IMRT

  • Intensity-modulated radiation therapy (IMRT) accurately irradiates a tumor with multiple small radiation beams(1). The complexity of an IMRT treatment is significantly longer than that of conventional radiation therapy because of the extra treatment time(2). 
  • IMRT vs. 3D radiation therapy (3DCRT) efficacy in prostate cancer treatment was reported in the journal PLOS One(3). Compared to 3DCRT, IMRT can provide higher doses with minor damage to healthy tissues(4). 
  • The use of more targeted radiation, such as IMRT, enables a more precise cancer therapy(5). The method treats cancer cells more efficiently and effectively while avoiding adverse effects.

What Is IMRT?

Intensity-modulated radiation therapy (IMRT) precisely irradiates a tumor (or tumour in British English) by using many tiny radiation beams(6). 

In addition to conforming to the tumor volume, as with 3D conformal radiotherapy, each IMRT beam’s radiation intensity is split into tiny segments and modulated during the treatment by the linear accelerator’s multi-leaf collimator (MLC). 

The multiple modulated radiation segments focus the radiation dose distribution on the tumor while sparing surrounding healthy tissue to the greatest extent possible(7).  The risk of radiation-induced side effects is significantly reduced compared to conventional non-modulated 3D conformal radiotherapy techniques. 

Also, the intricacy of IMRT treatment periods is somewhat longer than with conventional radiation(8). Before treatment begins, extra planning time and safety checks are necessary to ensure that all planning data from the treatment planning system to the treatment machine and that all modulated beams can be delivered and successfully transported.

Studies on IMRT

PLOS One published the effectiveness of IMRT versus three-dimensional radiation therapy in prostate cancer treatment(9).

Compared to three-dimensional radiation treatment (3DCRT), IMRT may give larger doses with less harm to healthy tissues(10). However, the findings remain equivocal in cases when IMRT outperforms 3DCRT in prostate cancer.

Researchers conducted a meta-analysis to determine if IMRT is superior to 3DCRT in clinical outcomes in patients diagnosed with prostate cancer(11).

The result shows that the use of IMRT was associated with a decrease in the incidence of 2–4 grade acute gastrointestinal (GI) toxicity. IMRT was also associated with better biochemical control(12). Compared with 3DCRT, IMRT is also more effective at reducing the morbidity of acute GI toxicity.

Moreover, a study published in the journal Radiation Oncology examined the efficacy and safety of IMRT versus three-dimensional conformal radiation treatment for individuals with gastric cancer(13).

Radiotherapy or radiation therapy commonly treats gastric cancer(14). 

Compared to three-dimensional conformal radiation therapy, IMRT has been shown to give superior dose conformity, allowing for dosage escalation and reduction of normal tissue exposure (3D-CRT). 

Although the use of 3D-CRT and IMRT in gastric cancer has been regarded as safe and effective, the efficacy of these two procedures remains controversial(15). Another meta-analysis compared the safety and efficacy of these two therapies.

The meta-analysis included nine controlled clinical trials, satisfying the inclusion criteria(16). The researchers included 516 patients with gastric cancer. The meta-analysis determined that the 3-year OS rate was somewhat higher in the IMRT group than in the 3D-CRT group, but this difference was not statistically significant. 

After three years, the IMRT group had a much greater local control rate than the 3D-CRT group(17). There was no difference in 3-year DFS (disease free survival) rates of the IMRT and 3D-CRT groups. 

Toxicity grades 2 to 4 were comparable across the IMRT and 3D-CRT groups.

Uses of IMRT

In addition to treating tumors, IMRT is also helpful in treating other types of cancer, such as those located near vital organs(18). IMRT allows oncologists to minimize the side effects of their treatment and to do the following:

  • Reduce the quantity of radiation that other surrounding tissues and organs are exposed to, reducing adverse effects and enhancing the overall quality of life.
  • Increase the quantity of radiation administered to a tumor to the recommended maximum level, increasing the possibility of eliminating all malignant cells.

Benefits of IMRT

One of the benefits of IMRT is that the high-dose region is more accurately limited to the tumor volume, while the surrounding area gets a lower dose(19). 

Also, more focused radiation like IMRT allows cancer treatment to be delivered to the tumor’s exact location(20). The procedure allows the cancer cells to be treated more efficiently and effectively and avoids the side effects of other treatments.

IMRT employs several X-ray beams with differing intensities aimed at the tumor from various angles surrounding the patient(21). 

A linear accelerator is the standard treatment equipment in Australia and New Zealand, and all modern devices can safely perform IMRT. These devices use a multi-leaf collimator (MLC) that permits the beam form and intensity to change during therapy. IMRT is always paired with image-guided radiation therapy (IGRT).

Moreover, IMRT is a type of radiation therapy used to deliver a higher dose of radiation to an unusually shaped tumor(22). Thus, the procedure can also create concave areas in the radiation therapy region, which allows the dose to be delivered to a sensitive organ. 

Therefore, IMRT is now commonly used for treating most types of cancer which include:

In some cases, IMRT can provide patients with a slightly longer treatment time. However, other technologies, such as volumetric modulated arc therapy, can reduce this treatment time. 

In addition, IMRT may provide a more significant body tissue dose due to the low doses of radiation delivered to the tissues surrounding cancer.

IMRT, like other external beam radiation therapy (EBRM) procedures, is painless(23). 

IMRT is a kind of external beam radiation therapy (EBRT) that uses hundreds of tiny radiation beams of varying strengths, entering the body from various angles(24). 

However, EBRT uses externally supplied focused radiation beams. It is a non-invasive radiation delivery technology. Radiation beams are shaped when they exit the linear accelerator and before reaching the patient to ensure precise targeting of the malignancy.

Meanwhile, a patient in pain due to the treatment posture or positioning devices can ask if the machine can be stopped(25). 

Risks and Side Effects of IMRT

During IMRT, some patients may experience adverse side effects. These negative effects are dependent on the normal tissue structures around the tumor. The radiation oncologist will discuss side effects and how to manage them.

Moreover, even though IMRT is a painless and non-invasive procedure that can treat various types of cancer, it can also cause problems, such as radiation damage to the surrounding healthy cells(26).

Early and late side effects can also occur after the procedure. Some of these include fatigue and sensitivity, which can occur immediately after the treatment(27). Other common side effects include swelling and soreness in the treatment area.

​​Other early side effects of IMRT may include the following(28):

  • Hair loss in the region of treatment
  • Consumption and digestion problems
  • Difficulty swallowing 
  • Diarrhea
  • Headaches
  • Vomiting and nausea
  • Changes in the urinary and bladder systems
  • Inflammation and swelling in the treatment region

Late side effects are uncommon but might emerge after months or years of therapy(29). 

Frequently, late side effects are irreversible. Late effects of IMRT radiation may include the following:

  • Joint changes
  • Infertility
  • Secondary cancer
  • Changes in the brain and spinal cord
  • Changes in the kidneys
  • Colon and rectal changes
  • Changes in the lungs

Who Operates the Equipment?

The radiation therapist operates radiation therapy equipment from a nearby radiation-protected location(30). Throughout the IMRT treatment, the radiation therapist communicates with the patient and monitors them through a closed-circuit video.

People Involved in the IMRT Procedure

RadiologyInfo.org specifies the experts involved in the IMRT procedure(31). Most institutions use a professionally trained IMRT crew. This team comprises a radiation oncologist, a medical physicist, a dosimetrist, and a radiation therapist. 

  • The radiation oncologist initially discusses with the patient whether IMRT is the best therapy option. After getting informed permission, the treatment plan is created.
  • A radiation physicist ensures the linear accelerator provides the proper dose of radiation. They collaborate with the medical physicist to design the IMRT planning and beam configurations required to give the radiation oncologist‘s dosage.
  • The medical physicist verifies the final treatment plan on the treatment machine using a phantom (a device that resembles the human body) to assess the dosage provided. This plan guarantees the machine supplies the radiation oncologist‘s dosage.
  • A radiation therapist runs the equipment and sets the patient.

The oncology nurse checks the patient during treatment and informs them about the therapy and probable side effects(32). The radiation oncology nurse’s consultation with the physician helps manage any treatment-related reactions or side effects.

Preparation

A physical assessment and medical history review will precede treatment planning(33). Then comes a treatment simulation session with a computed tomography scan or CT scan. 

On the first visit to a cancer center, patients will meet with a radiation oncologist(34). The IMRT procedure will be covered, and any concerns or questions patients may have. 

Patients will be informed of what to anticipate at each stage of the therapy(35). The radiation oncologist will oversee the therapy and handle any side effects. If patients agree to treatment, the insurance authorization procedure begins.

After a comprehensive medical history and a physical exam, the doctor will create a treatment plan based on the results of a CT simulation(36).

The body is where the radiation will be focused(37). To ensure that the beam is directed in the correct position, unique casts or molds will be made on body parts that may be affected by the radiation. A radiation therapist will then apply semi-permanent ink to the area. These marks will help align the patients with the treatment table.

Treatment and Procedure

RadiologyInfo.org briefly explains how treatment or IMRT procedure is conducted(38).

Multiple (fractionated) treatment sessions on separate days are often required with IMRT. The radiation oncologist examines the tumor’s kind, location, size, dosage to typical structures, and the patient’s health to determine the number of treatments. 

IMRT sessions are typically scheduled five days a week for five to eight weeks.

The radiation therapist sets the patient on the treatment table at the start of the session, guided by the markings on the skin (tattoos), denoting the treatment area. If molded devices are created, they will be employed to assist the patient in maintaining the correct posture.

During the process, the patient may be moved. On the treatment machine, imaging technologies such as X-ray or CT may be utilized to verify placement and marker location. Sessions of IMRT typically last between 15 and 60 minutes.

Expected Results

The attending physician will explain the results. 

For instance, the prostate is treated with IMRT five days a week for seven to nine weeks(39). Weekend rest periods enable the recovery of normal cells. However, the overall dosage of radiation and the number of treatments required is dependent on the following:

  • Cancer’s size and location
  • Cancer type
  • Overall health
  • Any other therapies patients are undergoing

Patients will need to see the physician once a week(40). Also, patients need to check their weight, vital signs, and treatment progress. Lab tests may also be drawn intermittently during the treatment. If patients have any questions or concerns, they can notify the therapist or nurse.

History

The concept of intensity-modulated radiotherapy therapy was first presented during the 1960s(41). However, until the 1980s and 1990s, the computing capabilities needed to perform complex calculations were not widely available.

In 1994, the first commercial IMRT system, the Peacock, was introduced. This device utilizes a dynamic multi-vane intensity-modulating collimator. This therapy is called serial tomotherapy and can be performed on slices.

The step and shoot IMRT technique is commonly used to split multiple static beams into sub-segments. In the sliding window technique, the window is defined to move across the treatment field at varying speeds.

In order to achieve the intensity modulation, a binary multi-channel device (MLC) is used. 

In contrast to serial tomography, helical tomotherapy utilizes a treatment couch that is translated into a spiral. This allows for the treatment of extensive field lengths in a single treatment.

The Peacock’s dual-energy source CT detector array allows for the reconstruction of images and dose levels during treatment. This system and the other IMRT systems share many requirements for quality assurance and physics support.

  1. IMRT
    https://radiationoncology.weillcornell.org/clinical-services-and-technologies/external-beam-radiation-therapy/imrt
  2. Ibid.
  3. The Effectiveness of Intensity Modulated Radiation Therapy versus Three-Dimensional Radiation Therapy in Prostate Cancer: A Meta-Analysis of the Literatures
    https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154499
  4. Ibid.
  5. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.targetingcancer.com.au/radiation-therapy/ebrt/intensity-modulated-radiation-therapy-imrt/
  6. IMRT
    https://radiationoncology.weillcornell.org/clinical-services-and-technologies/external-beam-radiation-therapy/imrt
  7. Ibid.
  8. Ibid.
  9. The Effectiveness of Intensity Modulated Radiation Therapy versus Three-Dimensional Radiation Therapy in Prostate Cancer: A Meta-Analysis of the Literatures
    https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154499
  10. Ibid.
  11. Ibid.
  12. Ibid.
  13. Efficacy and safety of intensity-modulated radiation therapy versus three-dimensional conformal radiation treatment for patients with gastric cancer: a systematic review and meta-analysis
    https://ro-journal.biomedcentral.com/articles/10.1186/s13014-019-1294-0
  14. Ibid.
  15. Ibid.
  16. Ibid.
  17. Ibid.
  18. IMRT (Intensity Modulated Radiation Therapy)
    https://moffitt.org/treatments/radiation-therapy/imrt-intensity-modulated-radiation-therapy/
  19. INTENSITY MODULATED RADIATION THERAPY (IMRT)
    https://www.petermac.org/services/treatment/radiation-therapy/types-radiation-therapy/intensity-modulated-radiation-therapy
  20. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.targetingcancer.com.au/radiation-therapy/ebrt/intensity-modulated-radiation-therapy-imrt/
  21. Ibid.
  22. Ibid.
  23. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.radiologyinfo.org/en/info/imrt?google=amp
  24. External Beam RadiatioExternal Beam Radiation Therapy (EBRT)
    https://www.targetingcancer.com.au/radiation-therapy/ebrt/
  25. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.radiologyinfo.org/en/info/imrt?google=amp
  26. Ibid.
  27. Intensity Modulated Radiation Therapy
    https://www.rwjbh.org/saint-barnabas-medical-center/treatment-care/radiation-oncology/radiation-oncology-treatment-options/intensity-modulated-radiation-therapy-imrt-/
  28. Ibid.
  29. Ibid.
  30. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.radiologyinfo.org/en/info/imrt
  31. Ibid.
  32. Ibid.
  33. Ibid.
  34. Advanced Urology Associates IMRT Radiation Therapy Treatment
    https://advuro.com/imrt-intensity-modulated-radiation-therapy/imrt-treatment-process/
  35. Ibid.
  36. Ibid.
  37. Ibid.
  38. Intensity-Modulated Radiation Therapy (IMRT)
    https://www.radiologyinfo.org/en/info/imrt
  39. Advanced Urology Associates IMRT Radiation Therapy Treatment
    https://advuro.com/imrt-intensity-modulated-radiation-therapy/imrt-treatment-process/
  40. Ibid.
  41. Intensity-modulated radiation therapy: emerging cancer treatment technology
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2361760/
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