J.R.N. Van der Voort van Zyp

MRI-guided prostate adaptive radiotherapy - A systematic review.

Dose escalated radiotherapy improves outcomes for men with prostate cancer. A plateau for benefit from dose escalation using EBRT may not have been reached for some patients with higher risk disease. The use of increasingly conformal techniques, such as step and shoot IMRT or more recently VMAT, has allowed treatment intensification to be achieved whilst minimising associated increases in toxicity to surrounding normal structures. To support further safe dose escalation, the uncertainties in the treatment target position will need be minimised using optimal planning and image-guided radiotherapy (IGRT). In particular the increasing usage of profoundly hypo-fractionated stereotactic therapy is predicated on the ability to confidently direct treatment precisely to the intended target for the duration of each treatment. This article reviews published studies on the influences of varies types of motion on daily prostate position and how these may be mitigated to improve IGRT in future. In particular the role that MRI has played in the generation of data is discussed and the potential role of the MR-Linac in next-generation IGRT is discussed.

PSA nadir as a predictive factor for biochemical disease-free survival and overall survival following whole-gland salvage HIFU following radiotherapy failure

Background:Treatment options for radio-recurrent prostate cancer are either androgen-deprivation therapy or salvage prostatectomy. Whole-gland high-intensity focussed ultrasound (HIFU) might have a role in this setting.Methods:An independent HIFU registry collated consecutive cases of HIFU. Between 2005 and 2012, we identified 50 men who underwent whole-gland HIFU following histological confirmation of localised disease following prior external beam radiotherapy (2005–2012). No upper threshold was applied for risk category, PSA or Gleason grade either at presentation or at the time of failure. Progression was defined as a composite with biochemical failure (Phoenix criteria (PSA>nadir+2 ng ml−1)), start of systemic therapies or metastases.Results:Median age (interquartile range (IQR)), pretreatment PSA (IQR) and Gleason score (range) were 68 years (64–72), 5.9 ng ml−1 (2.2–11.3) and 7 (6–9), respectively. Median follow-up was 64 months (49–84). In all, 24/50 (48%) avoided androgen-deprivation therapies. Also, a total of 28/50 (56%) achieved a PSA nadir <0.5 ng ml−1, 15/50 (30%) had a nadir ⩾0.5 ng ml−1 and 7/50 (14%) did not nadir (PSA non-responders). Actuarial 1, 3 and 5-year progression-free survival (PFS) was 72, 40 and 31%, respectively. Actuarial 1, 3 and 5-year overall survival (OS) was 100, 94 and 87%, respectively. When comparing patients with PSA nadir <0.5 ng ml−1, nadir ⩾0.5 and non-responders, a statistically significant difference in PFS was seen (P<0.0001). Three-year PFS in each group was 57, 20 and 0%, respectively. Five-year OS was 96, 100 and 38%, respectively. Early in the learning curve, between 2005 and 2007, 3/50 (6%) developed a fistula. Intervention for bladder outlet obstruction was needed in 27/50 (54%). Patient-reported outcome measure questionnaires showed incontinence (any pad-use) as 8/26 (31%).Conclusions:In our series of high-risk patients, in whom 30–50% may have micro-metastases, disease control rates were promising in PSA responders, however, with significant morbidity. Additionally, post-HIFU PSA nadir appears to be an important predictor for both progression and survival. Further research on focal salvage ablation in order to reduce toxicity while retaining disease control rates is required.

Electronic Poster: RTT track: Motion management and adaptive strategiesEP-1844: Clinical introduction of simple adaptive radiotherapy for transitional cell bladder carcinoma

Purpose or Objective Radiotherapy of bladder carcinoma requires substantial CTV-PTV margins to account for day-to-day bladder volume variations. A method to reduce these margins, and hence organs at risk (OAR) dose, is the Plan of the Day method (PotD). In preparation of a PotD approach, we introduced an offline adaptive radiotherapy (ART) procedure based on ConeBeam CT (CBCT) analysis to select individualized adequate margins for the bladder. Tight PTV margins were defined on a retrospective CBCT analysis (N=9, 56 CBCTs) (table 1).

OC-0066: Adaptive cone-beam CT planning improves progression-free survival for I-125 prostate brachytherapy

Material and Methods: This retrospective, single-institution study included 889 patients treated with Iodine-125 brachytherapy alone. All the patients had a baseline cystoscopy before the implant. Data were collected on all subsequent SPC diagnoses. SPC incidences were retrieved for all type of cancers and for cancers close to the radiation field. Interval since the implant was evaluated for potential association to the treatment. Standardized incidence ratios (SIRs) were calculated for all cancers and for bladder cancers and matched with the general population. The absolute excess risk (AER) was expressed in relation to 10000 personsyears in the study. Kaplan-Meier analysis was used to determine the actuarial second malignancy and pelvic malignancy rates and the death from SPC and from any cause

OC-0035: Catheter displacement and dosimetry for single fraction MRI guided focal prostate HDR brachytherapy

not received. SP-0033 Role of target and applicator localisation under treatment delivery conditions T.P. Hellebust Oslo University Hospital The Norwegian Radium Hospital, Department of Medical Physics, Oslo, Norway Since the last 10 years 3D image-guided brachytherapy using CT, MRI, and/or ultrasound (US) has been introduced into clinical practice worldwide enabling conformation of the dose distribution to the target volume and avoidance of high dose to organs at risk (OAR). To be able to optimise the dose distribution in brachytherapy both the anatomy (target volume/OAR) and the applicator(s) should be correctly localised in the images. If the image modality does not enables both of these criteria the dose delivered the patient may be calculated incorrectly. Another important aspect is that the images should reflect the true situation at the time of the treatment. Due to the large dose gradient in brachytherapy, even small changes in the position of the applicator and/or anatomical structures may lead to discrepancies between planned and delivered dose. Usually, this is achieved with as short time as possible between imaging and treatment delivery. The optimal image modality to use is depending on the site to be treated as well as the geometry and the material of the applicator. For cervical cancer MR imaging is the optimal modality to discriminate soft tissue and tumour. Concepts for image guided cervical brachytherapy have been developed by GEC-ESTRO and T2 weighted MR imaging is the preferred modality. In an interobserver study the mean interdelineation distance of around 4 mm were found for the high risk CTV (HR CTV). The impact of these uncertainties for D90 and D100 (dose to 90% and 100% of the volume) were 10% and 19%, respectively. Post-implant dosimetry after permanent prostate seed implantation is usually based on CT imaging. However, MR imaging has superior soft tissue contrast and is some times used nowadays. In an interobserver study the dosimetric consequence of the delineation uncertainty was estimated to be 18% for the prostate D90 when T2 and T1 weighted MR images were used. This figure was increased to 23% when the delineation was done on CT images. Functional MR imaging, such as dynamic-enhanced MR, diffusion weighted imaging and MR spectroscopy, gives the opportunity to image microenvironmental characteristics of a tumour. Specific areas within the target volume with a high burden of disease or with biological characteristics indicating radioresistance may be targeted for higher dose delivery. Even though MR imaging is excellent for target delineation, localisation of the applicators (i.e. the source path) or the seeds could be challenging. Some applicators (e.g. steel applicators or shielded applicators) are not even MR compatible. In general it is easier to visualise the applicator and source(s) in CT images. For rigid MR compatible applicators (e.g. plastic tandem-ring-applicator) so called library applicator files could be used. Then applicator file, including information about the applicator surface dimensions and the source path, can be imported into the MR images and rotated and translated until it matches the images. In some situations the needle tip could be difficult to localise in MR images. Then supplementary imaging could be used (e.g. CT) and image registration should be performed with the aim of matching the applicator geometry and not the bony anatomy. The dosimetric consequences of uncertainties in the applicator localisation are smaller compared to consequences of uncertainties in the target delineation. For the HR CTV D90 an average of 2% change per mm displacement of a ring applicator has been found in all directions. Transrectal US (TRUS) is extensively used in prostate brachytherapy and gives an excellent view of the prostate gland. However, the presence of needles will preclude the image quality. Additionally, localisation of the needle tip could be challenging during needle reconstruction. TRUS-based brachytherapy procedure offer a method for interactive treatment planning and, thus, short time between imaging and treatment delivery. Several groups have developed methods for “in treatment room” imaging with both CT and MR. However, for the latter method, challenges due to non MR compatible equipment is substantial. SP-0034 Importance of treatment delivery verification N . Tselis Klinikum Offenbach GmbH, Radiation Oncology, Offenbach,

34 Proof of concept: MRI Linac als behandeling van patiënten met kleine nierceltumoren

SamenvattingPartiële nefrectomie is de standaardbehandeling voor small renal masses (SRM). Minder invasief zijn radiofrequente ablatie (RFA) en cryoablatie. Focale radiotherapeutische behandeling met MRI-gestuurde bestraling is in ontwikkeling: MRI Linac (MRL).