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.

Whole bladder magnetic resonance image-guided radiotherapy using the 1.5 Telsa MR-linac is feasible. Full online adaptive planning workflow based on the anatomy seen at each fraction was performed. This was delivered within 45 min. Intra-fraction bladder filling did not compromise target coverage. Patients reported acceptable tolerance of treatment.

Magnetic resonance imaging (MRI) guided systems integrate a linear accelerator and MRI scanner enabling adaptive radiotherapy (RT) and real-time imaging. We report our experience of the first five patients treated with MRI-guided RT (MRIgRT) in the UK, within the Prostate RT Integrated with Simultaneous MRI (PRISM) trial (NCT03658525) designed to assess the feasibility, safety, and tolerability of prostate MRIgRT. Five patients with localized prostate cancer were recruited. One week following insertion of three fiducial markers, reference computed tomography (CT) and MRI scans were acquired and fused using markers. Clinical target volume 1 (CTV1) consisted of prostate plus proximal 1 cm of seminal vesicles (SV), CTV2 was prostate plus proximal 2 cm of SV. Planning target volume 1 (PTV1) was created from CTV1 by addition of a 5 mm margin, except 3 mm posteriorly. PTV2 was generated by expanding CTV2 by 5 mm isotropically. Dose fractionation of 60 Gy in 20 fractions was delivered to PTV1 (PTV2 received 48.6 Gy). Reference CT plan was generated using inverse planned step and shoot intensity modulated RT with 7 co-planar non-opposing beams using a treatment planning system. At every fraction, after acquisition of a 2 minute 3D T2-weighted MRI, a clinician amended CTVs according to daily anatomy. Organs at risk were amended when required. A new daily plan was created by optimizing the segment shapes from the reference plan, also known as ‘adapt to shape’ workflow. Following checking of the plan with a secondary dose calculation, a second MRI was acquired to determine whether further adaptation of the new plan was required due to intrafraction motion. RT delivery was carried out with real-time cine MRI. Acute toxicity was assessed prospectively by RTOG and CTCAE during weeks 2 and 4 of RT then 4, 8 and 12 weeks following RT. Table 1 summarizes mean (standard deviation in brackets) patient characteristics, timings and toxicity. Patients received all fractions on the MR-Linac with a new online plan in 99/100 fractions. Mean treatment time was 42 minutes, 97/100 fractions were delivered within 60 minutes. Treatment was well tolerated with no unexpected toxicity. Daily prostate MRIgRT with online replanning is feasible, safe and delivered within a reasonable time. PRISM recruitment is ongoing with formal safety analysis after 10 patients and total recruitment of 30 patients planned.Abstract 2690; Table 1Patient characteristicsMean age (years)69.6 (3.9)Mean presenting PSA (ug/l)8.8 (5.3)Gleason score3+3 (1 patient), 3+4 (4 patients)Mean CTV2 volume (cm3)55.3 (15.4)Treatment timings (min)CTV amending9.1 (2.3)Plan re-optimization5.2 (1.1)RT delivery4.7 (0.7)Total time to end of RT delivery42.0 (4.9)Acute toxicity to dateHighest gastrointestinalCTCAE- Grade (Gr) 2 proctitis RTOG- Gr 2 proctitis and diarrheaHighest genitourinaryCTCAE- Gr 2 frequency, cystitis, urgency RTOG- Gr 2 cystitis Open table in a new tab

S845ESTRO 38 the first search were charity/NGO sites (46%), followed by sponsored medical news sites (28%), hospital/university sites (20%) and governmental sites (6%).Websites operated by charity organizations had significantly higher DISCERN Plus scores (mean score: 55.5 ± 9.3) compared to hospital sites (mean score: 47.3 ± 9.6, p<0.042) and medical news sites (mean score: 46.1 ± 6.1, p<0.009), respectively.The JAMA benchmark criteria were fulfilled for all four sections in 13%, for three, two and one in 13%, 31% and 40%, respectively.Only 13% of all websites were HON code certified.All analyzed websites had a focus on curative teletherapy, 76%, 51% and 22% of all websites mentioned brachytherapy, active surveillance and palliative radiotherapy, respectively.In 57% the procedure of radiotherapy was described in detail.Special radiation techniques like "hypo-fractionation", "Intensity modulated Radiotherapy (IMRT)", "Image guided Radiotherapy (IGRT)" and "proton therapy" were mentioned in 37%, 72%, 27% and 31% of all analyzed websites, respectively. ConclusionThe quality of websites on radiotherapy and prostate cancer directed at laypersons is promising.The fact that

ConclusionA homogeneous calculation and extraction method of DVH data was applied to a grouped analysis of SBRT plans.A consistent multiple DVH analysis was performed.The bias due to different DVH calculation algorithms was eliminated by employing a single independent calculation method.The observed differences suggest that comparable standards in patient treatment among different centers can be obtained if a consistent highlevel data sharing capability is granted.In the strive to harmonize the planning process, this analysis constitutes a first step toward the creation of a platform of crowdknowledge-based planning guidelines.This platform could give an high-quality benchmark to less experienced centers that are willing to implement SBRT techniques.

ICTR-PHE 2016 S7two scenarios defined by different tissue parameter values (α/β)x representing high and low radio-sensitivity.We systematically compared RBE predictions as a function of (α/β)x and proton linear energy transfer (LET) values in a spread-out Bragg peak (SOBP) in water and analysed results on patient-CT anatomy for cranial irradiation in terms of absorbed dose-to-water, dose-averaged LET (LETD), RBEweighted dose-to-water and biological range shift distributions.Results: Different levels of agreement depending on (α/β)x and LET values were found in the systematic comparison of RBE predictions.The SOBP study emphasizes a variation of LETD and RBE not only as a function of depth but also of lateral distance from the central beam axis.Applying the different models to cranial treatment plans we observe consistent discrepancies from the values obtained for a constant RBE of 1.1 when using the variable RBE scheme in tissues with low (α/β)x, regardless of the model.An example is reported in figure 1. Biological range shifts of (0.6-2.4) mm (high (α/β)x) and (3.0-5.4)mm (low (α/β)x) were found in the fall-off analysis of individual profiles of RBE-weighted fraction dose along the beam penetration depth.Conclusions: Although more experimental evidence is required to validate the accuracy of the investigated models, their consistent trend suggests that their main RBE dependencies should be included in treatment planning systems.Evaluation of the impact of a variable RBE scheme on the plan optimized using a constant RBE would thus be enabled, constituting a first step towards a more robust choice of biological dose delivery in proton therapy.

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