Purpose: To optimize the dose in bladder and rectum and show the different shapes of the isodose volumes in Co60‐HDR brachytherapy, considering different utero and vaginal sources dwell ratio times (TU:TV). Methods: Besides Ir192‐HDR, new Co60‐HDR sources are being incorporated. We considered different TU:TV times and computed the dosis in bladder, rectum and at the reference points of the Manchester system. Also, we calculated the isodose volume and shape in each case. We used a EZAG‐BEBIG Co0.A86 model with TPS HDRplus3.0.4. and LCT42‐7, LCT42‐2(R,L) applicators. A reference dose RA= 1.00 Gy was given to the A‐right point. We considered the TU:TV dwell time ratios 1:0.25, 1:0.33, 1:0.5, 1:1, 1:2, 1:3, and 1:4. Given TU:TV, the stop time at each dwell position is fixed for each applicator. Results: Increasing TU:TV systematically results in a decreasing of the dose in bladder and rectum, e.g. 9% and 27% reduction were found in 1:0.25 with respect to 1:1, while 12% and 34% increase were found in 1:4 with respect to 1:1. Also, the isodose volume parameters height (h), width (w), thickness (t) and volume (hwt) increased from the 1:0.25 case to the 1:4 value: hwt is 25% lower and 31% higher than the 1:1 reference volume in these cases. Also w decreased for higher TU:TV and may compromise the tumoral volume coverage, decreasing 17% in the 1:0.25 case compared to the 1:1 case. The shape of the isodose volume was obtained for the different TU:TV considered. Conclusion: We obtained the shape of isodose volumes for different TU:TV values in gynecological Co60‐HDR. We studied the dose reduction in bladder and rectum for different TU:TV ratios. The volume parameters and hwt are strongly dependent on this ratio. This information is useful for a quantitative check of the TPS and as a starting point towards optimization.
The gynecological treatment with High Dose Rate (HDR) Brachytherapy implies delivering dose to the tumor and spare the dose in organs at risk. In this work, we apply the recommendations for prescribing dose given by the International Commission of Radiation Units (ICRU) reports 38, 89 and the American Brachytherapy Society (ABS). With both schemes of optimization, recommendation of ICRU 38 or ABS with vaginal point from ICRU 89. Doses received by the organs at risk were analyzws, in this case rectum and bladder and also the irradiated volume for patients that receive HDR brachytherapy treatment. An afterloading technique is applied with an Eckert & Ziegler MultiSource ® equipment using a 60 Co source, 30 patients with 4 applications with cervical cancer are planning with HDR brachytherapy. This work analyzes 120 single applications with orthogonal images using the treatment planning system (TPS) HDRplus version 3.0.4 through "Auto dwell time determination" optimization method, using the recommendation for optimization dose from the ABS and vaginal point from ICRU 89 . The volume of the isodose curve of prescription is 15% less using ABS recommendation than ICRU 38. The bladder dose is 11% and rectum dose is 21% less using ABS recommendation than ICRU 38. The analysis of dose prescription using ICRU 38 and ABS recommendations in the patients analyzed shows less irradiated volume at the dose prescribed and also less mean dose in rectum and bladder of applications using ABS in contrast with ICRU 38 recommendations.
Intracavitary gynecological brachytherapy use as aparameter for dose distribution the relationship among de length of pear in the three axes directions regards ICRU 38. The ratio h/w, h/t gives us a parameter to figure it how the uterus and vagina are covered. This work correlates these ratios with the dwell times inside the uterus (Tu) and vagina (Tv) intending to know if we can use these times as parameters for the dose shape distribution. It was made an optimized treatment planning for 120 sessions of 6 Gy each one, following ABS recommendations, the ICRU 38, and 89. The planning system used is HDRplus3.0.4 with an HDR EZAG‐ BEBIG Co0.A86 brachytherapy machine with Cobalt 60. Taking into account the time modulation in tandem and the time differences between the left and right irradiation in the vagina, It was studied the correlation variation with the number of sessions for the ratio Tu/Tv with h/w and h/t. It was found a correlation between Tu/Tv with h/w and h/t, and it is dependent on the number of data. There is a good correlation between de ratio Tu/Tv with h/w and h/t respectively, which is stronger for the first one.
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