A case of gastric lymphoma with marked interfractional gastric movement during radiation therapy

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.

[Stereotactic body radiotherapy for locally advanced pancreatic cancer: A systemic review]

Stereotactic body radiation therapy (SBRT) for locally advanced pancreatic cancer (LAPC) is an emerging treatment option. Most studies showed local control of approximately 75% with no evidence of improved overall survival. Gastrointestinal toxicities could be significant, ranging up to 22% for acute toxicities≥grade 3+ and 44% for late toxicities≥grade 3+. Currently, no standardized guidelines for treatment and management scheme. We conducted a systemic review of published prospective and retrospective trials to evaluate the efficacy, safety, technical data, and discuss future directions.

Role of Daily Plan Adaptation in MR-Guided Stereotactic Ablative Radiation Therapy for Adrenal Metastases

PURPOSE

To study interfractional organ changes during magnetic resonance (MR)-guided stereotactic ablative radiation therapy for adrenal metastases and to evaluate the dosimetric advantages of online plan adaptation.

METHODS AND MATERIALS

Seventeen patients underwent a total of 84 fractions of video-assisted, respiration-gated, MR-guided adaptive radiation therapy to deliver either 50 Gy (5 fractions), 60 Gy (8 fractions), or 24 Gy (3 fractions). An MR scan was repeated before each fraction, followed by rigid coregistration to the gross tumor volume (GTV) on the pretreatment MR scan. Contour deformation, planning target volume (PTV) (GTV + 3 mm) expansion, and online plan reoptimization were then performed. Reoptimized plans were compared with baseline treatment plans recalculated on the anatomy-of-the-day ("predicted plans"). Interfractional changes in organs at risk (OARs) were quantified according to OAR volume changes within a 3 cm distance from the PTV surface, center of mass displacements, and the Dice similarity coefficient. Plan quality evaluation was based on target coverage (GTV and PTV) and high dose sparing of all OARs (V_36Gy, V_33Gy, and V_25Gy).

RESULTS

Substantial center of mass displacements were observed for stomach, bowel, and duodenum, 17, 27 and 36 mm, respectively. Maximum volume changes for the stomach, bowel, and duodenum within 3 cm of PTV were 23.8, 20.5, and 20.9 cm³, respectively. Dice similarity coefficient values for OARs ranged from 0.0 to 0.9 for all fractions. Baseline plans recalculated on anatomy-of-the-day revealed underdosage of target volumes and variable OAR sparing, leading to a failure to meet institutional constraints in a third of fractions. Online reoptimization improved target coverage in 63% of fractions and reduced the number of fractions not meeting the V_95% objective for GTV and PTV. Reoptimized plans exhibited significantly better sparing of OARs.

CONCLUSIONS

Significant interfractional changes in OAR positions were observed despite breath-hold stereotactic ablative radiation therapy delivery under MR-guidance. Online reoptimization of treatment plans led to significant improvements in target coverage and OAR sparing.

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.

Fast and robust online adaptive planning in stereotactic MR-guided adaptive radiation therapy (SMART) for pancreatic cancer

BACKGROUND AND PURPOSE

To implement a robust and fast stereotactic MR-guided adaptive radiation therapy (SMART) online strategy in locally advanced pancreatic cancer (LAPC).

MATERIAL AND METHODS

SMART strategy for plan adaptation was implemented with the MRIdian system (ViewRay Inc.). At each fraction, OAR (re-)contouring is done within a distance of 3cm from the PTV surface. Online plan re-optimization is based on robust prediction of OAR dose and optimization objectives, obtained by building an artificial neural network (ANN). Proposed limited re-contouring strategy for plan adaptation (SMART_3CM) is evaluated by comparing 50 previously delivered fractions against a standard (re-)planning method using full-scale OAR (re-)contouring (FULLOAR). Plan quality was assessed using PTV coverage (V_95%, D_mean, D_1cc) and institutional OAR constraints (e.g. V_33Gy).

RESULTS

SMART_3CM required a significant lower number of optimizations than FULLOAR (4 vs 18 on average) to generate a plan meeting all objectives and institutional OAR constraints. PTV coverage with both strategies was identical (mean V_95%=89%). Adaptive plans with SMART_3CM exhibited significant lower intermediate and high doses to all OARs than FULLOAR, which also failed in 36% of the cases to adhere to the V_33Gy dose constraint.

CONCLUSIONS

SMART_3CM approach for LAPC allows good OAR sparing and adequate target coverage while requiring only limited online (re-)contouring from clinicians.

Novel Use of Endoscopic Clips as Fiducials for Radiotherapy in Small Bowel Lymphoma

A 31-year-old woman was diagnosed with duodenal grade 1 follicular lymphoma. The patient underwent radiotherapy and on surveillance enteroscopy, the lymphoma was persistently identified in the duodenum and jejunum. Endoscopic clips were used as fiducials to better localize the tumor during radiotherapy. Endoscopic clips are increasingly used as tumor localization tools because of their favorable risk-benefit ratio. In our case, endoscopic clipping was necessary to properly localize the tumor after prior treatment failure, and the patient now has no evidence of disease. Larger studies are needed to demonstrate the efficacy of clips in tumor localization and improved disease-related morbidity.

Chemoradiation for gastric cancer: controversies, updates and novel techniques

The INT0116 trial established the role of adjuvant chemoradiation (CRT) in the multidisciplinary approach to the management of locally advanced gastric cancer. However, whether adjuvant CRT is indispensable for patients undergoing D2 dissection remains undefined. The adjuvant chemoradiation therapy in stomach cancer (ARTIST) trial, which was designed to compare adjuvant chemotherapy to CRT, failed to demonstrate differences in disease-free and overall survival in the whole study group; however, subgroup analysis indicated that patients with lymph node metastasis may benefit from additional radiation. A follow-up ARTIST II trial is currently under way. The efficacy of adjuvant CRT remains controversial because of variation among studies in the inclusion criteria and treatment delivery methods; however, the identification of patients who would benefit from CRT is critical. Advanced radiotherapy techniques such as intensity-modulated radiotherapy protect normal tissues via motion management and decreased radiation-induced toxicity and contribute to plan optimization. Further studies integrating clinical and molecular factors as well as neoadjuvant CRT are warranted.

Efficient palliative involved-field radiotherapy on highly progressive diffuse large B-cell primary gastric lymphoma with liver cirrhosis

We report the case of a 73-year-old woman having diffuse large B-cell primary gastric lymphoma with a cirrhotic liver caused by hepatitis C virus infection. She visited our hospital with symptoms of nausea and vomiting, which appeared to be caused by stenosis due to the tumor. Metastatic tumors were seen in the gastric and jugular lymph nodes. The clinical stage was IVB with a high risk of poor prognosis according to the international index. Because of poor hepatic reserve function, standard chemotherapy could not be administered. To maintain her quality of life, palliative involved-field radiotherapy was performed. The symptoms and tumor markers significantly improved, and computed tomography and endoscopy indicated the disappearance of the primary gastric tumor. Two months after radiotherapy and her return home, she died of pneumonia. Autopsy showed neither lymphoma cells nor stenosis of gastric lesion. The significant anti-tumor effect on primary tumor in our case suggests that the involved-field radiotherapy, although palliative, can be a therapeutic option for primary gastric lymphoma patients with various complications.

Usefulness of 4D-CT for radiation treatment planning of gastric MZBCL/MALT

It is well known that significant variations in stomach size, shape, and respiratory motion lead to uncertainties in target localization during treatment for gastric lymphoma. In this study, the usefulness of 4D-CT for radiation planning of gastric MZBCL/MALT was evaluated. Treatment planning using 4DCT (plan A) and conventional planning with a uniform margin (plan B) were compared using dose volume histograms (DVH) of the planning target volume (PTV) and the organ at risk, as well as the dose coverage of the clinical target volume (CTV) assessed by weekly online cone beam CT (CBCT) during the treatment course. In addition, regarding the image quality of CBCT , the interobserver agreement for the delineated volume of the CTV on CBCT was analyzed. The mean PTV of plan A was significantly smaller than that of plan B (p = 0.008). The mean doses to the liver and heart in plan A were significantly lower than those in plan B (p = 0.02 and 0.03, respectively). The reductions of V(20) of each kidney in plan A compared with those in plan B were 4.8 ± 2.4% in the right kidney and 16.3 ± 10.4% in the left. There was no significant difference in the dose coverage of the CTV between the plans during the treatment course. The interobserver agreement for the volume of the CTV was moderate correlation. Treatment planning using 4DCT for gastric MZBCL/MALT was useful for effective and safe irradiation with minimizing exposure of the organ at risk.

Determination of planning target volume for whole stomach irradiation using daily megavoltage computed tomographic images

PURPOSE

Whole stomach radiation therapy is often used in the management of gastric lymphoma. However, very limited data exist with regard to planning target volume requirements for the whole stomach. This study retrospectively analyzed daily megavoltage computed tomographic (CT) scans of gastric lymphoma patients in order to help determine the interfraction variation of the stomach position.

METHODS AND MATERIALS

Forty-one daily megavoltage CT images from 3 gastric lymphoma patients were used for stomach contouring. Each patient's megavoltage CT images were rigidly registered to their CT simulation data sets, and the margin in each direction that covered at least 95% of the daily stomach volumes was computed using a simple grid search. Patient setup variation was also calculated from the daily patient shifts. The organ motion margin was then added to the setup margin to render the total margin.

RESULTS

A uniform margin of 2.2 cm is required to cover 95% of the stomach over the treatment course. However, direction-specific margins were observed from 1.72, 1.88, 0.92, 2.23, 1.90, and 0.86 cm for the right, left, posterior, anterior, superior, and inferior directions, respectively.

CONCLUSIONS

The results of this study provide helpful 3-dimensional volumetric information to the limited existing data on margin requirements for whole stomach radiation therapy.

Intrafractional gastric motion and interfractional stomach deformity using CT images

To evaluate the intra- and interfractional gastric motion using repeated CT scans, six consecutive patients with gastric lymphoma treated at our institution between 2006 and 2008 were included in this study. We performed a simulation and delivered RT before lunch after an overnight fast to minimize the stomach volume. These patients underwent repeated CT scanning at mild inhale and exhale before their course of treatment. The repeated CT scans were matched on bony anatomy to the planning scan. The center of stomach was determined in the X (lateral), Y (superior-inferior), and Z (ventro-dorsal) coordinate system to evaluate the intra- and interfractional motion of the stomach on each CT scan. We then calculated the treatment margins. Each patient was evaluated four to five times before their course of RT. The average intrafractional motions were -12.1, 2.4 and 4.6 mm for the superior-inferior (SI), lateral (LAT), and ventro-dorsal (VD) direction. The average interfractional motions of the center of the stomach were -4.1, 1.9 and 1.5 mm for the SI, LAT and VD direction. The average of the vector length was 13.0 mm. The systematic and random errors in SI direction were 5.1, and 4.6 mm, respectively. The corresponding figures in LAT and VD directions were 10.9, 5.4, 10.0, and 6.5 mm, respectively. Thus, the 15.9, 31.0 and 29.6 mm of margins are required for the SI, LAT, and VD directions, respectively. We have demonstrated not only intrafractional stomach motion, but also interfractional motion is considerable.