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 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.
Full-textDOI: · Available from: Ananya Choudhury, Mar 19, 2015
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ABSTRACT: To assess whether online adaptive radiotherapy for bladder cancer is feasible across multiple Radiation Oncology departments using different imaging, delivery and recording technology. A multi-centre feasibility study of online adaptive radiotherapy, using a choice of three "plan of the day", was conducted at 12 departments. Patients with muscle-invasive bladder cancer were included. Departments were activated if part of the pilot study or after a site-credentialing visit. There was real time review of the first two cases from each department. 54 patients were recruited, with 50 proceeding to radiotherapy. There were 43 males and 7 females with a mean age of 78years. The tumour stages treated included T1 (1 patient), T2 (35), T3 (10) and T4 (4). One patient died of an unrelated cause during radiotherapy. The three adaptive plans were created before the 10th fraction in all cases. In 8 (16%) of the patients, a conventional plan using a 'standard' CTV to PTV margin of 1.5cm was used for one or more fractions where the pre-treatment bladder CTV was larger than any of the three adaptive plans. The bladder CTV extended beyond the PTV on post treatment imaging in 9 (18%) of the 49 patients. From a technical perspective an online adaptive radiotherapy technique can be instituted in a multi-centre setting. However, without further bladder filling control or imaging, a CTV to PTV margin of 7mm is insufficient.Radiotherapy and Oncology 04/2014; 111(2). DOI:10.1016/j.radonc.2014.02.015 · 4.86 Impact Factor
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ABSTRACT: To measure the difference in cumulative doses received by the bladder (target) and integral doses with different clinical target volume (CTV) to planning target volume (PTV) margins, comparing set-up to skin tattoos versus image-guided radiotherapy to bone or soft tissue. Four plans were generated on each planning computed tomography dataset using the CTV with 5, 10, 15, 20 mm PTV margins using a three-dimensional conformal four-field technique. Set-up data based on skin, bone and soft tissue to the bladder on pre-treatment cone beam computed tomography (CBCT) were recorded. In total, 316 CBCTs were evaluable from 10 bladder cancer patients. Each CBCT was fused to the planning computed tomography dataset using the isocentre corresponding to each of the three pre-treatment matching conditions. The target was contoured on each CBCT and called the CTV of the day and the plan was re-calculated to determine the dose to this. The mean D95 with CTV to PTV margins of 5, 10, 15 and 20 mm for skin set-up was 89.4, 93.0, 97.2, 98.6; for bone 88.8, 92.6, 96.7, 98.6; and for soft tissue 96.3, 98.6, 98.7, 99.5. With soft-tissue matching, the mean (standard deviation) volume of normal tissue receiving 5 Gy with 5, 10, 15 and 20 mm margins was 3899 (1022), 4561 (1142), 5663 (1304) and 6315 (1426) in cm(3). Soft-tissue matching results in superior target coverage and a reduced integral dose to the surrounding tissues. With soft-tissue matching, increasing CTV to PTV margins progressively beyond 5 mm results in modest improvement in CTV coverage, but a large increase in integral dose.Clinical Oncology 04/2014; 26(8). DOI:10.1016/j.clon.2014.03.007 · 2.83 Impact Factor