title: IMRT dose escalation for positive para-aortic lymph nodes in patients with locally advanced cervical cancer while reducing dose to bone marrow and other organs at risk.
abstract: OBJECTIVE
  To evaluate the feasibility of dose-escalated para-aortic lymph node (PALN) intensity modulated radiation therapy (IMRT) in reducing the dose to bone marrow, bowel, spinal cord, and kidneys, compared with conventional radiation techniques of PALNs in patients with locally advanced cervical cancer and PALN metastases.
  
  
  METHODS
  Computed tomography scans and MRI studies of 5 cervical cancer patients with PALN involvement were transferred to an IMRT treatment planning workstation (Eclipse/Helios) for image fusion and definition of target volumes and critical structures. The positive PALNs identified on fused computed tomography-magnetic resonance images were defined as the gross target volume (GTV), and the PALN region was defined as the planning target volume. There were 2 distinct treatment regions: the PALN region superior to the isocenter and the whole-pelvis region inferior to the isocenter. Three treatment planning techniques were compared: AP/PA (both regions), 4-field box (both regions), and PALN-IMRT with 4-field box to the whole-pelvis field. With IMRT, the radiation dose to the GTV was escalated from the conventional 45 Gy to 60 Gy (2.4 Gy/fraction), whereas the planning target volume and whole-pelvis region received 45 Gy. The treatment planning isocenter was placed at the L4-L5 vertebral body interspace, and this allowed the two treatment regions to be abutted using independent jaws.
  
  
  RESULTS
  This study has demonstrated the feasibility of escalating the dose delivered to grossly positive PALNs to 60 Gy (2.4 Gy/fraction) with a 95.6% median GTV coverage, concomitantly with conventional treatment of the whole-pelvis region. PALN-IMRT significantly reduced V(40) bone marrow compared to the AP/PA and 4-field box techniques with a median of 21.3%, 98%, and 49.7%, respectively. The PALN-IMRT and 4-field box techniques showed a reduction in V(45) bowel over the AP/PA technique, but a level of statistical significance was not reached. The spinal cord received a significantly higher maximum dose when PALNs were treated with AP/PA fields. Alternatively, the use of the 4-field box technique yielded a significant increase in V(22) kidney on both sides. The placement of the treatment planning isocenter at the L4-L5 interspace allowed the PALN-IMRT and whole-pelvis regions to be treated with a relatively uniform dose at the abutment region.
  
  
  CONCLUSIONS
  In this dosimetric analysis, we demonstrated that dose-escalated PALN-IMRT with conventional whole-pelvis radiotherapy is feasible with significant sparing of critical normal structures compared to PALN conventional radiation techniques.
authors.affiliation: Department of Radiation Oncology, Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Raef S
authors.initials: RS
authors.lastname: Ahmed
authors.forename: Robert Y
authors.initials: RY
authors.lastname: Kim
authors.forename: Jun
authors.initials: J
authors.lastname: Duan
authors.forename: Streelatha
authors.initials: S
authors.lastname: Meleth
authors.forename: Jennifer F
authors.initials: JF
authors.lastname: De Los Santos
authors.forename: John B
authors.initials: JB
authors.lastname: Fiveash
mesh_terms: D001011:Aorta; D001853:Bone Marrow; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D015182:Lymphatic Irradiation / Q000379:methods*; D008207:Lymphatic Metastasis / Q000532:radiotherapy; D008279:Magnetic Resonance Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*