Rectal Motion in Patients Receiving Preoperative Radiotherapy for Carcinoma of the Rectum

Dealing with rectum motion during radiotherapy: How can we anticipate it?

Introduction

Intra- and inter-fraction rectum motion is important for pelvic radiotherapy (RT). This study assesses how RT session duration, the presence or the absence of an intra-rectal tumour, and the distance from the anorectal junction (ARJd) impact rectal motion.

Materials and methods

Analyses used cone-beam computed tomographies (CBCTs) from RT patients treated for rectal and prostate cancer. Three structures were evaluated: (1) the entire rectum in patients without a rectal tumour (RectumProstate); (2) the non-invaded portion (RectumRectum) and (3) the tumour-invaded portion (RectumTumour) in rectal cancer patients.Intrafraction motion was assessed using the Hausdorff distance 95% and the Mean distance-to-agreement between structures delineated on the first CBCT and the 2 subsequent CBCTs within a same RT session. Interfraction motion was quantified by comparing structures delineated on the planning-CT and the first CBCT of each session.Linear mixed model evaluated rectum motion in relation to time, tumour presence, and ARJd, respectively.

Results

We included 10 patients with and 10 without rectal cancer, collecting 385 CBCTs. A significant correlation (p < 0.05) between rectum motion and RT session duration was found. Intrafraction motion was significantly higher in prostate cancer patients (RectumProstate motion > RectumRectum and RectumTumour, p < 0.01). For interfraction motion, only the mean distance to agreement was significantly higher for RectumProstate (p < 0.05). Motion increased significantly with ARJd for all three structures (p < 0.001).

Conclusions

Session duration, absence of a tumour, and ARJd are associated with larger intra- and interfraction rectal motion. This highlights the need for tailored RT treatment, including online-adaptive RT, to manage intra- and interfraction variations. Rectal motion should be handled differently for patients with prostate cancer and those with rectal cancer.

Individual lymph node position variation for rectal cancer patients treated with long course chemoradiotherapy

Background and purpose

Delivery of high precision radiotherapy lymph node boosts requires detailed information on the interfraction positional variation of individual lymph nodes. In this study we characterized interfraction positional shifts of suspected malignant lymph nodes for rectal cancer patients receiving long course radiotherapy. Furthermore, we investigated parameters which could affect the magnitude of the position variation.

Materials and Methods

Fourteen patients from a prospective clinical imaging study with a total of 61 suspected malignant lymph nodes in the mesorectum, presacral, and lateral regions, were included. The primary gross tumor volume (GTVp) and all suspected malignant lymph nodes were delineated on six magnetic resonance imaging scans per patient. Positional variation was calculated as systematic and random errors, based on shifts of center-of-mass, and estimated relative to either bony structures or the GTVp using a hierarchical linear mixed model.

Results

Depending on location and direction, systematic and random variations (relative to bony structures) were within 0.6-2.8 mm and 0.6-2.9 mm, respectively. Systematic and random variations increased when evaluating position relative to GTVp (median increase of 0.6 mm and 0.5 mm, respectively). Correlations with scan time-point and relative bladder volume were found in some directions.

Conclusions

Using linear mixed modeling, we estimated systematic and random positional variation for suspected malignant lymph nodes in rectal cancer patients treated with long course radiotherapy. Statistically significant correlations of the magnitude of the lymph node shifts were found related to scan time-point and relative bladder volume.

Feasibility of artificial intelligence-driven interfractional monitoring of organ changes by mega-voltage computed tomography in intensity-modulated radiotherapy of prostate cancer

PURPOSE

High-dose radiotherapy (RT) for localized prostate cancer requires careful consideration of target position changes and adjacent organs-at-risk (OARs), such as the rectum and bladder. Therefore, daily monitoring of target position and OAR changes is crucial in minimizing interfractional dosimetric uncertainties. For efficient monitoring of the internal condition of patients, we assessed the feasibility of an auto-segmentation of OARs on the daily acquired images, such as megavoltage computed tomography (MVCT), via a commercial artificial intelligence (AI)-based solution in this study.

MATERIALS AND METHODS

We collected MVCT images weekly during the entire course of RT for 100 prostate cancer patients treated with the helical TomoTherapy system. Based on the manually contoured body outline, the bladder including prostate area, and rectal balloon regions for the 100 MVCT images, we trained the commercially available fully convolutional (FC)-DenseNet model and tested its auto-contouring performance.

RESULTS

Based on the optimally determined hyperparameters, the FC-DenseNet model successfully auto-contoured all regions of interest showing high dice similarity coefficient (DSC) over 0.8 and a small mean surface distance (MSD) within 1.43 mm in reference to the manually contoured data. With this well-trained AI model, we have efficiently monitored the patient's internal condition through six MVCT scans, analyzing DSC, MSD, centroid, and volume differences.

CONCLUSION

We have verified the feasibility of utilizing a commercial AI-based model for auto-segmentation with low-quality daily MVCT images. In the future, we will establish a fast and accurate auto-segmentation and internal organ monitoring system for efficiently determining the time for adaptive replanning.

Understanding the Benefit of Magnetic Resonance-guided Adaptive Radiotherapy in Rectal Cancer Patients: a Single-centre Study

AIMS

Neoadjuvant chemoradiotherapy followed by surgery is the mainstay of treatment for patients with rectal cancer. Standard clinical target volume (CTV) to planning target volume (PTV) margins of 10 mm are used to accommodate inter- and intrafraction motion of target. Treating on magnetic resonance-integrated linear accelerators (MR-linacs) allows for online manual recontouring and adaptation (MRgART) enabling the reduction of PTV margins. The aim of this study was to investigate motion of the primary CTV (CTVA; gross tumour volume and macroscopic nodes with 10 mm expansion to cover microscopic disease) in order to develop a simultaneous integrated boost protocol for use on MR-linacs.

MATERIALS AND METHODS

Patients suitable for neoadjuvant chemoradiotherapy were recruited for treatment on MR-linac using a two-phase technique; only the five phase 1 fractions on MR-linac were used for analysis. Intrafraction motion of CTVA was measured between pre-treatment and post-treatment MRI scans. In MRgART, isotropically expanded pre-treatment PTV margins from 1 to 10 mm were rigidly propagated to post-treatment MRI to determine overlap with 95% of CTVA. The PTV margin was considered acceptable if overlap was >95% in 90% of fractions. To understand the benefit of MRgART, the same methodology was repeated using a reference computed tomography planning scan for pre-treatment imaging.

RESULTS

In total, nine patients were recruited between January 2018 and December 2020 with T3a-T4, N0-N2, M0 disease. Forty-five fractions were analysed in total. The median motion across all planes was 0 mm, demonstrating minimal intrafraction motion. A PTV margin of 3 and 5mm was found to be acceptable in 96 and 98% of fractions, respectively. When comparing to the computed tomography reference scan, the analysis found that PTV margins to 5 and 10 mm only acceptably covered 51 and 76% of fractions, respectively.

CONCLUSION

PTV margins can be reduced to 3-5 mm in MRgART for rectal cancer treatment on MR-linac within an simultaneous integrated boost protocol.

Mesorectal motion evaluation in rectal cancer MR-guided radiotherapy: an exploratory study to quantify treatment margins

BACKGROUND

Mesorectal motion (MM) is a source of uncertainty during neoadjuvant chemoradiotherapy (nCRT) delivery for locally advanced rectal cancer (LARC). Previously published experiences using cone-beam computed tomography imaging have already described significant movement. Aim of this analysis is to assess inter-fraction MM using the higher tissue contrast provided by hybrid magnetic resonance imaging (MRI) in LARC patients (pts) treated with MRI guided radiation therapy (MRgRT).

METHODS

The total mesorectum, its superior (Msup), middle (Mmid) and lower (Mlow) regions were contoured on the positioning MRIs acquired on simulation day and on each treatment day. Six PTVs were obtained adding 0.5, 0.7, 1, 1.3, 1.5 and 2 cm margin to the whole mesorectum, starting from the simulation MRI. Margins including 95% of the mesorectal structures during whole treatment in 95% of patients (pts) were considered adequate.

RESULTS

A total number of 312 fractions of 12 consecutive pts was retrospectively analyzed. The different mesorectum regions show specific motion variability. In particular, Msup shows larger variability in left, right and anterior directions, while the Mlow in caudal and posterior ones. The anterior margin is significantly larger in the Msup than in the other regions.

CONCLUSION

Different mesorectal regions move differently throughout the radiotherapy treatment, with the largest MM in the Msup anterior direction. Asymmetrical margins are recommended.

Correcting rotational error in rectal cancer radiation therapy: Can planning target volume margins be safely reduced?

INTRODUCTION

The magnitude and impact of rotational error is unclear in rectal cancer radiation therapy. This study evaluates rotational errors in rectal cancer patients, and investigates the feasibility of planning target volume (PTV) margin reduction to decrease organs at risk (OAR) irradiation.

METHODS

In this study, 10 patients with rectal cancer were retrospectively selected. Rotational errors were assessed through image registration of daily cone beam computed tomography (CBCT) and planning CT scans. Two reference treatment plans (TPR ) with PTV margins of 5 mm and 10 mm were generated for each patient. Pre-determined rotational errors (±1°, ±3°, ±5°) were simulated to produce six manipulated treatment plans (TPM ) from each TPR . Differences in evaluated dose-volume metrics between TPR and TPM of each rotation were compared using Wilcoxon Signed-Rank Test. Clinical compliance was investigated for statistically significant dose-volume metrics.

RESULTS

Mean rotational errors in pitch, roll and yaw were -0.72 ± 1.81°, -0.04 ± 1.36° and 0.38 ± 0.96° respectively. Pitch resulted in the largest potential circumferential displacement of clinical target volume (CTV) at 1.42 ± 1.06 mm. Pre-determined rotational errors resulted in statistically significant differences in CTV, small bowel, femoral heads and iliac crests (P < 0.05). Only small bowel and iliac crests failed clinical compliance, with majority in the PTV 10 mm margin group.

CONCLUSION

Rotational errors affected clinical compliance for OAR dose but exerted minimal impact on CTV coverage even with reduced PTV margins. Both PTV margin reduction and rotational correction decreased irradiated volume of OAR. PTV margin reduction to 5 mm is feasible, and rotational corrections are recommended in rectal patients to further minimise OAR irradiation.

Mesorectal shape variation in rectal cancer radiotherapy in prone position using a belly board

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Mesorectal shape variation is diverse and largest in the upper-anterior region.

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Derived planning target volume margins for the upper-anterior region were larger in female patients.

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Planning target volume margins are comparable for radiotherapy and chemoradiotherapy groups.

Background and purpose

In rectal cancer patients, radiotherapy in prone position using a belly board can reduce the dose to organs at risk. For this patient group we investigated inter-fraction shape variation of the mesorectal part of the clinical target volume (CTV) and determined planning target volume (PTV) margins.

Materials and methods

Patients with rectal cancer receiving neoadjuvant (chemo)radiotherapy were eligible. For each patient a planning computed tomography (pCT) and five cone-beam CT (CBCT) scans were acquired in prone position using a belly board. The mesorectal CTV was delineated on all scans. Mesorectal shape variation was quantified relative to the pCT. PTV margins were derived locally and averaged for separate subregions of the mesorectal CTV. For each patient a total PTV was constructed using our clinical margins for mesorectal and lymph node CTVs. An artificial dose distribution conforming to this PTV was used to calculate the coverage for the mesorectal CTV using the CBCT delineations.

Results

In 19 rectal cancer patients the derived PTV margins were smallest in the upper-lateral region (6 mm) and largest in the upper-anterior region (16 mm). PTV margins for the upper-anterior region were larger for female patients (19 mm) compared to male patients (14 mm). Clinical margins for the total PTV were sufficient for a coverage of at least 97% of the mesorectal CTV for all patients.

Conclusions

Mesorectal shape variation is heterogeneous and largest in the upper-anterior region, in rectal cancer patients irradiated in prone position and using a belly board.

Intensity-modulated Radiotherapy for Rectal Cancer in the UK in 2020

AIMS

Preoperative (chemo)radiotherapy followed by total mesorectal excision is the current standard of care for patients with locally advanced rectal cancer. The use of intensity-modulated radiotherapy (IMRT) for rectal cancer is increasing in the UK. However, the extent of IMRT implementation and current practice was not previously known. A national survey was commissioned to investigate the landscape of IMRT use for rectal cancer and to inform the development of national rectal cancer IMRT guidance.

MATERIALS AND METHODS

A web-based survey was developed by the National Rectal Cancer IMRT Guidance working group in collaboration with the Royal College of Radiologists and disseminated to all UK radiotherapy centres. The survey enquired about the implementation of IMRT with a focus on the following aspects of the workflow: dose fractionation schedules and use of a boost; pre-treatment preparation and simulation; target volume/organ at risk definition; treatment planning and treatment verification. A descriptive statistical analysis was carried out.

RESULTS

In total, 44 of 63 centres (70%) responded to the survey; 30/44 (68%) and 36/44 (82%) centres currently use IMRT to treat all patients and selected patients with rectal cancer, respectively. There was general agreement concerning several aspects of the IMRT workflow, including patient positioning, use of intravenous contrast and bladder protocols. Greater variation in practice was identified regarding rectal protocols; use of a boost to primary/nodal disease; target volume delineation; organ at risk delineation and dose constraints and treatment verification. Delineation of individual small bowel loops and daily volumetric treatment verification were considered potentially feasible by most centres.

CONCLUSION

This survey identified that IMRT is already used to treat rectal cancer in many UK radiotherapy centres, but there is heterogeneity between centres in its implementation and practice. These results have been a valuable aid in framing the recommendations within the new National Rectal Cancer IMRT Guidance.

MR-Guided Radiotherapy for Rectal Cancer: Current Perspective on Organ Preservation

Online MRI-guided radiotherapy (MRgRT) is one of the most recent technological advances in radiotherapy. MRgRT permits the visualization of tumorous and healthy tissue while the patient is on the treatment table and online daily plan adaptations following the observed anatomical changes. In the context of rectal cancer, online MRgRT is a very promising modality due to the pronounced geographical variability of tumor tissues and the surrounding healthy tissues. This current paper will discuss the possible applications of online MRgRT, in particular, in terms of radiotherapy dose escalation and response prediction in organ preservation approaches for rectal cancer.

Current Status of Anatomical Magnetic Resonance Imaging in Brachytherapy and External Beam Radiotherapy Planning and Delivery

Radiotherapy planning and delivery have dramatically improved in recent times. Imaging is key to a successful three-dimensional and increasingly four-dimensional based pathway with computed tomography embedded as the backbone modality. Computed tomography has significant limitations for many tumour sites where soft-tissue discrimination is suboptimal, and where magnetic resonance imaging (MRI) has largely superseded in the diagnostic arena. MRI is increasingly used together with computed tomography in the radiotherapy planning pathway and is now established as a prerequisite for several tumours. With the advent of combined MRI and linear accelerator (MR-linac) systems, a transition to MRI-based radiotherapy planning is becoming reality, with increasing experience and research involving these new platforms. In this overview, we aim to highlight how magnetic resonance-guided imaging has improved radiotherapy, using gynaecological malignancies to illustrate, in both external beam radiotherapy and image-guided brachytherapy, and will assess the early evidence for magnetic resonance-guided radiotherapy using combined MR-linac systems.

Online adaptive radiotherapy compared to plan selection for rectal cancer: quantifying the benefit

Background

To compare online adaptive radiation therapy (ART) to a clinically implemented plan selection strategy (PS) with respect to dose to the organs at risk (OAR) for rectal cancer.

Methods

The first 20 patients treated with PS between May–September 2016 were included. This resulted in 10 short (SCRT) and 10 long (LCRT) course radiotherapy treatment schedules with a total of 300 Conebeam CT scans (CBCT). New dual arc VMAT plans were generated using auto-planning for both the online ART and PS strategy.

For each fraction bowel bag, bladder and mesorectum were delineated on daily Conebeam CTs. The dose distribution planned was used to calculate daily DVHs. Coverage of the CTV was calculated, as defined by the dose received by 99% of the CTV volume (D99%). The volume of normal tissue irradiated with 95% of the prescribed fraction dose was calculated by calculating the volume receiving 95% of the prescribed fraction or more dose minus the volume of the CTV. For each fraction the difference between the plan selection and online adaptive strategy of each DVH parameter was calculated, as well as the average difference per patient.

Results

Target coverage remained the same for online ART. The median volume of the normal tissue irradiated with 95% of the prescribed dose dropped from 642 cm3 (PS) to 237 cm3 (online-ART)(p < 0.001). Online ART reduced dose to the OARs for all tested dose levels for SCRT and LCRT (p < 0.001). For V15Gy of the bowel bag the median difference over all fractions of all patients was − 126 cm³ in LCRT, while the average difference per patient ranged from − 206 cm³ to − 40 cm³. For SCRT the median difference was − 62 cm³, while the range of the average difference per patient was − 105 cm3 to − 51 cm³.

For V15Gy of the bladder the median difference over all fractions of all patients was 26% in LCRT, while the average difference per patient ranged from − 34 to 12%. For SCRT the median difference of V95% was − 8%, while the range of the average difference per patient was − 29 to 0%.

Conclusions

Online ART for rectal cancer reduces dose the OARs significantly compared to a clinically implemented plan selection strategy, without compromising target coverage.

Trial registration

Medical Research Involving Human Subjects Act (WMO) does not apply to this study and was retrospectively approved by the Medical Ethics review Committee of the Academic Medical Center (W19_357 # 19.420; Amsterdam University Medical Centers, Location Academic Medical Center, Amsterdam, The Netherlands).

Cone-beam computed tomography for organ motion evaluation in locally advanced rectal cancer patients

PURPOSE

Due to a reported dose-response relationship in rectal cancer radiotherapy, a greater interest in dose intensification on small boost volume arises. Considering the need of an appropriate target movements evaluation, this retrospective study aimed to use cone-beam computed tomography (CBCT) for GTV and mesorectum organ motion (OM) evaluation, in locally advanced rectal cancer (LARC) patients treated with neoadjuvant chemo-radiotherapy, in prone and supine position.

METHODS

Thirty-two LARC patients were analyzed. GTV and mesorectum were delineated on MRI co-registrated with CT simulation. GTV and mesorectum OM was estimated on all CBCTs, performed during treatment, co-registrated with CT simulation. OM evaluation was obtained, as mean shift in left and right (L-R), postero-anterior (P-A) and cranio-caudal (Cr-C) directions. Volumes variability was calculated by DICE index.

RESULTS

A total of 296 CBCTs were analyzed. Mean shifts of the GTV and mesorectum in prone position were - 0.16 cm and 0.15 cm in L-R direction, 0.28 cm and - 0.40 cm in P-A direction, and 0.14 cm and - 0.21 cm, in Cr-C direction; for supine position the mean shifts of the GTV were - 0.10 cm and 0.17 cm in R-L direction, 0.26 cm and - 0.23 cm in A-P direction, 0.09 cm and - 0.11 cm in Cr-C direction. Mean DICE index for GTV and mesorectum was 0.74 and 0.86, in prone position, and 0.78 and 0.89 in supine position, respectively.

CONCLUSION

GTV and mesorectum OM was less than 4 mm in all directions in both positions, with a 1 mm less deviation in supine position. CBCTs resulted effective for OM assessment, and it could be an appropriate method for the implementation on an intensification treatment.

The importance of mesorectum motion in determining PTV margins in rectal cancer patients treated with neoadjuvant radiotherapy

New precision radiotherapy (RT) techniques reduce the uncertainties in localizing soft and moving tumors. However, there are still many uncontrollable internal organ movements. In our study, patients who underwent neoadjuvant chemoradiotherapy (NA-CRT) for rectal cancer were evaluated to determine inter-fraction mesorectum motion and dosimetric changes. Fourteen patients treated with NA-CRT for rectal cancer between 2014 and 2016 were included in the analysis. The mesorectum and clinical target volume (CTV) were delineated on planning computed tomography (CT) and cone-beam CT (CB-CT) scans. After planning with a volumetric modulated arc therapy (VMAT) plan, re-planning was performed on all CB-CTs. Finally, the volumetric and dosimetric changes of PTV and mesorectum were evaluated in all CB-CTs compared with the initial CT and VMAT plans. The geometrical center of mesorectum volume in CB-CTs had moved 1 (0.2-6.6), 1.6 (0.2-3.8) and 1.6 (0-4.9) mm in the x, y and z-axis respectively compared with the initial CT. The dosimetric parameters of PTV including D2, D95 and D98 on CB-CT showed a median 47.19 (46.70-47.80), 45.05 (44.18-45.68) and 44.69 (43.83-45.48) Gy and median 1% (1-2), 0% (0-2) and 1% (0-2) dosimetric change compared with the initial VMAT plan. In our study, we have shown that the mesorectum has moved up to 20 mm in the lateral and anterior-posterior direction and almost 10 mm in the superior/inferior direction during RT, causing a median of ~2% change in dosimetric parameters. Therefore, these movements must be considered in determining PTV margins to avoid dosimetric changes.

Dosimetric benefit of an adaptive treatment by means of plan selection for rectal cancer patients in both short and long course radiation therapy

BACKGROUND

To compare target coverage and dose to the organs at risk in two approaches to rectal cancer: a clinically implemented adaptive radiotherapy (ART) strategy using plan selection, and a non-adaptive (non-ART) strategy.

METHODS

The inclusion of the first 20 patients receiving adaptive radiotherapy produced 10 patients with a long treatment schedule (25x2Gy) and 10 patients with a short schedule (5X5Gy). We prepared a library of three plans with different anterior PTV margins to the upper mesorectum, and selected the most appropriate plan on daily Conebeam CT scans (CBCT). We also created a non-adaptive treatment plan with a 20 mm margin. Bowel bag, bladder and target volume were delineated on CBCT. Daily DHVs were calculated based on the dose distribution of the selected and non-adaptive plans. Coverage of the target volume was compared per fraction between the ART and non-ART plans, as was the dose to the bladder and small bowel, assessing the following dose levels: V15Gy, V30Gy, V40Gy, V15Gy and V95% for long treatment schedules, and V15Gy and V95% for short ones.

RESULTS

Target volume coverage was maintained from 98.3% (non-ART) to 99.0% (ART)(p = 0.878). In the small bowel, ART appeared to have produced significant reductions in the long treatment schedule at V15Gy, V40Gy, V45Gy and V95% (p <  0.05), but with small absolute differences. The DVH parameters tested for the short treatment schedule did not differ significantly. In the bladder, all DVH parameters in both schedules showed significant reductions (p <  0.05), also with small absolute differences.

CONCLUSIONS

The adaptive treatment maintained target coverage and reduced dose to the organs at risk.

TRIAL REGISTRATION

Medical Research Involving Human Subjects Act (WMO) does not apply to this study and was retrospectively approved by the Medical Ethics review Committee of the Academic Medical Center, W19_194 # 19.233.

Feasibility of Gold Fiducial Markers as a Surrogate for Gross Tumor Volume Position in Image-Guided Radiation Therapy of Rectal Cancer

PURPOSE

To evaluate the feasibility of fiducial markers as a surrogate for gross tumor volume (GTV) position in image-guided radiation therapy of rectal cancer.

METHODS AND MATERIALS

We analyzed 35 fiducials in 19 patients with rectal cancer who received short-course radiation therapy or long-course chemoradiation therapy. Magnetic resonance imaging examinations were performed before and after the first week of radiation therapy, and daily pre- and postirradiation cone beam computed tomography scans were acquired in the first week of radiation therapy. Between the 2 magnetic resonance imaging examinations, the fiducial displacement relative to the center of gravity of the GTV (COG_GTV) and the COG_GTV displacement relative to bony anatomy were determined. Using the cone beam computed tomography scans, inter- and intrafraction fiducial displacement relative to bony anatomy were determined.

RESULTS

The systematic error of the fiducial displacement relative to the COG_GTV was 2.8, 2.4, and 4.2 mm in the left-right, anterior-posterior (AP), and craniocaudal (CC) directions, respectively. Large interfraction systematic errors of up to 8.0 mm and random errors up to 4.7 mm were found for COG_GTV and fiducial displacements relative to bony anatomy, mostly in the AP and CC directions. For tumors located in the mid and upper rectum, these errors were up to 9.4 mm (systematic) and 5.6 mm (random) compared with 4.9 mm and 2.9 mm for tumors in the lower rectum. Systematic and random errors of the intrafraction fiducial displacement relative to bony anatomy were ≤2.1 mm in all directions.

CONCLUSIONS

Large interfraction errors of the COG_GTV and the fiducials relative to bony anatomy were found. Therefore, despite the observed fiducial displacement relative to the COG_GTV, the use of fiducials as a surrogate for GTV position reduces the required margins in the AP and CC directions for a GTV boost using image-guided radiation therapy of rectal cancer. This reduction in margin may be larger in patients with tumors located in the mid and upper rectum compared with the lower rectum.

EUS-guided fiducial marker placement for radiotherapy in rectal cancer: feasibility of two placement strategies and four fiducial types

Background and study aims  To facilitate image guidance during radiotherapy of rectal cancer, we investigated the feasibility of fiducial marker placement. This study aimed to evaluate technical success rate and safety of two endoscopic ultrasound (EUS)-guided placement strategies and four fiducial types for rectal cancer patients. Patients and methods  This prospective multicenter study included 20 participants who were scheduled to undergo rectal cancer treatment with neoadjuvant short-course radiotherapy or chemoradiation. EUS-guided endoscopy was used for fiducial placement at the tumor site (n = 10) or in the mesorectal fat and in the tumor (n = 10). Four fiducial types were used (Visicoil 0.75 mm, Visicoil 0.50 mm, Cook, Gold Anchor). The endpoints were technical success rate and retention of fiducials, the latter of which was evaluated on cone-beam computed tomography scans during the first five radiotherapy fractions. Results  A total of 64 fiducials were placed in 20 patients. For each fiducial type, at least three fiducials were successfully placed in all patients. Technical failure consisted of fiducial blockage within the needle (n = 2) and ejection of two preloaded fiducials at once (n = 4). No serious adverse events were reported. In three patients, one of the fiducials was misplaced without clinical consequences; two in the prostate and one in the intraperitoneal cavity. After a median time of 17 days after placement (range 7 - 47 days), a total of 42/64 (66 %) fiducials were still present (24/44 intratumoral vs. 18/20 mesorectal fiducials, P  = 0.009). Conclusions  Placement of fiducials in rectal cancer patients is feasible, however, retention rates for intratumoral fiducials were lower (55 %) than for mesorectal fiducials (90 %).

Realizing the potential of magnetic resonance image guided radiotherapy in gynaecological and rectal cancer

CT-based radiotherapy workflow is limited by poor soft tissue definition in the pelvis and reliance on rigid registration methods. Current image-guided radiotherapy and adaptive radiotherapy models therefore have limited ability to improve clinical outcomes. The advent of MRI-guided radiotherapy solutions provides the opportunity to overcome these limitations with the potential to deliver online real-time MRI-based plan adaptation on a daily basis, a true "plan of the day." This review describes the application of MRI guided radiotherapy in two pelvic tumour sites likely to benefit from this approach.

Rectal volume variations and estimated rectal dose during 8 weeks of image-guided radical 3D conformal external beam radiotherapy for prostate cancer

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Modern IGRT has given new insight regarding organ motion in radiotherapy.

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Rectal volume variation may increase the risk of biochemical and local failure.

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Rectal volume decreased significantly during eight weeks of radiotherapy.

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The percentage of irradiated rectal volume did not change statistically significant.

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Our study shows that IGRT ensures a close to stable dose to the rectum.

MRI-based tumor inter-fraction motion statistics for rectal cancer boost radiotherapy

BACKGROUND

In patients diagnosed with rectal cancer, dose escalation is currently being investigated in a large number of studies. Since there is little known on gross tumor volume (GTV) inter-fraction motion for rectal cancer, a wide variety in margins is used. Purpose of this study is to quantify GTV inter-fraction motion statistics on different timescales and to give estimates of planning target volume (PTV) margins.

MATERIAL AND METHODS

Thirty-two patients, diagnosed with rectal cancer, were included. To investigate motion from week-to-week, 16 patients underwent a pretreatment and five weekly MRIs, prior to a radiotherapy (RT) fraction of the chemoradiotherapy treatment. To investigate motion from day-to-day, the remaining 16 patients underwent five daily MRIs before each fraction in one week of RT. GTV was delineated on all scans according to guidelines. Scans were aligned on bony anatomy with the first MRI. For both datasets separately, GTV inter-fraction motion was determined based on center-of-gravity displacement. Therefrom, systematic and random errors were determined in left/right (LR), anterior/posterior and cranial/caudal (CC) direction. PTV margin estimates were calculated and evaluated on GTV coverage.

RESULTS

Systematic and random errors were found in the range of 2.3-4.8 mm and 1.5-3.3 mm from week-to-week, and 1.8-4.5 mm and 1.8-4.0 mm from day-to-day, respectively. On both timescales, similar motion patterns were found; the most motion was observed in CC whilst the least motion was observed in LR. On the week-to-week data more systematic and less random motion was observed compared to the day-to-day data. Overall, only slight differences in margin estimates were found. Derived PTV margin estimates were found to give adequate GTV coverage.

CONCLUSION

GTV inter-fraction motion, on a week-to-week and day-to-day timescale, can be accounted for using motion statistics presented in this study.

[Image-guided radiotherapy contribution and patient setup for anorectal cancer treatment]

Intensity-modulated radiation therapy is recommended in anal squamous cell carcinoma treatment and is increasingly used in rectal cancer. It adapts the dose to target volumes, with a high doses gradient. Intensity-modulated radiation therapy allows to reduce toxicity to critical normal structures and to consider dose-escalation studies or systemic treatment intensification. Image-guided radiation therapy is a warrant of quality for intensity-modulated radiation therapy, especially for successful delivery of the dose as planned. There is no recommended international or national anorectal cancer image-guided radiation therapy protocol currently available. Dose-escalation trials or expert opinions about intensity-modulated/image-guided radiation therapy good practice guidelines recommend daily volumetric imaging throughout the treatment or during the five first fractions and weekly thereafter as a minimum. Image-guided radiation therapy allows to reduce margins related to patient setup errors. Internal margin, related to the internal organ motion, needs to be adapted according to short- or long-course radiotherapy, gender, rectal location; it can be higher than current recommended planning target volume margins, particularly in the upper and anterior part of mesorectum, which has the most significant movement. Image-guided radiation therapy based on volumetric imaging allows to take target volume shrinkage into account and to develop adaptive strategies, in particular for mesorectum shrinkage during rectal cancer treatment. Lastly, the emergence of new image-guided radiation therapy technologies including MRI (which plays a major role in pelvic tumours assessment and diagnosis) opens up interesting perspectives for adaptive radiotherapy, taking into account both organs' movements and tumour shrinkage.

PET imaging in adaptive radiotherapy of gastrointestinal tumors

INTRODUCTION

Radiotherapy is a cornerstone in the multimodality treatment of several gastrointestinal (GI) tumors. Positron-emission tomography (PET) has an established role in the diagnosis, response assessment and (re-)staging of these tumors. Nevertheless, the value of PET in adaptive radiotherapy remains unclear. This review focuses on the role of PET in adaptive radiotherapy, i.e. during the treatment course and in the delineation process.

EVIDENCE ACQUISITION

The MEDLINE database was searched for the terms ("Radiotherapy"[Mesh] AND "Positron-Emission Tomography"[Mesh] AND one of the site-specific keywords, yielding a total of 1710 articles. After abstract selection, 27 papers were identified for esophageal neoplasms, 1 for gastric neoplasms, 9 for pancreatic neoplasms, 6 for liver neoplasms, 1 for biliary tract neoplasms, none for colonic neoplasms, 15 for rectal neoplasms and 12 for anus neoplasms.

EVIDENCE SYNTHESIS

The use of PET for truly adaptive radiotherapy during treatment for GI tumors has barely been investigated, in contrast to the potential of the PET-defined metabolic tumor volume for optimization of the target volume. The optimized target definition seems useful for treatment individualization such as focal boosting strategies in esophageal, pancreatic and anorectal cancer. Nevertheless, for all GI tumors, further investigation is needed.

CONCLUSIONS

In general, too little data are available to conclude on the role of PET imaging during radiotherapy for ART strategies in GI cancer. On the other hand, based on the available evidence, the use of biological imaging for target volume adaptation seems promising and could pave the road towards individualized treatment strategies.

Does setup on rectal wall improve rectal cancer boost radiotherapy?

BACKGROUND

Rectal cancer patients that show a pathological complete response (pCR) after neo-adjuvant chemo-radiotherapy, have better prognosis. To increase pCR rates several studies escalate the tumor irradiation dose. However, due to lacking tumor contrast on online imaging techniques, no direct tumor setup can be performed and large boost margins are needed to ensure tumor coverage. The purpose of this study was to evaluate the feasibility of performing a setup on rectal wall for rectal cancer boost radiotherapy, thereby using rectal wall nearby the tumor as tumor position surrogate.

METHODS

For sixteen patients, daily MRI's were performed during 1 week of radiotherapy. On each of these images, tumor and rectum were delineated. Residual displacements were determined per surface voxel after setup on bony anatomy or nearby rectal wall and setup errors for both setups were compared. Furthermore for every rectal wall voxel nearby the tumor, displacement was compared with the closest tumor point and correlation was determined.

RESULTS

Mean (SD) setup error was 2.7 mm (3.3 mm) and 2.2 mm (3.2 mm) after setup on bony anatomy and rectal wall respectively. Nevertheless, similar PTV-margin estimates i.e. 95th percentile distances, were found; 8.0 mm. Also, a merely moderate correlation; ρ = 0.66 was found between rectal wall and tumor displacement. Further investigation into tumor and rectal mobility differences showed that the rectal wall lacks appropriate anatomical landmarks to find true displacements, especially to capture motion along the rectal wall.

CONCLUSIONS

Setup on rectal wall slightly reduces mean setup errors but requires a similar PTV-margin as compared to setup on bony anatomy. Rectal mobility might be similar to tumor mobility, but due the absence of anatomical landmarks in the rectum, displacements along the rectal wall are not detected on current online imaging. Therefore, to further reduce tumor position uncertainties, direct or indirect online tumor visualization is needed.

Computational analysis of interfractional anisotropic shape variations of the rectum in prostate cancer radiation therapy

PURPOSE

To analyze the uncertainties of the rectum due to anisotropic shape variations by using a statistical point distribution model (PDM).

MATERIALS AND METHODS

The PDM was applied to the rectum contours that were delineated on planning computed tomography (CT) and cone-beam CT (CBCT) at 80 fractions of 11 patients. The standard deviations (SDs) of systematic and random errors of the shape variations of the whole rectum and the region in which the rectum overlapped with the PTV (ROP regions) were derived from the PDMs at all fractions of each patient. The systematic error was derived by using the PDMs of planning and average rectum surface determined from rectum surfaces at all fractions, while the random error was derived by using a PDM-based covariance matrix at all fractions of each patient.

RESULTS

Regarding whole rectum, the population SDs were larger than 1.0 mm along all directions for random error, and along the anterior, superior, and inferior directions for systematic error. The deviation is largest along the superior and inferior directions for systematic and random errors, respectively. For ROP regions, the population SDs of systematic error were larger than 1.0 mm along the superior and inferior directions. The population SDs of random error for the ROP regions were larger than 1.0 mm except along the right and posterior directions.

CONCLUSIONS

The anisotropic shape variations of the rectum, especially in the ROP regions, should be considered when determining a planning risk volume (PRV) margins for the rectum associated with the acute toxicities.

Validation of biomechanical deformable image registration in the abdomen, thorax, and pelvis in a commercial radiotherapy treatment planning system

PURPOSE

The accuracy of deformable image registration tools can vary widely between imaging modalities and specific implementations of the same algorithms. A biomechanical model-based algorithm initially developed in-house at an academic institution was translated into a commercial radiotherapy treatment planning system and validated for multiple imaging modalities and anatomic sites.

METHODS

Biomechanical deformable registration (Morfeus) is a geometry-driven algorithm based on the finite element method. Boundary conditions are derived from the model-based segmentation of controlling structures in each image which establishes a point-to-point surface correspondence. For each controlling structure, material properties and fixed or sliding interfaces are assigned. The displacements of internal volumes for controlling structures and other structures implicitly deformed are solved with finite element analysis. Registration was performed for 74 patients with images (mean vector resolution) of thoracic and abdominal 4DCT (2.8 mm) and MR (5.3 mm), liver CT-MR (4.5 mm), and prostate MR (2.6 mm). Accuracy was quantified between deformed and actual target images using distance-to-agreement (DTA) for structure surfaces and the target registration error (TRE) for internal point landmarks.

RESULTS

The results of the commercial implementation were as follows. The mean DTA was ≤ 1.0 mm for controlling structures and 1.0-3.5 mm for implicitly deformed structures on average. TRE ranged from 2.0 mm on prostate MR to 5.1 mm on lung MR on average, within 0.1 mm or lower than the image voxel sizes. Accuracy was not overly sensitive to changes in the material properties or variability in structure segmentations, as changing these inputs affected DTA and TRE by ≤ 0.8 mm. Maximum DTA > 5 mm occurred for 88% of the structures evaluated although these were within the inherent segmentation uncertainty for 82% of structures. Differences in accuracy between the commercial and in-house research implementations were ≤ 0.5 mm for mean DTA and ≤ 0.7 mm for mean TRE.

CONCLUSIONS

Accuracy of biomechanical deformable registration evaluated on a large cohort of images in the thorax, abdomen and prostate was similar to the image voxel resolution on average across multiple modalities. Validation of this treatment planning system implementation supports biomechanical deformable registration as a versatile clinical tool to enable accurate target delineation at planning and treatment adaptation.

Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

Objective:

Radiotherapy for prostate cancer does not explicitly take into account daily variation in the position of the rectum. It is important to accurately assess accumulated dose (D_A) to the rectum in order to understand the relationship between dose and toxicity. The primary objective of this work was to quantify systematic (Σ) and random (σ) variation in the position of the rectum during a course of prostate radiotherapy.

Methods:

The rectum was manually outlined on the kilo-voltage planning scan and 37 daily mega-voltage image guidance scans for 10 participants recruited to the VoxTox study. The femoral heads were used to produce a fixed point to which all rectal contours were referenced.

Results:

Σ [standard deviation (SD) of means] between planning and treatment was 4.2 mm in the anteroposterior (AP) direction and 1.3 mm left–right (LR). σ (root mean square of SDs) was 5.2 mm AP and 2.7 mm LR. Superior–inferior variation was less than one slice above and below the planning position.

Conclusion:

Our results for Σ are in line with published data for prostate motion. σ, however, was approximately twice as great as that seen for prostate motion. This suggests that D_A may differ from planned dose in some patients treated with radiotherapy for prostate cancer.

Advances in knowledge:

This work is the first to use daily imaging to quantify Σ and σ of the rectum in prostate cancer. σ was found to be greater than published data, providing strong rationale for further investigation of individual D_A.

Impact of advancing age on treatment and outcomes in anal cancer

BACKGROUND

Chemoradiotherapy (CRT) for squamous cell carcinoma of the anus (SCCA) may cause significant toxicity, and concerns exist about its tolerability in the elderly. The authors compared tolerability and outcomes across the age groups following CRT for SCCA.

METHODS

Single-institution retrospective analysis of patients with localized SCCA treated with CRT. CRT was standardized at 50.4-54 Gy, with concurrent infusional 5-fluorouracil and mitomycin C. Patients were arbitrarily categorized into three groups: Group 1 - age < 50 years; Group 2 - age ≥ 50 and < 70 years; and Group 3 - age ≥ 70 years.

RESULTS

Of 284 patients identified, 278 were evaluable. The number of patients in each age group was: Group 1 - 51; Group 2 - 140; and Group 3 - 93. Baseline and treatment characteristics, tumor stage, rates of overall acute toxicity, need for unplanned treatment breaks and chemotherapy delivery were largely similar across the age groups. However, nine patients in Group 3 did not complete CRT, compared with five and none in Groups 1 and 2, respectively (p = 0.006). In addition, five patients in Group 3 had diarrhea requiring treatment break, compared with none in the other two groups (p = 0.004). At a median follow-up 5.3 years, there was no significant difference in overall survival (p = 0.11), disease-free survival (p = 0.22) or local-recurrence free survival (p = 0.34), across the three age groups.

CONCLUSIONS

CRT is safe and tolerable in the elderly age group, and provides equivalent disease control rates compared with the younger age group. Age alone should therefore not preclude aggressive curative treatment.

Assessment of nonrespiratory stomach motion in healthy volunteers in fasting and postprandial states

PURPOSE

To characterize nonrespiratory stomach motion in the fasting state and postprandial.

METHODS AND MATERIALS

Ten healthy volunteers underwent 2-dimensional Fiesta cine magnetic resonance imaging studies in 30-second voluntary breath hold, in axial, coronal, and 2 oblique planes while fasting, and 5, 15, 30, 45, and 60 minutes postmeal. Each stomach contour was delineated and sampled with 200 points. Matching points were found for all contours in the same 30-second acquisition. Using deformable parametric analysis (Matlab, version 7.1), mean magnitude, and standard deviation of displacement of each point were determined for each patient. Maximal, minimal, and median population values in 6 cardinal, and in any direction, were calculated.

RESULTS

The median of mean displacements for the baseline position of each point was small and rarely exceeded 1.1 mm; greatest value was 1.6 mm superior-inferior. Median displacement (pooled across time) in the right-left, superior-inferior, and anterior-posterior directions was 0.3 (range, -0.7 to 1.3), 0.8 (-0.4 to 2.4), and 0.3 (-1.1 to 1.6) mm, respectively. Fasting and postprandial standard deviation did not differ.

CONCLUSIONS

Nonrespiratory stomach displacement is small and stomach position is stable after a small, standard meal. Radiation therapy may be delivered at any time within the first hour after eating without significant compromise of planned planning target volumes.

[Preoperative radiotherapy for rectal cancer: target volumes]

Preoperative radiochemotherapy followed by total mesorectal excision is the standard of care for T3-T4-N0 or TxN1 rectal cancer. Defining target volumes relies on the patterns of nodal and locoregional failures. The lower limit of the clinical target volume depends also on the type of surgery. Conformational radiotherapy with or without intensity-modulated radiotherapy implies an accurate definition of volumes and inherent margins in the context of mobile organs such as the upper rectum. Tumoral staging recently improved with newer imaging techniques such as MRI with or without USPIO and FDG-PET-CT. The role of PET-CT remains unclear despite encouraging results and MRI is a helpful tool for a reliable delineation of the gross tumour volume. Co-registration of such modalities with the planning CT may particularly guide radiation oncologists through the gross tumour volume delineation. Acute digestive toxicity can be reduced with intensity modulation radiation therapy. Different guidelines and CT-based atlas regarding the target volumes in rectal cancer give the radiation oncologist a lot of ground for reproducible contours.

Adaptive radiotherapy for long course neo-adjuvant treatment of rectal cancer

PURPOSE

To quantify the potential margin reduction with adaptive radiotherapy (ART) during neo-adjuvant treatment of locally-advanced rectal cancer.

METHODS AND MATERIALS

Repeat CT scans were acquired for 28 patients treated with 25×2 Gy, daily during the first week, and followed by weekly scans. The CTV was delineated on all scans, and shape variation was estimated. Five ART strategies were tested, consisting of an average CTV over the planning CT and one to five repeat CTs. Required PTV margins were calculated for adapted and non-adapted treatment. The strategy with the least PTV volume over the whole treatment was selected and bowel area dose reduction was estimated.

RESULTS

Substantial systematic and random shape variation demanded for a PTV margin up to 2.4 cm at the upper-anterior part of the CTV. Plan adaptation after fraction 4 resulted in a maximum 0.7 cm margin reduction and a significant PTV reduction from 1185 to 1023 cc (p<0.0001). The bowel area volume receiving 15, 45, and 50 Gy was reduced from 436 to 402 cc, 111 to 81 cc, and 49 to 29 cc, respectively (p<0.0001).

CONCLUSIONS

With adaptive radiotherapy, maximum required PTV margins can be reduced from 2.4 to 1.7 cm, resulting in significantly less dose to the bowel area.

Characterisation of rectal motion during neo-adjuvant radiochemotherapy for rectal cancer with image-guided tomotherapy: implications for adaptive dose escalation strategies

BACKGROUND

Interest in boosting the dose to the tumour during neo-adjuvant radiochemotherapy for rectal cancer is ever increasing, especially within the frame of adaptive radiotherapy. Rectal motion remains a potentially important obstacle to the full exploitation of this approach and needs to be carefully investigated.

MATERIAL AND METHODS

The main purposes of this work were to: a) quantify rectal motion on all fractions of a treatment course; and b) assess margins for adaptive boosting in the second part of the treatment in order to benefit of tumour reduction during treatment. Ten consecutive patients treated with image-guided tomotherapy (41.4 Gy, 18 fractions) were selected. The cranial half of the rectum (subject to motion) was contoured by a single observer on daily MVCTs. The variations of rectal volume and of the envelope of rectum positions were investigated (169 MVCTs). The impact of applying different margins to the rectum in including all its possible positions was also investigated when considering the planning kVCT, the first fraction MVCT, the half-treatment MVCT or the median rectal contours of the whole or second half of treatment as reference volumes.

RESULTS

Rectal volume reduced during treatment in all patients, with a significant time-trend in 6/10 patients. The median values of the envelope volumes were 129 cm(3) and 87 cm(3) in the first and second half of the treatment, respectively. On average, 95% of the rectal envelope was included by an isotropic expansion of 12 mm and 5 mm of the median contours when considering the whole or the second half of the treatment, respectively.

CONCLUSION

A significant reduction of rectal volume was found in the second part of the treatment where rectal mobility was limited. As a consequence, relatively small margins may be used around the residual tumour volume when adaptive boost is delivered in the second half of the treatment.