This study is an investigator-initiated, single-arm, single-center, prospective, observational study. The hypothesis is that during the implementation of deep inspiration breath-hold (DIBH) radiotherapy plans in postoperative breast cancer patients receiving internal mammary irradiation, the actual target dose coverage and organ-at-risk (OARs) dose parameters remain within clinically acceptable ranges.
For patients with left-sided breast cancer, postoperative radiotherapy can expose the heart to excessive radiation, increasing the risk of cardiac toxicity. DIBH displaces the heart away from the chest wall by expanding the thoracic cavity during breath-holding to reduce cardiac radiation doses. Although DIBH has demonstrated efficacy in reducing cardiac exposure in left-sided breast cancer, its application in internal mammary and regional lymph node irradiation remains uncertain due to potential issues related to dose robustness associated with larger target volumes near the heart. The success of DIBH depends on maintaining a stable respiratory gating window; however, individual variations in breath-holding capacity and fatigue may lead to intrafractional and interfractional positional errors, which can compromise target coverage and increase doses to OARs. Surface-guided systems monitor respiratory motion but may not accurately represent the positions of deep-seated targets and OARs, raising concerns about dose coverage, particularly for the internal mammary target. State-of-the art radiotherapy techniques such as Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) provide improved dose conformality and reduce high-dose cardiac exposure. However, the integration of these techniques with DIBH and the impact of positional errors on dose robustness remain inadequately studied. Proton therapy, due to its steep dose fall-off, minimizes cardiac and pulmonary exposure but is highly sensitive to positional changes. This sensitivity may amplify uncertainties during DIBH, particularly in the context of internal mammary irradiation. This study aims to evaluate the dose robustness of DIBH in left-sided breast cancer patients undergoing internal mammary irradiation, with a specific focus on the impact of respiratory motion amplitude during breath-holding on dose distribution, as well as intrafractional and interfractional positional errors. Using offline CT and Cone-Beam CT (CBCT) data, it will assess positional deviations and compare the performance of IMRT, VMAT, and Intensity-Modulated Proton Therapy (IMPT) during DIBH. The findings will provide critical evidence to optimize DIBH for internal mammary and regional lymph node irradiation, improving clinical outcomes while minimizing cardiac toxicity.
Study Type
OBSERVATIONAL
Enrollment
25
The patient will receive moderately hypofractionated radiotherapy targeting the ipsilateral breast, supraclavicular and internal mammary nodes, and high-risk axillary region, with a prescribed dose of 40 Gy (RBE) /15Fx. IMRT, VMAT, or proton therapy will be chosen based on the radiation oncologist's judgment and patient preference. Respiratory gating tolerance is set at ±1.5 mm (3 mm total). Three simulated CT scans during DIBH will assess gating window positions: CT1: Breath-hold at the center of the gating window. CT2: Breath-hold at the upper edge, simulating maximum thoracic expansion. CT3: Breath-hold at the lower edge, simulating minimum thoracic expansion. Setup errors (intrafraction and interfraction) and respiratory waveforms monitored via Surface Guided Radiation Therapy（SGRT）systems will be recorded for analysis.
The patient will receive moderately hypofractionated radiotherapy targeting the ipsilateral breast, supraclavicular and internal mammary nodes, and high-risk axillary region, with a prescribed dose of 40 Gy (RBE) /15Fx. IMRT, VMAT, or proton therapy will be chosen based on the radiation oncologist's judgment and patient preference. Respiratory gating tolerance is set at ±1 mm (2 mm total). Three simulated CT scans during DIBH will assess gating window positions: CT1: Breath-hold at the center of the gating window. CT2: Breath-hold at the upper edge, simulating maximum thoracic expansion. CT3: Breath-hold at the lower edge, simulating minimum thoracic expansion. Setup errors (intrafraction and interfraction) and respiratory waveforms monitored via SGRT systems will be recorded for analysis.
Ruijin Hospital, Shanghai Jiaotong University School of Medicine
Shanghai, Shanghai Municipality, China
RECRUITINGTarget coverage of the Planning treatment volume (PTV)
Target coverage of the PTV, defined by V95% (the percentage of the PTV volume receiving at least 95% of the prescribed dose).
Time frame: Upon completion of radiotherapy treatment planning, prior to the first fraction of treatment.
Additional dose-volume parameters of the PTV
PTV coverage as measured by V90%, and high-dose volume as measured by V105% and V110%.
Time frame: Upon completion of radiotherapy treatment planning, prior to the first fraction of treatment.
Dose-volume parameters of the organs at risk (OARs)
The dose-volume histograms (DVHs) of OARs will be analyzed. The evaluation will cover: Cardiac Structures: Mean dose, D1cc, and V2-V30 for the heart and left ventricle (LV), along with D0.1cc for the left anterior descending artery (LAD). Lungs: Mean dose and V5-V25 for the left lung, and V2 and V4 for the right lung. Serial Organs: Maximum dose for the spinal cord (Dmax), D0.1cc for the left brachial plexus, and D1cc for the esophagus. Other Structures: Mean dose for the left humeral head, contralateral right breast, and thyroid gland.
Time frame: Upon completion of radiotherapy treatment planning, prior to the first fraction of treatment.
Conformity Index (CI) of the PTV
Calculated as V95% / PTV volume. A value closer to 1 indicates better conformity.
Time frame: Upon completion of radiotherapy treatment planning, prior to the first fraction of treatment.
Homogeneity Index (HI) of the PTV
Calculated as (D2% - D98%)/D50%. A lower value indicates better homogeneity.
Time frame: Upon completion of radiotherapy treatment planning, prior to the first fraction of treatment.
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The patient will receive moderately hypofractionated radiotherapy targeting the ipsilateral breast, supraclavicular and internal mammary nodes, and high-risk axillary region, with a prescribed dose of 40 Gy (RBE) /15Fx. IMRT, VMAT, or proton therapy will be chosen based on the radiation oncologist's judgment and patient preference. Respiratory gating tolerance is set at ± 0.75 mm (1.5 mm total). Three simulated CT scans during DIBH will assess gating window positions: CT1: Breath-hold at the center of the gating window. CT2: Breath-hold at the upper edge, simulating maximum thoracic expansion. CT3: Breath-hold at the lower edge, simulating minimum thoracic expansion. Setup errors (intrafraction and interfraction) and respiratory waveforms monitored via SGRT systems will be recorded for analysis.
Intra-fractional Error-PTV
Intra-fractional error is defined as any patient movement occurring during a single radiotherapy fraction, measured by surface-guided or image-guided systems. This outcome evaluates the impact of intra-fractional motion on target coverage using DVH-based metrics. PTV Metrics include: V95%: percentage of PTV receiving ≥95% of prescribed dose, V90%: percentage of PTV receiving ≥90% of prescribed dose, High-dose volume: V105% and V110%, percentage of PTV receiving ≥105% or ≥110% of prescribed dose, HI: (D2% - D98%) / D50%, where D2%, D98%, D50% are doses covering 2%, 98%, and 50% of PTV, CI: (PTV volume covered by prescription dose)² / (PTV volume × prescription isodose volume).
Time frame: During each treatment fraction (daily, approximately 3-4 weeks per patient)
Intra-fractional Error-OARs
Intra-fractional error is defined as any patient movement occurring during a single radiotherapy fraction, measured by surface-guided or image-guided systems. This outcome evaluates the impact of intra-fractional motion on OAR doses using DVH-based metrics. OAR Dose Metrics: Heart and LV: mean dose, D1cc, V2-V30, LAD : D0.1cc, Lungs: mean dose and V5-V25 for left lung, V2 and V4 for right lung, Spinal cord: Dmax, Left brachial plexus: D0.1cc, Esophagus: D1cc, Other relevant structures: mean dose for left humeral head, contralateral breast, thyroid gland, Unit of measurement: Gy for absolute doses; % for volume-based metrics.
Time frame: During each treatment fraction (daily, approximately 3-4 weeks per patient)
Inter-fractional Error- PTV
Inter-fractional error is defined as positional variation occurring between different treatment days, measured using daily CBCT image registration and dose recalculation. This outcome evaluates the impact of inter-fractional motion on PTV coverage using DVH metrics. PTV Metrics include: V95%: percentage of PTV receiving ≥95% of prescribed dose, V90%: percentage of PTV receiving ≥90% of prescribed dose, High-dose volume: V105% and V110%, percentage of PTV receiving ≥105% or ≥110% of prescribed dose, HI: (D2% - D98%) / D50%, where D2%, D98%, D50% are doses covering 2%, 98%, and 50% of PTV, CI: (PTV volume covered by prescription dose)² / (PTV volume × prescription isodose volume).
Time frame: Across all treatment fractions (approximately 3-4 weeks per patient)
Inter-fractional Error- OAR
Inter-fractional error is defined as positional variation occurring between different treatment days, measured using daily CBCT image registration and dose recalculation. This outcome evaluates the impact of inter-fractional motion on OAR doses using DVH metrics. OAR Dose Metrics: Heart and LV: mean dose, D1cc, V2-V30, LAD : D0.1cc, Lungs: mean dose and V5-V25 for left lung, V2 and V4 for right lung, Spinal cord: Dmax, Left brachial plexus: D0.1cc, Esophagus: D1cc, Other relevant structures: mean dose for left humeral head, contralateral breast, thyroid gland, Unit of measurement: Gy for absolute doses; % for volume-based metrics.
Time frame: Across all treatment fractions (approximately 3-4 weeks per patient)