放射治疗（Radiation therapy）是指通过使用高能射线或粒子来杀死癌细胞的治疗方法。放疗可用于以下几种前列腺癌情况：

1. 作为局限于前列腺内的低级别癌症的初始治疗。这类癌症患者的治愈率与采取根治性前列腺切除术的患者相当。

2. （结合激素治疗）用于癌症已扩散到前列腺外和临近组织的前列腺癌的初次治疗。

3. 术后癌症没有被彻底清除或者癌症在前列腺内复发。

4. 在癌症进展情况下，用于缩小肿瘤大小和缓解当前和未来可能出现的症状。

有两种主要的放射疗法供使用：体外放射疗法（external beamradiation）和brachytherapy(internal radiation)近距离放射疗法(内部放疗)。两种类型都是治疗前列腺癌的好方式，尽管外部放疗在治疗结果上有比较长期的信息记录。（另一种类型的放射治疗，需要向人体注入含放射性的药物。）

External beam radiation therapy (EBRT)

体外放射疗法

体外放射治疗，是通过体外机器将放射光束聚集于前列腺。这种方式可用于治疗初期阶段的癌症，或者帮助缓解症状，比如癌症扩散到骨头特定区域引起的骨痛症状。

为了尽可能降低副作用，医生需要非常仔细地计算出放射所需的精确剂量，并且精确将光束瞄准目标区域。放疗开始前，需要做一些影像检查，如核磁共振成像、CT扫描或骨盆普通X线检查，以找寻前列腺的精确位置。放射医生团队可能会在你的皮肤上做个墨水标记，作为引导，使射线聚焦在正确区域。

通常你将需要一周5天在诊所接受治疗，持续7到9周。每次治疗更像是在做X线检查。辐射剂量比一次X线检查要强，但治疗过程是无痛的。每次治疗仅持续几分钟的时间，但治疗前的准备过程（调整治疗方位）则要花费比较长的时间。

体外放射疗法是治疗前列腺最常使用的技术。它在对前列腺使用较高放射剂量的同时，降低对周围健康组织的辐射。

Three-dimensional conformal radiation therapy(3D-CRT)

三维适形放射治疗

三维适形放射治疗，使用特殊的计算机精确地绘制出前列腺的位置，然后放射光束从几个方向对准前列腺，使其伤害到正常组织的可能性降到最低。你将可能需要配备一个塑料模具，类似人体模型，这样可以让你每天保持在同一个位置，进而使射线得以更精确的瞄准。这种方式，至少可以获得与标准放疗一样的疗效，却带来更少的副作用。

Intensity modulated radiation therapy(IMRT)

调强放射治疗

调强放射治疗是三维适形放疗的高级形式。它使用了一种电脑驱动的机器，在发送射线的同时会围绕患者移动。除了形成光束，从几个角度瞄准前列腺外，光束的强度还可以被调整，使到达最敏感正常组织的剂量最小化。这种方式使得医生能够向癌症区域发送更高剂量。对于前列腺癌患者来说，这是最常使用的体外放疗方式。

有些更新的放射仪器内置有成像扫描仪。这种先进的，被称为影像引导的放射疗法，让医生能够对前列腺照相，并能在发送射线前，在瞄准上做轻微调整。这种方式可能有助于更精确地发送射线，引起更少的副作用，尽管还需要更多的研究来证明这一点。

调强放射治疗有一种变形，称为强度调控弧形放射治疗。它使用了一种机器，当在身体周围旋转一次时会快速地发送射线。这种方式让每次治疗只要花上几分钟。虽然对于患者来说这样比较便捷，但是还未有证据显示这种方式比常规的调强放疗更有效。

另一种方式是在前列腺内置入微小的植入器，通过向外发送无线电波，告知放射治疗器该瞄准的方向。这种方式可以让机器弥补运动时的遗漏（比如呼吸瞬间），并且可能减少对正常组织的辐射量。理论上，这种方式应该会降低副作用。不过，迄今为止，还没有研究显示这种方式会比其他形式的调强放疗产生更少的副作用。这里用到机器被称为“卡吕普索”。

Stereotactic body radiation therapy(SBRT)

体部立体定向放射治疗

这种方式使用先进的图像制导技术，向某个精确区域，如前列腺，传送大剂量的射线。因为每一次使用的剂量都比较大，因此整个疗程时间就几天而已。

立体定向放疗通常也以所使用的放射机器名来称呼，比如伽马刀、X-刀、射波刀、医用直线加速器。

相比调强放疗，立体定向放疗的主要优势就在于花费比较少的治疗时间（几天代替几周）。然而，副作用方面并没有更好。事实上，有研究显示，对于男性前列腺癌患者，使用立体定向放疗比使用调强放疗，会产生一些比较糟糕的副作用。

Proton beam radiation therapy

质子束放射治疗

质子疗法是使用质子束代替X射线聚集于癌症细胞。质子是原子的正电部分。与X线不同，X线在击中目标的前后都释放能量，而质子束对所穿过的组织损伤小，而且仅在穿行一段距离后才会释放能量。这意味着，质子放射疗法，理论上，会传送更多的辐射到前列腺，而对临近的正常组织损伤更小。质子放射可以使用类似三维适形放疗和调强放疗的技术来进行定位瞄准。

虽然早期结果很有前景，但是，至今研究还没有显示说，从长远看质子疗法比其他类型的体外放射疗法更好。目前，质子疗法并没有被广泛使用。这种用来制造质子的仪器非常昂贵，而且在美国很多治疗中心并没有被使用。现阶段，质子放疗还不可能被所有的保险公司覆盖。

Possible side effects of EBRT

体外放疗可能产生的副作用

以下出现的数据是用来描述标准体外放疗方式可能产生的副作用，现在这种标准放疗方式用得比以前少了。上文提到的新的治疗方式的副作用风险很可能更低。

肠道问题：放射可刺激结肠和直肠，引起“放射性直肠炎”。这可能导致腹泻，时而便血，以及直肠泄漏。这些问题多数会随着时间推移而消失，但少数患者，在治疗结束后，无法恢复正常的肠道功能。过去，约有10%-20%的男性患者在接受体外放疗后出现肠道问题，但现在新的适形放疗技术可能比较少会引起这些问题。

膀胱问题：放射会刺激膀胱，引起“放射性膀胱炎”。这可能会导致尿频，排尿烧灼感，和/或血尿。这些膀胱问题通常会随着时间推移而改善，但在有些患者，这些症状会一直存在。大约每3个男性患者里就有一个会持续尿频。

尿失禁：总的来说，放疗后这种副作用比手术后少见。最初这种副作用风险较低，但在治疗几年后，这种风险概率逐年上升。

勃起问题，包括阳痿：体外放疗几年后，阳痿发生率接近手术后的阳痿发生率。通常放疗后不会立即引起阳痿，而是一年或更久以后才逐渐发展。这与术后发生阳痿情况不同。手术治疗后会立即引起阳痿，但这个问题会随着时间推移而改善。

在比较早的研究中，3/4的男性患者在接受体外放疗后的5年内出现了阳痿。但有些患者在治疗前就有勃起问题。治疗前有正常勃起功能的患者中，有约半数在5年内出现阳痿。这些数据是否也适用于新的放疗方式尚不清楚。而在手术方式中，年龄越大，出现勃起问题的几率越大。阳痿可通过治疗来改善，包括使用勃起功能障碍的药物。

感觉疲惫：放疗会引起疲乏感，这种症状通常要在治疗结束几个月后才会消失。

淋巴水肿：如果淋巴结接受了辐射，可能会引起腿部水肿或生殖器水肿。

尿道狭窄：少数情况下，负责将膀胱尿液输送到体外的管道，会因为放射而产生瘢痕和狭窄。这会引起排尿问题，需要进一步的治疗来疏通尿道。(好医友编译整理）

原文：

Radiationtherapy uses high-energy rays or particles to kill cancer cells.Radiation may be used:

·As theinitial treatment for low-grade cancer that is still confinedwithin the prostate gland. Cure rates for men with these types ofcancers are about the same as those for men gettingradical prostatectomy.

·As partof the first treatment (along with hormonetherapy) for cancers that have grownoutside of the prostate gland and into nearby tissues.

·If thecancer is not completely removed or comes back (recurs) in the areaof the prostate after surgery.

·If thecancer is advanced, to reduce the size of the tumor and to providerelief from present and possible future symptoms.

Two maintypes of radiation therapy can be used: external beam radiation andbrachytherapy (internal radiation). Both appear to be good methodsof treating prostate cancer, although there is more long-terminformation about the results of treatment with external beamradiation. (Another type of radiation therapy, in which a medicinecontaining radiation is injected into the body, is described in thesection "Preventing and treating prostate cancerspread to the bone.")

Externalbeam radiation therapy (EBRT)

In EBRT,beams of radiation are focused on the prostate gland from a machineoutside the body. This type of radiation can be used to try to cureearlier stage cancers, or to help relieve symptoms such as bonepain if the cancer has spread to a specific area ofbone.

To reducethe risk of side effects, doctors carefully figure out the exactdose of radiation needed and aim the beams as accurately as theycan to hit the carefully outlined target. Before treatments start,imaging tests such as MRIs, CT scans, or plain x-rays of the pelvisare done to find the exact location of your prostate gland. Theradiation team may then make some ink marks on your skin that theywill use later as a guide to focus the radiation in the rightarea.

You willusually be treated 5 days a week in an outpatient center for 7 to 9weeks. Each treatment is much like getting an x-ray. The radiationis stronger than that used for an x-ray, but the procedure ispainless. Each treatment lasts only a few minutes, although thesetup time — getting you into place for treatment — takeslonger.

EBRT forprostate cancer is most often given using techniques that letdoctors give higher doses of radiation to the prostate gland whilereducing the radiation exposure to nearby healthytissues.

Three-dimensional conformalradiation therapy (3D-CRT)

3D-CRT usesspecial computers to precisely map the location of your prostate.Radiation beams are then shaped and aimed at the prostate fromseveral directions, which makes it less likely to damage normaltissues. You will most likely be fitted with a plastic moldresembling a body cast to keep you in the same position each day sothat the radiation can be aimed more accurately. This method seemsto be at least as effective as standard radiation therapy withlower side effects.

Intensitymodulated radiation therapy (IMRT)

IMRT is anadvanced form of 3D therapy. It uses a computer-driven machine thatactually moves around the patient as it delivers radiation. Inaddition to shaping the beams and aiming them at the prostate fromseveral angles, the intensity (strength) of the beams can beadjusted to minimize the dose reaching the most sensitive normaltissues. This lets doctors deliver an even higher dose to thecancer areas. This is the most common method of giving externalbeam radiation for prostate cancer.

Some newerradiation machines have imaging scanners built into them. Thisadvance, known as image guided radiation therapy (IGRT),lets the doctor take pictures of the prostate and make minoradjustments in aiming just before giving the radiation. This mayhelp deliver the radiation even more precisely, which may result infewer side effects, although more research is needed to provethis.

A variationof IMRT is called volumetric modulated arc therapy. It usesa machine that delivers the radiation quickly as it rotates oncearound the body. This allows each treatment to be given over just afew minutes. Although this can be more convenient for the patient,it hasn’t yet been shown to be more effective than regularIMRT.

Anotherapproach is to place tiny implants into the prostate that send outradio waves to tell the radiation therapy machines where to aim.This lets the machine compensate for movement (like duringbreathing) and may allow less radiation to go to normal tissues. Intheory, this could lower side effects. So far, though, no study hasshown side effects to be lower with this approach than with otherforms of IMRT. The machines that use this are known asCalypso®.

Stereotactic body radiationtherapy (SBRT)

Thistechnique uses advanced image guided techniques to deliver largedoses of radiation to a certain precise area, such as the prostate.Because there are large doses of radiation in each dose, the entirecourse of treatment is given over just a few days.

SBRT isoften known by the names of the machines that deliver theradiation, such as Gamma Knife®,X-Knife®,CyberKnife®, andClinac®.

The mainadvantage of SBRT over IMRT is that the treatment takes less time(days instead of weeks). Side effects, though, are not better. Infact, one study showed that some side effects were actually worsewith SBRT as compared with IMRT in men treated for prostatecancer.

Protonbeam radiation therapy

Proton beamtherapy focuses beams of protons instead of x-rays on the cancer.Protons are positive parts of atoms. Unlike x-rays, which releaseenergy both before and after they hit their target, protons causelittle damage to tissues they pass through and release their energyonly after traveling a certain distance. This means that protonbeam radiation can, in theory, deliver more radiation to theprostate while doing less damage to nearby normal tissues. Protonbeam radiation can be aimed with similar techniques to 3D-CRT andIMRT.

Althoughearly results are promising, so far studies have not shown thatproton beam therapy is better in the long-run than other types ofexternal beam radiation. Right now, proton beam therapy is notwidely available. The machines needed to make protons are veryexpensive, and they aren’t available in many centers in the UnitedStates. Proton beam radiation might not be covered by all insurancecompanies at this time.

Possibleside effects of EBRT

Any numbersbelow used to describe the possible side effects relate to standardexternal radiation therapy, which is now used much less often thanin the past. The risks of the newer treatment methods describedabove are likely to be lower.

Bowelproblems: Radiation can irritate thelarge intestine and rectum and lead to a condition calledradiation proctitis. This can lead to diarrhea, sometimeswith blood in the stool, and rectal leakage. Most of these problemsgo away over time, but in rare cases normal bowel function does notreturn after treatment ends. In the past, about 10% to 20% of menreported bowel problems after EBRT, but the newer conformalradiation techniques may be less likely to cause theseproblems.

Bladderproblems: Radiation can irritate thebladder and lead to a condition called radiation cystitis. Youmight need to urinate more often, have a burning sensation whileyou urinate, and/or find blood in your urine. Bladder problemsusually improve over time, but in some men they never go away.About 1 man out of 3 continues to need to urinate moreoften.

Urinaryincontinence: Overall, this side effectis less common than after surgery. The risk is low at first, but itgoes up each year for several years after treatment.

Erectionproblems, including impotence: After a few years, theimpotence rate after radiation is about the same as that aftersurgery. It usually does not occur right after radiation therapybut slowly develops over a year or more. This is different fromsurgery, where impotence occurs immediately and may improve overtime.

In olderstudies, about 3 out of 4 men were impotent within 5 years ofhaving EBRT, but some of these men had erection problems beforetreatment. About half of men who had normal erections beforetreatment became impotent at 5 years. It's not clear if thesenumbers will apply to newer forms of radiation as well. As withsurgery, the older you are, the more likely it is you will haveproblems with erections. Impotence may be helped by treatments suchas those listed in the surgery section, including erectiledysfunction medicines.

For moreabout coping with erection problems and other sexuality issues, seeour document Sexuality for the Man WithCancer.

Feelingtired:Radiation therapy may causefatigue that may not go away until a few months after treatmentstops.

Lymphedema:Fluid buildupin the legs or genitals (described in thesurgery section) is possible if thelymph nodes receive radiation.

Urethralstricture: The tube that carriesurine from the bladder out of the body may, rarely, be scarred andnarrowed by radiation. This can cause problems with urination, andmay require further treatment to open it up again.

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