2204 - Observational Study Based on Interfractional Urinary Bladder Filling Variations during Image Guided Radiotherapy in Cervical Cancer Patients Using Cone Beam Computed Tomography

S. .¹, S. Nanda¹, D. P. Meher¹, D. S. S. Mishra², D. A. Parihar¹, and D. M. Dhakar³; ¹All India Institute of Medical Sciences(AIIMS), Raipur, Raipur, India, ²Paras HMRI Hospital, Patna, India, ³Prem Hospital, Panipat, India

Purpose/Objective(s): Organ motion is one of the most important factors limiting the precision of advanced radiation techniques, especially for pelvic malignancies like cervical cancer. The inter and intra-fractional movement of bladder wall can be as much as 3 cm due to changes in volume. Pelvic radiotherapy with a full bladder where the patient is instructed to drink a certain amount of water prior to treatment is presently followed worldwide with a rationale for better organ at risk (OAR) sparing in these patients. However, unpredictability may occur due to variable bladder filling during treatment. This occurs due to patients’ poor compliance, anatomical alterations during radiotherapy or toxicity. The aim of this study is to observe interfractional bladder-filling volume variations during image-guided radiotherapy in cervical cancer patients with the help of cone beam computed tomography (CBCT) after following a strict bladder protocol. Materials/

Methods: It was a single institution, nonrandomized, prospective study in which 15 cervical cancer patients who were treated with concurrent chemoradiation between May 2023 to August 2023 were included. All patients were counselled in detail regarding bladder filling protocol prior to radiation and weekly CBCT was done to quantify the volumetric changes in bladder throughout the treatment period. Urinary bladder was contoured in each CBCT image on treatment planning software and the bladder volume (in cc), maximum anteroposterior (AP), craniocaudal (CC) and Transverse (TR) diameters in centimeters(cms) were measured. Statistical analysis was performed using statistical software.
Results: A total of 90 CBCT scans were analyzed in 15 cervical cancer patients (6 CBCTs for each patient). The mean bladder volume for all 15 patients was 183.346 cc with a standard deviation of 107.66 cc (p value = 0.792). Maximum transverse, anteroposterior and craniocaudal diameter was 10.975 cm, 8.273 cm and 10.493 cm while minimum was 6.30 cm, 4.936 cm and 3.711 cm respectively. The mean standard deviation of transverse, anteroposterior and craniocaudal diameter was 8.634 cm +/- 1.153 cm, 6.088 cm +/- 0.908 cm and 5.38 cm +/- 1.69 cm respectively

Conclusion: Volume changes due to a full bladder showed asymmetrical change in size and shape, with most significant changes observed in craniocaudal diameter, followed by transverse and least changes were observed in anteroposterior diameter. Hence, more liberal margins should be considered in craniocaudal direction with a reduction of margin in transverse and anteroposterior direction. It is recommended to verify urinary bladder volume prior to treatment using a cone beam CT after instructing the patients with appropriate bladder filling protocol.