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CBCT-Guided Pencil Beam Scanning Proton Therapy for Moving Lung Tumours: PROMO Study- Standardised Workflow and Early
S Chilukuri1, S Sundar1, R Kamath1
1Department of Radiation Oncology, Apollo Proton Cancer Centre, Chennai, Tamil Nadu, India.
Aims:
This study aimed to describe and evaluate a standardised workflow for cone beam computed tomography (CBCT)-guided, motion-managed intensity-modulated proton therapy (IMPT) in non-small cell lung cancer (NSCLC), integrating four-dimensional (4D) robust optimisation, surface-guided setup verification, and a CBCT-triaged quality assurance CT (QACT) pathway for adaptive replanning (ARP).
Materials And Methods:
This retrospective study included 32 consecutive patients with biopsy-proven NSCLC (stages I-III and oligometastatic, oligoprogressive, or recurrent disease treated with curative intent) who underwent CBCT-guided IMPT at our centre. Patients were treated either in free breathing (FB), breath hold (BH), or FB with compression belt (CB), depending on tumour excursion on 4DCT scan. QACTs were obtained when CBCT showed anatomic or beam path changes (triggered QACT [T-QACT]) or at periodic intervals (periodic QACT [P-QACT]). Adverse events were graded per Common Terminology Criteria for Adverse Events (CTCAE) v5.0.
Results:
Most patients (53%) had stage III disease and were predominantly treated with conventionally fractionated IMPT. With a median follow-up of 28 months (3-70), 2-year local control, progression-free survival, and overall survival were 84.2%, 70.6%, and 73.9%, for the entire cohort and 94.4%, 78.5%, and 83.1% for nonmetastatic cohort, respectively. Local control (LC) was significantly better in the nonmetastatic cohort than in the metastatic/recurrent cohort (P = 0.017). ARP was required in 50% of patients, with 81% initiated within the first 3 weeks. Motion management included BH in 53%, FB in 28%, and FB + CB in 19%. Failures were predominantly distant (97%), with no marginal recurrences. Among 32 T-QACTs, 47% triggered replanning, whereas only 1.8% of P-QACTs led to changes, demonstrating redundancy of routine periodic scans. Acute grade 2 oesophagitis occurred in 12%; one patient (3%) died of neutropenic sepsis after 4 weeks of chemoradiation. Late grade 3 oesophagitis (3%) and airway complications (6%) were infrequent, with no reported grade 3 cardiac adverse events.
Conclusion:
CBCT-guided, 4D robustly optimised IMPT was feasible, safe, and effective, providing a reproducible ARP workflow for NSCLC.
