Inter-application displacement of brachytherapy dose received by the bladder and rectum of the patients with inoperable cervical cancer.

BACKGROUND: The aim of the study was to examine on the CT basis the inter-application displacement of the positions D0.1cc, D1cc and D2cc of the brachytherapy dose applied to the bladder and rectum of the patients with inoperable cervical cancer. PATIENTS AND METHODS: This prospective study included 30 patients with cervical cancer who were treated by concomitant chemo-radiotherapy. HDR intracavitary brachytherapy was made by the applicators type Fletcher tandem and ovoids. For each brachytherapy application the position D0.1cc was determined of the bladder and rectum that receive a brachytherapty dose. Then, based on the X, Y, and Z axis displacement, inter-application mean X, Y, and Z axis displacements were calculated as well as their displacement vectors (R). It has been analyzed whether there is statistically significant difference in inter-application displacement of the position of the brachytherapy dose D0.1cc, D1cc and D2cc of the bladder and rectum. The ANOVA test and post-hoc analysis by Tukey method were used for testing statistical importance of differences among the groups analyzed. The difference among the groups analyzed was considered significant if p < 0.05. RESULTS: There are significant inter-application displacements of the position of the brachytherapy dose D0,1cc, D1cc and D2cc of the bladder and rectum. CONCLUSIONS: When we calculate the cumulative brachytherapy dose by summing up D0,1cc, D1cc and D2cc of the organs at risk for all the applications, we must bear in mind their inter-application displacement, and the fact that it is less likely that the worst scenario would indeed happen.

[Selection of the optimal radiotherapy technique for locally advanced maxillary carcinoma using a three-dimensional treatment planning system]. / Izbor optimalne tehnike zracenja lokalno uznapredovalog karcinoma maksile primenom sistema za trodimenzionalno planiranje radioterapije.

AIM: To compare the isodose distribution of three radiotherapy techniques for locally advanced maxillary sinus carcinoma and analyze the potential of three-dimensional (3D) conformal radiotherapy planning in order to determine the optimal technique for target dose delivery, and spare uninvolved healthy tissue structures. METHODS: Computed tomography (CT) scans of fourteen patients with T3-T4, N0, M0 maxillary sinus carcinoma were acquired and transferred to 3D treatment planning system (3D-TPS). The target volume and uninvolved dose limiting structures were contoured on axial CT slices throughout the volume of interest combining three variants of treatment plans (techniques) for each patient: 1. A conventional two-dimensional (2D) treatment plan with classically shaped one anterior + two lateral opposite fields and two types of 3D conformal radiotherapy plans were compared for each patient. 2. Three-dimensional standard (3D-S) plan: one anterior + two lateral opposite coplanar fields, which outlines were shaped with multileaf collimator (MLC) according to geometric information based on 3D reconstruction of target volume and organs at risk as seen in the beam eye's view (BEV) projection. 3. Three-dimensional non-standard (3D-NS) plan: one anterior + two lateral noncoplanar fields, which outlines were shaped in the same manner as in 3D-S plans. The planning parameters for target volumes and the degree of neurooptic structures and parotid glands protection were evaluated for all three techniques. Comparison of plans and treatment techniques was assessed by isodose distribution, dose statistics, and dose-volume histograms. RESULTS: The most enhanced conformity of the dose delivered to the target volume was achieved with 3D-NS technique, and significant differences were found comparing 3D-NS vs. 2D (Dmax: p<0.05; Daver: p<0.01; Dmin: p<0.05; V90: p<0.05, and V95: p<0.01), as well as 3D-NS vs. 3D-S technique (Dmin: p<0.05; V90: p<0.05, and V95: p<0.01), while there were no differences between 2D vs. 3D-S technique. 3D-S conformal plans were significantly superior to 2D plans regarding the protection of parotid glands, and the additional improvement of dose conformity was achieved with 3D-NS technique. 3D-NS technique resulted in the decrease of Dmax for ipsilateral retina compared with 3D-S technique, while the level of Dmax for optic nerve was increased (within an acceptable range) with 3D-NS technique. CONCLUSION: In this study, 3D planning of radiotherapy for locally advanced maxillary sinus carcinoma with noncoplanar fields, which number did not exceed the number of fields for conventional arrangement enabled conformal delivering of the adequate dose to the target volume with the improved sparing of adjacent uninvolved healthy tissue structures.