343–The evolving role of radiation: cancer treatment, low-dose treatments for arthritis, & much more

KEYPOINTS

• 01

  Only ionizing radiation damages DNA, so cell phones and microwaves can't cause cancer that way.

  Houston radiation oncologist Sanjay Mehta (more than 25 years in practice) explains the spectrum: radio waves, microwaves and visible light are non-ionizing. They can heat tissue but can't knock out electrons, so 'fallacies about your cell phone giving you brain cancer are just that'. Ionizing radiation starts at UV and X-rays. Diagnostic radiology uses kilovoltage X-rays, while the linear accelerators used to treat cancer use megavoltage.

• 02

  Everyday exposures are tiny next to the 50 mSv annual limit.

  A gray is joules absorbed per kilogram of tissue. A sievert is the equivalent exposure measure, and one gray is roughly one sievert. Living at sea level gives about 1–2 mSv a year, Denver two to three times that, and a polar flight perhaps 3–4 mSv per trip. A chest X-ray or mammogram is under about 1 mSv. Modern cardiac CT angiograms are about 1–3 mSv (once about 25), and a whole-body PET-CT is perhaps 50–100. By contrast, prostate cancer treatment delivers 70–80 Gy, but only to the gland, split into daily 1.8–2 Gy doses. Mehta never skimps on dental X-rays, mammograms or cardiac imaging: 'the risk–benefit ratio is so heavily in favor'.

• 03

  Mehta believes the linear no-threshold model overstates the harm of very low doses.

  LNT extrapolates cancer risk downward from high-dose data (atomic bombs, Chernobyl). Mehta notes it rests partly on a Nobel laureate's 1940s fruit-fly work and argues there's effectively a threshold. He cites animal data suggesting hormesis at single-digit mSv (better bone healing) and reports of lower leukemia and thyroid cancer rates among people a few miles from Hiroshima and Nagasaki. He calls these controversial and not widely accepted, but thinks fear of low doses is 'overblown'. The ALARA principle (as low as reasonably achievable) still guides practice.

• 04

  Breast-conserving surgery plus radiation replaced radical mastectomy, and today's courses are shorter and gentler.

  Trials in the 1980s (Fisher) showed lumpectomy plus radiation matched mastectomy for survival. Today a typical course is about 40 Gy in 15 daily fractions over about 3 weeks, roughly biologically equivalent to the old 50 Gy in 25–28 fractions, plus an optional 10 Gy boost to the tumor bed. CT-based 3D planning, molded body casts, angled beams and deep-breath holds for left-sided tumors keep dose off the heart and lungs. Even dosing has replaced the old cobalt-era hot and cold spots, which caused severe skin burns or missed areas. Sessions take about 15 minutes, and patients often ask 'when do we start?' after it's already done.

• 05

  Mehta considers prostate radiation now as curative as surgery, with fewer urinary and sexual side effects.

  Radiation used to be reserved for men who couldn't have surgery, which made older results look worse. Precise beam shaping (IMRT/IGRT), a full bladder, an empty rectum and daily imaging now keep dose to the rectum, bladder and penile bulb very low. Mehta says he can't recall a continent patient leaving incontinent. The trade-off is hormone therapy (ADT) for higher-risk disease, with hot flashes and low libido. AI pathology (ArteraAI) and genomic tests (Decipher) now spare perhaps a quarter of Gleason 7 patients from ADT, and PSMA PET lets him treat isolated recurrences directly.

• 06

  In the brain, focused radiosurgery has largely replaced whole-brain radiation.

  Whole-brain radiation (30 Gy in 10 fractions) caused memory problems years later in metastasis patients who now live longer. Its use is perhaps 10% of what it was. Radiosurgery targets individual metastases, and when the whole brain must be treated, IMRT spares the hippocampi. Small-cell lung cancer patients with a complete response still get preventive cranial radiation (about 20 Gy in 5 fractions), which Mehta says cuts brain recurrences by roughly 70–80%. Glioblastoma gets about 60 Gy, and proton therapy limits the dose beyond the tumor, which matters for children.

• 07

  Low-dose radiation for arthritis and tendinopathy is routine in Germany but rare in the US.

  Mehta says Germany treats some 20,000–50,000 patients a year for osteoarthritis, tendinitis, bursitis and plantar fasciitis. The usual protocol is 0.5 Gy × 6 (Monday, Wednesday, Friday for two weeks; 3 Gy total, about one cancer fraction), with an optional repeat after 12 weeks. He describes a cortisone-like anti-inflammatory effect, quoting 60–80% response after one course and 90%+ after a repeat. He has treated about 70 cases, including his own Achilles. The evidence is mostly observational: the two randomized trials were small and, he says, poorly run.

• 08

  Benign treatments use large fields and very low total doses, the opposite of cancer treatment.

  The goal is to calm inflammatory cells across the whole painful region, so Mehta treats generously: for an Achilles, from the calf down to the heel and onto the sole. For superficial joints like hands, knuckles or the elbow he can use electron beams with the target removed, so dose stays shallow. With no vital organs nearby, the body-wide dose is about that of a CT scan. Patients keep training through the two weeks. Spine results are less reliable because nerve compression can't be fixed this way, though facet and SI joints respond.