WBRT: Planning Principles and Target Delineation<\/h2>\n![\"Standard](\"data:image\/svg+xml;base64,PHN2ZyB3aWR0aD0iMSIgaGVpZ2h0PSIxIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPjwvc3ZnPg==\")
Standard WBRT fields with lateral opposed beams. Source: Target Volume Delineation and Field Setup, 2nd Edition<\/figcaption><\/figure>\nConventional WBRT planning uses 3D-CRT with lateral opposed photon beams at 6 MV energy. The beams are rotated slightly off-axis into right and left anterior oblique (RAO\/LAO) positions to avoid divergence into the lenses. The multileaf collimator (MLC) blocks the lenses while ensuring adequate coverage of the cribriform plate and temporal lobes. A practical detail worth noting: the isocenter can alternatively be placed midline at the level of the canthus, which eliminates beam divergence to the eyes and lenses entirely without requiring beam rotation.<\/p>\n
The non-contrast planning CT scan extends from the vertex to the upper cervical spine with axial slice thickness \u22642.5 mm. The patient lies supine with the head in neutral position, immobilized using a thermoplastic mask, with a field of view of 600 mm. Setup verification relies on weekly orthogonal films with MV imaging for conventional WBRT. Daily kV imaging is reserved for IMRT-based WBRT, where delivery precision demands more frequent verification.<\/p>\n
Field edges in conventional WBRT follow a well-defined protocol: superiorly, 2 cm flash above the vertex; posteriorly, 2 cm flash with optional posterior neck coverage; inferiorly, the bottom of C1; and anteriorly, the MLC blocks from the 2 cm flash to the anterior aspect of C1, shielding the parotids and lenses. Coverage of the temporal lobes and cribriform plate is mandatory across all clinical scenarios.<\/p>\n
Clinical Scenarios and Suggested WBRT Fields<\/h3>\n
The planning approach changes based on the clinical indication. Diffuse brain metastases (numerous or “too many to count”) and prophylactic cranial irradiation (PCI) for small cell lung cancer (SCLC) receive standard conventional fields. Leptomeningeal disease requires additional coverage of the optic nerves, retroorbital region, and lamina cribosa, with expanded margins of 8\u201310 mm for penumbra and daily setup uncertainty at the temporal lobes and cribriform plate. CNS leukemia and lymphoma demand retinal coverage and, when ocular involvement is confirmed by slit lamp examination, inclusion of the entire bilateral globes.<\/p>\n
\n\n\nScenario<\/th>\n Fields<\/th>\n Target Volumes<\/th>\n Field Edges<\/th>\n<\/tr>\n<\/thead>\n \n\nConventional WBRT<\/td>\n 3D-CRT lateral opposed (RAO\/LAO)<\/td>\n Entire cranial contents<\/td>\n Sup: 2 cm flash; Post: 2 cm flash; Inf: bottom of C1; Ant: MLC blocks parotid and lenses<\/td>\n<\/tr>\n \nLeptomeningeal Disease<\/td>\n 3D-CRT lateral opposed<\/td>\n Cranial contents + optic nerves + retroorbital region + lamina cribosa<\/td>\n Temporal lobes and cribriform plate with additional 8\u201310 mm margin for penumbra and setup<\/td>\n<\/tr>\n \nCNS Lymphoma\/Leukemia<\/td>\n 3D-CRT lateral opposed<\/td>\n Cranial contents + optic nerves + retroorbital region + retina \u00b1 entire globes<\/td>\n Posterior 1\/3 of globes if no ocular involvement; entire bilateral globes if involvement present<\/td>\n<\/tr>\n \nScalp-Sparing<\/td>\n 3D-CRT lateral opposed<\/td>\n Entire cranial contents<\/td>\n MLC edges set at outer table of calvarium<\/td>\n<\/tr>\n \nHA-WBRT<\/td>\n IMRT\/VMAT<\/td>\n CTV: whole brain parenchyma to foramen magnum; PTV: CTV minus (hippocampi + 5 mm expansion)<\/td>\n No additional setup margin<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nSource: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.1)<\/em><\/p>\nWBRT field variations for different clinical scenarios. Source: Target Volume Delineation and Field Setup, 2nd Edition<\/figcaption><\/figure>\nThe scalp-sparing technique deserves special mention. Cosmetic outcome is the primary goal, but this approach can produce a “reverse Mohawk” alopecia pattern \u2014 a point worth discussing with patients before treatment to set expectations. The MLC edges are placed at the outer table of the calvarium rather than using the conventional 2 cm flash, reducing scalp dose while maintaining adequate brain parenchyma coverage.<\/p>\n
WBRT Dose and Fractionation<\/h3>\n
Fractionation varies by clinical indication and prognosis. The most common schedule for brain metastases and leptomeningeal disease is 30 Gy in 10 fractions. Re-irradiation with WBRT is feasible at 20\u201325 Gy in 10 fractions but requires a minimum 4\u20136 month interval between courses to allow neural tissue recovery.<\/p>\n
\n\n\nClinical Scenario<\/th>\n Dose and Fractionation<\/th>\n<\/tr>\n<\/thead>\n \n\nWBRT \/ Leptomeningeal disease<\/td>\n 30 Gy \/ 10 fx (most common), 37.5 Gy \/ 15 fx (RTOG), 30 Gy \/ 12 fx, 20 Gy \/ 5 fx (poor prognosis)<\/td>\n<\/tr>\n \nWBRT re-irradiation<\/td>\n 20\u201325 Gy \/ 10 fx (minimum 4\u20136 month interval)<\/td>\n<\/tr>\n \nPCI for SCLC<\/td>\n 25 Gy \/ 10 fx (most common)<\/td>\n<\/tr>\n \nCNS prophylaxis for ALL<\/td>\n 12 Gy \/ 8 fx<\/td>\n<\/tr>\n \nCNS leukemia (high-risk)<\/td>\n \u226518 Gy \/ 9\u201310 fx (dose based on systemic therapy intensity)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nSource: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.2)<\/em><\/p>\nHippocampal Avoidance WBRT (HA-WBRT)<\/h2>\nHA-WBRT: hippocampal contouring and avoidance zone per RTOG 0933. Source: Target Volume Delineation and Field Setup, 2nd Edition<\/figcaption><\/figure>\nNeurocognitive preservation strategies include adding memantine and\/or using HA-WBRT. Hippocampal sparing matters because adult neurogenesis occurs in the subgranular zone (SGZ) of the hippocampus \u2014 irradiating this region contributes significantly to post-WBRT cognitive decline, particularly memory and verbal learning deficits.<\/p>\n
HA-WBRT planning requires inverse-planned IMRT using a planning CT fused to a gadolinium contrast-enhanced MRI. The three-dimensional spoiled gradient sequence with axial slice thickness of 1.25\u20131.5 mm defines the hippocampal avoidance region with the necessary precision. Per RTOG 0933 contouring guidelines, only the SGZ portion of the hippocampi is contoured (not the entire structure), and a 5 mm volumetric expansion creates the avoidance zone. The PTV consists of the entire brain tissue (parenchyma to foramen magnum) minus the expanded hippocampi, with no additional setup margin.<\/p>\n
Dose constraints are strict and vary by indication. For brain metastases: hippocampi D100% \u22649 Gy, Dmax \u226416 Gy; optic nerves and chiasm Dmax \u226430 Gy. For PCI in SCLC with hippocampal sparing, limits tighten further: hippocampi D100% \u22647.5 Gy, Dmax \u226413.5 Gy; optic nerves and chiasm Dmax \u226425 Gy. A critical exclusion criterion: any lesion within 5 mm of the hippocampus disqualifies the patient from HA-WBRT.<\/p>\n
SRS: Planning Principles and Target Delineation<\/h2>\n
Stereotactic radiosurgery encompasses single-fraction and fractionated SRS (2\u20135 fractions) for both intact brain metastases and post-resection cavities. Available instruments include frame-based or frameless cobalt-60 Gamma Knife systems and LINAC-based platforms. Each system has practical differences: Gamma Knife uses PTV = CTV with no additional expansion, while LINAC-based SRS may require a small PTV margin depending on the system’s mechanical accuracy and image verification protocol.<\/p>\n
Target delineation and treatment planning rely on volumetric contrast-enhanced T1-weighted MRI with 1\u20132 mm slices as the preferred imaging modality. Contrast-enhanced CT serves as an alternative when MRI is contraindicated. For LINAC-based SRS, a thin-slice CT is acquired and co-registered with the MRI for accurate dose calculation. Daily imaging is mandatory for LINAC-based delivery.<\/p>\n
SRS Target Volume Delineation<\/h3>\n
Delineation differs substantially between intact metastases and post-surgical cavities. For intact lesions, the approach is straightforward: the GTV is the contrast-enhancing lesion on T1-weighted MRI, and the CTV equals GTV plus 0 mm \u2014 no additional margin. For post-resection cavities, two well-established methods exist in the literature, each with a distinct margin philosophy.<\/p>\n
\n\n\nTarget<\/th>\n GTV<\/th>\n CTV<\/th>\n<\/tr>\n<\/thead>\n \n\nUnresected metastases<\/td>\n Contrast-enhancing lesion on T1-weighted MRI<\/td>\n GTV + 0 mm<\/td>\n<\/tr>\n \nPost-resection cavity (Method 1 \u2014 Soltys et al.)<\/td>\n n\/a<\/td>\n 2 mm uniform expansion around resection cavity borders on post-contrast MRI<\/td>\n<\/tr>\n \nPost-resection cavity (Method 2 \u2014 Soliman et al.)<\/td>\n n\/a<\/td>\n Entire contrast-enhancing region + surgical cavity + surgical tract on postop MRI; 5\u201310 mm along bone flap if preop dural contact; 1\u20135 mm if no dural contact; 1\u20135 mm along venous sinus if prior contact<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nSource: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.3)<\/em><\/p>\nSRS cavity contouring: comparison of Method 1 (Soltys) and Method 2 (Soliman). Source: Target Volume Delineation and Field Setup, 2nd Edition<\/figcaption><\/figure>\nMethod 2 by Soliman et al. is more conservative and tends to produce larger CTV volumes. In the illustrated case, a 24 mm cavity in the left temporal lobe \u2014 following gross total resection of a 33 mm rectal cancer metastasis with preoperative dural contact but no venous sinus contact \u2014 would receive a 10 mm margin along the bone flap. Single-fraction SRS was selected because of the small cavity size (<3 cm) and sufficient distance from critical brain structures. With Gamma Knife, PTV equals CTV with no expansion. Method 1 by Soltys et al. applies a simple 2 mm uniform expansion around the cavity on post-gadolinium T1 MRI, yielding a smaller volume and potentially less toxicity.<\/p>\n
SRS Dose and Organ-at-Risk Constraints<\/h3>\nMultiple isocenter SRS for new brain metastases after prior WBRT. Source: Target Volume Delineation and Field Setup, 2nd Edition<\/figcaption><\/figure>\nSRS dose depends on lesion size or volume and proximity to critical structures. The fractionation schemes below follow the Alliance A071801 protocol, which provides guidance for post-operative cavities and intact metastases across 1, 3, and 5 fractions.<\/p>\n
![\"Standard](\"https:\/\/rtmedical.com.br\/wp-content\/uploads\/2026\/03\/brain-metastases-wbrt-fields-standard.jpeg\")
Conventional WBRT planning uses 3D-CRT with lateral opposed photon beams at 6 MV energy. The beams are rotated slightly off-axis into right and left anterior oblique (RAO\/LAO) positions to avoid divergence into the lenses. The multileaf collimator (MLC) blocks the lenses while ensuring adequate coverage of the cribriform plate and temporal lobes. A practical detail worth noting: the isocenter can alternatively be placed midline at the level of the canthus, which eliminates beam divergence to the eyes and lenses entirely without requiring beam rotation.<\/p>\n
The non-contrast planning CT scan extends from the vertex to the upper cervical spine with axial slice thickness \u22642.5 mm. The patient lies supine with the head in neutral position, immobilized using a thermoplastic mask, with a field of view of 600 mm. Setup verification relies on weekly orthogonal films with MV imaging for conventional WBRT. Daily kV imaging is reserved for IMRT-based WBRT, where delivery precision demands more frequent verification.<\/p>\n
Field edges in conventional WBRT follow a well-defined protocol: superiorly, 2 cm flash above the vertex; posteriorly, 2 cm flash with optional posterior neck coverage; inferiorly, the bottom of C1; and anteriorly, the MLC blocks from the 2 cm flash to the anterior aspect of C1, shielding the parotids and lenses. Coverage of the temporal lobes and cribriform plate is mandatory across all clinical scenarios.<\/p>\n
Clinical Scenarios and Suggested WBRT Fields<\/h3>\n
The planning approach changes based on the clinical indication. Diffuse brain metastases (numerous or “too many to count”) and prophylactic cranial irradiation (PCI) for small cell lung cancer (SCLC) receive standard conventional fields. Leptomeningeal disease requires additional coverage of the optic nerves, retroorbital region, and lamina cribosa, with expanded margins of 8\u201310 mm for penumbra and daily setup uncertainty at the temporal lobes and cribriform plate. CNS leukemia and lymphoma demand retinal coverage and, when ocular involvement is confirmed by slit lamp examination, inclusion of the entire bilateral globes.<\/p>\n
| Scenario<\/th>\n | Fields<\/th>\n | Target Volumes<\/th>\n | Field Edges<\/th>\n<\/tr>\n<\/thead>\n | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Conventional WBRT<\/td>\n | 3D-CRT lateral opposed (RAO\/LAO)<\/td>\n | Entire cranial contents<\/td>\n | Sup: 2 cm flash; Post: 2 cm flash; Inf: bottom of C1; Ant: MLC blocks parotid and lenses<\/td>\n<\/tr>\n | ||||||||||||||||||||||||
| Leptomeningeal Disease<\/td>\n | 3D-CRT lateral opposed<\/td>\n | Cranial contents + optic nerves + retroorbital region + lamina cribosa<\/td>\n | Temporal lobes and cribriform plate with additional 8\u201310 mm margin for penumbra and setup<\/td>\n<\/tr>\n | ||||||||||||||||||||||||
| CNS Lymphoma\/Leukemia<\/td>\n | 3D-CRT lateral opposed<\/td>\n | Cranial contents + optic nerves + retroorbital region + retina \u00b1 entire globes<\/td>\n | Posterior 1\/3 of globes if no ocular involvement; entire bilateral globes if involvement present<\/td>\n<\/tr>\n | ||||||||||||||||||||||||
| Scalp-Sparing<\/td>\n | 3D-CRT lateral opposed<\/td>\n | Entire cranial contents<\/td>\n | MLC edges set at outer table of calvarium<\/td>\n<\/tr>\n | ||||||||||||||||||||||||
| HA-WBRT<\/td>\n | IMRT\/VMAT<\/td>\n | CTV: whole brain parenchyma to foramen magnum; PTV: CTV minus (hippocampi + 5 mm expansion)<\/td>\n | No additional setup margin<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.1)<\/em><\/p>\n The scalp-sparing technique deserves special mention. Cosmetic outcome is the primary goal, but this approach can produce a “reverse Mohawk” alopecia pattern \u2014 a point worth discussing with patients before treatment to set expectations. The MLC edges are placed at the outer table of the calvarium rather than using the conventional 2 cm flash, reducing scalp dose while maintaining adequate brain parenchyma coverage.<\/p>\n Fractionation varies by clinical indication and prognosis. The most common schedule for brain metastases and leptomeningeal disease is 30 Gy in 10 fractions. Re-irradiation with WBRT is feasible at 20\u201325 Gy in 10 fractions but requires a minimum 4\u20136 month interval between courses to allow neural tissue recovery.<\/p>\n Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.2)<\/em><\/p>\n Neurocognitive preservation strategies include adding memantine and\/or using HA-WBRT. Hippocampal sparing matters because adult neurogenesis occurs in the subgranular zone (SGZ) of the hippocampus \u2014 irradiating this region contributes significantly to post-WBRT cognitive decline, particularly memory and verbal learning deficits.<\/p>\n HA-WBRT planning requires inverse-planned IMRT using a planning CT fused to a gadolinium contrast-enhanced MRI. The three-dimensional spoiled gradient sequence with axial slice thickness of 1.25\u20131.5 mm defines the hippocampal avoidance region with the necessary precision. Per RTOG 0933 contouring guidelines, only the SGZ portion of the hippocampi is contoured (not the entire structure), and a 5 mm volumetric expansion creates the avoidance zone. The PTV consists of the entire brain tissue (parenchyma to foramen magnum) minus the expanded hippocampi, with no additional setup margin.<\/p>\n Dose constraints are strict and vary by indication. For brain metastases: hippocampi D100% \u22649 Gy, Dmax \u226416 Gy; optic nerves and chiasm Dmax \u226430 Gy. For PCI in SCLC with hippocampal sparing, limits tighten further: hippocampi D100% \u22647.5 Gy, Dmax \u226413.5 Gy; optic nerves and chiasm Dmax \u226425 Gy. A critical exclusion criterion: any lesion within 5 mm of the hippocampus disqualifies the patient from HA-WBRT.<\/p>\n Stereotactic radiosurgery encompasses single-fraction and fractionated SRS (2\u20135 fractions) for both intact brain metastases and post-resection cavities. Available instruments include frame-based or frameless cobalt-60 Gamma Knife systems and LINAC-based platforms. Each system has practical differences: Gamma Knife uses PTV = CTV with no additional expansion, while LINAC-based SRS may require a small PTV margin depending on the system’s mechanical accuracy and image verification protocol.<\/p>\n Target delineation and treatment planning rely on volumetric contrast-enhanced T1-weighted MRI with 1\u20132 mm slices as the preferred imaging modality. Contrast-enhanced CT serves as an alternative when MRI is contraindicated. For LINAC-based SRS, a thin-slice CT is acquired and co-registered with the MRI for accurate dose calculation. Daily imaging is mandatory for LINAC-based delivery.<\/p>\n Delineation differs substantially between intact metastases and post-surgical cavities. For intact lesions, the approach is straightforward: the GTV is the contrast-enhancing lesion on T1-weighted MRI, and the CTV equals GTV plus 0 mm \u2014 no additional margin. For post-resection cavities, two well-established methods exist in the literature, each with a distinct margin philosophy.<\/p>\n Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 28.3)<\/em><\/p>\n Method 2 by Soliman et al. is more conservative and tends to produce larger CTV volumes. In the illustrated case, a 24 mm cavity in the left temporal lobe \u2014 following gross total resection of a 33 mm rectal cancer metastasis with preoperative dural contact but no venous sinus contact \u2014 would receive a 10 mm margin along the bone flap. Single-fraction SRS was selected because of the small cavity size (<3 cm) and sufficient distance from critical brain structures. With Gamma Knife, PTV equals CTV with no expansion. Method 1 by Soltys et al. applies a simple 2 mm uniform expansion around the cavity on post-gadolinium T1 MRI, yielding a smaller volume and potentially less toxicity.<\/p>\n SRS dose depends on lesion size or volume and proximity to critical structures. The fractionation schemes below follow the Alliance A071801 protocol, which provides guidance for post-operative cavities and intact metastases across 1, 3, and 5 fractions.<\/p>\n |
![\"Variations](\"https:\/\/rtmedical.com.br\/wp-content\/uploads\/2026\/03\/brain-metastases-wbrt-field-variations.jpeg\")
![\"Hippocampal](\"https:\/\/rtmedical.com.br\/wp-content\/uploads\/2026\/03\/brain-metastases-hippocampal-avoidance-wbrt.jpeg\")
![\"Single-fraction](\"https:\/\/rtmedical.com.br\/wp-content\/uploads\/2026\/03\/brain-metastases-srs-cavity-contouring.jpeg\")
![\"Multiple](\"https:\/\/rtmedical.com.br\/wp-content\/uploads\/2026\/03\/brain-metastases-srs-multiple-isocenter-1.jpeg\")