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The impact of intensity-modulated radiation therapy plan normalization in the postprostatectomy setting-does it
Mary Anne Stritch1, Elizabeth Forde1, Michelle Leech1
1Applied Radiation Therapy Trinity, Discipline of Radiation Therapy, School of Medicine, Trinity College Dublin, Ireland.
Summary
Plan normalization significantly impacts intensity-modulated radiation therapy (IMRT) outcomes for prostate cancer patients. Different methods, like dose received by 98% (D98) versus mean dose (Dmean), alter target coverage and organ at risk doses, necessitating clear reporting.
Area of Science:
- Radiation Oncology
- Medical Physics
- Radiotherapy Planning
Background:
- International Commission on Radiation Units & Measurements (ICRU) Report-83 recommends dose-volume prescribing for intensity-modulated radiation therapy (IMRT).
- Clinical practice shows variability in prostate IMRT plan prescription methods.
- Normalization is a critical step in IMRT planning, influencing dose distribution.
Purpose of the Study:
- To retrospectively investigate the impact of different plan normalization methods on postprostatectomy IMRT.
- To compare dosimetric outcomes between plans normalized to D98 (dose to 98% of PTV) and Dmean (mean PTV dose).
Main Methods:
- IMRT plans were created for 20 postprostatectomy patients.
- Plans were normalized using two methods: D98=100% prescribed dose and Dmean=100% prescribed dose.
- Dosimetric endpoints for targets and organs at risk (OARs) were extracted and statistically analyzed (Wilcoxon signed-rank test).
Main Results:
- Target coverage and OAR doses were significantly higher in D98-normalized plans compared to Dmean-normalized plans (p < 0.05).
- Exceptions included the D2 dose to the rectum and right femoral head, which were not significantly different.
- Normalization method demonstrably affects plan dosimetric endpoints.
Conclusions:
- The choice of normalization method critically influences IMRT plan quality and dosimetric outcomes.
- Reporting the specific normalization method is essential for accurate interpretation of IMRT dosimetric studies.
- Standardizing normalization reporting can reduce clinical variability and improve treatment consistency.
