Optimization of treatment planning for radiation therapy

There are two problems to be solved to apply quantitative optimization for treatment planning of radiation therapy. Firstly, an objective function which estimates both biological effect of non-uniform dose distribution and dose response relationship has to be developed. Secondly, precise radiobiological and clinical data are required to derive and justify the objective function. Hence, it is important to decrease the errors in dose measurement and calculation and to clarify the factors in data analysis. In this article, the methods of optimization reported in the past were reviewed and some subjects for future studies were discussed.     

Three-dimensional display techniques in radiation therapy treatment planning

Good radiation treatment planning requires that the target volume be treated with a high and uniform dose of radiation while irradiating normal tissue as little as possible. Even if the merits of a given treatment plan are judged only on the appearance of isodose lines in one or a few planes it can sometimes be difficult for the experienced radiation oncologist to select the best of several alternative plans. If consideration is given to the entire spatial distribution of dose, however, the problem becomes far more difficult because of the enormous amount of data that must be evaluated. We believe that the lack of suitable methods to display these data has greatly contributed to the slow incorporation of 3D considerations into routine radiation treatment planning. In the past few years there have been great advances in both the theory of how to produce effective 3D displays and in the display hardware itself. In this paper we survey some of the methods used at the University of North Carolina, and show specific examples of how these displays can be used in radiation therapy treatment planning.     

Use of the functional imaging modalities in radiation therapy treatment planning in patients with glioblastoma

Glioblastoma multiforme still remains, at present, the most frequent and deadly primary malignant glioma in adult. Despite safer and larger neurosurgical resections, patients almost always relapse very close or inside the tumor bed. Since more than 20 years, radiation therapy (RT) continue delivering the same dose of 60 Gy in 6 weeks, more precisely guided with CT-scanner and magnetic resonance imaging (MRI) in the treatment position. If morbidity has decreased with "non whole-brain" volumes, RT is nearly always failing locally, as surgery. Until now, all the series evaluating escalating doses (up to 80-90 Gy) in limited volumes have failed. One can really question : is the good dose delivered in the adequate volume? Main goal of new imaging techniques is to better visualize microscopic extension of malignant glioma cells. As based on metabolic principles, areas of abnormalities visualized with functional imaging have a different meaning, often complementary from conventional data. The four evaluated techniques are : magnetic resonance spectroscoy (MRS), functional MRI (fMRI), 18FDG or methionine PET, IMT (123iodine-alpha-methyl-thyrosine) SPECT. Each technique has potential interests and limits, MRS and fMRI appearing the most promising : they have both acceptable spatial resolution and can be executed just after conventional MRI acquisition. Areas of functional abnormalities are only partially including areas of hyperintensity in T1, T2 weighted MRI. It is therefore highly possible that, using it complementary to conventional CT and MRI for RT treatment planning, they add some precious informations; consequently, the very limited efficacy/toxicity ratio could be increased. This hypothesis will only be confirmed by prospective studies registering in parallel both functional and morphological abnormalities, linking them with sites of local recurrence. Once "targeted" the real microscopically invaded areas, one can speculate on new escalating dose studies, delivering RT in "adequate" volumes, combining it with new "targeted" drugs, as already recently demonstrated in head and neck cancers.     

The importance of optimal treatment planning in radiation therapy

There are two classes of failure in radiation therapy: local control not achieved and radiation-induced morbidity. Technical developments which permit the employment of treatment volumes which achieve a closer approximation to the target volume can confidently be asserted to yield clinical gains in terms of higher tumor control rates and/or reduced severity/frequency of radiation induced morbidity. The magnitude of the gains and the cost and effort to realize those gains may need to be assessed by the technique of the "clinical trial." Such gains will be the consequence of a higher dose to the target and/or the irradiation of smaller volumes of non-target tissues. An important fact is that unirradiated tissues do not develop radiation-related injury. Selected categories of radiation injuries that appear in non-target tissues are here reviewed. Valuable advances in the technology of radiation therapy are virtually certain for the near term. This bodes well, indeed, for our future patients.     

A simplified shielding approach for limiting fetal dose during radiation therapy of pregnant patients

Purpose: To investigate the effectiveness of a simple and practical shielding device to reduce fetal dose for a patient undergoing radiation therapy of nasopharyngeal carcinoma.

Methods and Materials: Using 5-cm-thick lead bricks and a heavy-duty steel cart, a 50 × 50-cm portable shield was designed and fabricated to reduce fetal dose due to collimator scatter and head leakage radiation. With the gantry at 90°/270° the shield can be easily positioned between the machine head and the fetus to reduce peripheral dose. Dose measurements for 6-MV X-rays and 9-MeV electrons have been made, utilizing a Rando phantom, to quantify the effect of the shield.

Results: Measurements show that the peripheral dose to the fetus can be reduced by 60% when the simple shielding device is used.     

Treatment planning technique in patients receiving postmastectomy radiation therapy

Many of the technical subtleties involved in postmastectomy radiation treatment planning will never be addressed in a robust clinical trial setting. However, these issues are faced daily by practicing radiation oncologists with little to guide them in the published literature. The purpose of this study was to survey a small number of breast care providers in both academic and private practice settings on practical aspects of postmastectomy radiation treatment planning. Topics addressed included the use of sophisticated dose-modulation algorithms, hypofractionation, bolus material, and dose-volume histogram (DVH) constraints. Fifty-two people responded to the survey, 50% in academics and 50% in private practice. As expected, wide variation in clinical practice was seen although a few general trends emerged. We include here, with the survey results, a review of the relevant literature for a number of different treatment-related issues. Although the use of postmastectomy radiation therapy is common, literature guiding the reader on technical aspects of delivery is sparse. The data presented here provide a general framework of what is considered acceptable by currently practicing radiation oncologists in many different practice settings.     

CT scanning for radiation therapy treatment planning of hepatoma

One hundred forty-five patients with hepatoma had CT scanning for radiation therapy treatment planning. In order to demonstrate the anatomical distortions that occur with hepatoma and its effect on treatment planning, a control group of 50 colorectal cancer patients with normal livers was analyzed for comparison. The objectives of planning were to deliver as homogeneous a dose to the whole liver as possible and not to treat more than one of two functional kidneys or more than one-half of both functional kidneys. Conventional AP/PA portals were defined by physical examination, intravenous pyelogram, and bowel gas patterns at simulation and were found to be inadequate for the treatment of 76% of patients with hepatoma and 10% of patients with normal livers. Among the control group patients with no hepatoma, only 10% required oblique portals and 6% could not be treated because of left hydronephrosis or a solitary right kidney. Because the distortion of the liver in hepatoma in relationship to the kidneys required portal modification in 76% of hepatoma cases; 39% required oblique planning, 24% AP/PA, 20% PA and left lateral portals, and 17% required 4-field, 3-field or other plans in order to meet the treatment planning objectives. We concluded that all patients receiving radiation therapy to the liver for hepatoma require CT scanning for optimum radiation therapy treatment planning because of the hepatic distortion that occurs in hepatoma and the requirements of renal tolerance.     

3-D radiation therapy treatment planning: overview and assessment

A 3-D treatment planning system is one that can represent all radiation therapy treatment machine motions, and which can calculate the dose at any point in the patient treatment volume. As a corollary to these two requirements, a 3-D planning system must also be able to display 3-D plan geometry and doses in some useful way. This article reviews three visible aspects of 3-D planning systems: graphic displays, dose computation methods, and ease of use. It also discusses a less visible, but no less important, aspect: the underlying software engineering. Although 3-D planning systems first appeared in research institutions more than a decade ago, and potential benefits have been demonstrated, they are used only rarely in routine clinical practice. This review concludes that adequate displays and computation techniques are now available, but improved packaging, engineering, and ease of use are required before 3-D planning will be practiced widely.     

Open low-field magnetic resonance imaging in radiation therapy treatment planning

To evaluate the possibilities of an open low-field magnetic resonance imaging (MRI) scanner in external beam radiotherapy treatment (RT) planning.

A custom-made flat tabletop was constructed for the open MR, which was compatible with standard therapy positioning devices. To assess and correct image distortion in low-field MRI, a custom-made phantom was constructed and a software algorithm was developed. A total of 243 patients (43 patients with non-small-cell lung cancer, 155 patients with prostate cancer, and 45 patients with brain tumors) received low-field MR imaging in addition to computed tomographic (CT) planning imaging between January 1998 and September 2001 before the start of the irradiation.

Open low-field MRI provided adequate images for RT planning in nearly 95% of the examined patients. The mean and the maximal distortions 15 cm around the isocenter were reduced from 2.5 mm to 0.9 mm and from 6.1 mm to 2.1 mm respectively. The MRI-assisted planning led to better discrimination of tumor extent in two-thirds of the patients and to an optimization in lung cancer RT planning in one-third of the patients. In prostate cancer planning, low-field MRI resulted in significant reduction (40%) of organ volume and clinical target volume (CTV) compared with CT and to a reduction of the mean percentage of rectal dose of 15%. In brain tumors, low-field MR image quality was superior compared with CT in 39/45 patients for planning purposes.

The data presented here show that low-field MRI is feasible in RT treatment planning when image correction regarding system-induced distortions is performed and by selecting MR imaging protocol parameters with the emphasis on adequate images for RT planning.     

Assessing the cost-effectiveness of postmastectomy radiation therapy

PURPOSE: To assess the cost-effectiveness of postmastectomy local-regional radiation therapy (RT) for patients with breast cancer with regard to local-regional relapse (LRR) and quality-adjusted life years (QALY). METHODS AND MATERIALS: Data from the literature are used to estimate the risk of LRR, and the impact of RT on the risk of LRR and survival. The risk of LRR is related linearly to the number of positive axillary nodes 1% rate of LRR = 10 + (4 x number of positive nodes)]. RT reduces the risk of LRR by 67%. LRRs are treated with excision or biopsy followed by RT; half being controlled locally and half receiving additional salvage surgery and chemotherapy. Absolute improvements in 10-year overall survival due to RT are assumed to vary between 1 and 12%; and accrue linearly during the initial 10-year follow-up period. Professional and technical charges are used as a surrogate for costs. Money spent and benefits recognized in future years are discounted to 1997 values using a 3% annual rate. Quality factors are used to adjust for treatment, disease, and toxicity status. RESULTS: The cost per LRR prevented with the addition of routine postmastectomy RT is highly dependent upon the number of positive axillary nodes and ranges from $100,000-$200,000 for patients with 0-2 nodes, and $25,000-$75,000 for > or = 4 nodes. The cost per QALY gained at 10 years is $10,000-$110,000 for survival benefits > or = 3%. CONCLUSIONS: The cost per LRR prevented decreases with increasing numbers of positive axillary nodes. There is not a sharp cutoff at the < or = 3 vs. > or = 4 lymph node number, suggesting that using this cutoff for recommending or not recommending RT following mastectomy is not economically logical. The cost per QALY of $10,000-$100,000 compares favorably to that of other accepted medical procedures. Modest changes in the quantitative assumptions do not qualitatively alter the results. Concerns regarding costs should not generally preclude the use of postmastectomy RT.     

Functional imaging in treatment planning in radiation therapy: a review

The remarkable technical developments obtained in radiation oncology have resulted in an increasing use of image-based treatment planning in radiation therapy for three-dimensional and intensity modulated radiation therapy, stereotactic irradiation and image-guided brachytherapy. There has been increased use of computer-based record and verify systems as well as electronic portal imaging to enhance treatment delivery. From the data presented it is evident that PET scanning and other functional imaging techniques play a major role in the definition of tumor extent and staging of patients with cancer. The recent introduction of a combined CT and PET scanner will substantially simplify image acquisition and treatment planning.     

Breast cancer treatment and ethnicity in British Columbia,Canada

Background  

Racial and ethnic disparities in breast cancer incidence, stage at diagnosis, survival and mortality are well documented; but few studies have reported on disparities in breast cancer treatment. This paper compares the treatment received by breast cancer patients in British Columbia (BC) for three ethnic groups and three time periods. Values for breast cancer treatments received in the BC general population are provided for reference.     

Spinal cord planning risk volumes for intensity-modulated radiation therapy of head-and-neck cancer

PURPOSE: To assess planning organ at risk volume (PRV) margins of the spinal cord in intensity-modulated radiotherapy (IMRT) of oropharyngeal cancers, by modeling the effect of geometric uncertainties to estimate the probability of the spinal cord receiving a particular dose. METHODS AND MATERIALS: Five patients with oropharyngeal cancer were treated by IMRT with simultaneous doses of 66 Gy (gross disease) and 54 Gy (subclinical disease) in 30 fractions. Spinal cord doses were limited to 45 Gy. The probability, due to random and systematic patient positioning uncertainties (3-mm standard deviation), of the cord receiving a particular dose was determined. The effect of an on-line setup correction protocol was also modeled. RESULTS: The mean probability of a maximum spinal cord dose of 45 Gy was 1%, with a 6-mm PRV margin. The mean probability of a maximum dose exceeding 40 Gy was 37% (range, 13-77%); this probability is reduced with a setup correction protocol. CONCLUSION: A spinal cord PRV generated with a 6-mm margin leads to a 99% probability of maintaining the maximum spinal cord dose below 45 Gy. The application of an on-line setup correction protocol reduces the cord dose by approximately 5 Gy.