Techniques of External Beam Radiation Therapy
2-D radiation therapy
Simple: This technique uses simple set-ups either clinical or on the standard simulator to deliver short courses of palliative radiation therapy for symptom control such as bone pain due to metastatic disease.
Intermediate: Similar technique as above. It is also based on standard simulation. It typically uses two parallel-opposed fields with shielding of normal adjacent tissues. Generally used with palliative intent.
3-D conformal radiation therapy
This is a widely used technique for the treatment of lung cancer and includes virtual simulation or CAT scan-based treatment planning. This technique requires identification of the exact anatomic location of the tumor for volume outline and field design as well as the exact location and outline of normal adjacent anatomic structures. Computerized treatment planning is complex and provides three-dimensional precise dosimetric information of the prescribed radiation dose to the intended targets as well as how much of this dose is received by surrounding critical organs. This information is also displayed as DVH's (Dose volume histograms) which allows detailed analysis of the distribution, percentage, and volumes of radiated targets and adjacent critical organs in order to select the plan that gives the best therapeutic ratio (odds of benefit vs. side effects).
IMRT (intensity modulated radiation therapy)
This technique is used with much less frequency in the lung as compare to other sites. Radiation is delivered using multiple beams of different intensities in order to modulate or shape the radiation distribution around critical organs such as the esophagus, to minimize side effects without compromising tumor dose. Only in selected cases of lung cancer is this technique preferred. Head and neck cancers and primary brain tumors are frequently treated with this technique.
4-D conformal radiation therapy
This state of the art system introduces a fourth dimension to the treatment planning and to the actual treatment delivery by controlling the respiratory motion during the CAT scan image acquisition for target design and for planning treatment volumes (PTV). This process of planning and treatment delivery using respiratory gating in practice accomplishes a reduction in the volume of tissue receiving radiation by turning a moving target or "flying duck" into a stationary target or "sitting duck" therefore instead of "shotgun radiation" a "sharp shooting" precision radiation therapy is used. This novel technique greatly improves the quality and sharpness of the images taken on the gated-CAT scan during the planning phase and in most cases the actual size of the targets to be treated are smaller than those obtained with conventional or non-gated CAT scans. This reduction in size of the target translates into smaller volumes of normal lung that need to be exposed to radiation and therefore better tolerance and less frequency and intensity of side effects. The radiation beam is synchronized or coordinated with the position of the tumor as it reaches the selected "window" of the breathing cycle to deliver the treatment and it turns itself "off" when the tumor is outside that window.
The overall benefit of treating lung cancer using 4-D conformal radiation therapy over 3-D conformal technique is threefold:
1. better tolerance during treatment delivery;
2. reduction of the frequency and intensity of acute and late side effects and
3. potential for dose escalation trials to increase chances of achieving local-regional control of the cancer sites so treated to improve overall outcome.
SBRT (stereotactic body radiation therapy)
The standard treatment for early stage lung cancer (non-small cell carcinoma) is to remove the cancer with surgery. However, a significant number of those patients cannot have surgery due other serious medical conditions such as severe emphysema, heart failure, coronary artery disease, diabetes, etc. Typically they are treated with standard radiation therapy which involves several weeks of daily treatment sessions. Although this modality of treatment is sometimes successful at eradicating the cancer, it is not as effective as surgery and it may cause considerable damage to the surrounding functional lung with further deterioration of an already compromised quality of life. However, left untreated, this early stage lung cancer eventually spreads and approximately half of those patients succumb to their cancer within two years of initial diagnosis before dying of progression of their severe chronic medical conditions mentioned above that preclude surgical intervention in the first place.
SBRT, stereotactic body radiation therapy, is the newest technological breakthrough to treat these patients using high doses of external beam radiation in very few fractions. Recent published results of successful local control of early stage non-small cell lung cancer using this technique range between 80-90% with very acceptable acute and sub-acute toxicity at less than 5%. If follow-up information holds out for these two end points, high local control rates and low percentage of side effects, it would give a great boost and encouragement to those non-surgical patients to seek a highly effective non-surgical option of definitive treatment, when diagnosed with early stage lung cancer. Due to the very limited or small target treated, their baseline lung function is not significantly affected and quality of life is preserved.
This mode of highly focused radiation treatment which converges with precision on the cancer bearing lung, is made possible by another technological breakthrough, IGRT (Image guided radiation therapy). This complex process performed on the treatment unit (Trilogy system) assures the accurate positioning of the patient before the actual treatment is delivered. This is accomplished by taking high resolution CAT scan images of the cancer bearing lung which are then "matched" with the images of the same tumor obtained for treatment planning and dosimetric calculations at the time of the initial simulation. A complement to the CBCT (cone beam CAT scan) is the acquisition of fluoroscopic kilo-voltage images of target motion during breathing-controlled conditions. This so-called KV/KV match re-assures complete coverage of the cancer by the multiple radiation beams according to the stereotactic radiation therapy plan. A third and final check is made before treatment delivery by the so-called DRR/MV match. These are images obtained using the live high energy treatment beam (megavoltage) with digitally reconstructed images (DRR's) obtained from each treatment field according to SBRT plan. They are also used for cine recording of tumor excursion. After the "matching process" is complete using this sophisticated combination of state of the art technology and skillful team approach for quality assurance and safety, the treatment is delivered to its intended target within millimeter accuracy.
Simple: This technique uses simple set-ups either clinical or on the standard simulator to deliver short courses of palliative radiation therapy for symptom control such as bone pain due to metastatic disease.
Intermediate: Similar technique as above. It is also based on standard simulation. It typically uses two parallel-opposed fields with shielding of normal adjacent tissues. Generally used with palliative intent.
3-D conformal radiation therapy
This is a widely used technique for the treatment of lung cancer and includes virtual simulation or CAT scan-based treatment planning. This technique requires identification of the exact anatomic location of the tumor for volume outline and field design as well as the exact location and outline of normal adjacent anatomic structures. Computerized treatment planning is complex and provides three-dimensional precise dosimetric information of the prescribed radiation dose to the intended targets as well as how much of this dose is received by surrounding critical organs. This information is also displayed as DVH's (Dose volume histograms) which allows detailed analysis of the distribution, percentage, and volumes of radiated targets and adjacent critical organs in order to select the plan that gives the best therapeutic ratio (odds of benefit vs. side effects).
IMRT (intensity modulated radiation therapy)
This technique is used with much less frequency in the lung as compare to other sites. Radiation is delivered using multiple beams of different intensities in order to modulate or shape the radiation distribution around critical organs such as the esophagus, to minimize side effects without compromising tumor dose. Only in selected cases of lung cancer is this technique preferred. Head and neck cancers and primary brain tumors are frequently treated with this technique.
4-D conformal radiation therapy
This state of the art system introduces a fourth dimension to the treatment planning and to the actual treatment delivery by controlling the respiratory motion during the CAT scan image acquisition for target design and for planning treatment volumes (PTV). This process of planning and treatment delivery using respiratory gating in practice accomplishes a reduction in the volume of tissue receiving radiation by turning a moving target or "flying duck" into a stationary target or "sitting duck" therefore instead of "shotgun radiation" a "sharp shooting" precision radiation therapy is used. This novel technique greatly improves the quality and sharpness of the images taken on the gated-CAT scan during the planning phase and in most cases the actual size of the targets to be treated are smaller than those obtained with conventional or non-gated CAT scans. This reduction in size of the target translates into smaller volumes of normal lung that need to be exposed to radiation and therefore better tolerance and less frequency and intensity of side effects. The radiation beam is synchronized or coordinated with the position of the tumor as it reaches the selected "window" of the breathing cycle to deliver the treatment and it turns itself "off" when the tumor is outside that window.
The overall benefit of treating lung cancer using 4-D conformal radiation therapy over 3-D conformal technique is threefold:
1. better tolerance during treatment delivery;
2. reduction of the frequency and intensity of acute and late side effects and
3. potential for dose escalation trials to increase chances of achieving local-regional control of the cancer sites so treated to improve overall outcome.
SBRT (stereotactic body radiation therapy)
The standard treatment for early stage lung cancer (non-small cell carcinoma) is to remove the cancer with surgery. However, a significant number of those patients cannot have surgery due other serious medical conditions such as severe emphysema, heart failure, coronary artery disease, diabetes, etc. Typically they are treated with standard radiation therapy which involves several weeks of daily treatment sessions. Although this modality of treatment is sometimes successful at eradicating the cancer, it is not as effective as surgery and it may cause considerable damage to the surrounding functional lung with further deterioration of an already compromised quality of life. However, left untreated, this early stage lung cancer eventually spreads and approximately half of those patients succumb to their cancer within two years of initial diagnosis before dying of progression of their severe chronic medical conditions mentioned above that preclude surgical intervention in the first place.
SBRT, stereotactic body radiation therapy, is the newest technological breakthrough to treat these patients using high doses of external beam radiation in very few fractions. Recent published results of successful local control of early stage non-small cell lung cancer using this technique range between 80-90% with very acceptable acute and sub-acute toxicity at less than 5%. If follow-up information holds out for these two end points, high local control rates and low percentage of side effects, it would give a great boost and encouragement to those non-surgical patients to seek a highly effective non-surgical option of definitive treatment, when diagnosed with early stage lung cancer. Due to the very limited or small target treated, their baseline lung function is not significantly affected and quality of life is preserved.
This mode of highly focused radiation treatment which converges with precision on the cancer bearing lung, is made possible by another technological breakthrough, IGRT (Image guided radiation therapy). This complex process performed on the treatment unit (Trilogy system) assures the accurate positioning of the patient before the actual treatment is delivered. This is accomplished by taking high resolution CAT scan images of the cancer bearing lung which are then "matched" with the images of the same tumor obtained for treatment planning and dosimetric calculations at the time of the initial simulation. A complement to the CBCT (cone beam CAT scan) is the acquisition of fluoroscopic kilo-voltage images of target motion during breathing-controlled conditions. This so-called KV/KV match re-assures complete coverage of the cancer by the multiple radiation beams according to the stereotactic radiation therapy plan. A third and final check is made before treatment delivery by the so-called DRR/MV match. These are images obtained using the live high energy treatment beam (megavoltage) with digitally reconstructed images (DRR's) obtained from each treatment field according to SBRT plan. They are also used for cine recording of tumor excursion. After the "matching process" is complete using this sophisticated combination of state of the art technology and skillful team approach for quality assurance and safety, the treatment is delivered to its intended target within millimeter accuracy.