20.1 Introduction Intracavitary brachytherapy can be performed using low dose rate (LDR), pulsed dose rate (PDR), or high dose rate (HDR) sources. LDR implants expose the patient care team to more radiation than HDR and require longer hospitalization of the patient and more resources dedicated to source storage and radiation safety measures. There is also an increased risk of error, for example, by selecting the incorrect…

19.1 Introduction One of the primary goals in radiation therapy is to maximize the dose to the target while minimizing the dose to healthy tissue. For targets that exhibit significant motion (>5 to 10 mm) during the respiratory cycle this creates a challenge. If a target is 3 cm in diameter (volume = 14.1 cm 3 ) and moves ±10 mm in one direction and ±5 mm in the other directions,…

18.1 Introduction Image-guided radiotherapy (IGRT) is well established; however it is important to note that there has never been a prospective randomized trial to examine its value. There are, however, a number of retrospective series examining the impact of IGRT as outlined in recent papers. The potential impact of IGRT can be appreciated by considering a recent study that linked biochemical failures in prostate cancer patients…

17.1 Introduction Stereotactic radiosurgery (SRS) was originally defined as fulfilling all of the following conditions: 1. Single-fraction treatment 2. High dose per fraction (>5 Gy) 3. Target with diameter of <3.5 cm in the brain 4. Delivery accuracy of <1 mm as defined by the Winston-Lutz test 5. No planning target volume (PTV) or internal target volume (ITV) margins are used; clinical target volume (CTV) margins may be used…

16.1 Introduction Intensity-modulated radiotherapy (IMRT) provides exceptional control over the delivery of dose. Figure 16.1 shows an example of a 7-field IMRT plan for a patient with T3 oropharyngeal carcinoma of the head and neck. This case illustrates the ability to sculpt dose around nearby organs at risk (in this case the cord and parotid) while irradiating the gross tumor volume and at-risk nodal regions to…

15.1 Introduction Electron beams have been used in radiotherapy since the 1940s but did not gain widespread use until the 1970s with the commercial development of linear accelerators (linacs). Electrons lose energy as they traverse a medium through various elastic and inelastic collisions with atomic electrons and the nucleus. Inelastic collisions with the nucleus result in a radiative loss of a photon, called bremsstrahlung production. The…

14.1 Introduction The overall goal of the treatment planning process is to produce the optimal dose distribution for the patient, taking into account the following factors: 1. Treatment intent (curative or palliative) 2. Stage of disease (extent of involvement) 3. Other therapies (chemotherapy, hormones, etc.) 4. Previous treatments 5. Reproducibility (immobilization, patient comfort) 6. Deliverability (collisions, modulation) 7. Safety (sensitivity to changes, robustness) The process can…

13.1 Introduction Prior to the early 1990s, “simulation” for an external beam radiotherapy consisted of just that: simulating the treatment with a device that mimicked a linear accelerator (linac) in all aspects except the delivery of a therapeutic beam. These devices (now called “conventional simulators”) are equipped with diagnostic x-ray tubes and imaging equipment and are still in use. They have largely given way, however, to…

12.1 Introduction Watershed Accidents in Radiation Oncology One way to view the issue of quality and safety in radiotherapy is to consider the serious accidents that have garnered the attention of the community and occasionally the media. The purpose of such an exercise is to understand the error pathways involved and prevent such events in the future. To this end, Table 12.1 summarizes selected watershed accidents…

11.1 Introduction Information technology (IT) in Radiation Oncology has developed into highly complex networks driving much of treatment delivery and other safety-critical tasks in the department. Based on the size of a Radiation Oncology clinic, the role of the physicist in IT can range from being the system administrator with all the responsibilities to being the liaison of the Radiation Oncology department to a large IT…

10.1 Introduction The National Council on Radiation Protection (NCRP) Report No. 116, Limitation of Exposure to Ionizing Radiation, outlines the goals and philosophies of radiation protection in Chapter 2 of that document. The specific objectives are: 1. “To prevent the occurrence of clinically significant radiation-induced deterministic effects by adhering to dose limits that are below the apparent threshold levels and 2. “To limit the risk of…

9.1 Introduction First proposed by Robert Wilson in 1946, radiation therapy with proton beams quickly became a reality with the first patient treatments performed in 1954 at Lawrence Berkeley National Labs. Starting in 1961 the Harvard Cyclotron Lab began treating patients (and continued up to 2002), and in 1990 the first hospital-based system became operational at Loma Linda University Medical Center, California, which featured the first…

8.1 Introduction Brachytherapy is defined as the temporary or permanent application of small, sealed radioactive sources in close proximity to or within the target volume. The treatment dose distribution is characterized by localized high dose and a steep dose drop-off. Soon after radium was first chemically isolated by Marie and Pierre Curie, the effects of radiation damage on skin were observed and led to the earliest…

7.1 Introduction A key component of safe and effective modern radiotherapy is the ability to align a patient with respect to the radiation beam during treatment. Current means of accomplishing this include 3D visualization of soft tissue structures (via computed tomography (CT) or ultrasound and soon magnetic resonance imaging (MRI)), 2D or 3D localization of bony landmarks or fiducials (planar kV/MV images or implanted marker tracking),…

6.1 Introduction Proper immobilization techniques accomplish a variety of clinical goals including the following: ▪ Reduce patient motion and improve day-to-day reproducibility of setup. External beam treatments typically require several tens of minutes to complete, and during this time the operator is essentially blind to any motion of the patient or tissue with notable exceptions (e.g., orthogonal fluoroscopic imaging, 3D surface mapping, or combination magnetic resonance…

5.1 Introduction In modern radiotherapy the vast majority of dose calculations are performed by computerized systems. There may be minor exceptions such as radiopharmaceuticals used in nuclear medicine. The system may calculate all or some of the following: point doses, 2D isodoses, 3D isodoses, and doses to volumes. In addition, a whole host of nondosimetric information may be used to inform clinicians as to the quality…