the results and sclera tolerance, it was concluded that the thickness of Silastic must not exceed 0.5 mm, because increasing the Silastic thickness from this area, increases absorbed dose by healthy tissues and also the treatment time.

https://ijmp.mums.ac.ir/article_2624_353267d0fde7df5cda8a87e020792667.pdf

Hosseini Daghigh Seyed Mohsen

Papers

Applicator Attenuation Effect on Dose Calculations of Esophageal High-Dose Rate Brachytherapy Using EDR2 Film

Silastic thickness optimization in uveal melanoma brachytherapy by monte carlo method