Comparison of adaptive radiotherapy techniques for the treatment of bladder cancer

Abstract

Objective: Day-to-day anatomical variations complicate bladder cancer radiotherapy treatment. This work quantifies the impact on target coverage and irradiated normal tissue volume for different adaptive strategies. Methods: 20 patients were retrospectively planned using different three-dimensional conformal radiotherapy treatment strategies for whole-bladder carcinoma: (i) ''conventional'' treatment used isotropic expansion of the clinical target volume (CTV) by 15 mm to the planning target volume (PTV) for daily treatment; (ii) ''plan of the day'' used daily volumetric on-treatment imaging [cone beam CT (CBCT)] to select from four available plans with varying superior PTV margins; (iii) ''composite'' strategies used ontreatment CBCTs from Fractions 1-3 to inform a composite CTV and adapted PTV (5-and 10-mm margins for composite 1 and composite 2, respectively) for subsequent treatment. Target coverage was evaluated from available CBCTs (the first three fractions then the minimum weekly thereafter), and the reduction in the irradiated volume (i.e. within the 95% isodose) was quantified. Results: Plan of the day improved target coverage (i.e. all of the bladder within the 95% isodose throughout the treatment) relative to conventional treatment (p50.10), while no such benefit was observed with composite 2. Target coverage was reduced with composite 1 relative to conventional treatment. The mean irradiated volume was reduced by 17.2%, 35.0% and 14.6% relative to conventional treatment, for plan of the day, composite 1 and composite 2, respectively (p,0.01 in all cases). No parameters predictive of large changes in bladder volume later in the treatment were identified. Conclusions: Adaptive techniques can maintain or improve target coverage while allowing for reduced irradiated volume and possibly reduced toxicity. The plan-of-theday technique appeared to provide the optimal balance between target coverage and normal tissue sparing. Advances in knowledge: This study suggests that plan-of-the-day techniques will provide optimal outcomes for adaptive bladder radiotherapy.

Adaptive radiotherapy strategies for pelvic tumors – a systematic review of clinical implementations

“…In addition to one in silico implementation of online compensation [58], these were the only studies where feedback from delivered dose triggered adaptations. Contributing to differences in applied strategies and workflows could be the additional manual contouring, which was a pre-requisite in over 70% of the simulated ART workflows [22,59,60,[62][63][64][65][66][68][69][70]72,74,78,79,[81][82][83]85,86,88,89,91,93,[95][96][97][98][100][101][102][103][104][105][106][107]. To reduce the need of manual contours, the segmentation could be propagated using deformable image registration.…”

A biological modeling based comparison of two strategies for adaptive radiotherapy of urinary bladder cancer

“…Previous treatment planning studies have compared different techniques to create PTVs in adaptive plan selection radiotherapy [5,18]. This study is the first to compare two clinically implemented ART strategies for bladder cancer directly, using both TCP modeling and calculation of normal tissue parameters from EQD2 distributions.…”

“…Recently, it has been shown that adaptive radiotherapy (ART) may reduce normal tissue dose by selecting an optimal plan from a patient-specific plan library, according to daily patient anatomy [3][4][5][6][7]. Several plan selection strategies have been proposed, all of which are based on creating multiple treatment plans prior to or during treatment, by imaging multiple anatomical variations [3][4][5][6][7]. For every treatment fraction, the plan best fitting the daily bladder volume as assessed on cone beam computed tomography (CBCT) is selected.…”

“…In general, two ART strategies are currently applied to obtain target volumes for the multiple plans: using multiple planning CT scans [3][4][5], or using the CBCT scans acquired during the first week of treatment [5][6][7]. Currently, no consensus exists regarding the best adaptive strategy.…”

“…Furthermore, two groups of fractionation schedules are commonly used for bladder cancer: a conventional schedule of 60-64 Gy in 30-32 fractions, or a moderate hypofractionation schedule with 50-57. 5 Gy delivered in 20 fractions. Each fractionation schedule is inherently associated with a different adaptive strategy, due to differences between the strategies.…”