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RTT Brachytherapy

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					December 31, 2008

A HAPPY NEW YEAR !

Brachytherapy:
Physical and Clinical Aspects

Zvi Bernstein M.D.
Oncology Division, RAMBAM HCC

Brachytherapy (also referred to as Curietherapy) is defined as a short-distance treatment of malignant disease with radiation emanating from small sealed (encapsulated) sources.
The sources are placed directly into the treatment volume or near the treatment volume.

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Advantages of brachytherapy Improved localized dose delivery to the target Sharp dose fall-off outside the target volume Better conformal therapy Disadvantages of brachytherapy Only good for well localized tumors Only good for small lesions Very labor intensive

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Brachytherapy sources
Photon sources Emit gamma rays through gamma decay and possibly characteristic x rays through electron capture and internal conversion (examples: Co-60, Cs-137, Ir-192, I-125, Pd-103)

Beta sources Emit electrons following beta source decay (example: Sr-90/Y-90)
Neutron sources Emit neutrons following spontaneous nuclear fission (example: Cf-252)

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Brachytherapy sources
The dose distribution around a hypothetical point source of radioactive material is isotropic; that is, it has a symmetric emission in all directions.
Actual brachytherapy sources are not simply points in space, however, and instead can measure up to several centimeters. Furthermore, brachytherapy sources are encased in metal, often steel. These factors result in some asymmetry of emission (anisotropy), particularly at the ends of the sources

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Brachytherapy sources

Asymmetric distribution of radiation (anisotropy) emitted from cesium-137 brachytherapy sources

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Basic Dose Calculation
• The rate of disintegration of a radioactive material is known as “ACTIVITY” (A)

• “Content Activity” – activity of actual radionuclide within a brachytherapy source.
• “Apparent Activity” – is equivalent to the activity of a bare point source that produces the same exposure rate at a reference point. • “Specific Activity” – activity per 1 mg of the source.

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Basic Dose Calculation
Exposure Rate Constant
•Exposure rate at a reference point (1 m.) along the transverse axis of a unit apparent activity source.
•One of the physical characteristics of the radionuclide. •Independent of the source design or encapsulation.

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Basic Dose Calculation

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Basic Dose Calculation
• Inverse Square Law is critical in BT. • EBRT (Teletherapy) : 1 cm. increase in distance reduce the dose rate by about 2%.

• BT: dose rate from a single source reduces by about 75%, by increasing the distance from 1 cm. to 2 cm.

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Brachytherapy classification with respect to dose rate:
Low dose rate (LDR)
Medium dose rate (MDR) High dose rate (HDR)

(0.4 - 2 Gy/h)
(2 - 12 Gy/h) ( > 12 Gy/h)

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Brachytherapy classification with respect to dose rate (2):
In addition to LDR, MDR, and HDR brachytherapy techniques, another type of afterloading brachytherapy has been developed in which a continuous low dose rate (LDR) treatment is simulated by a series of short duration “dose pulses” of the order of 30 minutes separated by intervals of 1 to several hours of no dose given. The technique is referred to as pulsed dose rate (PDR) brachytherapy.

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Types of brachytherapy implants:
Intracavitary: Interstitial: Sources are placed into a body cavity. Sources are implanted into the tumor volume.

Intraoperative: Sources are brought surgically into or near the tumor

Surface plaque: Sources are loaded into a plaque contact with a skin or eye surface lesion.
Intraluminal: Sources are inserted into a lumen.

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Brachytherapy classification with respect to treatment duration:
Temporary implant Dose is delivered over a period of time that is short in comparison with the half-life of the sources. Sources are removed when the prescribed dose has been reached. Permanent implant Dose is delivered over the lifetime of the sources. The sources undergo complete radioactive decay.

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Brachytherapy classification with respect to source loading:
Hot loading The applicator is pre-loaded and contains radioactive sources at time of placement into the patient. Afterloading The applicator is placed first into the patient and the radioactive sources are loaded later - either by hand (manual afterloading) - or by machine (automatic remote afterloading)

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Manual afterloading
Generally, the radiation sources are manually afterloaded into applicators or catheters that have been placed within the target volume. At the end of treatment the sources are removed, again manually. The manual loading and removal of sources from the applicators or catheters result in some radiation exposure to the medical and support staff.

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Remote afterloading
To minimize radiation exposure to medical and support staff several computer driven remote afterloading systems have been developed. The use of remote afterloading machines offers several practical advantages over manual procedures, such as: - Increased patient treatment capacity. - Consistent and reproducible treatment delivery. - Reduced radiation exposure to staff.

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Remote afterloading
Cobalt Diameter 3 mm Ir-192 Diameter 1.1 mm

Cobalt
Diameter 1.1 mm

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The Remote Automated HDR Afterloading Source: Ir-192 4~10 Ci

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Manual Preloading Source: The Iodine (I-125) Seeds

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Manual Afterloading Source: The Iridium (Ir-192) Wires

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Manual Afterloading Source: The Iridium (Ir-192) Hairpins

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Photon Source Characteristics

Brachytherapy sources are usually encapsulated and the capsule serves multiple purposes: - Contains the radioactivity - Provides source rigidity - Absorbs alpha and beta radiation

Cs-137 Tube

Cs-137 Needle

Au-198 Grains

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Characteristics of common radionuclides used in brachytherapy

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CLINICAL USE AND DOSIMETRY SYSTEMS

Gynecology
Intracavitary brachytherapy is mainly used for treatment of the cancer of the cervix, uterine body and vagina. Various applicators are in use to hold sources in an appropriate configuration in the tumor volume. A cervical applicator consists of a central tube (tandem) and lateral capsules (ovoids or colpostats).

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology

Rotterdam Applicator

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology

MANCHESTER

FLETCHER-SUIT

TANDEM-RING

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology

Types of sources:
The most widely used source for treatment of gynecological cancers is cesium-137. It is often necessary to use sources of differing strengths in order to achieve the desired dose distribution. (LDR) In modern remote afterloading machines iridium-192 is the commonly used radionuclide. (HDR)

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CLINICAL USE AND DOSIMETRY SYSTEMS Gynecology
-The Manchester system is characterized by dose to four points: point A, point B, bladder point and rectum point. -The duration of the irradiation is based on the dose rate at point A, which is located 2 cm superior to the cervical orifice and 2 cm lateral to the cervical canal. -Point B is defined 3 cm laterally to point A when the central canal is not displaced.

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CLINICAL USE AND DOSIMETRY SYSTEMS (Gynecology)

The Design of the Rotterdam Applicators allows the setup of a set of Standard Plans which may save the effort of reconstructions case by case

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CLINICAL USE AND DOSIMETRY SYSTEMS (Gynecology)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Gynecology)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Gynecology)

Vaginal Applicator

Reconstruction Film with Dummy Marker Wires

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CLINICAL USE AND DOSIMETRY SYSTEMS (Gynecology)

Vaginal Wall Treatment Isodoses

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CLINICAL USE AND DOSIMETRY SYSTEMS

IBU

Integrated Brachytherapy Unit

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

Brachytherapy for prostatic carcinoma
• • • • •

Stage: Gleason Score: Serum PSA: Prostate Volume: No previous TURP

T1 & T2 6  10 ng/ml  50 cc

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RAPID STRAND TECHNIQUE

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

Prostate Volume Study
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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

Planning

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) I-125 Seeds (Model 6711)
• Size: 4.5mm long, 0.8mm diameter • Photon energy: 27- 35 KeV () • Average energy: 27.4 KeV ( and X-rays) • Shell material: Titanium • Shell thickness: 0.05mm • HVL = 0.025mm Lead • T1/2 = 59.6 days

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

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“FREE” (MICK APPLICATOR) TECHNIQUE

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Pre-implant plan DVH

Post-implant DVH

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) A Dose-Response Study Freedom From Biochemical Failure
D90 value < 100 Gy 100-119.9 Gy 120-139 Gy 140-159.9 Gy >160 Gy p=0.02 4-Year FFBF rates 53% 82% 80% 95% 89%

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Accelerated Partial Breast Irradiation (APBI)

Definition
Delivery of larger doses/fx of RT to the lumpectomy cavity after BCS in patients with early stage BC using BT or EBRT . Complete RT in 1- 5 days instead of 6-7wks

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

APBI Scientific Rationale
Distribution of tumor cells confined to a limited area of 1-2 cm around the “index” lesion and most local recurrences occur at or near the tumor “bed” Rate of recurrences away from tumor bed („elsewhere‟ failure) equals rate of new primary cancers, and is similar after lumpectomy alone or after lumpectomy followed by whole breast RT

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy)

APBI Patient Selection
ABS: • Age > 45 yrs • Invasive duct ca only • Tu size < 3 cm • Negative margins • Negative axilla Amer Soc Breast Surgeons: • Age > 50 yrs • Invasive duct ca or DCIS • Tu size < 2 cm • Microscopic margins>2 mm • Negative axilla

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) APBI: Techniques
HDR-BT • Balloon catheter BT (MammoSite) • Multi-catheter interstitial BT EBRT • 3D – CRT (supine or prone) • IMRT • Tomotherapy • Proton beam IORT • Orthovoltage (50 kv,spherical device) • Electrons

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Balloon catheter BT (MammoSite)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Balloon catheter BT (MammoSite)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Balloon catheter BT (MammoSite)

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial BT

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial BT

An Illustration of the Paris System Dose Calculation
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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial BT

An Illustration of the Paris System Dose Calculation
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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

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CLINICAL USE AND DOSIMETRY SYSTEMS (Interstitial brachytherapy) Multi-catheter interstitial APBI

The Treatment Control Workstation (TCS)
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BT in H&N CANCERS
Molds / Obturators Technique

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Molds / Obturators Technique

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Molds / Obturators Technique

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Molds / Obturators Technique

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Molds / Obturators Technique

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Molds / Obturators Technique

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BT in H&N CANCERS
Multi-catheter interstitial BT (Tongue)

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BT in H&N CANCERS
Multi-catheter interstitial BT (Tongue)

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BT in H&N CANCERS
Multi-catheter intraoperative BT (Tongue)

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BT in H&N CANCERS
Multi-catheter intraoperative BT (Tongue)

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BT in H&N CANCERS
Multi-catheter intraoperative BT (Tongue)

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BT in H&N CANCERS
Multi-catheter intraoperative BT (Tongue)

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SOFT TISSUE SARCOMAS
Multi-catheter intraoperative BT

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SOFT TISSUE SARCOMAS
Multi-catheter intraoperative BT

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SOFT TISSUE SARCOMAS
Multi-catheter intraoperative BT

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“SURFACE” BT

The “Super Mould” Applicator for Superficial Treatments

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“SURFACE” BT

Plan Optimisation: Increased Weightings at the Peripheral Points

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“SURFACE” BT

Scalp Sarcoma Treatment with a Custom Mould

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“SURFACE” BT

Scalp Mould: A Dose Distribution Not Achievable by External Beams

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EYE PLAQUES
• Intraocular melanoma is the most common primary malignant eye tumor in adults, originating mostly in the choroid. Traditional treatment was enucleation More recent treatment approaches rely on radiotherapy: – External beam radiotherapy with high energy x rays or charged particles. – Brachytherapy with temporary implants based on radioactive seeds loaded onto an eye plaque.

• •

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EYE PLAQUES

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EYE PLAQUES

•Most commonly used seeds are iodine-125 seeds with typical activities of the order of 1 mCi.
•The number of seeds per plaque ranges from 7 to 24 for plaque diameters of 12 to 20 mm. •Typical treatment dose rates are of the order of 1 Gy/h and typical prescription doses are of the order of 100 Gy.

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Intraluminal BT

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The basic principles of brachytherapy have not changed much during the past 100 years of radiotherapy

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