Doc. Jiří Kubeš: The major benefit of proton therapy lies in protecting healthy tissues
Nearly 9,000 patients with oncological diseases have already undergone modern proton radiotherapy at the Proton Center in Prague. Which diagnoses are suitable for this treatment modality, what are its main benefits, and what is its place in the comprehensive therapy of malignant tumors? We discuss these topics with the chief physician of this medical facility, Doc. MUDr. Jiří Kubeš, Ph.D.
What are the main indications for proton therapy in the Czech Republic?
Proton therapy is conducted here for the same indications as in the western world. These include pediatric tumors, especially in the CNS area, tumors of the paranasal sinuses and the skull base, and tumors of the salivary glands. An interesting indication is adjuvant radiotherapy for HPV16-positive tumors of the palatine tonsils. Other targets for treatment include the middle and upper esophagus, selected lung tumors, and mediastinal tumors, especially lymphomas in young people, left-sided breast carcinomas, non-metastatic pancreatic carcinoma, prostate carcinoma, and retroperitoneal sarcomas.
Do you expect further expansion of indications?
Articles on proton therapy for laryngeal or rectal tumors have been published, but I think these diseases will not be treated at our center for the time being.
For which diagnoses is proton therapy most effective?
Convincing data exist for hepatocellular carcinoma and esophageal carcinoma, as well as for tumors of the paranasal sinuses, pediatric malignancies, and tumors of the skull base.
Is proton therapy the first choice for these indications?
Oncological treatment is always multidisciplinary, with surgeons, for example, playing a significant role. Treatment procedures can be utilized in various sequences and can complement each other.
How does the effectiveness of proton and photon radiotherapy differ?
Ideally, randomized studies comparing these two modalities would exist. However, we currently do not have such studies for any diagnosis, so we proceed based on the level of evidence. The most convincing evidence exists for ocular melanoma, hepatocellular carcinoma, esophageal carcinoma, and tumors of the paranasal sinuses. For other diagnoses, it might not be as clear, so we make decisions based on dosimetric parameters, for instance.
What are the limitations of proton therapy?
The main limitation for us is the reproducibility of the tumor position. Tumors that quickly change their position or shape over time are considered unsuitable for proton therapy. This applies to rectal cancer, bladder cancer, or gynecological malignancies, which we definitely will not be treating in the future.
Are the side effects of proton therapy lower compared to conventional radiotherapy due to more precise targeting?
It depends on the area being irradiated. It is very varied. For example, in the area of retroperitoneal lymph nodes, proton therapy has few side effects since the irradiation does not pass through the abdominal cavity. For nasopharyngeal tumors, the toxicity of both modalities is comparable, and the differences in the acute phase are not significant.
In terms of late effects, we are generally concerned about secondary malignancies induced by ionizing radiation. There's a direct correlation—lower radiation dosage leads to fewer secondary malignancies. Radiation is also cardiotoxic. The insidious nature of these late effects is that they manifest 10 to 20 years after irradiation. Typically, young patients irradiated at age 20 for lymphoma may develop valvular defects, cardiomyopathy, or early onset of ischemic heart disease by age 40. However, therapeutic doses are continually being reduced. Ten years ago, doses around 10 grays were considered acceptable; today, it's just 2 grays, and it's possible they will be even lower in the future.
Are there risks specifically associated with 'protons'?
The mechanisms of action for photon and proton radiation are not very different. Generally, it involves ionizing radiation that damages the DNA of all cells, including tumor cells.
How many patients are treated at the Proton Center in Prague?
We are at the maximum of our capacity, which is approximately 1,200 patients per year.
Do patients need to be referred by their treating oncologist, or can they come 'off the street'?
We are part of the National Oncology Center, which falls under FN Motol and is part of the network of public healthcare facilities, so patients can contact us directly through the client service department. They send in their medical documentation, which is then reviewed by a multidisciplinary team.
What are the conditions for reimbursement and accessibility of proton therapy?
All health insurance companies have contracts with the Proton Center in Prague, and treatment is subject to approval by a reviewing physician. Our relations with insurance companies are very good. We prioritize treatment based on the urgency of therapy. There are cases that need to be addressed urgently, such as malignant lymphomas in young patients. The second category includes tumors in the ENT area, the third category includes breast carcinomas, and the fourth category includes, for instance, prostate carcinoma. We are able to meet the time requirements for the first two categories, and for the others, it's a matter of agreement with the patient.
Is there professional consensus on the use of this method?
There are definitely some points of friction, especially in the field of radiation oncology. Some colleagues have different opinions regarding indications for proton radiotherapy. I believe that indications for a particular patient should be based on the physician's experience.
If opinions on the procedure differ, is it up to the patient to decide?
Yes. I can explain this with the example of prostate carcinoma. From a urologist's perspective, radical prostatectomy might be preferred. At a photon facility, photon radiotherapy is likely to be offered, and at our center, naturally, proton therapy. Patients must always be informed of all treatment options. For prostate carcinoma, they can be monitored, irradiated, or operated on. Surgery can be performed via open approach, laparoscopically, or robotically. And in the case of irradiation, they can choose between proton and photon therapy.
Summarize the main benefit of proton therapy...
The major benefit lies in protecting healthy tissues. A significant portion of the body receives minimal or no radiation dose. This is not the case for modern photon radiotherapy techniques, which, while targeted and precise, always distribute a non-negligible dose of radiation to surrounding tissues.
Does irradiation affect metastatic tumors as well?
Metastatic tumors can also be irradiated. I would like to highlight the increasing discussion about the synergy between immunotherapy and ionizing radiation. Our vision is that irradiating a tumor lesion combined with immunotherapy could potentially restart the immunological defense against the tumor, which might then affect metastatic lesions in the body.
MUDr. Andrea Skálová
editorial team of proLékaře.cz
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