Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers

Fukumitsu,Nobuyoshi; Hayakawa,Tomokatsu; Yamashita,Tomohiro; Mima,Masayuki; Demizu,Yusuke; Suzuki,Takeshi; Soejima,Toshinori

doi:10.3892/mco.2021.2458

Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers

Authors:
- Nobuyoshi Fukumitsu
- Tomokatsu Hayakawa
- Tomohiro Yamashita
- Masayuki Mima
- Yusuke Demizu
- Takeshi Suzuki
- Toshinori Soejima
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Affiliations: Department of Radiation Oncology, Kobe Proton Center, Kobe, Hyogo 650‑0047, Japan, Division of Radiation Therapy, Radiation and Proton Therapy Center, Shizuoka Cancer Center, Shizuoka, Shizuoka 411‑8777, Japan, Division of Medical Physics, Kobe Proton Center, Kobe, Hyogo 650‑0047, Japan, Department of Anesthesiology, Kobe Proton Center, Kobe, Hyogo 650‑0047, Japan
Published online on: December 1, 2021 https://doi.org/10.3892/mco.2021.2458
Article Number: 25
Copyright: © Fukumitsu et al. This is an open access article distributed under the terms of Creative Commons Attribution License.

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Abstract

The aim of the present study was to investigate the effects on the dose distribution and beam delivery time in spot scanning proton beam therapy (PBT) incorporating the spot deletion technique. A spot scanning plan was created for 30 patients with prostate cancer. The plan was then modified via two processes: Spots with lower weighting depositions were deleted (process A) and spots that were distant from the clinical target volume (CTV) were deleted (process B). The dose distribution to the organs at risk (OAR), the expanded CTV (exCTV), which was defined by a uniform expansion of the CTV by a radius of 5 mm, and the beam delivery time were compared among initial and modified plans. The V₅₀ _{Gy [relative biological effectiveness (RBE)]} to the rectum and bladder, and V_{60 Gy(RBE)} to the urethral bulb, inhomogeneity index (INH) of the exCTV showed a difference (P=1.1x10^‑14, P=6.4x10^‑14, P=2.7x10^‑7, P=3.2x10^‑17), although only changes by process B were significant. Modified plan by process B showed the V_{50 Gy(RBE)} to the rectum and bladder decreased by ‑2.4±1.6 and ‑2.3±1.4%, and the V_{60 Gy (RBE)} to the urethral bulb decreased by ‑15.9±19.4%. The INH of the exCTV increased by 0.05±0.03%. On the other hand, modification of the initial plan by process A did not affect the dose of the OAR, exCTV or beam delivery time. In spot scanning PBT, modification of the initial radiotherapy plan by systemic deletion of spots distant from the CTV could result in a dose reduction to the OAR.

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