Improving radiotherapy for bladder cancer: an opportunity to integrate new technologies

Image-guided Adaptive Radiotherapy for Bladder Cancer

Technological advancement has facilitated patient-specific radiotherapy in bladder cancer. This has been made possible by developments in image-guided radiotherapy (IGRT). Particularly transformative has been the integration of volumetric imaging into the workflow. The ability to visualise the bladder target using cone beam computed tomography and magnetic resonance imaging initially assisted with determining the magnitude of inter- and intra-fraction target change. It has led to greater confidence in ascertaining true anatomy at each fraction. The increased certainty of dose delivered to the bladder has permitted the safe reduction of planning target volume margins. IGRT has therefore improved target coverage with a reduction in integral dose to the surrounding tissue. Use of IGRT to feed back into plan and dose delivery optimisation according to the anatomy of the day has enabled adaptive radiotherapy bladder solutions. Here we undertake a review of the stepwise developments underpinning IGRT and adaptive radiotherapy strategies for external beam bladder cancer radiotherapy. We present the evidence in accordance with the framework for systematic clinical evaluation of technical innovations in radiation oncology (R-IDEAL).

MR-Guided Adaptive Radiotherapy for Bladder Cancer

Radiotherapy has an important role in the curative and palliative treatment settings for bladder cancer. As a target for radiotherapy the bladder presents a number of technical challenges. These include poor tumor visualization and the variability in bladder size and position both between and during treatment delivery. Evidence favors the use of magnetic resonance imaging (MRI) as an important means of tumor visualization and local staging. The availability of hybrid systems incorporating both MRI scanning capabilities with the linear accelerator (MR-Linac) offers opportunity for in-room and real-time MRI scanning with ability of plan adaption at each fraction while the patient is on the treatment couch. This has a number of potential advantages for bladder cancer patients. In this article, we examine the technical challenges of bladder radiotherapy and explore how magnetic resonance (MR) guided radiotherapy (MRgRT) could be leveraged with the aim of improving bladder cancer patient outcomes. However, before routine clinical implementation robust evidence base to establish whether MRgRT translates into improved patient outcomes should be ascertained.

Evaluating the need for adaptive therapy when delivering conformal bladder radiotherapy

Background and purpose

The purpose of this study was to audit positioning errors during bladder image-guided radiotherapy (IGRT) and quantify survival outcomes.

Materials and methods

We carried out a retrospective review of 141 patients treated between March 2007 and July 2010 with three-dimensional conformal radiotherapy. An offline imaging protocol using kV cone beam computed tomography (CBCT) was used. Positioning errors, clinical interventions and re-planning rates were quantified. Cancer outcomes and survival were collected by review of patient notes and a registry search.

Results

Among all, 43% of the patients required no intervention. Isocentre corrections were used for systematic bony set-up error in 13% and to improve bladder coverage in 28%. Clinical interventions to improve bladder coverage were required in 16% of the patients and repeat computed tomography planning in a further 16%. Overall, 44% of the patients demonstrated some form of organ deformation that would have resulted in inadequate dose to the bladder or significant overdose to an organ at risk if not corrected for. Post-treatment check cystoscopy was undertaken in 107 patients (76%) with 72 noted to have a complete response. Overall survival was 47·8% at 3 years.

Conclusions

Organ deformation during radiotherapy for bladder cancer is a significant problem for over 40% of patients. Strategies to compensate are essential to ensure optimal plan delivery.

Randomized noninferiority trial of reduced high-dose volume versus standard volume radiation therapy for muscle-invasive bladder cancer: results of the BC2001 trial (CRUK/01/004)

PURPOSE

To test whether reducing radiation dose to uninvolved bladder while maintaining dose to the tumor would reduce side effects without impairing local control in the treatment of muscle-invasive bladder cancer.

METHODS AND MATERIALS

In this phase III multicenter trial, 219 patients were randomized to standard whole-bladder radiation therapy (sRT) or reduced high-dose volume radiation therapy (RHDVRT) that aimed to deliver full radiation dose to the tumor and 80% of maximum dose to the uninvolved bladder. Participants were also randomly assigned to receive radiation therapy alone or radiation therapy plus chemotherapy in a partial 2 × 2 factorial design. The primary endpoints for the radiation therapy volume comparison were late toxicity and time to locoregional recurrence (with a noninferiority margin of 10% at 2 years).

RESULTS

Overall incidence of late toxicity was less than predicted, with a cumulative 2-year Radiation Therapy Oncology Group grade 3/4 toxicity rate of 13% (95% confidence interval 8%, 20%) and no statistically significant differences between groups. The difference in 2-year locoregional recurrence free rate (RHDVRT - sRT) was 6.4% (95% confidence interval -7.3%, 16.8%) under an intention to treat analysis and 2.6% (-12.8%, 14.6%) in the "per-protocol" population.

CONCLUSIONS

In this study RHDVRT did not result in a statistically significant reduction in late side effects compared with sRT, and noninferiority of locoregional control could not be concluded formally. However, overall low rates of clinically significant toxicity combined with low rates of invasive bladder cancer relapse confirm that (chemo)radiation therapy is a valid option for the treatment of muscle-invasive bladder cancer.

Comparison of adaptive radiotherapy techniques for the treatment of bladder cancer

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 on-treatment 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 (p=0.10), 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-the-day 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.

Trimodality treatment for bladder cancer: does modern radiotherapy improve the end results?

With the advancement in endoscopic surgery, radiation treatment planning and execution, as well as the use of new chemotherapeutic regimens, bladder conservation has evolved into a competing alternative to radical cystectomy. Trimodality treatment has the great advantage of preserving a normally functioning urinary bladder. Despite the absence of direct randomized trials comparing both modalities, trimodality treatment comprising maximal transuretheral resection of bladder tumors followed by different regimens of combined radiochemotherapy achieved comparable results to radical cystectomy in many trials. Those who did not achieve complete remission after induction radiochemotherapy were salvaged by radical cystectomy. Improving the radiotherapeutic window is a challenging issue. In radiotherapy for bladder cancer, uncertainties include set-up errors, patient movement, internal organ movement and volume changes due to bladder filling (both inter- and intrafraction). The advancement in treatment verification procedures in modern radiotherapy and the use of fiducial markers reduces set-up errors, while adaptive radiotherapy could decrease the unnecessary irradiation of normal tissues by tracking bladder volume changes. In addition, new radiotherapeutic techniques, such as intensity-modulated radiotherapy and volume-modulated radiotherapy, permit dose escalation to the target without increasing the dose to the surrounding normal tissues.

Adjuvant and neoadjuvant radiotherapy for bladder cancer: revisited

To date, radical cystectomy has continued to be the treatment of choice for muscle-invasive bladder cancer. It is associated with a 5-year disease-free survival rate ranging from 27–55%. This outcome is significantly worse when reporting upon locally advanced cases. The independent prognostic factors include: tumor stage, grade, pelvic nodal involvement and some other additional factors. Beside the higher reported incidence of distant metastasis, local recurrence either alone or combined with systemic relapse has been shown to be experienced by 23–50% of locally advanced patients – a rate that was much more frequent than previously believed. Nonrandomized trials of preoperative radiotherapy have suggested improved survival rates. However, only one out of the six randomized preoperative trials in the literature published in English has proved to be significant. On the other hand, the only randomized trial and most retrospective studies dealing with postoperative radiotherapy revealed a significant increase in disease-free survival. Late complications of post operative radiotherapy, contrary to former belief, were acceptable and generally depended upon the volume of the irradiated normal tissues and the radiotherapy techniques used. Most of these adjuvant or neoadjuvant reports were performed in the 1970s and 1980s using conventional radiation techniques. Modern radiotherapy, delivering higher doses to the tumor while saving a significant amount of the surrounding normal structure, has not been rigorously tested. However, these techniques have already succeeded in improving treatment end results in other pelvic tumors.