title: Re-planning for compensator-based IMRT with original compensators.
abstract: Compared with multileaf collimator (MLC)-based intensity-modulated radiotherapy (IMRT) for moving targets, compensator-based IMRT has advantages such as shorter beam-on time, fewer monitor units with potentially decreased secondary carcinogenesis risk, better optimization-to-deliverable dose conversion, and often better dose conformity. Some of the disadvantages include additional time for the compensators to be built and delivered, as well as extra cost. Patients undergoing treatment of abdominal cancers often experience weight loss. It would be necessary to account for this change in weight with a new plan and a second set of compensators. However, this would result in treatment delays and added costs. We have developed a method to re-plan the patient using the same set of compensators. Because the weight changes seen with the treatment of abdominal cancers are usually relatively small, a new 4D computed tomography (CT) acquired in the treatment position with markers on the original isocenter tattoos can be registered to the original planning scan. The contours of target volumes from the original scans are copied to the new scan after fusion. The original compensator set can be used together with a few field-in-field (FiF) beams defined by the MLC (or beams with cerrobend blocks for accelerators not equipped with a MLC). The weights of the beams with compensators are reduced so that the FiF or blocked beams can be optimized to mirror the original plan and dose distribution. Seven abdominal cancer cases are presented using this technique. The new plan on the new planning CT images usually has the same dosimetric quality as the original. The target coverage and dose uniformity are improved compared with the plan without FiF/block modification. Techniques combining additional FiF or blocked beams with the original compensators optimize the treatment plans when patients lose weight and save time and cost compared with generating plans with a new set of compensators.
authors.affiliation: Division of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Zhang
authors.forename: Vladimir
authors.initials: V
authors.lastname: Feygelman
authors.forename: Craig
authors.initials: C
authors.lastname: Stevens
authors.forename: Weiqi
authors.initials: W
authors.lastname: Li
authors.forename: Susan
authors.initials: S
authors.lastname: Leuthold
authors.forename: Gregory
authors.initials: G
authors.lastname: Springett
authors.forename: Sarah
authors.initials: S
authors.lastname: Hoffe
mesh_terms: D000008:Abdominal Neoplasms / Q000532:radiotherapy*; D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D011835:Radiation Protection / Q000295:instrumentation / Q000379:methods; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity