ROAR-A: re-optimization based Online Adaptive Radiotherapy of anal cancer, a prospective phase II trial protocol.

BACKGROUND: Chemo-radiotherapy with curative intent for anal cancer has high complete remission rates, but acute treatment-related gastrointestinal (GI) toxicity is significant. Toxicity occurs due to irradiation of surrounding normal tissue. Current radiotherapy requires the addition of large planning margins to the radiation field to ensure target coverage regardless of the considerable organ motion in the pelvic region. This increases the irradiated volume and radiation dose to the surrounding normal tissue and thereby toxicity. Online adaptive radiotherapy uses artificial intelligence to adjust the treatment to the anatomy of the day. This allows for the reduction of planning margins, minimizing the irradiated volume and thereby radiation to the surrounding normal tissue.This study examines if cone beam computed tomography (CBCT)-guided oART with daily automated treatment re-planning can reduce acute gastrointestinal toxicity in patients with anal cancer. METHODS/DESIGN: The study is a prospective, single-arm, phase II trial conducted at Copenhagen University Hospital, Herlev and Gentofte, Denmark. 205 patients with local only or locally advanced anal cancer, referred for radiotherapy with or without chemotherapy with curative intent, are planned for inclusion. Toxicity and quality of life are reported with Common Terminology Criteria of Adverse Events and patient-reported outcome questionnaires, before, during, and after treatment. The primary endpoint is a reduction in the incidence of acute treatment-related grade ≥ 2 diarrhea from 36 to 25% after daily online adaptive radiotherapy compared to standard radiotherapy. Secondary endpoints include all acute and late toxicity, overall survival, and reduction in treatment interruptions. RESULTS: Accrual began in January 2022 and is expected to finish in January 2026. Primary endpoint results are expected to be available in April 2026. DISCUSSION: This is the first study utilizing online adaptive radiotherapy to treat anal cancer. We hope to determine whether there is a clinical benefit for the patients, with significant reductions in acute GI toxicity without compromising treatment efficacy. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT05438836. Danish Ethical Committee: H-21028093.

Interim analysis of patient-reported outcome compliance and dosimetry in a phase 3 randomized clinical trial of oesophagus-sparing spinal radiotherapy.

BACKGROUND: The randomized clinical trial ESO-SPARE investigates if oesophagus-sparing radiotherapy (RT) can reduce dysphagia in patients with metastatic spinal cord compression (MSCC). Patient-reported outcome (PRO) is the only follow-up measure. Due to the fragile patient population, low respondent compliance was anticipated. We performed a planned interim analysis of dosimetry and respondent compliance, to ensure that the protocol requirements were met. METHODS: Patients >18 years referred for cervical/thoracic MSCC radiotherapy in 1-10 fractions were included from two centres. Patients were randomized (1:1) to standard RT or oesophagus-sparing RT, where predefined oesophageal dose constraints were prioritized over target coverage. Patients completed a trial diary with daily reports of dysphagia for 5 weeks (PRO-CTC-AE) and weekly quality of life reports for 9 weeks (QLQ-C30, EQ-5D-5L). According to power calculation, 124 patients are needed for primary endpoint analysis. The sample size was inflated to 200 patients to account for the fragile patient population. The co-primary endpoints, peak patient-reported dysphagia, and preserved ability to walk (EQ-5D-5L), are analysed at 5 and 9 weeks, respectively. The interim analysis was conducted 90 days after the inclusion of patient no 100. Respondent compliance was assessed at 5 and 9 weeks. In all RT plans, oesophagus and target doses were evaluated regarding adherence to protocol constraints. RESULTS: From May 2021 to November 2022, 100 patients were included. Fifty-two were randomized to oesophagus-sparing RT. In 23% of these plans, oesophagus constraints were violated. Overall, the dose to both target and oesophagus was significantly lower in the oesophagus-sparing plans. Only 51% and 41% of the patients were evaluable for co-primary endpoint analysis at five and nine weeks, respectively. Mortality and hospitalization rates were significantly larger in patients who completed <4 days PRO questionnaires. CONCLUSION: Compliance was lower than anticipated and interventions to maintain study power are needed.

Single-isocenter stereotactic non-coplanar arc treatment of 200 patients with brain metastases: multileaf collimator size and setup uncertainties.

PURPOSE: The purpose of this study was to evaluate our 2 years' experience with single-isocenter, non-coplanar, volumetric modulated arc therapy (VMAT) for brain metastasis (BM) stereotactic radiosurgery (SRS). METHODS: A total of 202 patients treated with the VMAT SRS solution were analyzed retrospectively. Plan quality was assessed for 5 mm (120) and 2.5 mm (high-definition, HD) central leaf width multileaf collimators (MLCs). For BMs at varying distances from the plan isocenter, the geometric offset from the ideal position for two image-guided radiotherapy workflows was calculated. In the workflow with ExacTrac (BrainLAB, München, Germany; W­ET), patient positioning errors were corrected at each couch rotation. In the workflow without ExacTrac (W-noET), only the initial patient setup correction was considered. The dose variation due to rotational errors was simulated for multiple-BM plans with the HD-MLC. RESULTS: Plan conformity and quality assurance were equivalent for plans delivered with the two MLCs while the HD-MLC plans provided better healthy brain tissue (BmP) sparing. 95% of the BMs had residual intrafractional setup errors ≤ 2 mm for W­ET and 68% for W­noET. For small BM (≤1 cc) situated >3 cm from the plan isocenter, the dose received by 95% of the BM decreased in median (interquartile range) by 6.3% (2.8-8.8%) for a 1-degree rotational error. CONCLUSION: This study indicates that the HD-MLC is advantageous compared to the 120-MLC for sparing healthy brain tissue. When a 2-mm margin is applied, W­noET is sufficient to ensure coverage of BM situated ≤ 3 cm of the plan isocenter, while for BM further away, W­ET is recommended.

Analysis of early respiratory-related mortality after radiation therapy of non-small-cell lung cancer: feasibility of automatic data extraction for dose-response studies.

Purpose: To examine the feasibility of automatic data extraction from clinical radiation therapy (RT) databases at four hospitals to investigate the impact of mean lung dose (MLD) and age on the risk of early respiratory-related death and early overall death for patients treated with RT for non-small-cell lung cancer (NSCLC).Material and methods: We included adult patients with NSCLC receiving curatively intended RT between 2002 and 2017 at four hospitals. A script was developed to automatically extract RT-related data. The cause of death for patients deceased within 180 days of the start of RT was retrospectively assessed. Using logistic regression, the risks of respiratory-related death and of overall death within 90 and 180 days were investigated using MLD and age as variables.Results: Altogether, 1785 patients were included in the analysis of early overall mortality and 1655 of early respiratory-related mortality. The respiratory-related mortalities within 90 and 180 days were 0.9% (15/1655) and 3.6% (60/1655). The overall mortalities within 90 and 180 days were 2.5% (45/1785) and 10.6% (190/1785). Higher MLD and older age were associated with an increased risk of respiratory-related death within 180 days and overall death within 90 and 180 days (all p<.05). For example, the risk of respiratory-related death within 180 days and their 95% confidence interval for patients aged 65 and 75 years with MLDs of 20 Gy was according to our logistic model 3.8% (2.6-5.0%) and 7.7% (5.5-10%), respectively.Conclusions: Automatic data extraction was successfully used to pool data from four hospitals. MLD and age were associated with the risk of respiratory-related death within 180 days of the start of RT and with overall death within 90 and 180 days. A model quantifying the risk of respiratory-related death within 180 days was formulated.

Surface guided radiotherapy (SGRT) improves breast cancer patient setup accuracy.

PURPOSE: The purpose of the study was to investigate if surface guided radiotherapy (SGRT) can decrease setup deviations for tangential and locoregional breast cancer patients compared to conventional laser-based setup (LBS). MATERIALS AND METHODS: Both tangential (63 patients) and locoregional (76 patients) breast cancer patients were enrolled in this study. For LBS, the patients were positioned by aligning skin markers to the room lasers. For the surface based setup (SBS), an optical surface scanning system was used for daily setup using both single and three camera systems. To compare the two setup methods, the patient position was evaluated using verification imaging (field images or orthogonal images). RESULTS: For both tangential and locoregional treatments, SBS decreased the setup deviation significantly compared to LBS (P < 0.01). For patients receiving tangential treatment, 95% of the treatment sessions were within the clinical tolerance of ≤ 4 mm in any direction (lateral, longitudinal or vertical) using SBS, compared to 84% for LBS. Corresponding values for patients receiving locoregional treatment were 70% and 54% for SBS and LBS, respectively. No significant difference was observed comparing the setup result using a single camera system or a three camera system. CONCLUSIONS: Conventional laser-based setup can with advantage be replaced by surface based setup. Daily SGRT improves patient setup without additional imaging dose to breast cancer patients regardless if a single or three camera system was used.

Determining intrafractional prostate motion using four dimensional ultrasound system.

BACKGROUND: In prostate radiotherapy, it is essential that the prostate position is within the planned volume during the treatment delivery. The aim of this study is to investigate whether intrafractional motion of the prostate is of clinical consequence, using a novel 4D autoscan ultrasound probe. METHODS: Ten prostate patients were ultrasound (US) scanned at the time of CT imaging and once a week during their course of radiotherapy treatment in an ethics-approved study, using the transperineal Clarity autoscan system (Clarity®, Elekta Inc., Stockholm, Sweden). At each US scanning session (fraction) the prostate was monitored for 2 to 2.5 min, a typical beam-on time to deliver a RapidArc® radiotherapy fraction. The patients were instructed to remain motionless in supine position throughout the US scans. They were also requested to comply with a bladder-filling protocol. In total, 51 monitoring curves were acquired. Data of the prostate motion in three orthogonal directions were analyzed. Finally, the BMI value was calculated to investigate correlation between BMI and the extent of prostate displacement. RESULTS: The patients were cooperative, despite extra time for applying the TPUS scan. The mean (±1SD) of the maximal intrafractional displacements were [mm]; I(+)/S: (0.2 ± 0.9); L(+)/R: (-0.2 ± 0.8); and A(+)/P: (-0.2 ± 1.1), respectively. The largest displacement was 2.8 mm in the posterior direction. The percentage of fractions with displacements larger than 2.0 mm was 4 %, 2 %, and 10 % in the IS, LR, and AP directions, respectively. The mean of the maximal intrafractional Euclidean distance (3D vector) was 0.9 ± 0.6 mm. For 12 % of the fractions the maximal 3D vector displacements were larger than 2.0 mm. At only two fractions (4 %) displacements larger than 3.0 mm were observed. There was no correlation between BMI and the extent of the prostate displacement. CONCLUSIONS: The prostate intrafractional displacement is of no clinically consequence for treatment times in the order of 2 - 2.5 min, which is typical for a RapidArc radiotherapy fraction. However, prostate motion should be considered for longer treatment times eg if applying conventional or IMRT radiotherapy.

Prostate displacement during transabdominal ultrasound image-guided radiotherapy assessed by real-time four-dimensional transperineal monitoring.

BACKGROUND: Transabdominal ultrasound (TAUS) imaging is currently available for localizing the prostate in daily image-guided radiotherapy (IGRT). The aim of this study was to determine the induced prostate displacement during such TAUS imaging. The prostate displacement was monitored using a novel transperineal four-dimensional (4D) US (TPUS) system. MATERIAL AND METHODS: Ten prostate cancer patients, with a mean age of 68 years (58/76), were US scanned in the computed tomography (CT) room utilizing the Clarity 4D TPUS monitoring system. The patients were asked to comply with a moderate bladder filling protocol. After US-CT fusion, the prostate volume was delineated and used as a reference for weekly US imaging in the treatment room. Immediately after treatment delivery the TPUS monitoring system was set up. During real-time monitoring of the prostate, a conventional 2D probe was applied to simulate a TAUS scan. The time dependent prostate displacements induced by the 2D probe pressure were recorded for the three orthogonal directions. In total 42 monitoring curves with applied 2D probe were recorded. RESULTS: Data analysis of 42 US scans resulted in pressure induced prostate displacements with mean values (± 1 SD) (mm); inferior (+)-superior (I/S): (-0.1 ± 0.8); left (+)-right (L/R): (0.2 ± 0.7); and anterior (+)-posterior (A/P): (-0.1 ± 1.0). The majority of the displacements were within 1-2 mm. Only two scans (5%) (A/P direction) and 16% of Euclidean distances were larger than 2.0 mm. The largest displacement was 2.6 mm in the anterior direction. CONCLUSION: The novel 4D TPUS system was capable of tracking and recording the prostate positional displacements. The study demonstrated that the prostate induced displacements due to applied TAUS IGRT are small, and in most cases clinically irrelevant to prostate radiotherapy.

Adaptation requirements due to anatomical changes in free-breathing and deep-inspiration breath-hold for standard and dose-escalated radiotherapy of lung cancer patients.

BACKGROUND: Radiotherapy of lung cancer patients is subject to uncertainties related to heterogeneities, anatomical changes and breathing motion. Use of deep-inspiration breath-hold (DIBH) can reduce the treated volume, potentially enabling dose-escalated (DE) treatments. This study was designed to investigate the need for adaptation due to anatomical changes, for both standard (ST) and DE plans in free-breathing (FB) and DIBH. MATERIAL AND METHODS: The effect of tumor shrinkage (TS), pleural effusion (PE) and atelectasis was investigated for patients and for a CIRS thorax phantom. Sixteen patients were computed tomography (CT) imaged both in FB and DIBH. Anatomical changes were simulated by CT information editing and re-calculations, of both ST and DE plans, in the treatment planning system. PE was systematically simulated by adding fluid in the dorsal region of the lung and TS by reduction of the tumor volume. RESULTS: Phantom simulations resulted in maximum deviations in mean dose to the GTV-T (GTV-T) of -1% for 3 cm PE and centrally located tumor, and + 3% for TS from 5 cm to 1 cm diameter for an anterior tumor location. For the majority of the patients, simulated PE resulted in a decreasing GTV-T with increasing amount of fluid and increasing GTV-T for decreasing tumor volume. Maximum change in GTV-T of -3% (3 cm PE in FB for both ST and DE plans) and + 10% (2 cm TS in FB for DE plan) was observed. Large atelectasis reduction increased the GTV-T with 2% for FB and had no effect for DIBH. CONCLUSION: Phantom simulations provided potential adaptation action levels for PE and TS. For the more complex patient geometry, individual assessment of the dosimetric impact is recommended for both ST and DE plans in DIBH as well as in FB. However, DIBH was found to be superior over FB for DE plans, regarding robustness of GTV-T to TS.

Artificial intelligence-generated targets and inter-observer variation in online adaptive radiotherapy of bladder cancer.

Background and purpose: Daily target re-delineation in online adaptive radiotherapy (oART) introduces uncertainty. The aim of this study was to evaluate artificial intelligence (AI) generated contours and inter-observer target variation among radiotherapy technicians in cone-beam CT (CBCT) guided oART of bladder cancer. Materials and methods: For each of 10 consecutive patients treated with oART for bladder cancer, one CBCT was randomly selected and retrospectively included. The bladder (CTV-T) was AI-segmented (CTV-TAI). Seven radiotherapy technicians independently reviewed and edited CTV-TAI, generating CTV-TADP. Contours were benchmarked against a ground truth contour (CTV-TGT) delineated blindly from scratch. CTV-TADP and CTV-TAI were compared to CTV-TGT using volume, dice similarity coefficient, and bidirectional local distance. Dose coverage (D99%>95 %) of CTV-TGT was evaluated for treatment plans optimized for CTV-TAI and CTV-TADP with clinical margins. Inter-observer variation among CTV-TADP was assessed using coefficient of variation and generalized conformity index. Results: CTV-TGT ranged from 48.7 cm3 to 211.6 cm3. The median [range] volume difference was 4.5 [-17.8, 42.4] cm3 for CTV-TADP and -15.5 [-54.2, 4.3] cm3 for CTV-TAI, compared to CTV-TGT. Corresponding dice similarity coefficients were 0.87 [0.71, 0.95] and 0.84 [0.64, 0.95]. CTV-TGT was adequately covered in 68/70 plans optimized on CTV-TADP and in 6/10 plans optimized on CTV-TAI with clinical margins. The median [range] coefficient of variation was 0.08 [0.05, 0.11] and generalized conformity index was 0.78 [0.71, 0.88] among CTV-TADP. Conclusions: Target re-delineation in CBCT-guided oART of bladder cancer demonstrated non-isotropic inter-observer variation. Manual adjustment of AI-generated contours was necessary to cover ground truth targets.

MR-guided stereotactic radiotherapy of infra-diaphragmatic oligometastases: Evaluation of toxicity and dosimetric parameters.

BACKGROUND AND PURPOSE: The SOFT trial is a prospective, multicenter, phase 2 trial investigating magnetic resonance (MR)-guided stereotactic ablative radiotherapy (SABR) for abdominal, soft tissue metastases in patients with oligometastatic disease (OMD) (clinicaltrials.gov ID NCT04407897). We present the primary endpoint analysis of 1-year treatment-related toxicity (TRAE). MATERIALS AND METHODS: Patients with up to five oligometastases from non-hematological cancers were eligible for inclusion. A risk-adapted strategy prioritized fixed organs at risk (OAR) constraints over target coverage. Fractionation schemes were 45-67.5 Gy in 3-8 fractions. The primary endpoint was grade ≥ 4 TRAE within 12 months post-SABR. The association between the risk of gastrointestinal (GI) toxicity and clinical and dosimetric parameters was tested using a normal tissue complication probability model. RESULTS: We included 121 patients with 147 oligometastatic targets, mainly located in the liver (41 %), lymph nodes (35 %), or adrenal glands (14 %). Nearly half of all targets (48 %, n = 71) were within 10 mm of a radiosensitive OAR. No grade 4 or 5 TRAEs, 3.5 % grade 3 TRAEs, and 43.7 % grade 2 TRAEs were reported within the first year of follow-up. We found a significant association between grade ≥ 2 GI toxicity and the parameters GI OAR D0.1cc, D1cc, and D20cc. CONCLUSION: In this phase II study of MR-guided SABR of oligometastases in the infra-diaphragmatic region, we found a low incidence of toxicity despite half of the lesions being within 10 mm of a radiosensitive OAR. GI OAR D0.1cc, D1cc, and D20cc were associated with grade ≥ 2 GI toxicity.

Impact of geometric correction on echo-planar imaging-based apparent diffusion coefficient maps for abdominal radiotherapy.

Objective. The apparent diffusion coefficient (ADC) extracted from diffusion-weighted magnetic resonance imaging (DWI) is a potential biomarker in radiotherapy (RT). DWI is often implemented with an echo-planar imaging (EPI) read-out due to speed, but unfortunately low geometric accuracy follows. This study aimed to investigate the influence of geometric distortions on the ADCs extracted from the gross tumor volume (GTV) and on the shape of the GTV in abdominal EPI-DWI.Approach. Twenty-one patients had EPI-DWI scans on a 1.5 T MRI sim before treatment and on a 1.5 T MRI-Linac at one of the first treatment fractions. Off-resonance correction with and without eddy current correction were applied to ADC maps. The clinical GTVs were deformed based on the same (but inverted) corrections to assess the local-regional geometric influence of distortions. Mean surface distance (MSD), Hausdorff distance (HD), and Dice similarity coefficient (DSC) were calculated to compare the original and distorted GTVs, and ADC values were calculated based on a mono-exponential model. Phantom measurements were performed to validate the applied correction method.Main results. The median (range) ADC change within the GTV after full distortion correction was 1.3% (0.02%-6.9%) for MRI-Sim and 1.5% (0.1%-6.4%) for MRI-Linac. The additional effect of the eddy current correction was small in both systems. The median (range) MSD, HD, and DSC comparing the original and off-resonance distorted GTVs for all patients were 0.43 mm (0.11-0.94 mm), 4.00 mm (1.00-7.81 mm) and 0.93 (0.82-0.99), respectively.Significance. Overall effect of distortion correction was small in terms of derived ADC values, indicating that distortion correction is unimportant for prediction of outcomes based on ADC. However, large local geometric changes occurred after off-resonance distortion correction for some patients, suggesting that if the spatial information from ADC maps is to be used for dose painting strategies, corrections should be applied.

Nivolumab with or without Ipilimumab Combined with Stereotactic Body Radiotherapy in Patients with Metastatic Biliary Tract Cancer: A Randomized Phase 2 Study.

PURPOSE: The purpose of this study was to evaluate the clinical benefits of nivolumab with/without ipilimumab combined with stereotactic body radiotherapy (SBRT) in patients with pretreated metastatic biliary tract cancer (mBTC). PATIENTS AND METHODS: The study was a phase 2 randomized trial with Simon's optimal two-stage design requiring 36 evaluable patients per group after second stage. Sixty-one patients were included from September 2018 to January 2022 and randomized (1:1) to receive SBRT (15 Gy × 1 on day 1 to a primary or metastatic lesion) and nivolumab (3 mg/kg intravenously on day 1 and every 2 weeks) with/without ipilimumab (1 mg/kg intravenously on day 1 and every 6 weeks). Primary endpoint was clinical benefit rate (CBR), defined as the percentage of patients with complete response, partial response, or stable disease. Decision to continue accrual into the second stage depended on the CBR from the first stage. RESULTS: Forty-two patients received SBRT/nivolumab/ipilimumab with a CBR of 31.0% [95% confidence interval (CI), 17.6-47.1]. Five patients (11.9%) achieved partial response with median duration of 4.4 months (range, 1.1-21.5). Nineteen patients received SBRT/nivolumab. This group was closed after the initial stage based on a CBR of 10.5% (95% CI, 1.3-33.1). Adverse events were graded with National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. Grade ≥3 treatment-related adverse events occurred in 13 (31%) and 3 (16%) patients in the SBRT/nivolumab/ipilimumab and SBRT/nivolumab groups, respectively. One patient died from immune-related hepatitis in the SBRT/nivolumab/ipilimumab group. CONCLUSIONS: Combining SBRT, nivolumab, and ipilimumab is well tolerated, feasible, and shows response in a subgroup of patients with mBTC.

Interfractional dose accumulation for MR-guided liver SBRT: Variation among algorithms is highly patient- and fraction-dependent.

BACKGROUND AND PURPOSE: Daily plan adaptations could take the dose delivered in previous fractions into account. Due to high dose delivered per fraction, low number of fractions, steep dose gradients, and large interfractional organ deformations, this might be particularly important for liver SBRT. This study investigates inter-algorithm variation of interfractional dose accumulation for MR-guided liver SBRT. MATERIALS AND METHODS: We assessed 27 consecutive MR-guided liver SBRT treatments of 67.5 Gy in three (n = 15) or 50 Gy in five fractions (n = 12), both prescribed to the GTV. We calculated fraction doses on daily patient anatomy, warped these doses to the simulation MRI using seven different algorithms, and accumulated the warped doses. Thus, we obtained differences in planned doses and warped or accumulated doses for each algorithm. This enabled us to calculate the inter-algorithm variations in warped doses per fraction and in accumulated doses per treatment course. RESULTS: The four intensity-based algorithms were more consistent with planned PTV dose than affine or contour-based algorithms. The mean (range) variation of the dose difference for PTV D95% due to dose warping by these intensity-based algorithms was 10.4 percentage points (0.3 to 43.7) between fractions and 8.6 (0.3 to 24.9) between accumulated treatment doses. As seen by these ranges, the variation was very dependent on the patient and the fraction being analyzed. Nevertheless, no correlations between patient or plan characteristics on the one hand and inter-algorithm dose warping variation on the other hand was found. CONCLUSION: Inter-algorithm dose accumulation variation is highly patient- and fraction-dependent for MR-guided liver SBRT. We advise against trusting a single algorithm for dose accumulation in liver SBRT.

Introducing multiple treatment plan-based comparison to investigate the performance of gantry angle optimisation (GAO) in IMRT for head and neck cancer.

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate the performance of gantry angle optimisation (GAO) compared to equidistant beam geometry for two inverse treatment planning systems (TPSs) by utilising the information obtained from a range of treatment plans. MATERIAL AND METHODS: The comparison was based on treatment plans generated for four different head and neck (H&N) cancer cases using two inverse treatment planning systems (TPSs); Varian Eclipse™ representing dynamic MLC intensity modulated radiotherapy (IMRT) and Oncentra® Masterplan representing segmented MLC-based IMRT. The patient cases were selected on the criterion of representing different degrees of overlap between the planning target volume (PTV) and the investigated organ at risk, the ipsilateral parotid gland. For each case, a number of 'Pareto optimal' plans were generated in order to investigate the trade-off between the under-dosage to the PTV (V(PTV,D < 95%)) or the decrease in dose homogeneity (D(5)-D(95)) to the PTV as a function of the mean absorbed dose to the ipsilateral parotid gland ((parotid gland)). RESULTS: For the Eclipse system, GAO had a clear advantage for the cases with smallest overlap (Cases 1 and 2). The set of data points, representing the underlying trade-offs, generated with and without using GAO were, however, not as clearly separated for the cases with larger overlap (Cases 3 and 4). With the OMP system, the difference was less pronounced for all cases. The Eclipse GAO displays the most favourable trade-off for all H&N cases. CONCLUSIONS: We have found differences in the effectiveness of GAO as compared to equidistant beam geometry, in terms of handling conflicting trade-offs for two commercial inverse TPSs. A comparison, based on a range of treatment plans, as developed in this study, is likely to improve the understanding of conflicting trade-offs and might apply to other thorough comparison techniques.

Online adaptive radiotherapy of anal cancer: Normal tissue sparing, target propagation methods, and first clinical experience.

BACKGROUND AND PURPOSE: Online adaptive radiotherapy (oART) potentially spares OARs as PTV margins are reduced. This study evaluates dosimetric benefits, compared to standard non-adaptive radiotherapy (non-ART), target propagation methods, and first clinical treatments of CBCT-guided oART of anal cancer. MATERIALS AND METHODS: Treatment plans with standard non-ART and reduced oART PTV margins were retrospectively generated for 23 consecutive patients with anal cancer. For five patients randomly selected among the 23 patients, weekly CBCT-guided oART sessions were simulated, where the targets were either deformed or rigidly propagated. Preferred target propagation method and dose to OARs were evaluated. Ten consecutive patients with anal cancer were treated with CBCT-guided oART. Target propagation methods and oART procedure time were evaluated. RESULTS: For the retrospective treatment plans, oART resulted in median reductions in bowel bag V45Gy of 11.4 % and bladder V35Gy of 16.1%. Corresponding values for the simulated sessions were 7.5% and 27.1%. In the simulated sessions, 35% of all targets were deformed while 65% were rigidly propagated. Manual editing and rigid propagation were necessary to obtain acceptable target coverage. In the clinical treatments, the primary and some elective targets were rigidly propagated, while other targets were deformed. The median oART procedure time, measured from CBCT acquisition to completion of plan review and QA, was 23 min. CONCLUSIONS: Simulated oART reduced the dose to OARs, indicating potential reduction in toxicity. Rigid propagation of targets was necessary to reduce the need for manual edit. Clinical treatments demonstrated that oART of anal cancer is feasible but time-consuming.

Online adaptive radiotherapy of urinary bladder cancer with full re-optimization to the anatomy of the day: Initial experience and dosimetric benefits.

BACKGROUND AND PURPOSE: Online adaptive radiotherapy (oART) potentially reduces the dose to organs at risk (OARs) as the planning target volume (PTV) margins are reduced compared to a non-adaptive approach (non-ART). This study evaluates the feasibility and dosimetric impact of cone-beam computed tomography (CBCT)-guided oART of urinary bladder cancer for the first patients treated, using patient-specific margins. MATERIALS AND METHODS: Sixteen consecutive patients with muscle-invasive bladder cancer received two or more (median = 23) fractions as oART, and remaining fractions as non-ART. The non-ART fractions were delivered with standard population-based margins, while reduced patient-specific margins based on intra-fractional variations extracted from 2-4 fractions were applied to the primary PTV (PTV-T) during the oART fractions. Target volume and coverage, and dose to OARs were compared between non-ART and oART plans, and the oART procedure time was recorded. RESULTS: In total, 297/512 fractions were delivered as oART with full re-optimization to the anatomy of the day. The median (interquartile range, IQR) oART procedure time, measured from the end of CBCT generation to completion of plan review, and quality assurance was 13.9 (11.9;16.6) min. The median (IQR) volume reduction in PTV-T volume was 33.9 (24.2;45.0)%, comparing oART and non-ART plans, resulting in median (IQR) reductions in bowel bag V45Gy of 18.8 (12.7;27.9)% and rectum V50Gy of 70.7 (35.9;94.8)%. By re-optimizing the plan to the daily anatomy, full target coverage was achieved at all oART fractions. CONCLUSIONS: oART resulted in large reductions in treatment volumes and doses to OARs, compared to non-ART, while ensuring target coverage. This indicates potential reductions in gastrointestinal toxicity.

Robust extraction of biological information from diffusion-weighted magnetic resonance imaging during radiotherapy using semi-automatic delineation.

Background and purpose: Diffusion-Weighted Magnetic Resonance imaging (DWI) quantifies water mobility through the Apparent Diffusion Coefficient (ADC), a promising radiotherapy response biomarker. ADC measurements depend on manual delineation of a region of interest, a time-consuming and observer-dependent process. Here, the aim was to introduce and test the performance of a new, semi-automatic delineation tool (SADT) for ADC calculation within the viable region of the tumour. Materials and methods: Thirty patients with rectal cancer were scanned with DWI before radiotherapy (RT) (baseline) and two weeks into RT (week 2). The SADT was based on intensities in b=1100 s mm-2 DWI and derived ADC maps. ADC values measured using the SADT and manual delineations were compared using Bland-Altman- and correlation analyses. Delineations were repeated to assess intra-observer variation, and repeatability was estimated using repeated DWI scans. Results: ADC measured using the SADT and manual delineation showed strong and moderate correlation at baseline and week 2, respectively, with the SADT measuring systematically smaller values. Intra-observer ADC variation was slightly smaller for the SADT compared to manual delineation both at baseline, [-0.00; 0.03] vs. [-0.02; 0.04] 10-3 mm2 s-1, and week 2, [-0.01; 0.00] vs. [-0.04; 0.07] 10-3 mm2 s-1 (68.3% limits of agreement). The ADC change between baseline and week 2 was larger than the ADC uncertainty ( ± 0.04 · 10-3 mm2 s-1) in all cases except one. Conclusion: The presented SADT showed performance comparable to manual expert delineation, and with sufficient consistency to allow extraction of potential biological information from the viable tumour.

Gating has a negligible impact on dose delivered in MRI-guided online adaptive radiotherapy of prostate cancer.

BACKGROUND AND PURPOSE: MR-guided radiotherapy (MRgRT) allows real-time beam-gating to compensate for intra-fractional target position variations. This study investigates the dosimetric impact of beam-gating and the impact of PTV margin on prostate coverage for prostate cancer patients treated with online-adaptive MRgRT. MATERIALS AND METHODS: 20 consecutive prostate cancer patients were treated with online-adaptive MRgRT SBRT with 36.25 Gy in 5 fractions (PTV D95% ≥ 95% (N = 5) and PTV D95% ≥ 100% (N = 15)). Sagittal 2D cine MRIs were used for gating on the prostate with a 3 mm expansion as the gating window. We computed motion-compensated dose distributions for (i) all prostate positions during treatment (simulating non-gated treatments) and (ii) for prostate positions within the gating window (gated treatments). To evaluate the impact of PTV margin on prostate coverage, we simulated coverage with smaller margins than clinically applied both for gated and non-gated treatments. Motion-compensated fraction doses were accumulated and dose metrics were compared. RESULTS: We found a negligible dosimetric impact of beam-gating on prostate coverage (median of 0.00 Gy for both D95% and Dmean). For 18/20 patients, prostate coverage (D95% ≥ 100%) would have been ensured with a prostate-to-PTV margin of 3 mm, even without gating. The same was true for all but one fraction. CONCLUSION: Beam-gating has negligible dosimetric impact in online-adaptive MRgRT of prostate cancer. Accounting for motion, the clinically used prostate-to-PTV margin could potentially be reduced from 5 mm to 3 mm for 18/20 patients.