Changes in applicator positions and dose distribution between high dose rate brachytherapy fractions in cervix carcinoma patients receiving definitive radiotherapy

Abstract

This study examines the change of applicator geometry and its effect on rectal/rectum (R) and bladder (B) doses, and obtained radiobiological equivalent doses (RED), between each high dose rate (HDR) brachytherapy (BT) fraction in cervical carcinoma patients. BT using a tandem (T) and two ovoids (O) is included, and any discrepancies in applicator positions among the fractions were calculated. Whether the change of applicator position had an effect on the calculated R and B doses was analysed. Furthermore, the relationship between the size of tumour, the magnitude of displacement and the change in R and B doses was also investigated. Lastly, the changes in R and B RED were noted. The average magnitude of displacement was between 2.0 mm and 16.9 mm, showing time trend. There was no relationship between tumour size and the magnitude of discrepancy of Left O, Right O, T, R, B, and neither change in R and B doses (p>0.05). The mean differences of R and B doses were between 49-78 cGy, and 70-84 cGy, respectively. The magnitude of discrepancy and changes in doses showed no correlation (p>0.05). There were no significant differences in REDs for bladder (p = 0.8) and rectum (p = 0.2). In conclusion, there were significant differences in the applicator positions R and B and R and B doses among the fractions, which confirm the necessity of treatment planning in each HDR BT fraction. However, the total calculated R and B REDs did not show a remarkable difference.

Magnitude and Implications of Interfraction Variations in Organ Doses during High Dose Rate Brachytherapy of Cervix Cancer: A CT Based Planning Study

“…Most of these authors have quantified the variations in terms of various angles and distances of fixed points on the bony pelvis from the applicator [2, 3, 5, 8, 9]. However this method does not give a true description of the actual moments and rotations that have occurred, as they are dependent on the frame of reference selected.…”

Uterine perforation and its dosimetric implications in cervical cancer high-dose-rate brachytherapy

“…Several reports investigated the effect of applicator displacement on brachytherapy plan dosimetry, and emphasized the importance of image guidance and comprehensive quality control in the practice of brachytherapy [ 27 – 30 ]. However, published data on the effect of mal-placement of brachytherapy applicators on plan quality are scarce, hence a comparison with our data was not possible.…”

Study of positional dependence of dose to bladder, pelvic wall and rectal points in High-Dose-Rate Brachytherapy in cervical cancer patients

“…Gauze packing is one of the factors affecting the dose to rectum and bladder. [8] In addition to packing the other factor is the position of the patient. [1819] Hoskin PJ[22] et al , discussed the influence of applicator angle on Dosimetry in vaginal vault brachytherapy.…”

“…All fractions require careful individualized planning due to the geometrical variation of applicators arising from the differences in the anatomy of the patient, variations in packing and position of the patient, keeping the rectal and bladder doses within the acceptable limits. [8910111213141516] The applicator, inserted into the patients’ uterine canal and vaginal cavity varies with the anatomical position of the patient. Due to this there is a variation in doses to various anatomical points.…”