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Updated: Jun 16, 2026
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Offline Plan Adaptation in Robustly Optimized CBCT-Guided Pencil Beam Scanning Proton Beam Therapy: Lessons From a
Srinivas Chilukuri1, Sham Sundar1, Utpal Gaikwad2
1Department of Radiation Oncology, Apollo Proton Cancer Centre, Chennai, Tamil Nadu, India.
Purpose:
Pencil beam scanning proton beam therapy (PBS-PBT) is highly sensitive to anatomic variations, often necessitating adaptive replanning (ARP) to ensure accurate dose delivery. While cone beam computed tomography (CBCT) is increasingly used for image guidance with PBT, many centers still rely on periodic quality assurance computed tomography scans (QACTs) to trigger ARP. This study reports a large real-world experience with a CBCT-guided offline adaptive PBS-PBT workflow.
Methods And Materials:
We retrospectively analyzed 300 consecutive patients treated with robustly optimized PBS-PBT. All patients underwent CBCT guided treatments, with QACTs performed either periodically (P-QACT) or triggered by CBCT (T-QACT) changes. We assessed ARP frequency, dosimetric and anatomic triggers, temporal patterns, indications, and workflow impacts across treatment sites. Strategic modifications were introduced after the first 100 patients, and their effect on ARP frequency was evaluated.
Results:
Of 761 QACTs performed, 541 were P-QACT and 220 were T-QACT. Overall, 94 ARPs were performed in 80 patients (27%), with the highest rates in head neck (62%) and thoracic (43%) cancers. The primary dosimetric trigger was organ-at-risk overdosage (52%), followed by target undercoverage (32%) and a combination of both (16%). T-QACT demonstrated 97% (91/94) sensitivity for triggering ARP with 41.4% (91/220) specificity. Most ARPs (64%) occurred in the first half of the treatment, with 32% in week 3. Beam path changes (52%) were the most frequent anatomic trigger, followed by target deformation (29%) and setup inconsistencies (13%). Strategic modifications reduced ARP frequency from 35% in the first 100 patients to 22.5% in the subsequent 200.
Conclusions:
PBS-PBT frequently necessitates ARP. A CBCT guided offline adaptive workflow, combined with stringent image review protocols, can largely eliminate the need for routine QACTs and streamline replanning. This approach offers practical guidance for PBS-PBT programs.
