Proton Therapy, Pediatric Radiotherapy and Emerging Modalities

Yes, that is brachytherapy. Historically, cervical cancer brachytherapy used preloaded sources, meaning the source had to be implanted directly. Technology has evolved to after-loading systems: the applicator, such as the Fletcher-Suit system, is placed first, and the radioactive source is then transferred into the tandem remotely through the treatment machine. That shift from preloading to after-loading has improved safety for patients and staff.

It depends on the treatment area. For oral cavity cancers such as carcinoma of the tongue, the parotid and submandibular glands, buccal mucosa and dysphagia-related structures are the relevant organs at risk. We keep parotid gland mean dose below 26 Gy, and esophagus and trachea mean dose below 45 Gy. Buccal mucosa constraints are not as robustly established in the literature, but our institute's practice is to keep dose there within about 32 to 35 Gy without compromising target coverage, and to keep overall oral cavity dose below 45 Gy. We follow RTOG, QUANTEC, Timmerman, and more recently HyTEC and PENTEC guidelines for these constraints.

For lung cancer, if the patient is operable, surgery is the treatment of choice. If a patient is medically inoperable due to comorbidity, we give SBRT, whether it is a primary early-stage lung cancer or a lung metastasis from elsewhere, such as breast cancer. Dose depends on tumour location: ultracentral tumours, close to the heart or mediastinum, get a more cautious regimen of around 60 to 70 Gy in 7 to 10 fractions; peripheral tumours can get 50 Gy in 5 fractions, or sometimes 55 Gy in 5 fractions. We follow established SBRT dose-constraint guidelines for all of this.

It depends heavily on where the tumour sits. In fractionated radiosurgery for brain tumours, the incidence of radiation necrosis runs below 10 percent, and brain edema is another recognised complication. Risk rises when the target is near a critical structure such as the motor cortex or brainstem; robust dosing data for the motor cortex are limited, but the working figure for a single SRS session is around 15 Gy to that structure. With fractionated SRT or SRS, clinicians have to be especially vigilant about the proximity of organs at risk during planning. Done with that vigilance, SRS can be delivered safely to metastatic brain lesions with minimal complications, though it demands real expertise and careful dose painting.

I have treated around ten pediatric patients from Ethiopia specifically, as part of a broader pediatric caseload. Pediatric malignancy needs to be treated very carefully. In medulloblastoma, for example, craniospinal irradiation planning has to be extremely precise to prevent radiation-related toxicity. Because survival in cancers like ependymoma and medulloblastoma is often good, the most important concern becomes preventing secondary malignancy later in life, which means paying close attention to low-dose spillage, or integral dose, across the whole treatment field. For pediatric cases needing long treatment fields, we generally use tomotherapy, and we get very good outcomes.

The Bragg peak is the physical phenomenon in which protons deposit the majority of their energy at a specific depth within tissue, with minimal or no exit dose beyond that point. This property lowers the overall integral dose delivered to the patient.

Proton therapy tends to be reserved for skull base tumors and cases demanding stronger local control, such as prostate cancer. It is also increasingly used in craniospinal irradiation for pediatric tumors such as medulloblastoma, as well as craniopharyngioma and other skull base malignancies.

The MRI-Linac layers real-time MRI imaging onto treatment delivery, tracking tumor motion and anatomical change as they happen and enabling rapid, adaptive replanning while the patient is still on the table.

PET-guided radiotherapy is a novel approach in which a radiolabeled tumor effectively acts as its own fiducial marker for targeting, reducing the chance of missing part of the target and potentially allowing treatment of multiple cancer sites within a single course.

FLASH radiotherapy delivers a very high dose rate over an extremely short period of time. Early evidence suggests it may reduce toxicity to normal tissue while maintaining tumor control, though the technique remains under active investigation and is not yet part of routine practice.