Rectal wall dose estimation in intracavitary brachytherapy: A preliminary comparison of an in-house rectal wire versus ICRU 38 recommendations

Background: In intracavitary brachytherapy for gynecological cancers, various techniques are used to locate the anterior rectal wall nearest to the sources but there is no consensus on the best method to do so. This study aimed to compare a technique used routinely in some centers that employs a wire marker to locate the position of the maximum rectal dose point, versus the method recommended by the ICRU Report 38. Materials and Methods: In a preliminary prospective study on 34 intracavitary insertions for patients with cervical or endometrial cancer, treated at our center based on the Manchester system, the dose distributions were obtained from a treatment planning system following the input of scanned orthogonal anteroposterior and lateral radiographs. For each case, an in-house marked wire was inserted in the rectal lumen and the doses were calculated on several points along the wire seen on the radiographs, to obtain the maximum dose. For the same insertions, the ICRU method was also applied by considering the rectal wall hot spot as a point 0.5 cm posterior to the posterior vaginal wall (visualized on the radiographs by vaginal packing material containing contrast medium). Results: Averaged over all insertions, mean rectal wall hot spot dose calculated using the positional information obtained by the wire technique was lower by 28.6% than that given by the ICRU method (P < 0.001). Conclusion: Our initial results add evidence to the suggestion that the wire technique underestimates the rectal wall hot spot dose significantly compared to the ICRU method.