Combined proton–photon treatment for breast cancer

Abstract

Objective. Proton therapy remains a limited resource due to gantry size and its cost. Recently, a new design without a gantry has been suggested. It may enable combined proton–photon therapy (CPPT) in conventional bunkers and allow the widespread use of protons. In this work, we explore this concept for breast cancer. Methods. The treatment room consists of a LINAC for intensity modulated radiation therapy (IMRT), a fixed proton beamline (FBL) with beam scanning and a motorized couch for treatments in lying positions with accurate patient setup. Thereby, proton and photon beams are delivered in the same fraction. Treatment planning is performed by simultaneously optimizing IMRT and IMPT plans based on the cumulative dose. The concept is investigated for three breast cancers where the goal is to minimize mean dose to the heart and lung while delivering 40.05 Gy in 15 fractions to the PTV with a SIB of 48 Gy to the tumor bed. The probabilistic approach is applied to mitigate the sensitivity to range uncertainties. Results. CPPT is particularly advantageous for irradiating concave target volumes that wrap around a curved chest wall. There, protons may deliver dose to the peripheral and medial parts of the target volume including lymph nodes. Thereby, the mean dose in normal tissues is reduced compared to single-modality IMRT. However, tangential photon beams may treat parts of the target volume near the interface to the lung. To ensure target coverage for range undershoot in an IMPT plan, proton beams have to deliberately overshoot into the lung tissue—a problem that can be mitigated via the photon component which ensures plan conformity and robustness. Conclusion. CPPT using an FBL may represent a realistic approach to make protons available to more patients. In addition, CPPT may generally improve treatment quality compared to both single-modality proton and photon treatments.

Patient‐specific quality assurance for deformable IMRT/IMPT dose accumulation: Proposition and validation of energy conservation based validation criterion

“…The CPPT Gantry plan simultaneously optimizes the IMPT Gantry with the IMRT fields, while the CPPT FHB is the optimal combination of the IMPT FHB and IMRT fields. The concept and potential of CPPT are described in other publications 23–27 . The purpose of examining various treatment modalities is to avoid limiting the investigations to a single treatment type.…”

“…The concept and potential of CPPT are described in other publications. [23][24][25][26][27] The purpose of examining various treatment modalities is to avoid limiting the investigations to a single treatment type.…”

Current Cardioprotective Strategies for the Prevention of Radiation-Induced Cardiotoxicity in Left-Sided Breast Cancer Patients

“…Proton Beam Therapy (PBT) has been used in clinical medicine since the mid 1980s, but not to a large extent; therefore, it poses limitations such as the cost of treatment facilities, as well as dose and range uncertainties due to radiation's sensitivity to the density of the substances it crosses [76,77]. Proton RT is a rapidly evolving irradiation modality because of its energy deposition according to Bragg Peaks, which means reduced entrance and exit doses and the administration of peak energy to the target volume, in an overall more advantageous dose-depth distribution [78].…”

Fraction optimization for hybrid proton‐photon treatment planning

“…The hybrid proton-photon RT has been clinically used for treating spine sarcoma, [9][10][11] for which photon and proton plans are optimized separately: protons are used to improve the OAR sparing that allows for dose escalation to targets, while photons are used to reduce the skin dose. Recently various hybrid proton-photon treatment planning methods with joint optimization of proton and photon variables have been proposed with different motivations and outcomes, [12][13][14][15][16][17][18][19] for various sites including skull-base, head-and-neck (HN), breast, and lung cancer. To solve the problem that proton RT is a limited resource, Unkelbach et al proposed a hybrid planning method with the plan quality that is no worse than proton plans.…”