Adaptive radiation therapy for bladder cancer: a review of adaptive techniques used in clinical practice

Abstract

Significant changes in the shape, size and position of the bladder during radiotherapy (RT) treatment for bladder cancer have been correlated with high local failure rates; typically due to geographical misses. To account for this, large margins are added around the target volumes in conventional RT; however, this increases the volume of healthy tissue irradiation. The availability of cone beam computed tomography (CBCT) has not only allowed in‐room volumetric imaging of the bladder, but also the development of adaptive radiotherapy (ART) for modification of plans to patient‐specific changes. The aim of this review is to: (1) identify and explain the different ART techniques being used in clinical practice and (2) compare and contrast these different ART techniques to conventional RT in terms of target coverage and dose to healthy tissue: A literature search was conducted using EMBASE, MEDLINE and Scopus with the key words ‘bladder, adaptive, radiotherapy/radiation therapy’. 11 studies were obtained that compared different adaptive RT techniques to conventional RT in terms of target volume coverage and healthy tissue sparing. All studies showed superior target volume coverage and/or healthy tissue sparing in adaptive RT compared to conventional RT. Cross‐study comparison between different adaptive techniques could not be made due to the difference in protocols used in different studies. However, one study found daily re‐optimisation of plans to be superior to plan of the day technique. The use of adaptive RT for bladder cancer is promising. Further study is required to assess adaptive RT versus conventional RT in terms of local control and long‐term toxicity.

Online Adaptive Radiation Therapy

“…These offline ART studies demonstrate a reduction in normal tissue irradiated, and indicated the potential for considerably reduced target volumes. 76,77 The disadvantage of any offline techniques is that they only correct for the systematic differences in bladder position and volume.…”

“…Kibrom et al reviewed offline ART studies for bladder cancer. 76 Of particular interest are the review of four composite volume offline ART techniques-in general, a composite volume technique uses the first few CBCTs to create composite target volumes for the offline adaptive plan. These offline ART studies demonstrate a reduction in normal tissue irradiated, and indicated the potential for considerably reduced target volumes.…”

Relaxin‐2 therapy reverses radiation‐induced fibrosis and restores bladder function in mice

“…Radiation is a major intervention in treating pelvic organ malignancies. However, the risk for developing complications such as radiation cystitis limits the radiation dose . The consequences of radiotherapy include a dose‐dependent detrimental effect on normal organ function within the irradiated field …”

The impact of intra-fractional bladder filling on “Plan of the day” adaptive bladder radiotherapy

“…The unpredictable variations in bladder volume due to intra-and inter-fractional filling during treatment have been evidently documented in bladder radiotherapy [2]. Large treatment planning margins are often used to ensure coverage and minimise geographical miss, however this also led to unnecessary irradiation vast areas of normal tissue [2,3].…”

“…Bladder cancer is the second most common urological cancer [4]. In order to strike a balance between local control and longterm toxicity for the bladder cancer patients, it is essential that the bladder target volume is covered adequately by high radiation dose whilst sparing the surrounding healthy tissue as much as possible [3]. This facilitated the development of adaptive techniques in bladder radiotherapy.…”