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DESCRIPTIONFor certain stages of certain cancers, postoperative radiation therapy improves outcomes for many patients. Adding radiation to chemotherapy also improves outcomes for those with inoperable tumors that have not metastasized beyond regional lymph nodes. Over the past several decades, methods to plan and deliver radiation therapy have evolved in ways that permit more precise targeting of tumors with complex geometries. Most early trials used 2-dimensional treatment planning based on flat images, and radiation beams with cross-sections of uniform intensity that were sequentially aimed at the tumor along 2 or 3 intersecting axes. Collectively, these methods are termed "conventional external-beam radiation therapy" (CRT).
Treatment planning evolved by using 3-dimensional images, usually from computed tomography (CT) scans, to delineate the tumor, its boundaries with adjacent normal tissue, and organs at risk for radiation damage. Radiation oncologists used these images, displayed from a "beam’s-eye view," to shape each of several beams with compensators, blocks, or wedges to conform to the patient’s tumor geometry perpendicular to the beam’s axis. Computer algorithms were developed to estimate cumulative radiation dose delivered to each volume of interest by summing the contribution from each shaped beam. Methods also were developed to position the patient and the radiation portal reproducibly for each fraction and immobilize the patient, thus maintaining consistent beam axes across treatment sessions. However, "forward" planning used a trial and error process to select treatment parameters, including the number of beams and the intensity, shape, and incident axis of each. The radiation oncologist modified one or more parameters and re-calculated dose distributions, if analysis predicted underdosing for part of the tumor or overdosing of nearby normal tissue. Furthermore, because beams had uniform cross-sectional intensity wherever they bypassed shaping devices, it was difficult to match certain geometries, in particular concave surfaces. Collectively, these methods are termed 3-dimensional conformal radiation therapy (3D-CRT).
In the mid-1990s, 3D conformal methods were further developed to permit beam delivery with non-uniform cross-sectional intensity. This approach often relies on a device (a multileaf collimator, MLC) situated between the beam source and patient that moves along an arc around the patient. As it moves, a computer varies aperture size independently and continuously for each leaf. Thus, MLCs divide beams into narrow "beamlets," with intensities that range from zero to 100% of the incident beam. With an alternative, termed tomotherapy, a small radiation portal emitting a single narrow beam moves spirally around the patient, with intensity varying as it moves. Each method (MLC-based or tomotherapy) is coupled to a computer algorithm for "inverse" treatment planning. The radiation oncologist delineates the target on each slice of a CT scan, and specifies the target’s prescribed radiation dose, acceptable limits of dose heterogeneity within the target volume, adjacent normal tissue volumes to avoid, and acceptable dose limits within the normal tissues. Based on these parameters and a digitally reconstructed radiographic image of the tumor and surrounding tissues and organs at risk, computer software optimizes the location and shape of beam ports, and beam and beamlet intensities, to achieve the treatment plan’s goals. Collectively, these methods are termed intensity-modulated radiation therapy (IMRT).
Multiple studies have generated 3D-CRT and IMRT treatment plans from the same scans, then compared predicted dose distributions within the target and in adjacent organs at risk. Results of such planning studies show that IMRT improves on 3D-CRT with respect to conformality to, and dose homogeneity within, the target. Dosimetry using stationary targets generally confirms these predictions. Thus, radiation oncologists hypothesized that IMRT may improve treatment outcomes compared with those of 3D-CRT by one or more of the following mechanisms.
Increased conformality may permit escalated tumor doses without increasing normal tissue toxicity, and may thus improve local tumor control. Better dose homogeneity within the target may also improve local tumor control by avoiding underdosing (cold spots) within the tumor and may decrease toxicity by avoiding overdosing (hot spots). Finally, enhanced conformality for standard doses may reduce the dose outside the target volume and thus decrease toxicity.
However, IMRT aims radiation at the tumor from many more directions, and thus subjects more normal tissue to low-dose radiation than occurs with conventional EBRT or 3D-CRT. This technique may increase late effects of radiation therapy. In addition, because most tumors move as patients breathe, dosimetry with stationary targets may not accurately reflect doses delivered within target volumes and adjacent tissues in patients. Furthermore, treatment planning and delivery are more complex, time consuming, and labor-intensive for IMRT than for 3D-CRT. Thus, clinical studies must test whether IMRT improves tumor control or reduces acute and late toxicities, when compared with 3D-CRT. Testing this hypothesis requires direct comparative data on outcomes for separate groups of similar patients treated with each method.
Related medical policies are Intensity-Modulated Radiation Therapy (IMRT) of the Prostate, Intensity Modulated Radiation Therapy (IMRT) of the Breast and Lung, and Intensity-Modulated Radiation Therapy (IMRT): Head and Neck Cancers.
POLICYIntensity modulated radiation therapy may be considered medically necessary as an approach to delivering radiation therapy for patients with squamous cell cancer of the anus/anal canal.
When dosimetric planning with standard 3-D conformal radiation predicts that the radiation dose to an adjacent organ would result in unacceptable normal tissue toxicity (see Policy Guidelines), intensity-modulated radiation therapy (IMRT) may be considered medically necessary for the treatment of cancer of the abdomen and pelvis, including but not limited to:
Intensity-modulated radiation therapy (IMRT) would be considered investigational for all other uses in the abdomen and pelvis.
POLICY EXCEPTIONSFederal Employee Program (FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.
POLICY GUIDELINESRadiation Tolerance Doses for Normal Tissues
aTD 5/5, the average dose that results in a 5% complication risk within 5 years
bTD 50/5, the average dose that results in a 50% complication risk within 5 years
In order for IMRT to provide outcomes that are superior to 3DCRT, there must be a clinically meaningful decrease in the radiation exposure to normal structures with IMRT compared to 3DCRT. There is not a standardized definition for a clinically meaningful decrease in radiation dose. In principle, a clinically meaningful decrease would signify a significant reduction in anticipated complications of radiation exposure. In order to document a clinically meaningful reduction in dose, dosimetry planning studies should demonstrate a significant decrease in the maximum dose of radiation delivered per unit of tissue, and/or a significant decrease in the volume of normal tissue exposed to potentially toxic radiation doses. While radiation tolerance dose levels for normal tissues are well-established, the decrease in the volume of tissue exposed that is needed to provide a clinically meaningful benefit has not been standardized. Therefore, precise parameters for a clinically meaningful decrease cannot be provided.
Investigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member’s specific benefit plan language.
POLICY HISTORY5/20/2009: Policy added
7/16/2009: Approved by Medical Policy Advisory Committee (MPAC)
08/12/2010: Policy description updated to add links to related medical policies. Policy statement revised to state that IMRT may be considered medically necessary as an approach to delivering radiation therapy for patients with squamous cell cancer of the anus/anal canal, effective 05/13/2010. IMRT remains investigational for other locations in the abdomen and pelvis. The definition of investigative service added to the policy guidelines. Coding information removed from the policy guidelines; this information is provided in the Code Reference section. FEP verbiage added to the Policy Exceptions section. All codes moved from non-covered to covered. Added CPT code 77338 and ICD-9 codes 154.2 and 154.3.
04/10/2013: Policy statement revised to state that IMRT may be considered medically necessary for the treatment of cancer of the abdomen and pelvis when dosimetric planning with standard 3-D conformal radiation predicts that the radiation dose to an adjacent organ would result in unacceptable normal tissue toxicity. IMRT remains investigational for all other uses in the abdomen and pelvis. Policy guidelines updated regarding radiation tolerance doses for normal tissues of the abdomen and pelvis.
SOURCESBlue Cross & Blue Shield Association Policy # 8.01.49
CODE REFERENCEThis is not intended to be a comprehensive list of codes. Some covered procedure codes have multiple descriptions.
The code(s) listed below are ONLY covered if the procedure is performed according to the "Policy" section of this document.