title: Are pitch and roll compensations required in all pathologies? A data analysis of 2945 fractions.
abstract: OBJECTIVE
  New linear accelerators can be equipped with a 6D robotic couch, providing two additional rotational motion axes: pitch and roll. These shifts in kilo voltage-cone beam CT (kV-CBCT) image-guided radiotherapy (IGRT) were evaluated over the first 6 months of usage of a 6D robotic couch-top, ranking the treatment sites for which the two compensations are larger for patient set-up.
  
  
  METHODS
  The couch compensations of 2945 fractions for 376 consecutive patients treated on the PerfectPitch™ 6D couch (Varian(®) Medical Systems, Palo Alto, CA) were analysed. Among these patients, 169 were treated for brain, 111 for lung, 54 for liver, 26 for pancreas and 16 for prostate tumours. During the set-up, patient anatomy from planning CT was aligned to kV-CBCT, and 6D movements were executed. Information related to pitch and roll were extracted by proper querying of the Microsoft(®) SQL server (Microsoft Corporation, Redmond, WA) ARIA database (Varian Medical Systems). Mean values and standard deviations were calculated for all sites. Kolmogorov-Smirnov (KS) test was performed.
  
  
  RESULTS
  Considering all the data, mean pitch and roll adjustments were -0.10° ± 0.92° and 0.12° ± 0.96°, respectively; mean absolute values for both adjustments were 0.58° ± 0.69° and 0.69° ± 0.72°, respectively. Brain treatments showed the highest mean absolute values for pitch and roll rotations (0.73° ± 0.69° and 0.80° ± 0.78°, respectively); the lowest values of 0.36° ± 0.47° and 0.49° ± 0.58° were found for pancreas. KS test was significant for brain vs liver, pancreas and prostate. Collective corrections (pitch + roll) >0.5°, >1.0° and >2.0° were observed in, respectively, 79.8%, 61.0% and 29.1% for brain and 56.7%, 39.4% and 6.7% for pancreas.
  
  
  CONCLUSIONS
  Adjustments in all six dimensions, including unconventional pitch and roll rotations, improve the patient set-up in all treatment sites. The greatest improvement was observed for patients with brain tumours.
  
  
  CONCLUSIONS
  To our knowledge, this is the first systematic evaluation of the clinical efficacy of a 6D Robotic couch-top in CBCT IGRT over different tumour regions.
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Mancosu
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Reggiori
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Gaudino
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Lobefalo
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Paganini
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Palumbo
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Stravato
authors.affiliation: 1Physics Service of Radiation Oncology Department, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tomatis
authors.affiliation: 2Radiation Oncology Department, Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Scorsetti
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy; D002138:Calibration; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy; D008175:Lung Neoplasms / Q000532:radiotherapy; D008297:Male; D009369:Neoplasms / Q000532:radiotherapy*; D010190:Pancreatic Neoplasms / Q000532:radiotherapy; D010315:Particle Accelerators; D056888:Patient Positioning; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D061089:Radiotherapy, Image-Guided; D012371:Robotics