What are the recommended radiation therapy (RT) doses and guidelines for conventional fractionation schemes, including lung bath RT and volume-based contouring?

Radiation Therapy Doses and Guidelines for Conventional Fractionation

Conventional RT Doses for Definitive Treatment

For high-risk sites (primary tumor and involved lymph nodes), conventional definitive fractionation requires 66-70 Gy at 2.0-2.2 Gy per fraction, with doses exceeding 72 Gy at 2.0 Gy/fraction leading to unacceptable normal tissue injury. 1

High-Risk Sites (Primary Tumor and Involved Lymph Nodes)

• Total dose: 66 Gy (2.2 Gy/fraction) to 70 Gy (2.0 Gy/fraction) 1
• For doses >70 Gy, fractionation should be modified to <2.0 Gy/fraction for at least part of treatment to minimize toxicity 1
• Maximum safe dose: 72 Gy using conventional fractionation (2.0 Gy/fraction) - exceeding this causes unacceptable normal tissue injury 1
• Hyperfractionation alternative: up to 81.6 Gy at 1.2 Gy/fraction 1

Low-Risk and Intermediate-Risk Sites (Subclinical Disease)

• 3D conformal RT or sequential IMRT: 44-50 Gy at 2.0 Gy/fraction 1
• IMRT: 54-63 Gy at 1.6-1.8 Gy/fraction 1
• Selection depends on estimated tumor burden and treatment modality 1

Site-Specific Conventional Fractionation Guidelines

Non-Small Cell Lung Cancer (Stage III)

For stage III NSCLC with concurrent chemotherapy, the standard dose is 60 Gy in 2 Gy fractions, as doses of 74 Gy demonstrated inferior survival (median OS 20.3 vs 28.7 months, P=0.0072). 1

• Standard with concurrent chemotherapy: 60 Gy at 2.0 Gy/fraction 1
• Higher doses (64-70 Gy at 1.8-2.0 Gy/fraction) may be considered in well-selected patients with strict normal tissue constraints 1
• Without chemotherapy: Consider dose escalation with modest hypofractionation (2.15-4 Gy/fraction) 1
• Sequential chemoradiotherapy: 66 Gy in 24 fractions is a valuable alternative 1

Critical normal tissue constraints for lung RT: 1

• Spinal cord maximum: 50 Gy (once daily) or 41 Gy (twice daily)
• Lung V20 <40% or mean lung dose ≤20 Gy
• Mean esophageal dose <34 Gy
• Heart: 60 Gy to <1/3,45 Gy to <2/3,40 Gy to <100%

Small Cell Lung Cancer (Limited Stage)

Deliver either 45 Gy at 1.5 Gy twice daily (category 1) or 60-70 Gy at 2.0 Gy once daily, starting concurrent with chemotherapy cycle 1 or 2. 1

• Twice-daily regimen: 45 Gy at 1.5 Gy bid (minimum 6-hour interfraction interval) 1
• Once-daily regimen: 60-70 Gy at 2.0 Gy/fraction 1
• Timing: Start with chemotherapy cycle 1 or 2 (category 1) 1

Cervical Cancer

For definitive treatment, deliver 70-85 Gy total point A dose combining external beam RT with brachytherapy, based on conventional fractionation and low-dose-rate brachytherapy equivalents. 1

• Stage IA1 (no LVSI): 70-80 Gy total point A dose 1
• Stage IB1/IIA1: 80-85 Gy total point A dose ± concurrent cisplatin 1
• Stage IB2/IIA2: 75-80 Gy total point A dose with concurrent cisplatin 1
• Doses represent summation of conventional external-beam fractionation and low-dose-rate (40-70 cGy/h) brachytherapy 1

Breast Cancer (Whole Breast RT)

Conventional whole breast RT is 46-50 Gy in 23-25 fractions, though hypofractionated regimens (39-42.9 Gy in 2.6-3.3 Gy fractions) demonstrate at least equivalent local control with less normal tissue toxicity. 1

• Conventional: 46-50 Gy in 23-25 fractions 1
• Hypofractionated alternative: 39-42.9 Gy at 2.6-3.3 Gy/fraction 1
• Tumor bed boost: Consider in patients <50 years, high-grade disease, or focally positive margins 1

Volume-Based Contouring Guidelines

Target Volume Definitions

Radiation target volumes should be defined using pretreatment PET and CT scans following ICRU Reports 50 and 62, with contemporary nomenclature specifying planning target volume (PTV) rather than traditional field borders. 1

• High-risk sites: Primary tumor and involved lymph nodes receive high-dose volume 1
• Intermediate/low-risk sites: Sites of suspected subclinical spread receive lower-dose volume 1
• Use CT-based treatment planning to ensure adequate target coverage and limit normal tissue dose 1

Lung Cancer Specific Contouring

For lung cancer, define target volumes based on pretreatment PET and CT at time of RT planning, using 4D imaging to assess tumor movement with motion management to achieve <1 cm movement or appropriately increased PTV margins. 1

• Three-dimensional conformal techniques preferred; IMRT may be considered in selected patients 1
• Calculate radiation doses with inhomogeneity corrections 1
• Assess tumor movement with 4D imaging and implement motion management 1

Conventional RT Field Borders vs. Modern Approach

Modern volume-based planning has replaced traditional standard field borders, with elective nodal irradiation no longer recommended when using contemporary diagnostic and treatment strategies. 1

Elective Nodal Irradiation

• Prophylactic irradiation of non-involved mediastinal nodes is NOT recommended with modern PET-CT staging and chemoradiotherapy 1
• Microscopic disease assumed treated by systemic chemotherapy combined with radiation 1
• Selective nodal irradiation only when FDG-PET-CT shows locoregional involvement 1

Postoperative RT Doses

Postoperative RT requires 60-66 Gy for high-risk features (extracapsular disease and/or positive margins), with preferred interval ≤6 weeks between resection and RT commencement. 1

• Standard postoperative dose: 60-66 Gy for high-risk features 1
• Indications: Advanced T stage, depth of invasion, multiple positive nodes, perineural/lymphatic/vascular invasion 1
• Timing: Begin within 6 weeks of resection 1

Fractionation Principles

For rapidly proliferating tumors treated with RT alone, deliver at least 1000 cGy/week, as daily fractions <200 cGy with cumulative weekly dose <1000 cGy show higher recurrence rates. 1

• Minimum weekly dose: 1000 cGy for squamous cell cancers to overcome accelerated repopulation 1
• Optimum overall treatment time: 21-35 days for head and neck tumors 2
• No single fractionation schedule proven best for all tumors 1