TL;DR: Hyperbaric oxygen therapy (HBOT) has two distinct roles relative to radiation therapy. Before radiation, HBOT has been investigated as a radiosensitiser – increasing tumour oxygen levels to make radiation more effective. After radiation, HBOT is an established treatment for delayed radiation tissue injury, helping heal damage that can appear months or years later. These are fundamentally different uses with different evidence bases, and understanding the distinction matters for patients and clinicians alike.
Estimated reading time: 5 minutes
What Is the Difference Between Pre-Radiation and Post-Radiation HBOT?
HBOT and radiation therapy interact in two completely different ways depending on when the hyperbaric treatment is delivered. A 2026 evidence review described this as a “fascinating paradox” – the same therapy can theoretically enhance radiation’s cancer-killing effect when given before treatment, and then heal the tissue damage that radiation causes when given afterward (Meijnders et al., 2026).
| Timing | Purpose | Evidence Level | Availability in Canada |
|---|---|---|---|
| Before radiation | Radiosensitisation – make tumour more responsive to radiation | Investigational (historical trials, limited modern data) | Not standard practice |
| After radiation (acute phase) | Prevent or reduce acute side effects during treatment | Limited evidence | Not routinely offered |
| After radiation (months-years later) | Treat delayed radiation tissue injury (LRTI) | Strong – RCTs, systematic reviews, Cochrane review | Covered by provincial health plans at hospital programmes |
During Daffodil Month, it is important for cancer survivors to understand that the strongest evidence for HBOT is in treating the lasting effects of radiation – not in enhancing the radiation itself.
Can HBOT Before Radiation Improve Cancer Treatment?
The idea behind pre-radiation HBOT is straightforward: many tumours are hypoxic (oxygen-starved), and radiation works best when cells are well-oxygenated. By flooding the tumour with oxygen immediately before a radiation session, the radiation should theoretically be more effective at damaging cancer cells.
This concept was tested in clinical trials as far back as the 1970s and 1980s, particularly for head and neck cancers. Some early trials showed improved local tumour control rates when HBOT was delivered 10 to 20 minutes before irradiation. However, the approach fell out of favour for several practical reasons:
- Logistical complexity – patients needed HBOT immediately before each radiation fraction, requiring a hyperbaric chamber adjacent to the radiation suite
- Modern radiation techniques (IMRT, proton therapy) have improved outcomes without HBOT
- Other radiosensitisers (nimorazole, carbogen breathing) are simpler to administer
- The oxygenation effect is temporary and difficult to time precisely with radiation delivery
A 2025 safety evaluation confirmed that HBOT does not promote tumour growth – an important concern that has been thoroughly addressed in the literature (Hyperbaric Oxygen Safety Evaluation, 2025). Preclinical research continues to explore whether HBOT could modulate the tumour microenvironment to enhance immunotherapy responses (Tumour Microenvironment Review, 2023).
Pre-radiation HBOT is not standard practice in Canada or internationally. The strongest clinical evidence for HBOT in cancer care is in treating the tissue damage that radiation causes, not in enhancing the radiation itself.
How Does HBOT Help After Radiation Therapy?
This is where the evidence is strongest. Radiation therapy saves lives, but it can also cause progressive damage to the blood vessels in the treated area. Over months or years, the irradiated tissue becomes hypoxic, hypocellular, and hypovascular – the “three H” pathology. This leads to delayed radiation tissue injury (LRTI), which can affect the bladder (radiation cystitis), rectum (radiation proctitis), jawbone (osteoradionecrosis), soft tissue, and other structures.
HBOT addresses this by:
- Growing new blood vessels (angiogenesis) in irradiated tissue
- Activating fibroblasts to strengthen damaged tissue
- Reducing chronic inflammation that drives ongoing tissue breakdown
- Restoring oxygen supply to enable the tissue to heal itself
The 2023 Cochrane systematic review (18 studies, 1,071 participants) confirmed that HBOT may result in complete resolution or significant improvement of late radiation tissue injury in the head, neck, bladder, and rectum (Cochrane Review, 2023). The HONEY randomised clinical trial (2024) demonstrated measurable improvements in irradiated breast tissue (HONEY RCT, 2024).
When Should Cancer Survivors Consider HBOT?
If you have completed radiation therapy and are experiencing any of the following symptoms in the area that was irradiated, HBOT may be worth discussing with your oncologist or family physician:
- Rectal bleeding or chronic bowel changes after pelvic radiation
- Bladder bleeding, urgency, or frequency after pelvic radiation
- Jaw pain, tooth loss, or bone exposure after head and neck radiation
- Non-healing wounds or skin breakdown in a previously irradiated area
- Chronic pain, fibrosis, or restricted movement in the treatment area
- Lymphoedema following breast cancer radiation
These symptoms can develop 3 months to many years after completing radiation. HBOT has been shown to be effective even when the radiation was delivered years earlier.
Is Post-Radiation HBOT Covered in Canada?
Delayed radiation injury is one of the 14 conditions recognised under Health Canada’s device licensing framework. It is covered by OHIP at hospital-based programmes in Ontario, by Alberta Health at hospital facilities, and by MSP at Vancouver General Hospital in British Columbia.
For details by province, visit the Canada Hyperbarics coverage guide. To find hospitals and regulated facilities, use the facility directory.
Frequently Asked Questions
Does HBOT make cancer worse or promote tumour growth?
No. Multiple studies and systematic reviews have confirmed that HBOT does not promote tumour growth. A 2025 safety evaluation specifically assessed this concern and found no evidence of increased cancer risk from HBOT treatment.
Can I receive HBOT while undergoing active radiation treatment?
This is not standard practice. Pre-radiation HBOT (radiosensitisation) was studied in historical trials but is not routinely used today. HBOT for late radiation effects is typically started after radiation is complete and symptoms have developed.
How long after radiation can I start HBOT for tissue injury?
Delayed radiation tissue injury is typically diagnosed at least 3 to 6 months after completing radiation, though it can develop years later. HBOT can be started at any point after diagnosis. There is no upper time limit – patients have been successfully treated many years after their original radiation therapy.
This Daffodil Month, Learn About Your Options
If you have finished cancer treatment and are living with the lasting effects of radiation therapy, evidence-based treatment options exist at hospitals and regulated facilities across Canada. Talk to your care team about whether a referral for HBOT assessment is appropriate.
Find a hyperbaric facility near you across Canada.
This April, in recognition of Daffodil Month, Canada Hyperbarics is dedicated to helping cancer survivors understand and access treatments for the lasting effects of cancer therapy.
References
- Meijnders P, et al. Between hope and uncertainty: the elusive evidence on hyperbaric oxygen therapy and radiotherapy. Supportive Care in Cancer. 2026. View in Canada Hyperbarics Research Database.
- Lin ZC, Bennett MH, et al. Hyperbaric oxygen therapy for late radiation tissue injury. Cochrane Database of Systematic Reviews. 2023. View in Canada Hyperbarics Research Database.
- Hyperbaric oxygen therapy and late local toxic effects in patients with irradiated breast cancer: the HONEY randomized clinical trial. JAMA Oncology. 2024. View in Canada Hyperbarics Research Database.
- Hyperbaric oxygen therapy for managing cancer treatment complications: a safety evaluation. Medicina. 2025. View in Canada Hyperbarics Research Database.
This content is for informational purposes only and does not constitute medical advice. Hyperbaric oxygen therapy should only be administered by qualified healthcare professionals in accredited facilities. Consult your physician or a certified hyperbaric medicine specialist for treatment decisions. Canada Hyperbarics is an independent educational resource and is not affiliated with any specific clinic or manufacturer.