Dosimetric comparison of advanced radiotherapy approaches using photon techniques and particle therapy in the postoperative management of thymoma

Abstract

Background: The purpose of this study was to compare dosimetric differences related to target volume and organs-at-risk (OAR) using 3D-conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), TomoTherapy (Tomo), proton radiotherapy (PRT), and carbon ion radiotherapy (CIRT) as part of postoperative thymoma irradiation. Material and methods: This single-institutional analysis included 10 consecutive patients treated with adjuvant radiotherapy between December 2013 and September 2016. CT-datasets and respective RT-structures were anonymized and plans for all investigated RT modalities (3DCRT, VMAT, Tomo, PRT, CIRT) were optimized for a total dose of 50 Gy in 25 fractions. Comparisons between target volume and OAR dosimetric parameters were performed using the Wilcoxon rank-sum test. Results: The best target volume coverage (mean PTV V 95% for all patients) was observed for Tomo (97.9%), PRT (97.6%), and CIRT (96.6%) followed by VMAT (85.4%) and 3DCRT (74.7%). PRT and CIRT both significantly reduced mean doses to the lungs, breasts, heart, and esophagus, as well as the spinal cord maximum dose compared with photon modalities. Among photon-based techniques, VMAT showed improved OAR sparing over 3DCRT. Tomo was associated with considerable low-dose exposure to the lungs, breasts, and heart. Conclusions: Particle radiotherapy (PRT, CIRT) showed superior OAR sparing and optimal target volume coverage. The observed dosimetric advantages are expected to reduce toxicity rates. However, their clinical impact must be investigated prospectively.

Particle therapy tumour outcomes: An updated systematic review

“…There is a substantial body of evidence from in silico comparative planning studies across a broad range of tumour sites comparing dose distributions between photon RT and PT demonstrating superiority in regard to normal tissue sparing. [2][3][4][5][6][7]44,[81][82][83] Proponents of PT view these data as indicating that PT will become the treatment of choice for specific indications once its availability is wide enough, in part for its compliance with the generally agreed As Low As Reasonably Achievable (ALARA) principle.…”

“…1 When compared to photon RT, PT delivers radiation dose at least as conformally to the target volume, but allows better sparing of nearby and more distant organs at risk, as well as allowing for dose escalation. [2][3][4][5][6][7] As of the end of 2018, over 220,000 patients have been treated with PT worldwide. 8 Ninety-five PT centres (13 offering CIT alone or with PBT, the remainder PBT alone) are operational across Europe, Asia, the United States of America (USA) and Africa with another 66 centres under construction or in planning stages.…”

“…Owing to its physical properties, particle therapy (PT), including proton beam therapy (PBT) and carbon ion therapy (CIT), offers promise in achieving this objective 1 . When compared to photon RT, PT delivers radiation dose at least as conformally to the target volume, but allows better sparing of nearby and more distant organs at risk, as well as allowing for dose escalation 2‐7 …”

Induction Strategy for Locally Advanced Thymoma

“…In the field of thymoma, Haefner et al conducted dosimetric comparison between photon and particle radiotherapy in the postoperative management of thymoma. The results revealed that particle radiotherapy showed superior organs at risk sparing and optimal target volume coverage (48). However, up to now, no data were reported about the implementation of particle radiation in induction radiation of thymoma.…”

Bystander effect and abscopal effect in recurrent thymic carcinoma treated with carbon-ion radiation therapy: A case report

“…To date, there have been no reports of both effects in one patient, even with photon or proton irradiation. Carbon-ion radiotherapy is a form of heavy-ion radiation modality with stronger effects on tumor cells by physical dose (higher relative biological effect) and better dose distribution compared with photon-based therapies[ 11 , 12 ].…”