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«Department of Radiation Oncology Massachusetts General Hospital, Harvard Medical School 30 Fruit Street, Boston MA 02114 Introduction 2 Principles of ...»

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Northeast Proton Therapy Center Marc R. Bussière, M.Sc., DABR 7/7/05

Department of Radiation Oncology

Massachusetts General Hospital, Harvard Medical School

30 Fruit Street, Boston MA 02114

Introduction 2

Principles of Proton Therapy 3

The Treatment Team 5

Treatment Options 8

General Description

Proton Stereotactic Radiotherapy (PSRT) Planning & Treatment Process Proton Stereotactic Radiosurgery (PSRS) Planning & Treatment Process Proton Ocular Radiotherapy (PORT) Planning & Treatment Process Frequently Asked Questions (FAQ) 22 Introduction The Northeast Proton Therapy Center (NPTC), located on the main hospital campus of the Massachusetts General Hospital (MGH), represents the forefront of technological advancement in radiation therapy. The construction of the facility was jointly funded by the MGH and the National Cancer Institute to meet the increasing medical demand for high precision radiation therapy provided by proton therapy. The program builds on more than forty years of pioneering work and experience gained by MGH physicians, physicists, and clinical support personnel at Harvard University’s Cyclotron Laboratory where more than nine thousand patients were treated with proton therapy from 1961 to it’s closing in 2002.

At the NPTC protons (charged particles) are accelerated with a large magnetic field in a machine called a cyclotron.

Large magnets help guide the proton beam to three treatment rooms. Two of the treatment rooms incorporate 110Ton gantries. These 3 story high gantries can be rotated to aim the proton beam from various directions. In the gantry rooms patients lie on robotic beds that can be adjusted for precise alignment of targets contained throughout the body. The third treatment room contains two specialized “beamlines”. The first beamline is specially designed to treat lesions contained in the eye. The second beamline is dedicated to high precision stereotactic treatments within the head.

At the NPTC there is a large research program aimed at improving current treatment techniques as well as developing new equipment and approaches. The NPTC is proud to be a leader in the revolution of proton therapy.

40 feet Layout of the NPTC treatment level showing the FDA approved radiation delivery system, which includes a cyclotron (upper left insert) and an array of over 50 magnets, each weighing between 1,000 and 5,000 pounds (highlighted in orange, blue and green). Protons can be delivered sequentially to any of the 3 treatment rooms by bending the beam using the magnets. Radiation is isolated to individual treatment rooms with 5 feet thick concrete walls.

Principles of Proton Therapy Irregularly shaped lesions with awkward configurations near critical structures are well suited for proton therapy.

Protons have a physical advantage over gamma rays and x-rays when it comes to sparing normal tissues. Protons deposit most of their radiation energy in what is known as the Bragg peak, which occurs at the point of greatest penetration of the protons in tissue. The exact depth to which protons penetrate, and at which the Bragg peak occurs, is dependent on the energy of the beam. This energy can be very precisely controlled to place the Bragg peak within a tumor or other tissues that are targeted to receive the radiation dose. Because the protons are absorbed at this point, normal tissues beyond the target receive very little or no radiation.

Radiation levels from a conventional x-ray therapy unit (Linac) and protons of various energies as they penetrate in tissue or water. X-rays have a maximum dose near the surface followed by a continuously reducing dose with depth. Proton energy can be adjusted to match the depth of the target with a sharp drop in dose beyond the Bragg peak.

A broadened proton beam as well as an x-ray beam adjusted to treat an 8 cm thick target with a maximum depth of 23 cm. The x-ray beam “spills” unnecessary dose beyond the target compared to protons.

The proton Bragg peak is generally narrower than most lesions therefore special equipment is used to combine protons of various energies to broaden the Bragg peak to match the thickness of individual targets. Properly selecting the thickness of the broadened Bragg peak ensures uniform dose coverage of a target with optimal reduction of dose at the entry surface of the beam. Tumors can have very irregular shapes and can be located close to critical organs. Every patient’s tumor shape, size and location are unique. Patient specific hardware, which helps sculpt the proton beam, is customized to maximize the dose to the tumor while minimizing the dose to normal structures. Aiming proton beams, each with customized hardware, from various directions further ensures that the dose to normal tissues is reduced as much as possible therefore reducing the risk of treatment related complications.

Customized dose-shaping devices used for proton therapy. A brass aperture shaped to the outline of a target blocks the proton beam outside a specified safety margin. The penetration depth of the protons that pass through the aperture opening is adjusted to match the shape of the target with a Lucite range compensator. A target is depicted in red on the rightmost figure with the proton radiation dose conforming to its shape and avoiding a critical structure shown in green.

The Treatment Team Jay S. Loeffler, MD Chairman, Department of Radiation Oncology Paul M. Busse, MD, PhD Clinical Director, Department of Radiation Oncology Thomas F. DeLaney, MD Medical Director, Northeast Proton Therapy Center

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There are many individuals involved in the treatment process. Some of these professionals are directly involved with patients while others work behind the scene to provide the necessary services to treat patients. A multidisciplinary approach often requires coordinating radiation treatments with procedures performed in other departments such as Radiology, Surgery and Medical Oncology. These departments have their own group of professionals to ensure the highest quality medical care. The professionals directly involved with treatments at the NPTC are listed in the sequence of their role in the treatment process.

Radiation Oncologists:

Physicians who specialize in the use of ionizing radiation to treat various types of cancers and malformations. They determine the most appropriate radiation treatment by defining what needs to be treated (disease) and what needs to be avoided (critical organs and tissues). They prescribe the daily and total radiation dose to be delivered to the disease and the dose limits to critical organs. They determine what radiation delivery methods are most appropriate (protons, x-rays, electrons, brachytherapy) to achieve their treatment goals.


Physicians who specialize in the treatment and diagnosis of various neurological disorders. Neurosurgeons are involved with high-dose, high-precision radiation treatments (radiosurgery) delivered in one or two sessions. Their services are needed to fit patients with certain stereotactic fixation devices as well as implantation of reference markers used for alignment. They also help radiation oncologists with defining neurological lesions.


Physicians who administer general and local anesthetics, and manage anesthesiological services. They are responsible for determining the anesthetics to be used, considering such factors as patient's age, weight, and medical condition. They monitor the patient’s vital signs and record observations prior, during and after treatments. Their involvement is usually with pediatric patients.

Radiation Oncology Nurses:

Licensed nurses specializing in the care of patients who receive radiation therapy. They assist physicians with various medical procedures including regular health assessments before, during and following treatments. Their regular contact with patient allows them to coordinate treatments with the various social services offered to patients.

Oncology Social Worker:

There are many aspects to undergoing daily radiation treatments for a period of 1-8 weeks. Some patients are from out of town/country and must find lodging. Some patients are local and are trying to maintain as much as is reasonable their daily routine. The role of the social worker is to help patients by providing them with the resources to manage their life during treatments. These include help with lodging, financial services, nutritional services, psychiatric services, education, health/fitness programs, support groups…

Immobilization Specialists:

The role of radiation therapy is to irradiate diseased areas while sparing adjacent normal tissue. If patients weren’t immobilized it would be necessary to treat a margin, which reflects the motion of the diseased target. This would unnecessarily treat normal tissues surrounding the diseased area. This is especially important when using a high precision approach such as proton therapy. The immobilization specialist understands the treatment requirements so as to customize an appropriate device to be used for both the pretreatment imaging such as a planning-CT as well as the treatments.

Immobilization devices minimize motion of the diseased target ensuring that the treatment margins are reduced as much as possible. Different approaches are required depending on the treatment area being considered. These include masks, bite molds, body casts, arm and leg rests…

CT technologists RT(R):

Licensed radiological technician operate the CT (Computer Tomography) Scanner that is used for planning most of the proton therapy cases. The CT scanner obtains images as if it were slicing through the body like sliced bread. It allows physicians to see internal as well as external anatomy. The radiological technicians administer contrast material that makes internal body parts more visible. They also make sure patients are ready for the imaging procedure.

The CT scan provides physicians with cross-sectional views of the body. Outlining structures on the individual CT images enables the treatment-planning computer to generate a 3D model of the body. This 3D model is used to determine the optimal directions to aim the proton radiation at the targets while avoiding nearby critical structures.

The above images represent a typical case where the targets (red & purple) are near the brainstem (green), optic nerves (yellow), optic chiasm (cyan), eyes (white), lenses (blue), cochlea (blue) and temporal lobes (not shown).

Medical Dosimetrists:

Members of the treatment team who are skilled in calculating and planning doses in radiation therapy.

Working closely with the radiation oncologist they generate a treatment plan using sophisticated computer programs. They design special hardware that is used to shape individual proton beams so they conform to the targeted volume while avoiding critical normal structures.

A dosimetrist plans a proton radiation therapy case using sophisticated computer equipment.


Special devices called apertures ensure that only the intended target is irradiated. Compensators further conform the dose to the target shape. Using precision milling equipment the machinists fabricate apertures from brass and the compensators from Lucite for every treatment directions for every patient. The milling coordinates are directly obtained from the treatment-planning computer.

Medical Physicists:

Physicists who specializes in the technical and clinical aspects of radiation therapy. Physicists oversee the technical aspect of the clinical operation of the facility by ensuring that the delivery system, imaging systems, planning systems are functioning properly. They also oversee all aspect of quality assurance and quality control of treatment plans including devices used for patient treatments. In some complicated cases they are directly involved in treatment planning.

Cyclotron Operators:

The cyclotron operators run and monitor the radiation delivery system during treatments. With mechanical, electrical, software, hardware and controls backgrounds they maintain, upgrade and repair the cyclotron and radiation delivery system.

An operator monitors the status of the radiation delivery system in the facility’s main control room.

Radiation Therapists:

Technologists licensed to deliver therapeutic radiation to patients in accordance to a medical prescription.

At the NPTC the radiation therapists use x-ray and ultra-sound imaging to ensure patients are set-up for treatment according to the treatment plan. Corrections are made using a robotic treatment table. Patients become very familiar with the radiation therapists since they see them on a daily basis.

While in the treatment room a radiation therapist compares an x-ray image, obtained just prior to treatment, to an image from the treatment-planning CT. Once the treatment position is confirmed the therapists step out of the treatment room and verify the final proton radiation parameters prior to administering the radiation treatment.

Treatment Options

The NPTC has three broad radiation therapy programs. They are:

Proton Stereotactic Radiotherapy (PSRT) • Involves treating lesions throughout the body over an extended 1-8 week course (5-40 sessions). PSRT treatment sessions are usually limited to once per day and lasting 20-40 minutes each.

Proton Stereotactic Radiosurgery (PSRS) • Involves treating lesions, usually contained within the head with a high dose of radiation delivered in 1-2 sessions. PSRS treatment sessions are around one hour.

Proton Ocular Radiotherapy (PORT) • Treats ocular lesions contained within the eye with the radiation delivered in 2-5 sessions. PORT treatment sessions are usually limited to once per day and lasting 10-20 minutes each.

The leftmost figure shows a patient lying on the robotic bed in one of the two gantry treatment rooms. The gantries are used to treat lesions throughout the body. The middle figure shows a patient sitting in an adjustable chair in preparation for treatment of the eye. The rightmost image shows a patient lying in a high-precision robotic bed used for stereotactic radiosurgery.

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