title: Adaptive radiation therapy for pediatric head and neck malignancies: Dosimetric implications.
abstract: OBJECTIVE
  This study was designed to evaluate the role of adaptive radiation therapy for children receiving curative radiation therapy to the head and neck region.
  
  
  METHODS
  Ten children receiving definitive, conformal radiation therapy to the head and neck region were prospectively evaluated for anatomic changes during the course of radiation therapy. Images were acquired midway through the number of planned radiation therapy fractions during the planned course of radiation therapy. Body contours, target volumes, and organs at risk were redrawn on the new set of images. Two sets of additional treatment plans were generated: (1) a nonoptimized plan (plan 2), that is, an overlay of the original plan (plan 1) on the new set of contours, and (2) an optimized plan (plan 3) with the new set of contours. These 3 sets of plans were then compared for dosimetric differences.
  
  
  RESULTS
  Five children had nasopharynx carcinoma, whereas the other 5 had embryonal rhabdomyosarcoma. The average reduction in gross tumor volume was 40% (mean volume, 41.87 mL; P = .005). The average changes in right and left parotid volumes were 2.72 and 1.92 mL, respectively. With nonoptimized plans, the average increase in maximum dose to the spinal cord was 15% (79.99%-94.99%; P = .013). With reoptimization, the maximum dose to the spinal cord decreased from 94.99% to 85.26% (mean difference, -9.73%; P = .02). Average D99 for the planning target volume (dose received by 99% of the target volume) was 88.66% and 86.89% with the original and reoptimized plans, respectively (P = .50). For the entire group, the mean conformation number index with nonoptimized plans was reduced from 0.734 to 0.628 (P = .013). This improved with reoptimization (P = .114). The homogeneity index improved with reoptimization from a mean value of 0.113 to 0.098 (P = 0.28). For nonoptimized plans, the average integral dose increased from 74.66 to 76.27 L-Gy (P = .486) compared with the original plans. Reoptimization resulted in a 5% average reduction in the integral dose, from 76.27 to 72.28 L-Gy (P = .007).
  
  
  CONCLUSIONS
  This study demonstrates the usefulness of adaptive radiation therapy for children receiving radiation therapy to the head and neck region.
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India. Electronic address: laskars2000@yahoo.com.
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Laskar
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Prakash
authors.initials: P
authors.lastname: Pandit
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Suman
authors.initials: S
authors.lastname: Mallik
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Pramod
authors.initials: P
authors.lastname: Tike
authors.affiliation: Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Suresh
authors.initials: S
authors.lastname: Chaudhari
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Nehal
authors.initials: N
authors.lastname: Khanna
authors.affiliation: Department of Pediatric Oncology, Tata Memorial Hospital, Mumbai, Maharashtra, India.
authors.forename: Tushar
authors.initials: T
authors.lastname: Vora
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007223:Infant; D008297:Male; D011446:Prospective Studies; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods