Dependence of achievable plan quality on treatment technique and planning goal refinement: a head-and-neck intensity modulated radiation therapy application.
OBJECTIVE
To develop a practical workflow for retrospectively analyzing target and normal tissue dose-volume endpoints for various intensity modulated radiation therapy (IMRT) delivery techniques; to develop technique-specific planning goals to improve plan consistency and quality when feasible.


METHODS
A total of 165 consecutive head-and-neck patients from our patient registry were selected and retrospectively analyzed. All IMRT plans were generated using the same dose-volume guidelines for TomoTherapy (Tomo, Accuray), TrueBeam (TB, Varian) using fixed-field IMRT (TB_IMRT) or RAPIDARC (TB_RAPIDARC), or Siemens Oncor (Siemens_IMRT, Siemens). A MATLAB-based dose-volume extraction and analysis tool was developed to export dosimetric endpoints for each patient. With a fair stratification of patient cohort, the variation of achieved dosimetric endpoints was analyzed among different treatment techniques. Upon identification of statistically significant variations, technique-specific planning goals were derived from dynamically accumulated institutional data.


RESULTS
Retrospective analysis showed that although all techniques yielded comparable target coverage, the doses to the critical structures differed. The maximum cord doses were 34.1 ± 2.6, 42.7 ± 2.1, 43.3 ± 2.0, and 45.1 ± 1.6 Gy for Tomo, TB_IMRT, TB_RAPIDARC, and Siemens_IMRT plans, respectively. Analyses of variance showed significant differences for the maximum cord doses but no significant differences for other selected structures among the investigated IMRT delivery techniques. Subsequently, a refined technique-specific dose-volume guideline for maximum cord dose was derived at a confidence level of 95%. The dosimetric plans that failed the refined technique-specific planning goals were reoptimized according to the refined constraints. We observed better cord sparing with minimal variations for the target coverage and other organ at risk sparing for the Tomo cases, and higher parotid doses for C-arm linear accelerator-based IMRT and RAPIDARC plans.


CONCLUSIONS
Patient registry-based processes allowed easy and systematic dosimetric assessment of treatment plan quality and consistency. Our analysis revealed the dependence of certain dosimetric endpoints on the treatment techniques. Technique-specific refinement of planning goals may lead to improvement in plan consistency and plan quality.
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California. Electronic address: xqi@mednet.ucla.edu.
X Sharon
XS
Qi
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Dan
D
Ruan
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Steve P
SP
Lee
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Andrew
A
Pham
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Patrick
P
Kupelian
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Daniel A
DA
Low
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Michael
M
Steinberg
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
John
J
Demarco
D000704:Analysis of Variance; D003051:Cochlea / Q000528:radiation effects; D005240:Feasibility Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008334:Mandible / Q000528:radiation effects; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects*; D010306:Parotid Gland / Q000528:radiation effects; D011787:Quality of Health Care; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D012189:Retrospective Studies; D013116:Spinal Cord / Q000528:radiation effects