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DESCRIPTIONFor prostate cancer, external-beam radiation therapy (EBRT) is one accepted option for treatment. 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. These methods 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 EBRT.
Treatment planning first 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 (e.g., 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 (the number of beams and the intensity, shape, and incident axis of each). The planner/therapist 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, since beams had uniform cross-sectional intensity wherever they bypassed shaping devices, it was difficult to match certain geometries (e.g., concave surfaces). Collectively, these methods are termed 3-dimensional conformal radiation therapy (3D-CRT).
Over the past decade, other methods were developed to permit beam delivery with non-uniform cross-sectional intensity. This often relies on a device (a multi-leaf 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 planner/radiotherapist 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 (e.g., proctitis), 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 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 may increase late effects of radiation therapy. 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.
Note: IMRT of the breast and lung is considered separately in another policy
POLICYIntensity-modulated radiation therapy (IMRT) may be considered medically necessary in the treatment of localized prostate cancer at radiation doses of 75 to 80 Gy.
POLICY GUIDELINESThe coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY1/19/2009: Policy added
5/15/09: Policy reviewed, no changes
12/28/2009: Added prior Approval for FEP members effective January 1, 2010.
07/16/2010: Policy Exceptions section revised to state that as of July 1, 2010, prior approval is no longer required for outpatient IMRT provided for the treatment of prostate cancer for FEP members.
08/17/2010: Added CPT code 77338 to the Covered Codes table.
04/26/2012: Policy reviewed; no changes.
08/09/2013: Policy reviewed; no changes.
SOURCE(S)Blue Cross Blue Shield Association policy # 8.01.47
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.
The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.