Intrafractional gastric motion and interfractional stomach deformity using CT images

Online Adaptive Radiotherapy for Planning Target Volume (PTV) Reduction in Gastric Mucosa-Associated Lymphoid Tissue (MALT) Lymphoma

Online adaptive radiotherapy (oART) uses daily imaging to identify changes in the patient's anatomy and generate a new treatment plan adapted to these changes, and it can be used for treating gastric mucosa-associated lymphoid tissue (MALT) lymphomas. This study aimed to determine the intrafraction motion and planning target volume (PTV) margins required for an oART workflow on a cone beam computed tomography (CBCT)-based dedicated system (Ethos®, Varian Medical Systems, Palo Alto, California, United States) and investigate the potential benefits for patients compared with a non-adaptive workflow. Involving three patients treated for gastric MALT lymphoma with the oART under breath-hold (BH) technique, the study determined a PTV margin for adaptive treatment using CBCT scans performed at the beginning and just before treating the patients for 34 fractions. Different PTVs were made by isotropically extending the clinical target volume (CTV) contoured on the first CBCT (CTV1) at intervals of 1 mm to evaluate intrafraction gastric motion, with the expansion covering the contoured CTV on the second CBCT (CTV2) quantifying the intrafraction motion (adaptive treatment) and the expansion from the CTV delineated on the planning scanner (CTVplanning) that could cover both CTV1 and CTV2 defining the interfraction motion (non-adaptive treatment). PTV margins were then determined as the extension of the CTV allowing coverage of 95% of its volume in 90% of fractions, and the dosimetric impact on dose constraints between an adaptive plan and a non-adaptive plan based on the predetermined margins was evaluated. A total of 68 CBCTs were analyzed, revealing that the PTV margin for oART was 4 mm, while for non-adaptive treatment it was 12 mm, with an average time elapsed between CBCT1 and CBCT2 of 11.62 minutes and no correlation between inter-CBCT timing and PTV margins (Pearson R-coefficient=0.10). All dosimetric constraints were met in both adaptive and non-adaptive plans, but the adaptive plan allowed for reduced organ-at-risk (OAR) doses in each patient. The study concluded that oART could reduce PTV margins in the treatment of gastric MALT lymphoma, especially with a BH strategy, impacting OAR dosimetry, though more prospective studies are required to validate these findings and determine their clinical impact on patients.

Evaluation of PTV margin in CBCT-based online adaptive radiation therapy for gastric mucosa-associated lymphoid tissue lymphoma

The aim of this study was to investigate planning target volume (PTV) margin in online adaptive radiation therapy (oART) for gastric mucosa-associated lymphoid tissue (MALT) lymphomas. Four consecutive patients with gastric MALT lymphoma who received oART (30 Gy in 15 fractions) on the oART system were included in this study. One hundred and twenty cone-beam computed tomography (CBCT) scans acquired pre- and post-treatment of 60 fractions for all patients were used to evaluate intra- and interfractional motions. Patients were instructed on breath-holding at exhalation during image acquisition. To assess the intrafraction gastric motion, different PTVs were created by isotropically extending the CTV contoured on a pre-CBCT image (CTVpre) at1 mm intervals. Intrafraction motion was defined as the amount of expansion covering the contoured CTV on post-CBCT images (CTVpost). Interfractional motion was defined as the amount of reference CTV expansion that could cover each CTVpre, as well as the evaluation of the intrafractional motion. PTV margins were estimated from the cumulative proportion of fraction covering the intra- and interfractional motions. The extent of expansion covering the CTVs in 90% of fractions was adopted as the PTV margin. The PTV margin for intrafractional gastric motion using the oART system with breath-holding was 14 mm. In contrast, the PTV margin for interfractional gastric organ motion without the oART system was 25 mm. These results indicated that the oART system can reduce the PTV margin by >10 mm. Our results could be valuable data for oART cases.

Stomach Motion and Deformation: Implications for Preoperative Gastric Cancer Radiation Therapy

PURPOSE

Selection and development of image guided strategies for preoperative gastric radiation therapy requires quantitative knowledge of the various sources of anatomic changes of the stomach. This study aims to investigate the magnitude of interfractional and intrafractional stomach motion and deformation using fiducial markers and 4-dimensional (4D) imaging.

METHODS AND MATERIALS

Fourteen patients who underwent preoperative gastric cancer radiation therapy received 2 to 6 fiducial markers distributed throughout the stomach (total of 54 markers) and additional imaging (ie, 1 planning 4D computed tomography [pCT], 20-25 pretreatment 4D cone beam [CB] CTs, 4-5 posttreatment 4D CBCTs). Marker coordinates on all end-exhale (EE) and end-inhale (EI) scans were obtained after a bony anatomy match. Interfractional marker displacements (ie, between EE pCT and all EE CBCTs) were evaluated for 5 anatomic regions (ie, cardia, small curvature, proximal and distal large curvature, and pylorus). Motion was defined as displacement of the center-of-mass of available markers (COMstomach), deformation as the average difference in marker-pair distances. Interfractional (ie, between EE pCT and all EE CBCTs), respiratory (between EE and EI pCT and CBCTs), and pre-post (pre- and posttreatment EE CBCTs) motion and deformation were quantified.

RESULTS

The interfractional marker displacement varied per anatomic region and direction, with systematic and random errors ranging from 1.6-8.8 mm and 2.2-8.2 mm, respectively. Respiratory motion varied per patient (median, 3-dimensional [3D] amplitude 5.2-20.0 mm) and day (interquartile range, 0.8-4.2 mm). Regarding COMstomach motion, respiratory motion was larger than interfractional motion (median, 10.9 vs 8.9 mm; P < .0001; Wilcoxon rank-sum), which was larger than pre-post motion (3.6 mm; P < .0001). Interfractional deformations (median, 5.8 mm) were significantly larger than pre-post deformations (2.6 mm; P < .0001), which were larger than respiratory deformation (1.8 mm; P < .0001).

CONCLUSIONS

The demonstrated sizable stomach motions and deformations during radiation therapy stress the need for generous nonuniform planning target volume margins for preoperative gastric cancer radiation therapy. These margins can be decreased by daily image guidance and adaptive radiation therapy.

Quantifying intrafractional gastric motion using auto-segmentation on MRI: Deformation and respiratory-induced displacement compared

BACKGROUND AND PURPOSE

For accurate pre-operative gastric radiotherapy, intrafractional changes must be taken into account. The aim of this study is to quantify local gastric deformations and compare these deformations with respiratory-induced displacement.

MATERIALS AND METHODS

Coronal 2D MRI scans (15-16 min; 120 repetitions of 25-27 interleaved slices) were obtained for 18 healthy volunteers. A deep-learning network was used to auto-segment the stomach. To separate out respiratory-induced displacements, auto-segmentations were rigidly shifted in superior-inferior (SI) direction to align the centre of mass (CoM) within every slice. From these shifted auto-segmentations, 3D iso-probability surfaces (isosurfaces) were established: a reference surface for P_Occ  = 0.50 and 50 other isosurfaces (from P_Occ  = 0.01 to 0.99), with P_Occ indicating the probability of occupation by the stomach. For each point on the reference surface, distances to all isosurfaces were determined and a cumulative Gaussian was fitted to this probability-distance dataset to obtain a standard deviation (SD_deform ) expressing local deformation. For each volunteer, we determined median and 98^th percentile of SD_deform over the reference surface and compared these with the respiratory-induced displacement SD_resp , that is, the SD of all CoM shifts (paired Wilcoxon signed-rank, α = 0.05).

RESULTS

Larger deformations were mostly seen in the antrum and pyloric region. Median SD_deform (range, 2.0-2.9 mm) was smaller than SD_resp (2.7-8.8 mm) for each volunteer (p < 0.00001); 98^th percentile of SD_deform (3.2-7.3 mm) did not significantly differ from SD_resp (p = 0.13).

CONCLUSION

Locally, gastric deformations can be large. Overall, however, these deformations are limited compared to respiratory-induced displacement. Therefore, unless respiratory motion is considerably reduced, the need to separately include these deformation uncertainties in the treatment margins may be limited.

Development of Organ-Preserving Radiation Therapy in Gastric Marginal Zone Lymphoma

Simple Summary

Gastric marginal zone lymphoma of the stomach is a rare cancer type primarily treated with oral proton pump inhibitors. If the disease does not respond to this, radiation is the treatment of choice. This review presents the development of radiation therapy over the last decades. Earlier, the stomach was surgically removed and irradiation was performed using large-field techniques and high doses of radiation. Currently, the standard treatment is the use of small-volume radiation therapy (with few side effects) with the preservation of the stomach, which provides excellent outcomes. In addition, this paper provides an outlook on current studies and possible future developments.

Abstract

Gastric marginal zone lymphoma (gMZL) of mucosa-associated lymphoid tissue (MALT) may persist even after H. pylori eradication, or it can be primarily Helicobacter pylori (H. pylori) independent. For patients without the successful eradication of lymphoma, or with progressive disease, treatment options have historically included partial or total gastrectomy. Presently, in these instances, curative radiation therapy (RT) is the current standard of care. This review emphasizes the historically changing role of radiation therapy in gMZL, progressing from large-volume RT without surgery, to localized RT, on its own, as a curative organ-preserving treatment. This overview shows the substantial progress in radiation therapy during the recent two to three decades, from high-dose, large-field techniques to low-dose, localized target volumes based on advanced imaging, three-dimensional treatment planning, and advanced treatment delivery techniques. RT has evolved from very large extended field techniques (EF) with prophylactic treatment of the whole abdomen and the supradiaphragmatic lymph nodes, applying doses between 30 and 50 Gy, to involved-field RT (IF), to the current internationally recommended involved site radiation therapy (ISRT) with a radiation dose of 24–30 Gy in gMZL. Stage-adapted RT is a highly effective and safe treatment with excellent overall survival rates and very rare acute or late treatment-related toxicities, as shown not only in retrospective studies, but also in large prospective multicenter studies, such as those conducted by the German Study Group on Gastrointestinal Lymphoma (DSGL). Further de-escalation of the radiation treatments with low-dose 20 Gy, as well as ultra-low-dose 4 Gy radiation therapy, is under investigation within ongoing prospective clinical trials of the International Lymphoma Radiation Oncology Group (ILROG) and of the German Lymphoma Alliance (GLA).

Assessment and validation of the internal gross tumour volume of gastroesophageal junction cancer during simultaneous integrated boost radiotherapy

Background

Respiratory motion may introduce errors during radiotherapy. This study aims to assess and validate internal gross tumour volume (IGTV) margins in proximal and distal borders of gastroesophageal junction (GEJ) tumours during simultaneous integrated boost radiotherapy.

Methods

We enrolled 10 patients in group A and 9 patients in group B. For all patients, two markers were placed at the upper and lower borders of the tumour before treatment. In group A, within the simulation and every 5 fractions of radiotherapy, we used 4-dimensional computed tomography (4DCT) to record the intrafractional displacement of the proximal and distal markers. By fusing the average image of each repeated 4DCT with the simulation image based on the lumbar vertebra, the interfractional displacement could be obtained. We calculated the IGTV margin in the proximal and distal borders of the GEJ tumour. In group B, by referring to the simulation images and cone-beam computed tomography (CBCT) images, the range of tumour displacement in proximal and distal borders of GEJ tumour was estimated. We calculated the proportion of marker displacement range in group B lay within the IGTV margin calculated based on the data obtained in group A to estimate the accuracy of the IGTV margin.

Results

The intrafractional displacement in the cranial–caudal (CC) direction was significantly larger than that in the anterior–posterior (AP) and left–right (LR) directions for both the proximal and distal markers of the tumour. The interfractional displacement in the AP and LR directions was larger than that in the CC direction (p = 0.001, p = 0.017) based on the distal marker. The IGTV margins in the LR, AP and CC directions were 9 mm, 8.5 mm and 12.1 mm for the proximal marker and 15.8 mm, 12.7 mm and 11.5 mm for the distal marker, respectively. In group B, the proportions of markers that located within the IGTV margin in the LR, AP and CC directions were 96.5%, 91.3% and 96.5% for the proximal marker and 100%, 96.5%, 93.1% for the distal marker, respectively.

Conclusions

Our study proposed individualized IGTV margins for proximal and distal borders of GEJ tumours during neoadjuvant radiotherapy. The IGTV margin determined in this study was acceptable. This margin could be a reference in clinical practice.

Does Radiation Dose to Gastric Fundus during Neoadjuvant Chemoradiotherapy for Esophageal Carcinoma Have an Impact on Postoperative Anastomotic Leak?

Background

Radiation dose received by the gastric fundus (GF) in neoadjuvant chemoradiotherapy (NACRT) may influence the development of postoperative anastomotic leak (AL) in the management of resectable esophageal carcinoma (EC) by trimodality therapy. The present study aims to evaluate dose-volume parameters of the GF and their association with occurrence of AL in EC.

Materials and Methods

A retrospective analysis was performed of 27 patients with EC who underwent NACRT followed by esophagectomy with cervical esophagogastric anastomosis between January 2015 and July 2018. The GF was retrospectively contoured; dose-volume parameters of the GF were recorded. Postoperative AL was identified from surgical records. Logistic regression analysis was used to identify risk factors associated with AL.

Results

The mean age of the patients was 51 ± 10.5 years; 56% (15/27) had involvement of lower 1/3 esophagus, 10/27 (37%) midthoracic esophagus, and 2/27 (7%) upper thoracic esophagus; 40% (11/27) patients developed postoperative AL and 7/11 had distal and 4/11 had mid thoracic esophageal lesions. Four of five (80%) patients treated by 3-dimensional conformal radiotherapy versus 7/22 (32%) patients treated by volumetric modulated arc therapy developed AL (p = 0.12). Univariate logistic regression revealed no significant correlation between D_mean, D_max, V20, V25, V30, V35, D50, and AL. 8/27 patients underwent ischemic preconditioning of gastric conduit, and 2/8 had AL; 19/27 did not undergo preconditioning, and 9/19 patients experienced AL (p = 0.4).

Conclusion

There was no significant negative impact of the dose received by the GF in NACRT upon AL rates. Further studies with a larger sample size are required to clarify this issue.

Impact of four-dimensional cone-beam computed tomography on target localization for gastric mucosa-associated lymphoid tissue lymphoma radiotherapy: reducing planning target volume

Background

Radiotherapy of gastric mucosa-associated lymphoid tissue (MALT) lymphoma should be delivered to the entire stomach with planning target volume (PTV) that accounts for variations in stomach volume, respiratory movement, and patient set-up error. In this study, we evaluated whether the use of four-dimensional cone-beam computed tomography (4D-CBCT) reduces the PTV.

Methods

Eight patients underwent radiotherapy with 15 fractions of gastric MALT lymphoma using 4D-CBCT. PTV structures of 5–30 mm margins (5 mm intervals) from the clinical target volume (CTV) delineated based on the 4D-CT images (CTV-4D) were generated. For the target localization, we performed matching based on skin marking (skin matching), bone anatomy (bone matching), and stomach anatomy (4D soft-tissue matching) based on registration between planning CT and 4D-CBCT images from 10 phases. For each patient, we calculated the covering ratio (CR) of the stomach with variable PTV structures, based on the 4D-CBCT images, with a total of 150 phases [CR (%) = (number of covering phases/150 phases) × 100], for three target localization methods. We compared the CR values of the different target localization methods and defined the PTV with an average CR of ≥ 95% for all patients.

Results

The average CR for all patients increased from 17.9 to 100%, 19.6 to 99.8%, and 33.8 to 100%, in the skin, bone, and 4D soft-tissue matchings, respectively, as the PTV structures increased from 5 to 30 mm. The CR obtained by 4D soft-tissue matching was superior to that obtained by skin (P = 0.013) and bone matching (P = 0.008) for a PTV structure of 15 mm margin. The PTV required an additional margin of 20 mm (average CR: 95.2%), 25 mm (average CR: 99.1%), and 15 mm (average CR: 98.0%) to CTV-4D for the skin, bone, and 4D soft-tissue matchings, respectively.

Conclusions

This study demonstrates that the use of 4D-CBCT reduces the PTV when applying 4D soft-tissue matching, compared to skin and bone matchings. Additionally, bone matching does not reduce the PTV as compared with traditional skin matching.

Impact of organ motion on volumetric and dosimetric parameters in stomach lymphomas treated with intensity-modulated radiotherapy

Purpose

Interplay effects may influence dose distributions to a moving target when using dynamic delivery techniques such as intensity‐modulated radiotherapy (IMRT). The aim of this study was to evaluate the impact of organ motion on volumetric and dosimetric parameters in stomach lymphomas treated with IMRT.

Methods

Ten patients who had been treated with IMRT for stomach lymphomas were enrolled. The clinical target volume (CTV) was contoured as the whole stomach. Considering interfractional uncertainty, the internal target volume (ITV) margin was uniformly 1.5 cm to the CTV and then modified based on the 4DCT images in case of the large respiratory motion. The planning target volume (PTV) was created by adding 5 mm to the ITV. The impact of organ motion on the volumetric and dosimetric parameters was evaluated retrospectively (4D simulation). The organ motion was reproduced by shifting the isocenter on the radiation treatment planning system. Several simulation plans were created to test the influence of the beam‐on timing in the respiration cycle on the dose distribution. The homogeneity index (HI), volume percentage of stomach covered by the prescribed dose (V_p), and D₉₉ of the CTV were evaluated.

Results

The organ motion was the largest in the superior‐inferior direction (10.1 ± 4.5 mm [average ± SD]). Stomach volume in each respiratory phase compared to the mean volume varied approximately within a ± 5% range in most of the patients. The PTV margin was sufficiently large to cover the CTV during the IMRT. There was a significant reduction in V_p and D₉₉ but not in HI in the 4D simulation in free‐breathing and multiple fractions compared to the clinically‐used plan (P < 0.05) suggesting that interplay effects deteriorate the dose distribution. The absolute difference of D₉₉ was less than 1% of the prescribed dose.

Conclusions

There were significant interplay effects affecting the dose distribution in stomach IMRT. The magnitude of the dose reduction was small when patients were treated on free‐breathing and multiple fractions.

Dosimetric impact of gastrointestinal air column in radiation treatment of pancreatic cancer

OBJECTIVE

Dosimetric evaluation of air column in gastrointestinal (GI) structures in intensity modulated radiation therapy (IMRT) of pancreatic cancer.

METHODS

Nine sequential patients were retrospectively chosen for dosimetric analysis of air column in the GI apparatus in pancreatic cancer using cone beam CT (CBCT). The four-dimensional CT (4DCT) was used for target and organs at risk (OARs) and non-coplanar IMRT was used for treatment. Once a week, these patients underwent CBCT for air filling, isocentre verification and dose calculations retrospectively.

RESULTS

Abdominal air column variation was as great as ±80% between weekly CBCT and 4DCT. Even with such a large air column in the treatment path for pancreatic cancer, changes in anteroposterior dimension were minimal (2.8%). Using IMRT, variations in air column did not correlate dosimetrically with large changes in target volume. An average dosimetric deviation of mere -3.3% and a maximum of -5.5% was observed.

CONCLUSION

CBCT revealed large air column in GI structures; however, its impact is minimal for target coverage. Because of the inherent advantage of segmentation in IMRT, where only a small fraction of a given beam passes through the air column, this technique might have an advantage over 3DCRT in treating upper GI malignancies where the daily air column can have significant impact. Advances in knowledge: Radiation treatment of pancreatic cancer has significant challenges due to positioning, imaging of soft tissues and variability of air column in bowels. The dosimetric impact of variable air column is retrospectively studied using CBCT. Even though, the volume of air column changes by ± 80%, its dosimetric impact in IMRT is minimum.

Daily CT guidance improves target coverage during definitive radiation therapy for gastric MALT lymphoma

PURPOSE

Radiation therapy (RT) for gastric mucosa-associated lymphoid tissue (MALT) lymphoma is challenging because of variation in the stomach's position, size, and shape. We investigated the interfractional changes in stomach location, consequent dosimetric effects, and impact of daily computed tomography image guidance RT (CT-IGRT).

METHODS AND MATERIALS

Twelve patients treated for gastric MALT lymphoma with intensity modulated radiation therapy, using a breath-hold technique and restriction of oral intake, were studied retrospectively. The planning target volume (PTV) comprised a 0.5 to 1.0 cm expansion of the stomach. The prescription dose was 30 Gy in 15 to 20 fractions. CT-IGRT was performed daily using CT-on-Rails. Dosimetry was calculated on 229 daily CT images after bony versus CT-based soft tissue alignment, and doses delivered to the target and adjacent structures were compared with the treatment plan. Target coverage was expressed as the percent of the clinical target volume (CTV) and PTV receiving ≥95% of the prescribed dose (V95%).

RESULTS

The average change in stomach volume was -12.4% (range, -47.6% to 38.6%). The average shift required for target coverage was 1.0 cm (maximum, 2.2 cm). With CT-based alignment to the stomach, the average V95% was 98.5% for CTV and 94.9% for PTV; with bony alignment, these values were 94.5% and 90.4%, respectively (P < .01 for CTV and PTV). With bony alignment, the PTV V95% was ≤90% in 4 patients (33%) over the course of treatment and was as low as 72.5% for 1 fraction. The kidney position varied with respect to the stomach and bony anatomy. Consequently, the dose to the left kidney was higher based on daily CT scans than on planning scans. Dose to other organs at risk did not vary significantly.

CONCLUSIONS

Substantial interfractional variation in stomach volume was observed, despite treatment with breath-hold and restriction of oral intake. Daily CT-IGRT improved target coverage, enabling excellent coverage despite the use of small PTV margins.

4D-Listmode-PET-CT and 4D-CT for optimizing PTV margins in gastric lymphoma : Determination of intra- and interfractional gastric motion

PURPOSE

New imaging protocols for radiotherapy in localized gastric lymphoma were evaluated to optimize planning target volume (PTV) margin and determine intra-/interfractional variation of the stomach.

METHODS

Imaging of 6 patients was explored prospectively. Intensity-modulated radiotherapy (IMRT) planning was based on 4D/3D imaging of computed tomography (CT) and positron-emission tomography (PET)-CT. Static and motion gross tumor volume (sGTV and mGTV, respectively) were distinguished by defining GTV (empty stomach), clinical target volume (CTV = GTV + 5 mm margin), PTV (GTV + 10/15/20/25 mm margins)  plus paraaortic lymph nodes and proximal duodenum. Overlap of 4D-Listmode-PET-based mCTV with 3D-CT-based PTV (increasing margins) and V95/D95 of mCTV were evaluated. Gastric shifts were determined using online cone-beam CT. Dose contribution to organs at risk was assessed.

RESULTS

The 4D data demonstrate considerable intra-/interfractional variation of the stomach, especially along the vertical axis. Conventional 3D-CT planning utilizing advancing PTV margins of 10/15/20/25 mm resulted in rising dose coverage of mCTV (4D-Listmode-PET-Summation-CT) and rising D95 and V95 of mCTV. A PTV margin of 15 mm was adequate in 3 of 6 patients, a PTV margin of 20 mm was adequate in 4 of 6 patients, and a PTV margin of 25 mm was adequate in 5 of 6 patients.

CONCLUSION

IMRT planning based on 4D-PET-CT/4D-CT together with online cone-beam CT is advisable to individualize the PTV margin and optimize target coverage in gastric lymphoma.

Resected gastric cancer with D2 dissection: advances in adjuvant chemoradiotherapy and radiotherapy techniques

Surgery is the main treatment option for locally advanced gastric cancer. D2 dissection has been recommended worldwide as standard lymphadenectomy for resectable gastric cancer. Furthermore, the role of peri- or postoperative chemotherapy for D2-dissected gastric cancer has been established in both Western and European countries. It has been disputed whether adding radiotherapy to chemotherapy could further benefit those patients. Until recently, studies from Korea and China may have made it clear. In North America, however, the INT-0116 trial does not rule out that chemoradiotherapy is effective in patients with D2 dissection, but the ongoing CRITICS trial will, hopefully, clarify this. In addition, literature published in the past decade supports the theory that improved radiotherapy techniques are likely to accurately deliver radiation dose and significantly reduce radiation toxicity. Finally, the status of E2F-1 and HER-2 may be associated with efficacy of radiotherapy based on retrospective studies.

Optimizing the performance of magnetic-assisted capsule endoscopy of the upper GI tract using multiplanar CT modelling

BACKGROUND AND AIMS

This study used computed tomography modelling of the abdomen to determine the optimal placements of a magnetic capsule endoscope in the stomach that allows complete mucosal visualization and determined the optimal placement of the handheld magnet to aid pyloric traversing.

MATERIALS AND METHODS

Using multiplanar reformatting, 100 abdominal computed tomography scans were analysed to assess gastric luminal visualization by a capsule endoscope from five fixed stations throughout the stomach. From each station, we assessed the ability of a capsule endoscope to visualize six gastric landmarks. The pyloric canal angles were calculated to create a vector. We mapped the position of this vector on the patient to determine the optimal placement of the magnet that would aid pyloric traversing.

RESULTS

Complete visualization of the stomach (viewing all landmarks) was only achievable in up to 29% of cases when viewed from a sole station. Maximal visualization required combining stations. Fundal dependent (station 1) and opposite antral dependent (station 4) was the best, achieving visualization in 85% (P<0.01). The optimal positioning of the magnet to aid pyloric traversing was posteriorly between vertebrae T5 and L2 in an area 10 cm to the left and 18 cm to the right (83% cases). Age older than 55 years (P=0.03) and the ability to view the pylorus from station 3 (P=0.04) were associated with an extreme pyloric vector.

CONCLUSION

Although there is some extreme variation in the upper gastrointestinal anatomy, the majority of cases will allow the use of a single standard method in performing MACE, which may be very useful for screening purposes.

Four-dimensional versus 3-dimensional computed tomographic planning for gastric mucosa associated lymphoid tissue lymphoma

PURPOSE

This study compares dosimetric parameters of 4-dimensional (4D) and 3-dimensional (3D) computed tomographic (CT) planning for gastric mucosa-associated lymphoid tissue (MALT) lymphoma in an attempt to identify any potential benefit of 4DCT planning.

METHODS AND MATERIALS

We identified 18 patients who received definitive 4DCT radiation planning from September 2006 to September 2011 for gastric MALT lymphoma at our institution. In addition to the kidneys and liver, we contoured an internal target volume (ITV) and static clinical target volume (sCTV) for each patient based on the 4D and 3D images, respectively, to develop 3D conformal radiation plans. Using the static and motion plans, we measured the volume of ITV covered by at least 95% of the prescribed dose (V95), the minimum dose received by 95% of the ITV (D95), and the volume of organs receiving at least 20 Gy or 30 Gy (V20 or V30).

RESULTS

Volumes of the ITV, motion liver, left kidney, and right kidney were significantly larger than their static counterparts. The static plan significantly lowered the ITV V95 and D95 compared with the motion plan. However, this undercoverage was significantly associated with the superior-inferior (SI) respiratory excursions. A V95 of >98% was observed in 92% of patients with SI excursions <15 mm versus 33% of patients with SI excursions >15 mm (P = .02). When compared with the motion plan, the static plan also significantly lowered the liver V30 and left kidney V20.

CONCLUSIONS

The 3DCT planning can result in undercoverage of the ITV and altered estimation of doses to normal structures. However, in patients with limited respiratory excursions (<15 mm), 4D and 3D images generated similar ITV coverage.