title: Monitoring dosimetric impact of weight loss with kilovoltage (kV) cone beam CT (CBCT) during parotid-sparing IMRT and concurrent chemotherapy.
abstract: OBJECTIVE
  Parotid-sparing head-and-neck intensity-modulated radiotherapy (IMRT) can reduce long-term xerostomia. However, patients frequently experience weight loss and tumor shrinkage during treatment. We evaluate the use of kilovoltage (kV) cone beam computed tomography (CBCT) for dose monitoring and examine if the dosimetric impact of such changes on the parotid and critical neural structures warrants replanning during treatment.
  
  
  METHODS
  Ten patients with locally advanced oropharyngeal cancer were treated with contralateral parotid-sparing IMRT concurrently with platinum-based chemotherapy. Mean doses of 65 Gy and 54 Gy were delivered to clinical target volume (CTV)1 and CTV2, respectively, in 30 daily fractions. CBCT was prospectively acquired weekly. Each CBCT was coregistered with the planned isocenter. The spinal cord, brainstem, parotids, larynx, and oral cavity were outlined on each CBCT. Dose distributions were recalculated on the CBCT after correcting the gray scale to provide accurate Hounsfield calibration, using the original IMRT plan configuration.
  
  
  RESULTS
  Planned contralateral parotid mean doses were not significantly different to those delivered during treatment (p > 0.1). Ipsilateral and contralateral parotids showed a mean reduction in volume of 29.7% and 28.4%, respectively. There was no significant difference between planned and delivered maximum dose to the brainstem (p = 0.6) or spinal cord (p = 0.2), mean dose to larynx (p = 0.5) and oral cavity (p = 0.8). End-of-treatment mean weight loss was 7.5 kg (8.8% of baseline weight). Despite a ≥10% weight loss in 5 patients, there was no significant dosimetric change affecting the contralateral parotid and neural structures.
  
  
  CONCLUSIONS
  Although patient weight loss and parotid volume shrinkage was observed, overall, there was no significant excess dose to the organs at risk. No replanning was felt necessary for this patient cohort, but a larger patient sample will be investigated to further confirm these results. Nevertheless, kilovoltage CBCT is a valuable tool for patient setup verification and monitoring of dosimetric variation during radiotherapy.
authors.affiliation: Academic Radiation Oncology, The Christie NHS Foundation Trust, Manchester, UK. hokeanfatt@hotmail.com
authors.forename: Kean Fatt
authors.initials: KF
authors.lastname: Ho
authors.forename: Tom
authors.initials: T
authors.lastname: Marchant
authors.forename: Chris
authors.initials: C
authors.lastname: Moore
authors.forename: Gareth
authors.initials: G
authors.lastname: Webster
authors.forename: Carl
authors.initials: C
authors.lastname: Rowbottom
authors.forename: Hazel
authors.initials: H
authors.lastname: Penington
authors.forename: Lip
authors.initials: L
authors.lastname: Lee
authors.forename: Beng
authors.initials: B
authors.lastname: Yap
authors.forename: Andrew
authors.initials: A
authors.lastname: Sykes
authors.forename: Nick
authors.initials: N
authors.lastname: Slevin
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001933:Brain Stem / Q000000981:diagnostic imaging; D016190:Carboplatin / Q000627:therapeutic use; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000532:radiotherapy*; D059248:Chemoradiotherapy / Q000379:methods; D002945:Cisplatin / Q000627:therapeutic use; D054893:Cone-Beam Computed Tomography; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007830:Larynx / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D009055:Mouth / Q000000981:diagnostic imaging; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000000981:diagnostic imaging; D009959:Oropharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000532:radiotherapy*; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects; D011446:Prospective Studies; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000000981:diagnostic imaging; D047368:Tumor Burden / Q000528:radiation effects; D015431:Weight Loss
chemical_list: D000970:Antineoplastic Agents; D016190:Carboplatin; D002945:Cisplatin