Targeting the Tumor: Assessing the Impact of Bladder Volume and Position on Accuracy of Radiation Delivery for Patients with Bladder Cancer

Abstract

ContextDaily variations in bladder size and position can negatively impact the ability to accurately deliver radiation.AimsWe attempted to quantify how bladder volumes and positions change over the course of radiotherapy for muscle invasive bladder cancer and the planning target volume (PTV) margins required to account for such changes.Methods and materialCone-beam computed tomography (CT) images of 28 patients during their first, second, and third fractions and weekly thereafter were acquired. Bladders were contoured and the volume, centre of mass, and the maximal positions were recorded and compared to the planning CT scan.Statistical analysisBladder parameters were analysed using regression analysis examining for time trends and correlation to the patient, tumour, or treatment-related factors.ResultsThere was great variability in the mean bladder volumes during the radiotherapy courses (154.17 +/- 129.38 cm3). There were no statistically significant trends for volume changes. Deviations in bladder positions were seen but were small in magnitude. No patient factors were identified which could help predict bladder changes clinically. Bladder variability resulted in a high percentage of fractions (39.6%) in which part of the bladder was outside the PTV. Calculated PTV margins (for 90% of the population to receive 95% of the prescription dose) were 1.48 cm right, 1.15 cm left, 2.13 cm posterior, 1.52 cm anterior, 2.23 cm superior, and 0.52 cm inferior.ConclusionsBecause of random bladder changes, a significant number of fractions were treated in which the clinical target volume (CTV) fell outside of the PTV. Methods to minimize the amount of CTV that is missed on a fraction to fraction basis should be explored.

Predicting dice similarity coefficient of deformably registered contours using Siamese neural network

“…The specificity for the bladder was 0.04, meaning that only 4% of well registered contours were identified. This might be due to artifacts from bowel gas that could obscure the bladder outline superiorly, as reported by other groups (Kochan et al 2017). Nonetheless, as the model's ability to identify poorly registered contours has a higher clinical importance, its high sensitivity of 0.97 for the bladder can still provide utility in an ART workflow.…”

Pacientų, Sergančių Šlapimo Pūslės Vėžiu, Šlapimo Pūslės Tūrio Pokyčio Ir Dubens Pozicionavimo Tikslumo Įvertinimas Radioterapijoje

“…Ne visi radioterapijos centrai atlieka kasdienes vaizdines verifikacijas. Dažnai jos kartojamos pirmąsias tris dienas, o po to atliekamos tik kartą per savaitę [13].…”

Retrospective evaluation of planning margins for patients undergoing radical radiation therapy treatment for bladder cancer using volumetric modulated arc therapy and cone beam computed tomography

“… 1 The potential changes in the size and shape of the bladder, depending on the degree of bladder filling, pose a challenge in accurate treatment delivery. 2 , 3 , 4 Historically, this was overcome by the use of generous margins expanded from the clinical target volume (CTV). 5 , 6 Generally, bladders fill anisotropically – that is, with the greatest magnitude in the superior aspect followed by anterior then in all other dimensions.…”