KEY POINTS
- This single-center retrospective series included only 7 patients with 8 bulky tumor sites, all with locally advanced or metastatic disease unsuitable for surgery. Median age was 69 years, median ECOG performance status was 2, and tumors were large: median maximum diameter 8.6 cm and median gross tumor volume 308 cc, ranging up to 792.4 cc.
- Unlike many contemporary lattice implementations using flattening-filter-free beams, all treatments were delivered with 6 MV VMAT in standard flattening-filter mode on an Elekta Synergy. Lattice doses varied substantially between patients, from 1–5 fractions, with individual vertex prescriptions ranging across approximately 6–15 Gy per fraction, either alone or integrated with external-beam radiotherapy.
- Lattice geometry was individualized but followed institutional rules: vertices were 1.0–1.5 cm in diameter, generally spaced 3–4 cm center-to-center, kept at least 1.5 cm from critical organs, and confined within a 1-cm contracted GTV. Median peak-to-valley dose ratio was 2.9, and the median proportion of the GTV receiving ablative hotspots was 2.4%.
- Treatment was technically feasible on conventional hardware. All eight plans achieved ≥95% gamma passing at 3%/2 mm. Median beam-on time was 9 minutes 31 seconds, although individual fractions ranged from 4 minutes 15 seconds to 23 minutes 44 seconds, an important practical consideration in patients with poor performance status.
- Symptoms improved in 6 of 8 treatment sites (75%), usually within approximately two weeks. At a median follow-up of 8 months, 5 of 8 sites (62.5%) achieved a partial response, two had stable disease and one progressed, giving an early disease-control rate of 87.5%.
- Treatment schedules were highly heterogeneous. Three sites received lattice radiotherapy alone, two received a single lattice boost followed by conventional or moderately hypofractionated RT, and three received alternating lattice and external-beam blocks. Five of seven patients also received concurrent systemic therapy, including chemotherapy, immunotherapy, targeted therapy or an antibody-drug conjugate.
- Acute toxicity was limited to grade 1–2 events in three patients, with no grade ≥3 toxicity reported. However, symptom assessment was retrospective and physician-adjudicated, no standardized patient-reported quality-of-life instrument was used, and the tiny mixed-histology cohort precludes reliable efficacy comparisons.
CLINICAL TAKEAWAY
The most useful finding is technical rather than oncologic: VMAT lattice radiotherapy can be delivered and verified on a conventional flattening-filter linac, potentially broadening access beyond centers with FFF platforms. The 75% symptom-relief and 62.5% response signals are encouraging, but seven patients with eight different treatment sites and highly individualized regimens are nowhere near enough to establish efficacy.