- •A new range optimization procedure was developed for adaptive proton therapy.
- •The new method accounts for tumor dose coverage and dose sparing in OARs.
- •The new method was applied to an abdominal metastasis.
- •Unless the new method is used, dose exposure in OARs may be increased.
- •The new method achieves better tumor coverage and dose sparing in OARs.
The purpose of this study was to design and develop a new range optimization for target and organs at risk (OARs) in dynamic adaptive proton beam therapy (PBT).
The new range optimization for target and OARs (RO-TO) was optimized to maintain target dose coverage but not to increase the dose exposure of OARs, while the other procedure, range optimization for target (RO-T), only focused on target dose coverage. A retrospective analysis of a patient who received PBT for abdominal lymph node metastases was performed to show the effectiveness of our new approach. The original plan (OP), which had a total dose of 60 Gy (relative biological effectiveness; RBE), was generated using six treatment fields. Bone-based registration (BR) and tumor-based registration (TR) were performed on each pretreatment daily CT image dataset acquired once every four fractions, to align the isocenter.
Both range adaptive approaches achieved better coverage (D95%) and homogeneity (D5%−D95%) than BR and TR only. However, RO-T showed the greatest increases in D2cc and Dmean values of the small intestine and stomach and exceeded the limitations of dose exposure for those OARs. RO-TO showed comparable or superior dose sparing compared with the OP for all OARs.
Our results suggest that BR and TR alone may reduce target dose coverage, and that RO-T may increase the dose exposure to the OARs. RO-TO may achieve the planned dose delivery to the target and OARs more efficiently than the OP. The technique requires testing on a large clinical dataset.
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Accepted: November 15, 2018
Received in revised form: September 26, 2018
Received: May 28, 2018
© 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.