What are the guidelines for following ICRU (International Commission on Radiation Units and Measurements) 89 in gynecology intracavitary therapy?

ICRU 89 Guidelines for Gynecology Intracavitary Brachytherapy

The International Commission on Radiation Units and Measurements (ICRU) Report 89 provides comprehensive guidelines for gynecological intracavitary brachytherapy that emphasize 3D volumetric planning over traditional point-based approaches to improve target coverage while reducing toxicity to organs at risk.

Key Principles of ICRU 89

• ICRU 89 builds upon previous reports (ICRU 38) by transitioning from 2D point-based dosimetry to 3D volumetric assessment for gynecological brachytherapy, allowing for better evaluation of dose to target volumes and organs at risk 1, 2
• The report recommends using CT-based 3D treatment planning to accurately assess dose distribution to the target volume and organs at risk, moving beyond the traditional Manchester Point A approach 2, 3
• Radiation doses should be calculated with inhomogeneity corrections, with three-dimensional conformal radiation techniques preferred for optimal dose distribution 4

Target Volume Definition

• ICRU 89 follows standardized definitions for volumes including Gross Tumor Volume (GTV), Clinical Target Volume (CTV), and treated volume, ensuring consistency in reporting across institutions 1
• Target volumes should be defined based on imaging studies (CT/MRI) obtained at the time of radiotherapy planning 4, 2
• For gynecological applications, the report recommends contouring the high-risk CTV (HR-CTV) and intermediate-risk CTV (IR-CTV) to ensure adequate coverage of the target while minimizing dose to surrounding normal tissues 2, 5

Dose Reporting Guidelines

• ICRU 89 recommends reporting the D90 (dose covering 90% of the target volume) for the HR-CTV rather than solely relying on Point A doses 2, 3
• For organs at risk (OARs), the report emphasizes volumetric dose parameters such as D2cc (minimum dose to the most exposed 2cc volume) for the rectum, bladder, and sigmoid, rather than just ICRU reference point doses 3, 5
• Studies have shown that the D2cc of the rectum and bladder are typically higher than the ICRU reference point doses by approximately 25%, highlighting the importance of volumetric assessment 3, 5

Applicator Placement and Dose Optimization

• ICRU 89 maintains that proper applicator placement is crucial for optimal dose distribution, with CT/MRI verification of position recommended 2, 6
• The report recommends using rectal retractors and/or vaginal packing to displace organs at risk away from high-dose regions, with studies showing significant reductions in rectal dose when proper techniques are employed 6
• According to recent guidelines, de-escalating the dose to the ICRU rectovaginal point from 75 to 65 Gy can reduce grade 2 or more vaginal stenosis by approximately 7% 4

Normal Tissue Constraints

• ICRU 89 emphasizes limiting doses to organs at risk with specific constraints:
  • Bladder: D2cc ≤80 Gy EQD2 to reduce the risk of severe late urinary toxicity 7, 8
  • Rectum: D2cc should be kept below 65-70 Gy EQD2 to minimize the risk of late rectal complications 4, 3
  • Sigmoid: D2cc constraints similar to rectum to avoid late toxicity 3

Reporting Requirements

• Total Reference Air Kerma (TRAK) should be reported for each brachytherapy application as a measure of the overall radiation delivered 1, 2
• Both physical and biologically equivalent doses (using the linear-quadratic model with appropriate α/β values) should be reported for target volumes and organs at risk 3
• For consistency, all doses should be reported in terms of EQD2 (equivalent dose in 2 Gy fractions) when combining external beam and brachytherapy doses 3

Clinical Implementation and Quality Assurance

• Three-dimensional conformal radiation techniques are preferred, with intensity-modulated radiotherapy (IMRT) considered in selected patients for improved dose distribution 4
• Quality assurance programs should follow ICRU recommendations to ensure uniformity in dose and volume specification for reporting across institutions 1
• Regular assessment of vaginal toxicity is recommended, as studies show approximately 29% probability of grade 2 or more vaginal morbidity within the first two years after treatment 4

Common Pitfalls and Caveats

• Standard dosimetry according to previous ICRU recommendations does not account for individual patient anatomy variations that can significantly affect dose distribution 8
• ICRU rectal point dose correlates reasonably well with maximum rectal dose, but ICRU bladder point often underestimates the maximum bladder dose by approximately 24% 3, 5
• Vaginal dose assessment requires multiple vaginal points for comprehensive evaluation, as targeting a single point does not provide adequate information about dose distribution throughout the vagina 4

By following these ICRU 89 guidelines for gynecological intracavitary brachytherapy, clinicians can optimize treatment outcomes while minimizing toxicity to surrounding normal tissues, ultimately improving patient quality of life.