What contouring protocol should be used for a typical adult male with localized prostate cancer undergoing moderate hypofractionation (e.g., 60 Gy in 20 fractions or 70 Gy in 28 fractions)?

Contouring Protocols for Moderate Hypofractionation in Prostate Cancer

Critical Technical Requirements

For moderate hypofractionation radiotherapy (60 Gy in 20 fractions or 70 Gy in 28 fractions), image-guided radiation therapy (IGRT) with daily prostate localization is mandatory, and intensity-modulated radiation therapy (IMRT) or more advanced techniques must be used to ensure safe delivery and minimize toxicity. 1

Image Guidance Requirements

• Daily prostate localization is required using one of the following methods: CT imaging, ultrasound, implanted fiducial markers, electromagnetic targeting/tracking, or endorectal balloon 1
• IGRT is considered essential for all hypofractionated regimens, as the vast majority of successful moderate hypofractionation trials utilized IGRT 2
• Without adequate image guidance, the risk of geographic miss and increased toxicity substantially increases 1

Radiation Delivery Technique

• IMRT or more advanced techniques (such as volumetric modulated arc therapy) are strongly recommended to minimize toxicity 1
• Non-modulated 3-dimensional conformal techniques should be avoided due to significantly increased risk of toxicity 1
• The higher dose per fraction in hypofractionation (2.4-3.4 Gy versus conventional 1.8-2.0 Gy) demands superior dose conformality to organs at risk 2

Dose-Volume Constraints

At least 2 dose-volume constraint points must be established for both rectum and bladder: 2, 1

• One constraint at the high-dose end (near the total prescribed dose)
• One constraint in the mid-dose range (near the midpoint of the total dose)

Specific Rectal Constraints

• For hypofractionated regimens, rectal volume receiving 65 Gy should be kept ≤15% to minimize late GI toxicity 3
• When rectal V65 exceeds 15%, the 8-year late grade 2-3 GI toxicity increases from 8.6% to 12.6% 3

Critical Warning on Dose Constraints

• Deviating from published reference study dose-volume constraints is strongly discouraged due to substantial risk of both acute and late toxicity 2
• Each hypofractionation regimen has been validated with specific constraints; altering these without evidence increases complication rates 2, 1

Target Volume Delineation

Prostate-Only Treatment (Standard Risk)

• Clinical target volume (CTV) includes the entire prostate gland 2
• For intermediate-risk disease, consider including proximal seminal vesicles based on risk factors 2
• Planning target volume (PTV) margins should account for setup uncertainty and organ motion, typically informed by institutional IGRT protocols 1

Prostate Plus Pelvic Nodes (High-Risk Disease)

• For high-risk patients, whole pelvis IMRT to pelvic lymph nodes (50 Gy in 25 fractions) with simultaneous integrated boost to prostate (68 Gy in 25 fractions) has demonstrated improved biochemical failure-free survival 2
• Moderate hypofractionation to prostate and pelvic nodes (60 Gy/20 fractions to prostate, 44 Gy/20 fractions to nodes) using simultaneous integrated boost is feasible and well-tolerated 4
• Elective nodal irradiation for high-risk patients may be offered given reasonable morbidity profile and reductions in biochemical failure and distant metastases 2

Common Pitfalls to Avoid

• Using inadequate image guidance: Without daily localization, the precision required for hypofractionation cannot be achieved 1
• Employing non-IMRT techniques: 3D conformal radiation increases toxicity risk unacceptably 1
• Exceeding validated dose constraints: Particularly rectal V65 >15% significantly increases late GI complications 3
• Treating high-risk patients with ultrahypofractionation outside trials: Insufficient evidence exists for this approach 2
• Ignoring prostate size limitations: For ultrahypofractionation (if considered for low/intermediate-risk), prostate size should be <100 cm³ 2

Risk-Stratified Approach

All Risk Groups (Low, Intermediate, High)

• Moderate hypofractionation (60 Gy/20 fractions or 70 Gy/28 fractions) should be offered regardless of patient age, comorbidity, anatomy, or urinary function 2
• These regimens are supported by the largest evidentiary base with high-quality evidence 2
• No single moderately hypofractionated regimen is superior to another for cancer control across risk groups 2

Integration with Androgen Deprivation Therapy

• High-risk patients require 18-36 months of ADT with radiation therapy 2
• Intermediate-risk patients may receive 4-6 months of ADT at physician discretion 2, 1
• Low-risk patients do not require ADT 1
• ADT should start 2-3 months before hypofractionated radiotherapy when indicated 4

Quality Assurance Considerations

• Treatment planning must replicate the technical parameters used in the reference trials that established safety and efficacy 2
• Institutional experience with IMRT and IGRT is essential before implementing hypofractionation 1
• Prospective toxicity monitoring should follow Common Terminology Criteria for Adverse Events to detect and manage complications early 4