Innovations in Radiation Therapy: Current Advances and Impacts
Introduction
Cancer is a multigenic and multicellular disease that can arise from all cell types and organs. It remains the leading cause of death globally. The International Agency for Research on Cancer (IARC) recently estimated that 7.6 million deaths worldwide were due to cancer, with 12.7 million new cases being reported per year. Radiation therapy is an important modality used in cancer treatment, along with surgery and chemotherapy. Approximately 50% of all cancer patients will receive radiation therapy during their course of illness, and radiation therapy contributes to around 40% of curative treatment.
The main goal of radiation therapy is to prevent cancer cells from multiplication, this would occur by exposing the tumor to a high dose of radiation while sparing normal tissue. The rapid evolution in this field is being boosted by advances in imaging techniques, computerized treatment planning systems, and an improved understanding of the radiobiology of radiation therapy. The progression of radiation therapy techniques is on the path of increasing the survival rate and reducing treatment side effects for cancer patients. This article sheds light on the current advances in radiation therapy.
Advances in radiation therapy will lead to an increase in survival rates and reduce treatment side effects for cancer patients.
3D Conformal Radiotherapy (3DCRT)
Conventional radiation therapy, which delivered energy to a target volume based on a simple two-dimensional clinical reference, evolved in the 1980s. Tumor targeting was inaccurate, limiting the curative potential of radiation therapy and increasing the risk of radio-induced toxicity. Three-dimensional conformal radiotherapy (3DCRT) emerged in the 1980s and 1990s through the use of CT scan imaging. By conforming the beams of irradiation to the tumor volume to be treated, 3DCRT allows fine and precise irradiation of the tumor volume while preserving surrounding tissues.
3DCRT allows fine and precise irradiation of the tumor volume while preserving surrounding tissues.
Intensity Modulated Radiation Therapy (IMRT)
Intensity-modulated radiation therapy allows for modulating the intensity of the energy of radiation delivered during the session. This technique allows for minimizing radio-induced toxicity, increasing the dose if necessary, and often achieving better curative treatment results. The latest generations of linear accelerators are now equipped with collimators composed of several dozens of thin leaves (multi-leaf collimator, or MLC, composed of 80 to 160 leaves) which allow it to precisely match the shape of the tumor that can be very complex or amorphous. The collimator leaves can also move during irradiation and modulate the flow of the treatment beam. IMRT makes it possible to obtain the desired irradiation at the target tumor volume using successive multibeam techniques, and a very rapid decrease in the dose at its periphery, thus offering better radiation protection of healthy tissue.
Along with this technical evolution of linear accelerators, a parallel evolution of computerized dose calculation systems has profoundly changed the habits of radiation oncologists. While in a conventional irradiation technique, the dose is calculated from a predefined position of the beams and lead blocks, the new dosimetry planning algorithms allow the desired dose to be chosen beforehand at the target and critical volumes. This reverse planning of treatment has been made possible thanks to advances in information technology which offer medical physicists the possibility of optimizing individually for each patient the dose delivered by each beam while controlling in real time the position and speed of movement of the MLC leaves.
Two different treatment techniques are commonly available:
- Static “Step and Shoot” mode: the movement of the leaves is discontinuous during irradiation, and the emission of X-rays is interrupted during the movement of the leaves
- Dynamic mode: the leaves move continuously during irradiation, and the X-ray emission is therefore continuous
IMRT makes it possible to modulate the intensity of the energy delivered and minimize radio-induced toxicity.
Dynamic Conformal Arc Therapy (DCAT)
DCAT reduces treatment time and eliminates the need for complex image guidance procedures, thereby protecting healthy surrounding organs. It is used in cases where the static beams without modulation are not adequate to deliver the dose to the tumor and protect the organs at risk. It allows the leaves to conform to the external volume of the target with a margin of a few millimeters. Thanks to this method, the irradiation time is reduced, and healthy organs are better protected.
DCAT shortens the treatment time and reduces the need for complex image guidance procedures, thus allowing easy protection of healthy organs.
Volumetric Intensity Modulated Arc Therapy (VMAT)
VMAT allows irradiating cancer tissues with more precision than conventional radiation therapy using control of the irradiation beams on a full arc of 360 degrees. It combines image-guided irradiation with intensity modulation. The process of dose delivery using the VMAT technique is very complex, requiring experts in radio-physics and dosimetry. Quality assurance is mandatory at each stage of the process. VMAT offers faster and more precise treatment with minimal side effects compared to conformal techniques.
VMAT allows more precise irradiation of cancer tissues through a very complex process of dose delivery.
Image-Guided Radiation Therapy (IGRT)
Image-guided radiation therapy aims to precisely locate the target tumor volume before and/or during the treatment session, to ensure its correct position with the irradiation beams. It brings together all imaging techniques, allowing direct visualization of the target volume, or indirect visualization with the use of intra-tumor markers. The most recent technologies available include those making it possible to obtain three-dimensional computed tomography images in the treatment position at each session. These anatomical data repeated during all radiotherapy sessions offer the possibility of adapting the irradiation parameters to morphological changes in the patient or in the target tumor volume that may occur during treatment.
IGRT aims to precisely locate the target tumor volume before and/or during the treatment session, to ensure its correct position with the irradiation beam.
Stereotactic Radiation Therapy
SRT uses convergent microbeams, allowing access to tumors inaccessible to conventional RT, with high dose irradiation of small volumes and very good sparing of neighboring organs at risk. It is a high-precision technique using a dedicated machine such as the Gamma-knife or an adjusted linear accelerator. SRT is based on the use of convergent microbeams, allowing access to tumors inaccessible to conventional radiotherapy. It makes it possible to concentrate more radiation on the tumor with very good sparing of neighboring organs at risk. This technique allows the administration of high doses to very small volumes. Though originally implemented for intracranial tumors, it has uses for lesions near the spinal cord and tumors that move with respiration.
SRS is performed in a single session, for intracranial tumors, while SRT is performed during a series of sessions, usually ranging from 3 to 5. And when it comes to tumors of the body (non-intra-cranial), we speak of SBRT.
Associated with an embarked or external imaging system, it makes it possible to monitor the patient’s position during treatment and to follow the movements of organs and the tumor linked to the patient’s breathing in real time, called tracking, to reduce margins of error and to give higher doses at the tumor level.
During treatment, the gantry rotates around the patient, delivering multiple beams ranging from 100 to 400. To better understand the scenario, imagine that we are painting the tumor, as if a beam was a small brushstroke, and thus by applying several hundred beams, the precise drawing of the tumor is obtained.
Stereotactic radiation therapy is of infra-millimetric precision. Parameters and positioning are controlled by the associated X-ray imaging systems, allowing correction of the patient’s position in real time to ensure that the region to be irradiated is always included in the PTV. It thus allows the administration of high doses to very small volumes.
SRT uses convergent microbeams, allowing access to tumors inaccessible to conventional RT, with high dose irradiation of small volumes and very good sparing of OAR.
Respiratory Gated Radiation Therapy
Conformal radiation therapy appears to be the culmination of an old approach to improving the precision and quality of treatment with ionizing radiation, made possible by the appearance of new tools stemming from technological progress. A new reflection on the target volumes of irradiation is one of the most stimulating contributions of the conformal approach, noting that the amplitude of the safety margins closely determines the precision of the treatment. Overestimating these margins leads to increased exposure of healthy tissue with an increased risk of complications, hence the advantage of reducing the causes of positioning error.
The main objective of the respiratory gating is to limit the internal target volume ITV (being a volume that considers the movements linked to breathing) while ensuring the continuous presence of the tumor target in the radiation beams. With conventional radiotherapy without respiratory gating, the use of larger beams is necessary to ensure sufficient isodose in the irradiated volume at all phases of the respiratory cycle. These additional margins logically increase the irradiation of healthy organs. Thus, the use of respiratory gating makes it possible to reduce the irradiation of critical volumes such as the heart, lungs, and esophagus, without compromising the target volumes of interest.
All breathing control methods also benefit from the contribution of image-guided radiation therapy. Visualizing the actual position of the target volume during breathing improves the overall quality of the treatment.
The objectives and the practical implementation are different depending on whether one or the other of the techniques or strategies is applied. It is of course the clinical objectives and their adaptations to the patient that, in general, guide the choice of the method. Even though the implementation of a breathing control procedure is not extremely complex, patient management is inescapably personalized. Patients have different apprehensions about participating in their treatment, these differences being linked to the location of the cancer, age, general condition, and understanding. In practice, care for patients requires compulsory adaptation to all the situations encountered. Thus, despite very diverse approaches, the teams that have so far implemented breathing control have all integrated its personalized aspect, knowing that currently, no technique covers at once all the clinical situations encountered.
Respiratory gating limits the ITV while ensuring the continuous presence of the tumor target in the radiation beams, thus reducing the irradiation of critical volumes without compromising the target volume of interest.
Radiation therapy has had a significant impact on cancer treatment outcomes. Approximately 50% of all cancer patients will receive radiation therapy during their course of illness, and radiation therapy contributes to around 40% of curative treatment. The use of radiation therapy has increased the survival rate of cancer patients and improved their quality of life. Radiation therapy has also allowed for the preservation of organs that are critical for normal function. The use of radiation therapy has reduced the need for surgical intervention, and in some cases, radiation therapy has been used as a substitute for surgery.
Ongoing advancements in RT technology and techniques will ultimately lead to continued improvement in cancer treatment.
Future of Radiation Therapy
Radiation therapy will continue to play a vital role in cancer treatment in the future. Ongoing advancements in radiation therapy technology and techniques will ultimately lead to continued improvement in cancer treatment. The use of personalized medicine will become increasingly important in determining the most effective radiation therapy technique for individual patients. The development of new radiation treatment modalities and techniques will continue to improve the survival and quality of life of cancer patients.
While radiation therapy remains an important modality for cancer treatment, it is important to note that each patient’s treatment plan is unique and should be determined by a team of medical professionals. The selection of the appropriate radiation therapy technique depends on several factors, including the type of cancer, the location of the tumor, the stage of the cancer, the patient’s overall health, and the treatment goals. Therefore, it is essential to consult with a medical professional before undergoing any radiation therapy treatment.
In summary, radiation therapy has come a long way, and the current advances in radiation therapy have allowed for more precise targeting of tumors while minimizing radiation therapy-related toxicities. Ongoing advancements in radiation therapy technology and techniques will ultimately lead to continued improvement in cancer treatment, and hopefully, one day, we will find a cure for cancer.
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