Purpose: To evaluate the dosimetric and short-term clinical efficacy of proton SBRT for solitary NSCLC using pencil beam scanning and beam repainting technique.
Methods: Retrospectively reviewed over 26 patients at age of 79.5 (58 to 93) years old, with a total of 32 lesions histologically and/or clinically diagnosed as solitary NSCLC treated with proton SBRT. Each proton plan was designed to maximally avoid beam exiting towards the heart and optimized with 3-5 mm/3.5% robustness and computed on a Varian Eclipse with AcurosPT algorithm. To reduce the motion uncertainties, a range shifter with an extended (~15 cm) airgap was routinely used. The prescribed dose Almost all was treated with two coplanar modulated proton scanning beams with a range shifter at ~15 cm air gap, each followed by an identical repainted beam, on a Varian ProBeam Compact™.
Results: The treated include17 (53%) peripheral lesions and 10 (31.3%) for retreatments. All received 35 to 50 GyE in 5 consecutive fractions, covering ITV plus 5-10 mm margins (PTV) ranging from 8.2 to 172.7 cm3. Scanning spots of each beam fluctuate from 172 to 3250 and were delivered over 27.5 ± 9.6 seconds per treatment, corresponding to 6.3 ± 2.2 respiratory cycles. The mean follow-up time is 5.3 months with a max of 24.2 months. 11 (34%) patients showed grade ≤ 2 symptoms of lung function and pneumonitis. No local recurrence and severe adverse effects were identified within this serial.
Conclusion: Lung proton SBRT with pencil beam scanning for both centrally and peripherally located solitary NSCLC in this study appeared to be an effective modality with its satisfactory near-term local tumor control and low acute toxicities. The author strongly supports beam repainting in addition to other techniques to overcome the dosimetry uncertainties from respiratory motion during the extended duration of proton scanning beam delivery.
Protons, Lung, Stereotactic Radiosurgery
TH- External Beam- Particle/high LET therapy: Proton therapy - Motion management - interfraction