Authors: Lei Hu, PhD^∗,†,1, Anna Zhai, MS^∗, Qing Chen, MS^∗, Vandana Puri, MS^∗, Chin-Cheng Chen, PhD^∗,‡, Francis Yu, MS^∗, Jana Fox, MD^§, Suzanne Wolden, MD^#, Jonathan Yang, MD, PhD^#,Charles B. Simone, II, MD^∗,#, Haibo Lin, PhD^∗,§,#

^∗ New York Proton Center, New York, NY, USA
^† Department of Radiation Oncology, Inova Schar Cancer Institute, FairFax, VA, USA
^‡ St. Jude Children’s Research Hospital, Memphis, TN, USA
^§ Department of Radiation Oncology, Albert Einstein College of Medicine and Monte?ore Medical Center, Bronx, NY, USA
^# Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA

This study explores the feasibility and potential dosimetric and time e?ciency benefit of proton Pencil Beam Scanning (PBS) craniospinal irradiation with a single posterior-anterior (SPA) brain field. The SPA approach was compared to our current clinical protocol using Bilateral Posterior Oblique brain fields (BPO). Ten consecutive patients were simulated in the head-?rst supine position on a long BOS frame and scanned using 3 mm CT slice thickness. A customized thermoplastic mask immobilized the patient’s head, neck, and shoulders. A vac-lock was used to secure the legs. PBS proton plans were robustly optimized with 3mm setup errors and 3.5% range uncertainties in the Eclipse V15.6 treatment planning system (n = 12 scenarios). In order to achieve a smooth gradient dose match at the junction area, at least 5 cm overlap region was maintained between the segments and 5 mm uncertainty along the cranial-cauda direction was applied to each segment independently as additional robust optimization scenarios. The brain doses were planned by SPA or BPO fields. All spine segments were planned with a single PA field. Dosimetric differences between the BPO and SPA approaches were compared, and the treatment efficiency was analyzed according to timestamps of beam delivery. Results: The maximum brain dose increases to 111.1 ± 2.1% for SPA vs. 109.0 ± 1.7% for BPO (p < 0.01). The dose homogeneity index (D5/D95) in brain CTV was comparable between techniques (1.037 ± 0.010 for SPA and 1.033 ± 0.008 for BPO). Lens received lower maximum doses by 2.88 ± 1.58 Gy (RBE) (left) and 2.23 ± 1.37 Gy (RBE) (right) in the SPA plans (p < 0.01). No significant cochlea dose change was observed. SPA reduced the treatment time by more than 4 minutes on average and ranged from 2 to 10 minutes, depending on the beam waiting and allocation time. SPA is dosimetrically comparable to BPO, with reduced lens doses at the cost of slightly higher dose inhomogeneity and hot spots. Implementation of SPA is feasible and can help to improve the treatment efficiency of PBS CSI treatment.

As of January 1, 2022, ARRT requires CE Credits for Directed Journal Readings to be based on the word count for each article. So, the number of CE Credits for each DJR article will vary for ARRT. For this article, the ARRT CE Credit will be 0.75 Credit. The MDCB CE Credits will remain at 2.5 Credits.

ARRT CQR Credit Distribution
Proton Therapy:
Procedures        
   Prescription, Geometric Parameters, and Dose Calculation = 0.75