Purpose:
To evaluate to treatment consistency over the total number of fractions when treatment what HDR brachytherapy using the ML cylinders. At the same time the dosimetric impact on the critical organs is monitored over the total number of fractions.
Methods:
A retrospective analysis of 10 patients treated with Cylinder applicators, from 2015–2016 were considered for this study. The CT scans of these patients, taken before each treatment were separately imported in to the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused together with respective to the applicator, using landmark registration. The doses of each plan were imported as well and a cumulative dosimetric analysis was made for bladder, bowels, and rectum and PTV.
Results:
No contour of any of the OAR was exactly similar when CT images were fused on each other. The PTV volumes vary from fraction to fraction. There was always a difference between the doses received by the OARs between treatments. The maximum dose varied between 5% and 30% in rectum and bladder. The minimum dose varied between 5% and 8% in rectum and bladder. The average dose varied between 15% and 20% in rectum and bladder. Deviation in placement were noticed between fractions.
Conclusion:
The variation in volumes of OARs and isodoses near the OARs, indicate that the estimated doses to OARs on the planning system may not be the same dose delivered to the patient in all the fractions. There are no major differences between the prescribed dose and the delivered dose over the total number of fractions. In some cases the critical organs will benefit if the consecutive plans will made after the CT scans will be registered with the initial scan and then planned.
Purpose:
High dose rate brachytherapy is a highly localized radiation therapy that has a very high dose gradient. Thus one of the most important parts of the treatment is the immobilization. The smallest movement of the patient or applicator can result in dose variation to the surrounding tissues as well as to the tumor to be treated. We will revise the ML Cylinder treatments and their localization challenges.
Methods:
A retrospective study of 25 patients with 5 treatments each looking into the applicator's placement in regard to the organs at risk. Motion possibilities for each applicator intra and inter fractionation with their dosimetric implications were covered and measured in regard with their dose variance. The localization immobilization devices used were assessed for the capability to prevent motion before and during the treatment delivery.
Results:
We focused on the 100% isodose on central axis and a 15 degree displacement due to possible rotation analyzing the dose variations to the bladder and rectum walls. The average dose variation for bladder was 15% of the accepted tolerance, with a minimum variance of 11.1% and a maximum one of 23.14% on the central axis. For the off axis measurements we found an average variation of 16.84% of the accepted tolerance, with a minimum variance of 11.47% and a maximum one of 27.69%. For the rectum we focused on the rectum wall closest to the 120% isodose line. The average dose variation was 19.4%, minimum 11.3% and a maximum of 34.02% from the accepted tolerance values
Conclusion:
Improved immobilization devices are recommended. For inter‐fractionation, localization devices are recommended in place with consistent planning in regards with the initial fraction. Many of the present immobilization devices produced for external radiotherapy can be used to improve the localization of HDR applicators during transportation of the patient and during treatment
Purpose/Objective(s): This study investigated the feasibility of using intraoperative directional brachytherapy for treatment of squamous cell carcinoma of the anus. The patient had received 2 prior courses of external beam therapy of 55.8 Gy in 2014 and 30 Gy in 2015. Due to the increased risk of additional external radiation, brachytherapy was considered as a treatment option. Materials/Methods: A commercially available flexible, bioabsorbable polymer membrane embedded with an array of discrete 103 Pd sources was used for the implant. The 103 Pd sources were spaced 8 mm apart on a 5x15 cm sheet yielding 108 sources. Unidirectional dose was achieved by a 0.05-mm thick gold disk-shaped foil on the reverse side of each source. A dose of 120 Gy at 5-mm depth was prescribed, dictating an air kerma of 3.0 U for each source. 120 Gy was selected because that dose has been used successfully to treat adenocarcinoma of the prostate with LDR brachytherapy. After the abdominoperineal resection, the entire sheet was placed on the treatment area in the patient to determine the needed dimensions. The polymer sheet was then removed and easily cut to size with scissors leaving 51 103 Pd sources remaining. The sheet was manufactured with holes in the membrane located between each source, through which a surgical tack could have been inserted to attach the sheet. However the surgeon elected to use sutures for attachment in a concave shape to the pelvic sidewall. The sheet was cut to cover the high-risk surgical bed and specifically a 3x4 cm area of muscle invasion and involved margins. The sheet was sutured with the radioactive side in contact with the pelvic sidewall and the gold, shielded side facing away. The surgical team completed the procedure and the patient recovered without any problems. Results: One week after the implant the patient received a CT scan in the radiation oncology department. The images were transferred to the brachytherapy treatment planning system for a post plan. The treatment plan indicated that the sources remained in position in a concave array pattern. Due to the dose fall-off of 103 Pd, the calculated dose to critical structures was minimized. Conclusion: The surgical implant of the sheet proceeded as expected with no complications. The post plan indicated that the sheet remained in position with the radioactive side contacting the treatment area. The dosevolume histogram demonstrated good coverage with minimal dose to adjacent critical structures. Directional LDR intraoperative brachytherapy is a feasible alternative for retreatment of the high-risk margin of resection in pelvic malignancies.Purpose/Objective(s): High-dose-rate (HDR) brachytherapy is a highly localized mode of radiation therapy that has a very sharp dose falloff. Thus one of the most important parts of the treatment is the immobilization. The smallest movement of the patient or applicator can result in dose variation to the surrounding tissues as well as to the tumor to be treated. Our purpose is to revise the MML cylinder treatmen...
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