title: Volumetric-modulated arc therapy (RapidArc) vs. conventional fixed-field intensity-modulated radiotherapy for ¹⁸F-FDG-PET-guided dose escalation in oropharyngeal cancer: a planning study.
abstract: Fluorine-18-fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET)-guided focal dose escalation in oropharyngeal cancer may potentially improve local control. We evaluated the feasibility of this approach using volumetric-modulated arc therapy (RapidArc) and compared these plans with fixed-field intensity-modulated radiotherapy (IMRT) focal dose escalation plans.
  
  
  METHODS
  An initial study of 20 patients compared RapidArc with fixed-field IMRT using standard dose prescriptions. From this cohort, 10 were included in a dose escalation planning study. Dose escalation was applied to ¹⁸F-FDG-PET-positive regions in the primary tumor at dose levels of 5% (DL1), 10% (DL2), and 15% (DL3) above standard radical dose (65 Gy in 30 fractions). Fixed-field IMRT and double-arc RapidArc plans were generated for each dataset. Dose-volume histograms were used for plan evaluation and comparison. The Paddick conformity index (CI(Paddick)) and monitor units (MU) for each plan were recorded and compared. Both IMRT and RapidArc produced clinically acceptable plans and achieved planning objectives for target volumes. Dose conformity was significantly better in the RapidArc plans, with lower CI(Paddick) scores in both primary (PTV1) and elective (PTV2) planning target volumes (largest difference in PTV1 at DL3; 0.81 ± 0.03 [RapidArc] vs. 0.77 ± 0.07 [IMRT], p = 0.04). Maximum dose constraints for spinal cord and brainstem were not exceeded in both RapidArc and IMRT plans, but mean doses were higher with RapidArc (by 2.7 ± 1 Gy for spinal cord and 1.9 ± 1 Gy for brainstem). Contralateral parotid mean dose was lower with RapidArc, which was statistically significant at DL1 (29.0 vs. 29.9 Gy, p = 0.01) and DL2 (29.3 vs. 30.3 Gy, p = 0.03). MU were reduced by 39.8-49.2% with RapidArc (largest difference at DL3, 641 ± 94 vs. 1261 ± 118, p < 0.01). ¹⁸F-FDG-PET-guided focal dose escalation in oropharyngeal cancer is feasible with RapidArc. Compared with conventional fixed-field IMRT, RapidArc can achieve better dose conformity, improve contralateral parotid sparing, and uses fewer MU.
authors: Department of Oncology, St. Luke's Cancer Centre, Royal Surrey County Hospital, Guildford, Surrey, UK. m.teoh@nhs.net
authors: May
authors: M
authors: Teoh
authors: Sabeena
authors: S
authors: Beveridge
authors: Katie
authors: K
authors: Wood
authors: Stephen
authors: S
authors: Whitaker
authors: Elizabeth
authors: E
authors: Adams
authors: Donna
authors: D
authors: Rickard
authors: Tom
authors: T
authors: Jordan
authors: Andrew
authors: A
authors: Nisbet
authors: Catharine H
authors: CH
authors: Clark
mesh_terms: D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D009959:Oropharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18