Sensitive Normal Structures Research Articles

ACR-ASTRO Practice Parameter for the Performance of Proton Beam Radiation Therapy.

The American College of Radiology (ACR) and the American Society for Radiation Oncology (ASTRO) have jointly developed the following practice parameter for proton beam radiation therapy. Proton radiotherapy is the application of a high-energy proton beam to a patient in a clinical setting with therapeutic intent. Proton radiotherapy may permit improved therapeutic ratios with lower doses to sensitive normal structures and greater dose to target tumor tissues. A literature search was performed to identify published articles regarding clinical outcomes, reviews, quality assurance methodologies, and guidelines and standards for proton radiation therapy. Selected articles are referenced in the text. The following recommendations are based on firsthand experiences of multiple clinical authorities who employ proton therapy and have been peer reviewed by experts at different practicing institutions. This practice parameter is developed to serve as a tool in the appropriate application of this evolving technology in the care of cancer patients or other patients with conditions where radiation therapy is indicated. It addresses clinical implementation of proton radiation therapy, including personnel qualifications, quality assurance standards, indications, and suggested documentation. This practice parameter is a tool to guide technical use of proton therapy and does not assess the relative clinical indication of proton radiotherapy when compared with other forms of radiotherapy, but to focus on the best practices required to deliver proton therapy safely and effectively, when clinically indicated. Costs of proton treatments are high, and the economic costs of proton radiotherapy may also need to be considered.

Panoptes: Calibration of a dosimetry system for eye brachytherapy

Intraocular cancer is a serious threat to the lives of those that suffer from it. Dosimetry for eye brachytherapy presents a significant challenge due to the inherently steep dose gradients that are needed to treat such small tumours in close proximity to sensitive normal structures. This issue is addressed by providing much needed quality assurance to eye brachytherapy, a novel volumetric dosimetry system, called Panoptes was developed. This study focuses on the preliminary characterisation and calibration of the system. Using ion beam facilities, the custom, pixelated silicon detector of Panoptes was shown to have good charge collection uniformity and a well defined sensitive volume. Flat-field calibration was conducted on the device using a 250 kVp orthovoltage beam. Finally, the detector and phantom were simulated with Monte Carlo in Geant4, to create water equivalent dose correction factors for each pixel across a range of angles.

Improved Cosmesis in Early Breast Cancer Using Conformal Radiotherapy

Improved Cosmesis in Early Breast Cancer Using Conformal Radiotherapy

Radiation Therapy Options for Malignant Pleural Mesothelioma

The role of radiation therapy (RT) in the curative treatment of malignant pleural mesothelioma remains undefined. No data clearly support treatment of unresected mesothelioma with definitive RT. Early reports showed that RT was associated with unacceptable toxicity, but recent limited data suggest that treatment with intensity-modulated radiation therapy (IMRT) may be tolerable. Adjuvant RT after pleurectomy is also challenging, and similarly, no clear efficacy has been demonstrated. Some approaches, such as IMRT to the circumferential pleural envelope, appear feasible, but the fact that this approach does not address the disease in the fissures is problematic. The best setting in which to deliver RT is after extrapleural pneumonectomy, but the large and irregular target volume and multiple and adjacent sensitive normal structures make this complex. The Memorial Sloan-Kettering Cancer Center matched photon/electron technique is associated with acceptable efficacy and toxicity, but is limited in that it does not achieve complete coverage of the target volume to the prescription dose. The best dosimetry is achieved using IMRT, and this approach is the most promising to date. However, the toxicity profile can be severe, and the relevant predictive factors for complications are not fully understood. For these reasons, physicians should exercise caution, and IMRT after extrapleural pneumonectomy is probably best offered only by experienced teams or on protocol until further data have been gathered. New techniques such as helical tomotherapy and/or IMRT with the addition of electrons may also have a role in future treatment. RT can palliate symptoms provided the disease is confined to a tolerable radiation field.

DOSE TO NORMAL TISSUES OUTSIDE THE RADIATION THERAPY PATIENT’S TREATED VOLUME: A REVIEW OF DIFFERENT RADIATION THERAPY TECHNIQUES

Radiation therapy treatment planning and delivery capabilities have changed dramatically since the introduction of three-dimensional treatment planning and are continuing to change relatively rapidly in response to the implementation of new advanced technologies. Three-dimensional conformal radiation therapy (3DCRT) is now firmly in place as the standard of practice in clinics around the world. Medical accelerator manufacturers have employed advanced computer technology to produce treatment planning/delivery systems capable of precise shaping of dose distributions via computer-controlled multileaf collimator (MLC) systems, by which the beam fluence is varied optimally to achieve the desired dose distribution. This mode of conformal therapy is referred to as intensity modulated radiation therapy (IMRT), and is capable of generating dose distributions (including concave isodose volumes) that closely conform the prescription dose to the target volume and/or avoid specific sensitive normal structures. The increasing use of IMRT has focused attention on the need to better account for the intra- and inter-fraction spatial uncertainties in the dose delivery process. This has helped spur the development of treatment machines with integrated planar and volumetric advanced imaging capabilities, providing a new treatment modality referred to as image-guided IMRT (IG-IMRT), or simply image-guided radiation therapy (IGRT). In addition, there is a growing interest in replacing x rays with protons because of the physical characteristics of the depth dose curve, which peaks at the end of particle range, and eventually with even heavier charged particles to take advantage of the greater density of energy deposition close to the Bragg peak and hence larger relative biological effectiveness (RBE). Three-dimensional CRT, IMRT and proton beam therapy all provide improved target coverage and lower doses to surrounding normal tissues as compared to the previously used two-dimensional radiation therapy techniques. However, this is achieved at the expense of a greater volume of normal tissue in the irradiated volume receiving some dose and a higher whole body dose (or peripheral dose) to distant normal tissues. The higher whole body dose is a result of the increased x-ray leakage radiation to the patient due to the longer beam-on times associated with IMRT, and also from neutron leakage radiation associated with high energy x-ray beams (>10 MV) and proton beams. Dose distributions for the various CRT techniques and the current status of available data for normal tissues, and whole body dose are reviewed.

Sci-Sat AM(2): Brachy-09: Investigation of catheter displacement in HDR prostate brachytherapy.

During prostate cancer treatment with HDR brachytherapy, catheters are inserted into the prostate. Between planning and treatment, catheters may move inferiorly due to edema. If undetected, treatment proceeds without correcting the catheter displacement, and an incorrect treatment is delivered. The purpose of this study was to investigate the consequences of catheter displacement on prostate coverage and critical structure avoidance. Ten patient plans were selected in which movement of the catheters had been observed. The original treatment plan, generated using Nucletron PLATO (ver. 14.3.2), was adjusted introducing inferior catheter offsets of 5, 10, 20, and 30 mm. The original treatment dwell times were re-entered into the offset plans to determine the consequences of the displacement. DVH data was calculated for the prostate, rectum, urethra, and bladder. Prostate V100 decreased from 99% to 36% over the ten patients studied. For the urethra, the D10 increased (114.1% to 128.2%), as did the V125 (2.7% to 12.8%). In the rectum the V75 initially increased as the catheters shifted inferiorly, but dropped as the shift increased beyond 10 mm. In the penile bulb the V75 increased as a function of shift (from 2.1% to 44.8%). Every effort should be made to ensure that the catheters do not move during prostate treatment. A small shift, 5 mm, would result in a small deviation of the dose distribution. In this case a re-optimization of the plan is unnecessary. Larger shifts will have a serious impact on the dose delivered to the prostate and to sensitive normal structures.

SU-GG-T-23: A Dosimetric Study Investigating the Impact of Catheter Displacement in HDR Prostate Brachytherapy

Purpose: During prostate cancer treatment with HDR brachytherapy catheters are inserted into the prostate. Between planning, and treatment, catheters can displace inferiorly due to edema or swelling of the prostate. If this is not detected, then treatment proceeds without correcting the catheter displacement and in turn an incorrect treatment is delivered. The purpose of this study was to investigate the consequences of catheter displacement on prostate coverage and contribution to critical structures. Method and Materials: Ten patient plans where selected in which movement of the catheters had been observed. The original treatment plan generated using Nucletron PLATO (v14.3.2) was adjusted with catheter offsets of 5, 10, 20, and 30 mm from their original position (inferiorly). The original treatment dwell times were re‐entered into the offset plans to show the dose consequence of the displacement. DVH data was calculated on the prostate, rectum, urethra and bladder. Results: Prostate V100 began at 99% and decreased to 36% over the ten patients studied. For the urethra, the D10 increased (114.1% to 128.2%), as did the V125 (2.7 to 12.8%). In the rectum the V75 initially increased as the catheters shifted from 0 to 10 mm inferiorly (from 5.3 to 6.4%), but dropped as the shift increased from 20 to 30 mm (6.0 to 4.0%). In the penile bulb the V75 increased as a function of shift (from 2.1 to 44.8%). Conclusion: Every effort should be made to ensure that the catheters do not move during prostate treatment. A small shift, 5 mm, would result in a small deviation of the dose distribution. In this case a re‐optimization of the plan is unnecessary. Larger shifts will have a serious impact on the dose delivered to the prostate and sensitive normal structures.

Evaluation of Intra- and Inter-fraction Motion in Breast Radiotherapy Using Electronic Portal Cine Imaging

Breast irradiation is one of the most challenging problems in radiotherapy due to the complex shape of the target volume, proximity of radiation sensitive normal structures and breathing motion. It was the aim of the present study to use electronic portal imaging (EPI) during treatment to determine intra- and inter-fraction motion in patients undergoing radiotherapy and to correlate the magnitude of motion with patient specific parameters. EPI cine images were acquired from the medial tangential fields of twenty radiotherapy patients on a minimum of 5 days each over the course of their treatment. The treatments were administered using 10 MV X-rays and dynamic wedges on a Varian Clinac 2100CD linear accelerator. Depending on the incident dose and the angle of the wedge, between 4 and 16 images could be acquired in one session using an EPI device based on liquid ionization chambers (Varian). The border between lung and chest-wall could be easily detected in all images and quantitative measurements were taken for the amount of lung in the field and the distance of the breast tissue from the field edges. Inter-fraction variability was found to be about twice as large as intra-fraction variability. The largest variability was detected in cranio/caudal direction (intra-fraction: 1.3 +/- 0.4 mm; inter-fraction: 2.6 +/- 1.3 mm) while the lung involvement varied by 1.1 +/- 0.2 mm and 1.8 +/- 0.6 mm intra- and inter-fraction, respectively. This indicates that the effect of breathing motion on the amount of radiated lung was not of major concern in the patients studied. Of other patient specific parameters such as body weight, breast separation, field size and location of the target, only increasing age was significantly correlated with larger inter-fraction motion. Acquisition of EPI cine loops proved to be a quick and easy technique to establish the amount of patient movement during breast radiotherapy. The relatively small variability found in the present pilot study justifies considerations for more conformal dose delivery.

Forward or inversely planned segmental multileaf collimator IMRT and sequential tomotherapy to treat multiple dominant intraprostatic lesions of prostate cancer to 90 Gy

Purpose: To investigate the technical feasibility of using forward or inversely planned segmental multileaf collimator (SMLC) intensity-modulated radiotherapy and sequential tomotherapy (ST) to escalate to a dose of 90 Gy to multiple dominant intraprostatic lesions within the prostate gland while delivering a dose of 75.6 Gy to the remaining prostate. Methods and Materials: A selected case with one dominant intraprostatic lesion located at the left base and a second dominant intraprostatic lesion at the right apex of the prostate was planned using three different intensity modulation techniques. Two plans were generated with inverse treatment planning, using either SMLC or ST with a special multivane collimator. The third plan also employed SMLC but was generated using forward planning. All three plans were compared based on dose-volume histograms, isodose distributions, and doses to sensitive normal structures. Results: All three plans meet and exceed the desired dose constraints, limiting doses to the rectum and bladder to an estimated RTOG Grade 2 complication rate of <10%. The ST plan achieved the best dose conformality, whereas the inverse SMLC plan gave the lowest dose to the rectal wall, and the forward SMLC plan obtained the best dose homogeneity inside the targets. Conclusions: Using any of the three intensity-modulated techniques, it is technically feasible to concurrently treat multiple selected high-risk regions within the prostate to 90 Gy and the remaining prostate to 75.6 Gy, while keeping the doses to the rectum and the bladder significantly lower than those associated with a Grade 2 complication rate of 10%.

Eye metastasis from carcinoma of the breast: diagnosis, radiation treatment and results

The experience at the Gershenson Radiation Oncology Center of 32 cases of metastases to the eye or orbit from breast cancer are presented with a review of the literature. The 32 patients were referred for radiation therapy in the period of 1980–1991. Eighteen patients had metastasis to the choroid, 2 patients had involvement of other parts of the eye (anterior chamber±choroid), and 11 patients had orbital metastasis. In one patient, the diffuse nature of the disease prevents subsite assignment. Ten of the patients with eye metastases also had brain or meningeal metastases (8 patients concurrent with eye metastases). Four of the 32 patients had bilateral choroidal metastases. A complete course of radiation therapy was delivered to 28 patients, one patient was not treated and 3 patients received only partial treatment because of general deterioration due to other widespread metastases from breast cancer. Of 21 evaluable patients, 15 had definite improvement. There was no progression of the eye metastases in the other 6 patients. The rest (7 patients) were lost to detailed follow-up of the response of the eye metastases. Four patients are still alive without any severe long-term side-effects. The diagnosis, treatment and outcome is presented with a review of the literature. The importance of emergency treatment for rapidly progressing lesions is stressed as well as the need for detailed treatment planning, careful delivery of daily treatments with a high degree of reproducibility and precision to prevent possible damage to sensitive normal structures.

Proton beam penumbra: effects of separation between patient and beam modifying devices.

The sharp lateral penumbra of a proton beam is often used to spare sensitive normal structures in treating clinical sites in which the target volume abuts, or even wraps around, these structures. Using Monte Carlo calculations and measurements, the factors which influence the penumbra of the proton beam at the Harvard Cyclotron Laboratory were investigated, with particular emphasis on the effects of separation between the patient and any beam modifying devices. Penumbra broadening, characterized by the distance over which the dose rises from 20% to 80% of the central dose, increases with greater amounts of scatterer introduced into the beam line. The broadening due to separation of the beam modifying devices and the patient is essentially linear with increasing air gap; the rate of increase depends on the details of these devices and on the depth of interest in the patient. For a particular portal, most of the parameters which affect the penumbra width are fixed by the patient's anatomy and the target volume. Only the thickness of the compensating bolus around the aperture edge and any air gap between the patient and the beam modifying devices can vary. Families of curves relating combinations of bolus thickness and air gap that maintain a constant penumbra width have been developed for guidelines during patient setup.

Application of linear programming to dose optimization in intracavitary implant therapy.

Linear programming can be used to optimize intracavitary brachytherapy for carcinoma of the cervix. A method has been developed which gives meaningful output and is described. A set of reference points were necessary in addition to the standard reference points. Point A as well as an array of points for adjacent radiation sensitive normal structures were used in order to obtain isodose curves conforming to those commonly used for therapy. In addition, arbitrary upper and lower limits of dose at selected points were needed and were set to conform to systems commonly used clinically for intracavitary therapy. It was immediately evident that a wide variety of loadings can be used that deliver appropriate or improved doses to reference points while minimizing normal tissue dose. The loadings represent arrangements which are not commonly used in many clinics but offer potential for clinical use.