Francis Newman

Toxicity assessment of pelvic intensity-modulated radiotherapy with hypofractionated simultaneous integrated boost to prostate for intermediate- and high-risk prostate cancer.

PURPOSE To evaluate the toxicity of pelvic intensity-modulated radiotherapy (IMRT) with hypofractionated simultaneous integrated boost (SIB) to the prostate for patients with intermediate- to high-risk prostate cancer. METHODS AND MATERIALS A retrospective toxicity analysis was performed in 30 consecutive patients treated definitively with pelvic SIB-IMRT, all of whom also received androgen suppression. The IMRT plans were designed to deliver 70 Gy in 28 fractions (2.5 Gy/fraction) to the prostate while simultaneously delivering 50.4 Gy in 28 fractions (1.8 Gy/fraction) to the pelvic lymph nodes. The National Cancer Institute Common Terminology Criteria for Adverse Events, version 3.0, was used to score toxicity. RESULTS The most common acute Grade 2 events were cystitis (36.7%) and urinary frequency/urgency (26.7%). At a median follow-up of 24 months, late toxicity exceeding Grade 2 in severity was uncommon, with two Grade 3 events and one Grade 4 event. Grade 2 or greater acute bowel toxicity was associated with signficantly greater bowel volume receiving > or =25 Gy (p = .04); Grade 2 or greater late bowel toxicity was associated with a higher bowel maximal dose (p = .04) and volume receiving > or =50 Gy (p = .02). Acute or late bladder and rectal toxicity did not correlate with any of the dosimetric parameters examined. CONCLUSION Pelvic IMRT with SIB to the prostate was well tolerated in this series, with low rates of Grade 3 or greater acute and late toxicity. SIB-IMRT combines pelvic radiotherapy and hypofractionation to the primary site and offers an accelerated approach to treating intermediate- to high-risk disease. Additional follow-up is necessary to fully define the long-term toxicity after hypofractionated, whole pelvic treatment combined with androgen suppression.

How should we describe the radiobiologic effect of extracranial stereotactic radiosurgery: Equivalent uniform dose or tumor control probability?

Extracranial stereotactic radiosurgery (ESR) is now undergoing clinical investigation at numerous institutions as a treatment for solitary malignant lesions. Because there is no standard ESR technique, the same minimum dose might be applied through widely variable target dose-volume histograms. For multicenter trials of ESR or interinstitutional comparisons, a reliable index of radiobiological dose equivalency might facilitate the evaluation of dose-response relationships. Equivalent uniform dose (EUD) and tumor control probability (TCP) were considered for this application. While EUD appears more robust for the prospective description of ESR, TCP is expected to remain more valuable for a post hoc estimation of radiosensitivity parameters.

Respiration Induced Heart Motion and Indications of Gated Delivery for Left-Sided Breast Irradiation

PURPOSE To investigate respiration-induced heart motion for left-sided breast irradiation using a four-dimensional computed tomography (4DCT) technique and to determine novel indications to assess heart motion and identify breast patients who may benefit from a gated treatment. METHODS AND MATERIALS Images of 4DCT acquired during free breathing for 20 left-sided breast cancer patients, who underwent whole breast irradiation with or without regional nodal irradiation, were analyzed retrospectively. Dose distributions were reconstructed in the phases of 0%, 20%, and 50%. The intrafractional heart displacement was measured in three selected transverse CT slices using D(LAD) (the distance from left ascending aorta to a fixed line [connecting middle point of sternum and the body] drawn on each slice) and maximum heart depth (MHD, the distance of the forefront of the heart to the line). Linear regression analysis was used to correlate these indices with mean heart dose and heart dose volume at different breathing phases. RESULTS Respiration-induced heart displacement resulted in observable variations in dose delivered to the heart. During a normal free-breathing cycle, heart-induced motion D(LAD) and MHD changed up to 9 and 11 mm respectively, resulting in up to 38% and 39% increases of mean doses and V(25.2) for the heart. MHD and D(LAD) were positively correlated with mean heart dose and heart dose volume. Respiratory-adapted gated treatment may better spare heart and ipsilateral-lung compared with the conventional non-gated plan in a subset of patients with large D(LAD) or MHD variations. CONCLUSION Proposed indices offer novel assessment of heart displacement based on 4DCT images. MHD and D(LAD) can be used independently or jointly as selection criteria for respiratory gating procedure before treatment planning. Patients with great intrafractional MHD variations or tumor(s) close to the diaphragm may particularly benefit from the gated treatment.

TECHNICAL CONSIDERATIONS IN THE APPLICATION OF INTENSITY- MODULATED RADIOTHERAPY AS A CONCOMITANT INTEGRATED BOOST FOR LOCALLY-ADVANCED CERVIX CANCER

The technical aspects of IMRT applied to cervix cancer are discussed in this paper, as well as issues related to tumor delineation, target volume definitions, inverse planning, and IMRT delivery. A theoretical example illustrating how IMRT can accurately mimic dose distributions obtained using conventional planning plus HDR brachytherapy is also shown. The notion of clinical optimization parameters is introduced to account for the radiation delivery variables, which affect the overall treatment time. This is especially relevant to the possible introduction of intrafractional movement and resulting inaccuracy, as well as facility efficiency.

Automated lesion detection and lesion quantitation in MR images using autoassociative memory

Previous efforts concerning lesion extraction in radiologic images indicated that autoassociative memory models can be a valuable tool in automated lesion detection. Preliminary results are expanded to resolve the technical problems of image registration and magnification. Instead of operating on selected portions of the MR images, each entire image matrix is operated upon as image vector comprising all stacked columns of the matrix. Spin density weighted images (TR = 3000 ms and TE = 40 ms) of 42 normal subjects were remapped and standardized with respect to location and magnification. All image vectors were orthonormalized to span a linear manifold. Standardized abnormal image vectors were then tested by the stored autoassociative memory and the abnormalities (novelties) were extracted by application of an autocorrelation matrix to the input vector. The autocorrelation matrix is computed using image vectors from normal subjects. The lesions (multiple sclerosis and tumors) are then identified as the orthogonal component to the linear manifold spanned by the basis vectors of the normal brain scans. Lesion extraction has been achieved with the intention of quantitating and staging diseased parenchyma after automated edge detection.

Supine Craniospinal Irradiation Setup with Two Spine Fields

Craniospinal irradiation is an integral part of treatment for a number of cancers. Typically, patients are positioned prone, which allows visualization of field matches. However, a supine position allows better airway access for patients requiring anesthesia, and is more comfortable for patients. One potential difficulty with supine positioning occurs when the patient is tall and requires matching 2 spine fields. We describe a technique to match the spine fields using light fields on the bottom of the treatment table, and verified the approach on a phantom. The accuracy of the technique is demonstrated for the first 4 patients, with the majority of field gaps and overlaps below our clinical tolerance of 2 mm.

Esophageal cancer patients undergoing external beam radiation after placement of self-expandable metal stents: is there a risk of radiation dose enhancement?

BACKGROUND Self-expandable metal stents (SEMSs) are used for palliation of malignant dysphagia. It is not known whether dose adjustments are required when there is a stent in the radiation field. OBJECTIVE To measure the effects of esophageal stents of various designs and materials on radiation dose to the tissue adjacent to the stent in the radiation field to determine whether there should be any dose adjustment. DESIGN Simulated clinical protocol. SETTING Linear accelerator radiation treatment center. PATIENTS Solid Water phantoms were used to mimic the tissue environment of the human esophagus as well as stents of various designs and materials and controls. INTERVENTIONS Radiation beams composed of photons (x-rays) delivered in split dosing with energies of 6, 10, and 15 million volts. MAIN OUTCOME MEASUREMENTS Film and image-based evidence of dose enhancement; Monte Carlo calculations. RESULTS Dose enhancement from single beams was seen only on the anterior surface, particularly in the stainless steel Z-stent (3.5%-7.8%) and the nonmetal Polyflex stent (5.5%-8.8%); less dose enhancement was seen on the anterior surface of the Alimaxx and Ultraflex nitinol stents (2%-2.5%). A negligible dose effect was seen on the posterior wall of all the stents tested. Monte Carlo calculation results were roughly similar to actual dosimeter measurements. LIMITATIONS Simulated clinical protocol. CONCLUSIONS This tissue-mimicking model reveals that radiation dose enhancement is a function of stent design and material, and the dose reduction is unnecessary as long as multiple fields are used.

An optimization model and solution for radiation shielding design of radiotherapy treatment vaults

In radiation shielding design, one is usually faced with a set of conflicting goals that are navigated by an experienced physicist. If one has abundant space, the task is simplified because concrete is relatively inexpensive and will provide adequate shielding for high energy photons and neutrons, when applicable. However, if space is constrained (which is usually the case), the design becomes more difficult since one will likely have to employ combinations of steel, lead, and concrete, or other new materials--each with different properties and costs. Very experienced shielding designers can draw upon previous plans, but they do not know if their design is optimal in any sense. We have constructed a linear program that minimizes the cost of the shielding materials and minimizes the dose at the protection point or the shielding thickness subject to space constraints and to Federal or State regulations regarding the allowable exposure to individuals adjacent to the radiotherapy vault. In spite of what appears to be a simple model, the solution may require iterations of the optimization to arrive at the optimal solution.

Visual sensations during megavoltage radiotherapy to the orbit attributable to Cherenkov radiation

During megavoltage photon and electron beam radiotherapytreatment involving the eye, patients commonly report visual sensations; “nerve stimulation” is the conventional explanation. We propose that the phenomenon can be attributed to Cherenkov radiation inside the eye. The threshold electron energy for Cherenkov radiation in water is 260 keV . The human retina is able to perceive approximately 5–14 visible photons in 0.001 s . A single 500 keV electron traversing 1 mm of water will induce nearly 15 Cherenkov visible range photons. We propose that a portal image involving the eye will produce sufficient Cherenkov radiation to be detected by the retina.

Left-sided breast cancer irradiation using rotational and fixed-field radiotherapy.

The 3-dimensional conformal radiotherapy (3DCRT) technique is the standard for breast cancer radiotherapy. During treatment planning, not only the coverage of the planning target volume (PTV) but also the minimization of the dose to critical structures, such as the lung, heart, and contralateral breast tissue, need to be considered. Because of the complexity and variations of patient anatomy, more advanced radiotherapy techniques are sometimes desired to better meet the planning goals. In this study, we evaluated external-beam radiation treatment techniques for left breast cancer using various delivery platforms: fixed-field including TomoDirect (TD), static intensity-modulated radiotherapy (sIMRT), and rotational radiotherapy including Elekta volumetric-modulated arc therapy (VMAT) and tomotherapy helical (TH). A total of 10 patients with left-sided breast cancer who did or did not have positive lymph nodes and were previously treated with 3DCRT/sIMRT to the entire breast were selected, their treatment was planned with Monaco VMAT, TD, and TH. Dosimetric parameters including PTV coverage, organ-at-risk (OAR) sparing, dose-volume histograms, and target minimum/maximum/mean doses were evaluated. It is found that for plans providing comparable PTV coverage, the Elekta VMAT plans were generally more inhomogeneous than the TH and TD plans. For the cases with regional node involvement, the average mean doses administered to the heart were 9.2 (± 5.2) and 8.8 (± 3.0)Gy in the VMAT and TH plans compared with 11.9 (± 6.4) and 11.8 (± 9.2)Gy for the 3DCRT and TD plans, respectively, with slightly higher doses given to the contralateral lung or breast or both. On average, the total monitor units for VMAT plans are 11.6% of those TH plans. Our studies have shown that VMAT and TH plans offer certain dosimetric advantages over fixed-field IMRT plans for advanced breast cancer requiring regional nodal treatment. However, for early-stage breast cancer fixed-field radiotherapy is potentially more beneficial in terms of OAR sparing.