Knowledge Hub · Breast & Lung Positioning
Some breast-radiotherapy patients treat reliably supine; others benefit from prone. The per-patient selection is a clinical decision; the equipment has to support both modes. This page is the physics of supine vs prone, the DIBH heart-sparing framework, and what AAPM TG-66 expects on the validation chain.
Why this matters
Supine vs prone per patient
Smaller breasts treat reliably supine — standard chest-wall geometry, simple tangential fields, easy patient comfort. Larger breasts treat better prone — the breast hangs free in the board cut-out, displacing tissue anteriorly and reducing ipsilateral lung dose by 30–50 %. Patients with axillary involvement or where supine breast positioning crosses the contralateral breast also benefit from prone. The per-patient selection is a clinical decision; the equipment has to support both modes. A breast-positioning accessory family that covers only supine forces every patient into the same workflow.
Based on: AAPM TG-66 — Clinical radiotherapy treatment planning; published prone-vs-supine breast comparison literature.
Read source ↗DIBH heart-sparing
Deep-inspiration breath-hold (DIBH) gating for left-breast tangential treatment reduces heart-mean-dose by 30–50 % compared to free-breathing. The benefit is reproducible only when the patient achieves the same DIBH posture every fraction — same arm position (above-head via wing-board T-grip), same chest-wall angle (indexed breast-board angle), same cushion support. Any drift in posture between fractions reduces the heart-dose benefit. The wing-board + cushion + indexed breast-board chain is what locks the DIBH posture; without it, DIBH gating still works but the heart-dose reproducibility degrades.
Based on: AAPM TG-76 — Management of respiratory motion; published left-breast DIBH heart-dose reduction studies.
Read source ↗Prone breast cut-out physics
In supine, the breast lies on the chest wall — the treatment field passes from the lateral tangent through the breast volume and into ipsilateral lung. The lung-volume exposed to ≥ 20 Gy (V20) drives radiation pneumonitis risk. In prone with a breast-board cut-out, the breast hangs free below the board — gravity displaces it away from the chest wall. The treatment field now passes through more breast tissue and less lung at the same chest-wall depth. Ipsilateral lung V20 typically drops by 30–50 % for larger breasts (≥ C-cup); patient skin dose also reduces because the high-dose region tracks breast tissue more cleanly.
Based on: AAPM TG-66; published prone-breast lung-dose-reduction literature for breast radiotherapy.
Read source ↗Belly-cushion bowel displacement
A prone belly-board cushion has a cut-out under the lower abdomen. The patient lies prone with the abdomen draped into the cut-out — gravity displaces the small-bowel loops anteriorly, away from the dorsally-placed pelvic target. Small-bowel V45 (volume receiving ≥ 45 Gy) drops by 10–15 % typically for pelvic IMRT and rectum IMRT workflows; small-bowel toxicity drops correspondingly. For prostate-bed irradiation post-prostatectomy and for rectum IMRT, the prone belly cushion is the dominant intervention reducing small-bowel dose without compromising target coverage.
Based on: AAPM TG-176 — Dosimetric effects of immobilisation devices; published prone-belly-board small-bowel-sparing literature.
Read source ↗Indexed to thorax baseplate
A breast board floating freely on the linac couch gives reproducible per-fraction angle but no reproducible per-fraction position. The patient setup depends on the operator placing the breast-board assembly at the same couch position every fraction — error-prone, time-consuming, manual-laser-mark dependent. Indexing the breast-board assembly to the thorax baseplate via the standard couch-bar pitch removes the per-room alignment work. The CT-sim setup, the linac setup and (where used) the MR-sim setup all read the same indexing. The breast accessory family is a chain partner of the baseplate platform, not a standalone product.
Based on: AAPM TG-176 — Dosimetric effects of couch tops and immobilisation devices; AAPM TG-66 setup-reproducibility expectations.
Read source ↗Wipe-down reusability
All breast boards, cushions and the wing-board T-grip are wipe-down decontaminable with standard radiotherapy decontaminants — quaternary ammonium, dilute bleach, ethanol-isopropanol mixes. The wipe-down between patients is part of the standard linac-room turnover; reusability across the patient panel brings per-patient accessory cost to a small fraction of single-use alternatives. For facilities with patient-allergy protocols, the family is available in PVC-free and latex-free variants.
Based on: AAPM TG-176 — Decontamination guidance; ISO 14644 cleanroom decontamination protocols.
Read source ↗AAPM references that anchor breast and lung positioning workflows.
AAPM task-group report covering treatment-planning QA including breast-radiotherapy planning.
AAPM task-group report on respiratory motion management including DIBH heart-sparing workflows.
AAPM framework for standardised nomenclatures used in breast-radiotherapy treatment planning.
AAPM task-group report on immobilisation-device dosimetric handling and decontamination guidance.
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