Inoperable for internal or other reasons for which curative RT was indicated. This small group of patients clearly benefits from stereotactic body radiation therapy (SRBT). Some studies even demonstrate non-inferiority over surgical treatment.
Proton RT may be used in these patients in some carefully selected indications, as recommended by the Particle Therapy Co-Operative Group (PTCOG):
Accelerated radiotherapy can be used for these indications.
Locally advanced non-small cell lung cancer (NSCLC) represents the most frequently diagnosed disease and at the same time the greatest therapeutic challenge in the NSCLC treatment strategy. It is an inoperable disease without distant dissemination, where the treatment method of choice is concomitant chemoradiotherapy followed by immunotherapy. Due to the extent and location of the disease, there are situations where photons do not allow for the application of curative doses while protecting the structures of the mediastinum and healthy lung tissue. Proton radiotherapy minimizes the radiation dose to these structures and the toxicity of the treatment. The aim is to reduce the burden on the lungs, heart, spinal cord and esophageal toxicity, thereby improving the patient’s quality of life and overall survival.
The aim is a maximum protection of healthy lung tissue in patients with postoperative reduced ventilation capacity.
Toxicity during postoperative radiotherapy results from the need to irradiate central structures, respectively mediastinal structures due to their higher risk of radiation induced heart disease (RIHD) in postoperative patients with lower functional lung capacity with possible pre-existing lung disease. Therefore, the dosimetric benefits of proton RT appear to be a good alternative in postoperative RT tactics in N2 NSCLC.
This is a group of patients after successful surgery (complete resection), when no adjuvant RT was indicated (there was no N2 involvement), with localized recurrence in the mediastinal nodes, possibly locally without evidence of distant dissemination. There is no standard therapeutic approach for these patients and the most appropriate is probably a combined approach – radical local radiotherapy in combination with chemotherapy and immunotherapy. The biggest problem remains the risk of distant relapse.
Since these patients are at risk of increased toxicity in the area of central mediastinal structures, proton radiotherapy has an advantage as it allows for the application of a radical dose to the tumor while maintaining low doses to surrounding high-risk organs.
The risk of isolated locoregional recurrence after NSCLC treatment is around 25%, often in previously irradiated areas. Proton RT appears to be a very promising, well-tolerated method with acceptable toxicity and relatively high efficacy in this indication.
In the case of re-irradiation, photon RT encounters dose limitations of previously irradiated tissues with a high-risk of damage to surrounding tissues.
The most numerous appear to be patients with localized recurrence according to PET/CT in the mediastinum after previous RT normofractionation by photon beam into CLD 50Gy for N2 involvements. However, this group also includes patients diagnosed with recurrence in the chest, who have already been irradiated. These are most often patients with lymphoma in complete remission after previous treatment and patients with a history of breast cancer.
This is a group of patients that presents a huge problem in the treatment of NSCLC. Regular dispensary treatment of these patients in lung clinics may lead to a relatively early detection of lung cancer, but therapy is limited.
Surgical treatment is burdened by substantial lung morbidity and postoperative mortality.
It is often not possible to perform photon RT due to the impossibility of adhering to dose limits when trying to administer a curative dose, and treatment is burdened with life-threatening post-radiation pnemonitis. Proton RT can be performed more safely in patients with idiopathic pulmonary fibrosis (IPF) thanks to lower toxicity, although even here side effects require special attention. The goal is maximum lung conservation and dose limits should adhere to the well-known as low as reasonably achievable (ALARA) principle.
It is also worth mentioning patients with oligometastasis in the lungs, regardless of the location of the primary tumor. The most common is colorectal cancer, breast cancer, but also metastatic involvement of the primary lung tumor.
A German restrospective multicenter study published in the Lancet 2019, which compared stereotactic ablative radiotherapy (SABR) with palliative RT, clearly demonstrated an improvement in overall survival (OS) and significantly longer progression free survival (PFS) in patients treated with radical SABR.
Studies with proton RT in the treatment of pulmonary oligometastases have also shown promising results. It is a well-tolerated treatment with effective local control.
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