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 rou nely in some centers that employs a wire marker to locate the posi on of the maximum rectal dose point, versus the method recommended by the ICRU Report 38. Materials and Methods: In a preliminary prospec ve study on 34 intracavitary inser ons for pa ents with cervical or endometrial cancer, treated at our center based on the Manchester system, the dose distribu ons 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 inser ons, 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 inser ons, mean rectal wall hot spot dose calculated using the posi onal informa on obtained by the wire technique was lower by 28.6% than that given by the ICRU method (P < 0.001). Conclusion: Our ini al results add evidence to the sugges on that the wire technique underes mates the rectal wall hot spot dose significantly compared to the ICRU method.