OAR Dose Constraints for Malignant Phyllodes Tumour Radiotherapy
For malignant phyllodes tumors requiring adjuvant radiotherapy, apply standard breast cancer organ-at-risk constraints: limit lung inclusion to ≤3-3.5 cm as projected on beam radiographs, minimize cardiac volume in tangential fields (especially for left-sided lesions), and avoid excess dose to heart and lungs. 1
Lung Dose Constraints
The critical lung constraint is geometric rather than volumetric: not more than 3 to 3.5 cm of lung (as projected on the radiograph at isocenter) should ordinarily be treated, with a minimum of 1 to 1.5 cm of lung required for adequate coverage. 1 This geometric approach minimizes the risk of radiation pneumonitis while ensuring adequate target coverage. 1
Cardiac Dose Constraints
For left-sided malignant phyllodes tumors, efforts must be made to minimize the amount of heart included in tangential fields. 1 The guidelines explicitly state that excess dose to the heart through tangential irradiation must be avoided. 1 While specific cardiac dose-volume constraints are not provided in the phyllodes-specific literature, standard breast cancer constraints apply since the radiotherapy technique is identical. 2
Technical Considerations for Treatment Planning
Use supervoltage equipment to ensure dose homogeneity, with high-energy photons (≥10 MV) indicated for very large-breasted women or patients with significant dose inhomogeneity on treatment planning. 1
Bolus should not be used during whole breast or chest wall irradiation. 1
Three-dimensional dose distributions accounting for lower lung tissue density may be used, though this is not considered standard and its impact on patient outcomes has not been demonstrated. 1
Radiation Dose and Target Volume
Deliver 50-60 Gy to the whole breast (after breast-conserving surgery) or chest wall (after mastectomy) using opposed tangential fields at 180-200 cGy per fraction. 2, 3 The clinical target volume should include the entire remaining breast tissue or chest wall, extending from the skin surface to the pectoralis major muscle posteriorly. 2
Critical Pitfall: Regional Nodal Irradiation
Do not contour or irradiate regional lymph nodes (axillary, supraclavicular, internal mammary) for phyllodes tumors. 2 Phyllodes tumors are sarcomas, not epithelial breast cancers, and nodal metastases are exceedingly rare (<1% have positive nodes). 4, 2, 5 This represents a fundamental difference from invasive breast cancer management and is a common error to avoid. 4
Modern Dose Constraint Context
While the foundational OAR constraints derive from 2002 breast cancer guidelines 1, these remain the standard approach for phyllodes tumors since the radiotherapy technique is identical to breast cancer treatment. 2 More recent evidence confirms that adjuvant radiotherapy for malignant phyllodes tumors improves local control (reducing local recurrence from 34-42% to 90-100% at 5 years) without impacting overall survival. 2, 6 A 2023 study using moderate dose-escalation (median BED 92.7 Gy) showed no local recurrences with acceptable toxicity, though this approach requires individualized assessment. 7