Definitive carbon ion radiotherapy for tracheobronchial adenoid cystic carcinoma: a preliminary report

Dose-Escalated Radiotherapy for Primary Tracheobronchial Adenoid Cystic Carcinoma

Primary tracheobronchial adenoid cystic carcinoma (ACC) is a rare malignancy, so the optimal radiotherapy (RT) dose remains unestablished. We aimed to evaluate the effectiveness of dose-escalated RT for primary tracheobronchial ACC. We retrospectively reviewed 48 patients who had undergone definitive or postoperative RT. Patients classified into the low- and high-dose groups received RT doses <70.0 and ≥70.0 Gy in EQD2, respectively. The primary endpoint was freedom from local progression (FFLP) and overall survival (OS). Throughout the follow-up period, seven patients (14.6%) experienced local progression, while 31 (64.6%) exhibited distant metastasis, most commonly in the lungs. In total, the 5-year FFLP and OS rates were 85.7 and 84.7%, respectively. Multivariate analysis revealed that regional lymph node metastasis at diagnosis and receipt of definitive RT were associated with poorer OS. In the subgroup analysis, the definitive RT group had a 5-year FFLP rate of 33.3 and 78.2% in the low- and high-dose groups (p = 0.065), whereas 5-year OS rates were 66.7 and 79.0%, respectively (p = 0.022). Four patients (8.3%) experienced Grade 3 toxicity with tracheal or main bronchus stenosis. Dose-escalated RT with conventional fractionation may be effective in patients with tracheobronchial ACC, especially for a definitive aim.

[Tracheal Tumours]

Malignant primary tracheal tumours are rare. The most common histological subtypes are squamous cell carcinoma and adenoid cystic carcinoma. These two entities have different prognoses and growth patterns. Tracheobronchoscopy and thoracic sectional imaging are standard diagnostic tools for tumour staging and local evaluation. Complete surgical resection of the affected tracheal segment is the treatment of choice for limited disease without distant metastases. Incomplete gross tumour resection with additional irradiation is an acceptable therapeutic option for adenoid cystic carcinoma. Interventional endoscopy with tumour debulking or tracheal stenting and/or definitive mediastinal radiotherapy are treatment alternatives in either a locally advanced or palliative setting.

Current diagnosis and treatment of salivary gland-type tumors of the lung

Salivary gland-type tumors of the lung are thought to originate from the submucosal exocrine glands of the large airways. Due to their rare occurrence, reports of their study are limited to small-scale or case reports. Therefore, daily clinical practices often require a search for previous reports. In the last 20 years, several genetic rearrangements have been identified, such as MYB::NF1B rearrangements in adenoid cystic carcinoma, CRTC1::MAML2 rearrangements in mucoepidermoid carcinoma, EWSR1::ATF1 rearrangements in hyalinizing clear cell carcinoma and rearrangements of the EWSR1 locus or FUS (TLS) locus in myoepithelioma and myoepithelial carcinoma. These molecular alterations have been useful in diagnosing these tumors, although they have not yet been linked to molecularly targeted therapies. The morphologic, immunophenotypic, and molecular characteristics of these tumors are similar to those of their counterparts of extrapulmonary origin, so clinical and radiologic differential diagnosis is required to distinguish between primary and metastatic disease of other primary sites. However, these molecular alterations can be useful in differentiating them from other primary lung cancer histologic types. The management of these tumors requires broad knowledge of the latest diagnostics, surgery, radiotherapy, bronchoscopic interventions, chemotherapy, immunotherapy as well as therapeutic agents in development, including molecularly targeted agents. This review provides a comprehensive overview of the current diagnosis and treatment of pulmonary salivary gland tumors, with a focus on adenoid cystic carcinoma and mucoepidermoid carcinoma, which are the two most common subtypes.

Calibration and evaluation of the relative biological effectiveness for carbon-ion radiotherapy in a new relative to a clinically applied treatment planning system

BACKGROUND

The study objective was to validate the relative biological effectiveness (RBE) in RayStation for carbon-ion radiotherapy (CIRT) using the Syngo treatment planning system as reference.

METHODS

Local effect model I was established in RayStation (Ray-LEM) with the same parameters as in LEM I in Syngo (Syngo-LEM). Three cube plans covering most of the tumors treated at our center were generated with Syngo-LEM. Ray-LEM re-calculated the Syngo plans and compared the RBEs to the Syngo counterparts. The results showed that RayStation RBE was smaller than Syngo RBE. To ensure that Ray-LEM reproduced Syngo RBE, the observed deviations were used to scale the maximum RBE (RBEmax) in Ray-LEM. After this calibration, we further compared the RayStation RBE to Syngo RBE using additional plans in both homogeneous phantoms and patients, to ensure that the calibrated Ray-LEM reproduced Syngo RBE even with more complex planning features.

RESULTS

The calibration increased the RBEmax by 2.3% to raise the Ray-LEM RBE. The target mean RBE deviations in the phantom evaluation plans were median: 0.0 (minimum: - 1.1 to maximum: 0.7) %, and the target mean RBE deviations of the clinical target volumes of 16 patient cases were - 0.4 (- 1.5 to 0.2) %.

CONCLUSIONS

The residual RBE difference between RayStation and Syngo was found to be ≤ 1.0%. Thus, we can propose to use RayStation for clinical CIRT treatment planning. However, the potential differences due to the absorbed beam model warrants further exploration.

Flourish of Proton and Carbon Ion Radiotherapy in China

Proton and heavy ion therapy offer superior relative biological effectiveness (RBE) in the treatment of deep-seated tumors compared with conventional photon radiotherapy due to its Bragg-peak feature of energy deposition in organs. Many proton and carbon ion therapy centers are active all over the world. At present, five particle radiotherapy institutes have been built and are receiving patient in China, mainly including Wanjie Proton Therapy Center (WPTC), Shanghai Proton Heavy Ion Center (SPHIC), Heavy Ion Cancer Treatment Center (HIMM), Chang Gung Memorial Hospital (CGMH), and Ruijin Hospital affiliated with Jiao Tong University. Many cancer patients have benefited from ion therapy, showing unique advantages over surgery and chemotherapy. By the end of 2020, nearly 8,000 patients had been treated with proton, carbon ion or carbon ion combined with proton therapy. So far, there is no systemic review for proton and carbon ion therapy facility and clinical outcome in China. We reviewed the development of proton and heavy ion therapy, as well as providing the representative clinical data and future directions for particle therapy in China. It has important guiding significance for the design and construction of new particle therapy center and patients’ choice of treatment equipment.

Biological Rationale and Clinical Evidence of Carbon Ion Radiation Therapy for Adenoid Cystic Carcinoma: A Narrative Review

Adenoid cystic carcinoma (ACC) is a rare, basaloid, epithelial tumor, arising mostly from salivary glands. Radiation therapy can be employed as a single modality for unresectable tumors, in an adjuvant setting after uncomplete resection, in case of high-risk pathological features, or for recurrent tumors. Due to ACC intrinsic radioresistance, high linear energy transfer (LET) radiotherapy techniques have been evaluated for ACC irradiation: while fast neutron therapy has now been abandoned due to toxicity concerns, charged particle beams such as protons and carbon ions are at present the beams used for hadron therapy. Carbon ion radiation therapy (CIRT) is currently increasingly used for ACC irradiation. The aim of this review is to describe the immunological, molecular and clinicopathological bases that support ACC treatment with CIRT, as well as to expose the current clinical evidence that reveal the advantages of using CIRT for treating ACC.