This study of internal mammary lymph node chain (IMC) irradiation in patients with left breast cancer aimed at comparing the merits of using, on one hand, a dedicated direct IMC electron field versus ...a wide tangent photon field covering both breast and IMC on the other. The objective was to produce guidelines allowing clinicians to readily determine the preferred method for each patient.
For 19 patients with cancer of the left breast/chest wall, we produced 2 treatment plans each using a different technique: the electron technique using 2 standard opposed photon tangents covering only the breast or chest wall along with a matching adjacent electron field targeting the IMC only or the wide tangent technique using 2 opposed wide tangents covering simultaneously IMC and breast or chest wall. All plans were then optimized for acceptable target coverage.
For patients where the left anterior descending coronary artery (LAD) was located outside of the wide tangent fields (13 patients), the wide tangent technique resulted in lower dose to the LAD, left lung, and heart. When the LAD was inside the wide tangents (6 patients), dose was lower with the electron technique for LAD and heart. In all cases, regardless of LAD location, the wide tangent technique returned strictly superior dose homogeneity but much higher right (contralateral) breast dose.
A flowchart was produced based on LAD location that allows the clinician to readily determine the preferred technique for each patient without having to perform and compare 2 treatment plans, thus saving valuable planning time.
This study explores the feasibility of SRS/SRT treatment with MLC leaves wider than 2.5 mm at isocenter by inter-comparing treatment plans produced with 2.5, 5.0, and 10.0 mm leaves for various ...target sizes and shapes.
Forty previously treated patients were re-planned using 2.5, 5.0, and 10.0 mm wide MLC leaves. For each patient, all three plans were evaluated and contrasted between them in terms of five metrics: target dose homogeneity, conformity index, organs at risk dose, dose fall off outside the target, and dose to normal tissues. A regularity index RI was introduced that quantified the degree of target shape irregularity. The effect of target size and shape irregularity on feasibility of 5.0 and 10.0 mm leaves was analyzed.
Consistent plan degradation was observed for 10.0 mm (sometimes for 5.0 mm) compared to 2.5 mm MLC in terms of the above five plan metrics, but this degradation was small to clinically insignificant. As an exception, when target (PTV) size was smaller than about 1 cm diameter, clinically significant differences were found between 2.5, 5.0, and 10.0 mm MLC.
5.0 and 10.0 mm MLC can be used in SRS/SRT for targets (PTV) diameter larger than 1 cm. For smaller targets, 2.5 mm MLC is clinically superior, 5.0 is acceptable and 10.0 mm MLC is discouraged in terms of PTV dose conformity.
Background
Linear accelerator–based stereotactic radiosurgery delivered to cardiac arrhythmogenic foci could be a promising catheter‐free ablation modality. We tested the feasibility of in vivo ...atrioventricular (AV) node ablation in swine using stereotactic radiosurgery.
Methods and Results
Five Large White breed swine (weight 40–75 kg; 4 females) were studied. Single‐chamber St Jude pacemakers were implanted in each pig. The pigs were placed under general anesthesia, and coronary/cardiac computed tomography simulation scans were performed to localize the AV node. Cone beam computed tomography was used for target positioning. Stereotactic radiosurgery doses ranging from 35 to 40 Gy were delivered by a linear accelerator to the AV node, and the pigs were followed up with weekly pacemaker interrogations to observe for potential electrocardiographic changes. Once changes were observed, the pigs were euthanized, and pathology specimens of various tissues, including the AV node and tissues surrounding the AV node, were taken to study the effects of radiation. All 5 pigs had disturbances of AV conduction with progressive transition into complete heart block. Macroscopic inspection did not reveal damage to the myocardium, and pigs had preserved systolic function on echocardiography. Immunostaining revealed fibrosis in the target region of the AV node, whereas no fibrosis was detected in the nontargeted regions.
Conclusions
Catheter‐free radioablation using linear accelerator–based stereotactic radiosurgery is feasible in an intact swine model.
The purpose of this study was to evaluate patient-related non-dosimetric predictors of cardiac sparing with the use of deep inspiration breath-hold (DIBH) in patients with left-sided breast cancer ...undergoing irradiation (RT).
We retrospectively reviewed charts and treatment plans of one-hundred and three patients with left-sided breast cancer. All patients had both free-breathing (FB) and DIBH (with body surface tracking) plans available. (MHD) and V4 (heart volume receiving at least 4 Gy) were extracted from dose volume histograms. Fisher's exact and Chi-square tests were used to identify predictors of reductions in MHD and V4 after DIBH.
One-hundred and three patients were identified and most underwent mastectomy. MHD and V4 decreased significantly in DIBH plans (0.74 ± 0.25 Gy vs. 1.72 ± 0.98 Gy,
< 0.0001 for MHD; 4 ± 4.98 cc vs. 20.79 ± 18.2 cc,
< 0.0001 for V4). Body mass index (BMI), smoking and timing of CT simulation (spring/winter vs. summer/fall) were significant predictors of reduction in MHD whereas BMI, field size, chemotherapy, axillary dissection, and timing of CT simulation predicted reduction in V4. On multivariate analysis, BMI, and timing of CT simulation remained significant predictors of the heart-sparing effect of DIBH.
In the setting of limited resources, identifying patients who will benefit the most from DIBH is extremely important. Prior studies have identified multiple dosimetric predictors of cardiac sparing and hereby we identified new non-dosimetric factors such as BMI and timing of treatments.
IntroductionStereotactic radiosurgery (SRS) delivered to arrhythmogenic foci within the heart is a promising treatment modality. We dosimetrically evaluated the radiation dose to the organs at risk ...of four swine that were successfully treated with linear-accelerator-based SRS for atrioventricular (AV) node ablation.Materials and methodsSingle‐chamber pacemakers were implanted in four large white breed swine. Cardiac computed tomography simulation scans were performed to localize the AV node and organs at risk. SRS (35-40 Gy) was delivered to the AV node, and the pigs were followed up with pacemaker interrogations. One-sample t-tests were used to evaluate Dmax of great vessels, esophagus, and chest wall as compared to known normal tissue constraints as per RTOG 0631 and AAPM Task Group 101.ResultsAll pigs had disturbances of AV conduction with progressive transition into complete heart block. Macroscopic and microscopic evaluation showed fibrosis in the AV node but did not reveal any changes in non-nodal cardiac tissue or vessels. The mean Dmax±SD (p-value) of the chest wall (14.7±3.3 (0.02)), esophagus (10.7±1.1 (<0.01)) superior vena cava (3.3±4.1 (<0.01)), right pulmonary artery (16.1±6.4 (<0.01)), right pulmonary vein (15.7± 5 (<0.01)), left pulmonary artery (11.1±1.7 (<0.01)) and left pulmonary vein (14.1±2.6 (<0.01)), and the inferior vena cava (33.68±1.6 (0.026)) were significantly below the normal tissue constraint cutoffs. Mean±SD (p-value) of the ascending aorta (19.4±16.1 (0.12)) was not significantly different than normal tissue constraint cutoffs. One swine model treated at 40 Gy had small area of hotspot in the ascending aorta (40.65 (0.4 cc)).ConclusionWe have demonstrated in our swine models that SRS using 35-40 Gy can be done without exceeding known human normal tissue constraints to the chest wall, esophagus, and great vessels.
Every year, almost 62,000 are diagnosed with a head and neck cancer (HNC) and 13,000 will succumb to their disease. In the primary setting, intraoperative radiation therapy (IORT) can be used as a ...boost in select patients in order to optimize local control. Addition of external beam radiation to limited volumes results in improved disease control over surgery and IORT alone. In the recurrent setting, IORT can improve outcomes from salvage surgery especially in patients previously treated with external beam radiation. The use of IORT remains limited to select institutions with various modalities being currently employed including orthovoltage, electrons, and high-dose rate brachytherapy. Practically, execution of IORT requires a coordinated effort and careful planning by a multidisciplinary team involving the head and neck surgeon, radiation oncologist, and physicist. The current review summarizes common uses, outcomes, toxicities, and technical aspects of IORT in HNC patients.
•A total body irradiation technique based on CT simulation was newly introduced.•This technique succeeded in reducing the length of the overall treatment session.•This new technique reduced patient ...discomfort while ensuring accurate shielding of the lungs.
During total body irradiation (TBI), customized shielding blocks are positioned in front of the lungs to reduce radiation dose. The difficulty is to accurately position the blocks to cover the entire lungs. A new technique based on Computed Tomography (CT) simulation was developed to determine the exact position of lung blocks prior to treatment in order to decrease overall treatment time and reduce patient discomfort.
Patients were CT simulated and lungs were contoured using a treatment planning system. Anteroposterior/posteroanterior (AP/PA) fields were designed with MLC aperture conforming to lung contours. The fields were used to represent the extent of the lungs, which was subsequently marked on the patient’s skin. The lung blocks were positioned with their shadow matching the lungs’ marks. Their position was radiographically verified prior to the delivery of each beam. To evaluate the efficiency of this technique, the treatment session time and the number of repeated attempts to correctly position the shielding blocks was recorded for each beam. Exact treatment times for patients treated with the old technique were not available and were hence approximated based on previous experience.
We succeeded in positioning the shielding blocks from the first attempt in 10/12 beams. The position of the shielding blocks was adjusted only one time prior to treatment in 2/12 beams. These results are compared to an average of 3 attempts per beam for each patient using the conventional technique of trial and error. The average time of a treatment session was 29min with a maximum of 41min versus approximately 60min in past treatments and a maximum of 120min.
This new technique succeeded in reducing the length of the overall treatment session of the conventional TBI procedure and hence reduced patient discomfort while ensuring accurate shielding of the lungs.
Children receiving radiotherapy face the probability of a subsequent malignant neoplasm (SMN). In some cases, the predicted SMN risk can be reduced by proton therapy. The purpose of this study was to ...apply the most comprehensive dose assessment methods to estimate the reduction in SMN risk after proton therapy vs. photon therapy for a 13-year-old girl requiring craniospinal irradiation (CSI). We reconstructed the equivalent dose throughout the patient's body from therapeutic and stray radiation and applied SMN incidence and mortality risk models for each modality. Excluding skin cancer, the risk of incidence after proton CSI was a third of that of photon CSI. The predicted absolute SMN risks were high. For photon CSI, the SMN incidence rates greater than 10% were for thyroid, non-melanoma skin, lung, colon, stomach, and other solid cancers, and for proton CSI they were non-melanoma skin, lung, and other solid cancers. In each setting, lung cancer accounted for half the risk of mortality. In conclusion, the predicted SMN risk for a 13-year-old girl undergoing proton CSI was reduced vs. photon CSI. This study demonstrates the feasibility of inter-institutional whole-body dose and risk assessments and also serves as a model for including risk estimation in personalized cancer care.
Pre-existing methods for photon beam spectral reconstruction are briefly reviewed. An alternative reconstruction method by scatter analysis for linear accelerators is introduced. The method consists ...in irradiating a small plastic phantom at standard 100 cm SSD and inferring primary beam energy spectral information based on the measurement with a standard Farmer chamber of scatter around the phantom at several specific scatter angles: a scatter curve is measured which is indicative of the primary spectrum at hand. A Monte Carlo code is used to simulate the scatter measurement set-up and predict the relative magnitude of scatter measurements for mono-energetic primary beams. Based on mono-energetic primary scatter data, measured scatter curves are analysed and the spectrum unfolded as the sum of mono-energetic individual energy bins using the Schiff bremsstrahlung model. The method is applied to an Elekta/SL18 6 MV photon beam. The reconstructed spectrum matches the Monte Carlo calculated spectrum for the same beam within 6.2% (average error when spectra are compared bin by bin). Depth dose values calculated for the reconstructed spectrum agree with physically measured depth dose data to within 1%. Scatter analysis is preliminarily shown to have potential as a practical spectral reconstruction method requiring few measurements under standard 100 cm SSD and feasible in any radiotherapy department using a phantom and a Farmer chamber.
Many institutions worldwide currently deliver left breast radiotherapy in free breathing mode, mostly due to the unavailability of a Deep Inspiration Breath Hold technique (DIBH). This study aims at ...quantifying the error in dose delivery (compared to treatment plan) due to respiratory motion in free breathing irradiation of left breast or chest wall. Since subfields often consist in small, fine-tuned, highly targeted fields, slight intrafractional target motion may compromise their subtle benefit. Thus we analyzed the respiratory motion effect on target dose coverage, dose homogeneity and left lung dose.
Treatment plans for twenty left breast or chest wall cancer patients previously treated at our center were retrieved and retrospectively planned with the introduction of an appropriate shift in isocenter location to simulate free breathing target motion.
No clinically significant dosimetric changes were found in all twenty cases when breathing motion was accounted for. Changes in target dose coverage (V95%), in target maximum dose (D2%) and in V20Gy lung dose were respectively less than 1.5%, 0.3% and 2.6%.
The findings suggest that breast irradiation in free breathing mode does not undermine the dosimetric merits of the field-in-field technique and does not produce clinically significant dosimetric differences in dose delivery for target and lung compared to plan.
•Breathing has a negligible effect on dose delivery accuracy in breast cancer radiotherapy.•Free breathing during breast radiotherapy treatment does not invalidate the use of field-in-field technique.•The dosimetric error from free breathing breast motion during radiotherapy treatment is clinically negligible.
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