Pain (Professional) (cont.)
IN THIS ARTICLE
Radiation therapy (RT) has been established as an effective treatment for pain caused by bony metastases. Local, half-body, or whole-body RT enhances the effectiveness of analgesic drugs and other noninvasive therapies by directly affecting the cause of pain (i.e., reducing primary and metastatic tumor bulk).[Level of evidence: I] RT reduces pain and its interference with function among ambulatory cancer patients with symptomatic bone metastases.
External-beam radiation for bone metastases
External-beam radiation therapy (EBRT) produces significant reduction in bone pain in 50% to 80% of patients, with complete pain relief in 30% to 50% of patients. Dose fractionation schedules utilized for painful bone metastases vary considerably. Common fractionation schemes include 30 Gy in ten fractions, 24 Gy in six fractions, 20 Gy in five fractions, and 8 Gy in one fraction. Single- or multiple-fraction regimens of EBRT are equally effective when RT is administered for pain relief; however, re-treatment is needed more frequently after single-fraction RT.[Level of evidence: I]; Fractionated RT courses have been associated with a need for re-treatment in 8% of patients versus a need for re-treatment in 20% of patients after a single fraction.[3,4,5,6,7,8][Level of evidence: I]
The dose and fractionation schedule must achieve a balance between the amount of RT required to kill tumor cells and the amount that would adversely affect normal cells or allow repair of damaged tissue. Data from several prospective randomized trials have failed to show any increased rates of long-term toxicity with single-fraction palliative RT compared with multiple-fraction therapy. In addition to pain control considerations, impact on the patient and caregiver related to the number of treatments delivered must be considered, with many patients finding increased convenience with single-fraction treatment. Another consideration is treatment cost, with single-dose fractionation regimens being less costly because of the smaller number of RT treatments delivered.
Stereotactic body RT (SBRT) is used to treat bone metastases by delivering large doses of RT in a highly conformal manner. Most commonly used to treat spinal metastatic disease, SBRT delivers large doses with a steep dose gradient, thereby potentially sparing adjacent neural structures. Most published data on SBRT have come from single-institution, retrospective studies. The complexities of target delineation, total dose, and fractionation have yet to be fully defined. SBRT may also be used when re-treatment is required in previously irradiated areas. Data regarding RT dose or patient selection for the treatment of recurrent, painful spinal bony metastases with SBRT are not yet definitive.
Pain flare, defined as an increase in pain after palliative RT, can occur, although the incidence has not been well documented. A relatively small, prospective, randomized, controlled trial comparing 8 Gy in one fraction with 20 Gy in five fractions reported pain flare in 15 of 44 patients (34%) for a median duration of 3 days. The flare occurred in 10 of 23 patients (44%) in the 8-Gy group and in 5 of 21 patients (24%) in the 20-Gy group.[Level of evidence: I] A multicenter study included three outpatient clinics and 111 patients to determine the incidence of pain flare after palliative RT. Pain flare was defined in this study as an increase in pain severity before achieving pain relief as distinguished from progression of pain by requiring the worst pain score and analgesic intake return to baseline levels after the increase/flare. Most patients received 8 Gy in one fraction (64%) or 20 Gy in five fractions (25%). The overall pain flare incidence was 40% (39% with 8 Gy and 41% with multiple fractions).[Level of evidence: II]
The use of RT with bisphosphonates has been evaluated in several prospective trials. The combination of zoledronic acid with either higher-dose palliative RT (30 Gy in ten fractions) or lower-dose RT (15 Gy in five fractions) for the treatment of single or multiple osteolytic or osteoblastic painful bony metastases in breast cancer patients was evaluated in a phase IV, randomized, controlled trial. Zoledronic acid, 4 mg, was given every 28 days starting with RT. There was no difference in analgesic or pain scores between the two regimens. However, it has not been shown that the combination of these agents with RT is superior to RT alone for pain relief. Additional prospective trials are needed.
Radiopharmaceuticals are also utilized in the palliation of painful bony metastases. Single intravenous injections of beta-emitting agents such as iodine 131, phosphorus-32-orthophosphate, and strontium 89 and newer agents such as rhenium 186 and samarium 153 can relieve pain in widespread bony metastases.[13,14][Level of evidence: II];[15,16] Response rates range from 20% to 85%, depending on the agent used.
These agents have most commonly been used to treat osteoblastic metastases when there are several symptomatic sites and/or when the number of sites exceeds reasonable treatment with EBRT. Small-volume osteolytic metastases may respond to radiopharmaceuticals, but large-volume osteolytic disease usually does not respond. In patients with inadequate pain relief, studies have demonstrated that approximately one-half of patients treated with radiopharmaceuticals respond to a second treatment. A prospective, multicenter, open-label trial of samarium suggested that multiple doses (i.e., more than two doses) may be administered to patients with advanced cancer and painful bone metastases with repeated benefit and adequate safety if there was an initial response to the initial samarium dose.[Level of evidence: II]
Available data do not suggest that these radiopharmaceuticals eliminate the need for palliative EBRT. Limited studies compare the effectiveness of one radiopharmaceutical with another. In a small randomized trial comparing strontium with samarium in patients with painful bony metastases, there was no statistically significant difference in the degree of analgesia seen. Toxicity, primarily hematologic, was likewise similar.
Radiofrequency ablation (RFA) is a relatively new method for treating symptomatic bony metastasis. Through the use of electromagnetic energy, RFA induces thermal energy that damages tissue around the inserted electrode. The destruction of tissue depends on the temperature achieved and the duration of heating. With the use of image guidance, the goal of RFA is to maintain temperatures between 55°C and 100°C for 4 to 6 minutes to achieve cell kill. Because of slow thermal conduction through tissue, treatment time may increase up to 30 minutes. Preliminary results suggest that RFA may achieve palliation in patients with painful bony metastases.[19,20,21,22];[Level of evidence: III]
In a nonconsecutive 27-month period, 43 patients underwent RFA. Of the 43 patients, 41 (95%) experienced a decrease in worst pain (at least 2 points on an 11-point scale) that continued for up to 24 hours. After peaking at week 1, the morphine-equivalent daily dose decreased significantly at weeks 8 and 12 before rising again at week 24. Three patients experienced adverse events that included a second-degree skin burn at the grounding pad site, transient bladder and bowel incontinence after treatment of a sacral lesion, and an acetabular fracture 6 weeks after RFA of a pelvic lesion. Other uncontrolled case reports confirm these findings. Further study is needed to determine potential risks and benefits.
Invasive Palliative Interventions
Less-invasive analgesic approaches should precede invasive palliative approaches; however, for a minority of patients in whom behavioral, physical, and drug therapy do not alleviate pain, invasive therapies are useful.
Control of otherwise intractable pain can be achieved by the application of a local anesthetic or neurolytic agent. Nerve blocks are performed for several reasons:
A single injection of a nondestructive agent such as lidocaine or bupivacaine, alone or in combination with an anti-inflammatory corticosteroid for a longer-lasting effect, can provide local relief from nerve or root compression. Placement of an infusion catheter at a sympathetic ganglion extends the sympathetic blockade from hours to days or weeks. Destructive agents such as ethanol or phenol can be used to effect neurolysis at sites identified by local anesthesia as appropriate for permanent pain relief and may also be used to cause destruction of central nervous system structures. The efficacy of neurolytic sympathetic blocks may vary depending on the underlying pain mechanisms involved. For patients with multiple pain mechanisms, neurolytic sympathetic blocks may serve as adjuvant techniques to analgesic medications.[Level of evidence: II]
Neurosurgery can be performed to implant devices that deliver drugs or electrically stimulate neural structures. Surgical ablation of pain pathways should, like neurolytic blockade, be reserved for situations in which other therapies are ineffective or poorly tolerated. In general, the choice of neurosurgical procedure is based on location and type of pain (somatic, visceral, deafferentation), the patient's general condition and life expectancy, and the expertise and follow-up available.
Management of procedural pain
Many diagnostic and therapeutic procedures are painful to patients. Anticipated procedure-related pain should be treated prophylactically, integrating pharmacologic and nonpharmacologic interventions in a complementary style.
Local anesthetics and short-acting opioids can be used to manage procedure-related pain, when adequate time is allotted for the drug to achieve full therapeutic effect. Anxiolytics and sedatives may be used to reduce anxiety or to produce sedation.
Cognitive-behavioral interventions such as imagery or relaxation may be useful in managing procedure-related pain and anxiety. (Refer to the Cognitive-Behavioral Interventions section of this summary for examples of relaxation exercises.) Patients generally tolerate procedures better when they are informed about what to expect.
Offering the option for a relative or friend to accompany the patient for support can be useful.
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