title: Daily CT guidance improves target coverage during definitive radiation therapy for gastric MALT lymphoma.
abstract: OBJECTIVE
  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
  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.
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas.
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas. Electronic address: samilgrom@mdanderson.org.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Milgrom
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas.
authors.forename: Bouthaina S
authors.initials: BS
authors.lastname: Dabaja
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas.
authors.forename: Grace L
authors.initials: GL
authors.lastname: Smith
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas.
authors.forename: Mary
authors.initials: M
authors.lastname: Martel
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center, Houston, Texas.
authors.forename: Chelsea C
authors.initials: CC
authors.lastname: Pinnix
mesh_terms: D062485:Breath Holding; D004032:Diet; D005753:Gastric Mucosa / Q000473:pathology; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging / Q000528:radiation effects; D008228:Lymphoma, Non-Hodgkin / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D059351:Organ Sparing Treatments; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D013274:Stomach Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome