Tomohisa Furuya

The dosimetric impact of respiratory breast movement and daily setup error on tangential whole breast irradiation using conventional wedge, field-in-field and irregular surface compensator techniques

To evaluate the dosimetric impact of respiratory breast motion and daily setup error on whole breast irradiation (WBI) using three irradiation techniques; conventional wedge (CW), field-in-field (FIF) and irregular surface compensator (ISC). WBI was planned for 16 breast cancer patients. The dose indices for evaluated clinical target volume (CTVevl), lung, and body were evaluated. For the anterior-posterior (AP) respiratory motion and setup error of a single fraction, the isocenter was moved according to a sine function, and the dose indices were averaged over one period. Furthermore, the dose indices were weighted according to setup error frequencies that have a normal distribution to model systematic and random setup error for the entire treatment course. In all irradiation techniques, AP movement has a significant impact on dose distribution. CTVevlD95 (the minimum relative dose that covers 95 % volume) and V95 (the relative volume receiving 95 % of the prescribed dose) were observed to significantly decrease from the original ISC plan when simulated for the entire treatment course. In contrast, the D95, V95 and dose homogeneity index did not significantly differ from those of the original plans for FIF and CW. With regard to lung dose, the effect of motion was very similar among all three techniques. The dosimetric impact of AP respiratory breast motion and setup error was largest for the ISC technique, and the second greatest effect was observed with the FIF technique. However, these variations are relatively small.

Comparison of 4 MV photon surface dose among Varian, Siemens, and Elekta linear accelerators for tangential breast treatment: a phantom study

PurposeWe have compared the differences in a 4-MV photon surface dose among Varian, Siemens, and Elekta linear accelerators (linacs) with wedges for tangential breast treatment.Materials and methodsThe wedge factor and the surface dose were measured using a solid water phantom and an ion chamber for each linear accelerator with various field sizes and wedge angles. A tangential treatment plan was applied to an elliptical hollow cylinder water phantom with a radiochromic film placed thereon. A dose was delivered to a simulated target in the phantom, and the resulting dose distribution was analyzed using a film scanner.ResultsVarians wedges resulted in the highest wedge factors, ranging from 0.37 to 0.75 depending on the wedge angles. Varians wedges led to the highest normalized skin doses, ranging between 0.40 and 0.73 depending on the wedge angles and field sizes. In the cylinder phantom test with two tangential beams, the Varian linac provided a nearly 20% higher maximum dose than the Siemens and Elekta linacs.ConclusionThe Varian linac resulted in the highest surface doses, and the Elekta linac led to the lowest for nearly all the measurement conditions we employed, including open beams.

Full-dose capecitabine with local radiotherapy: one of the treatment options for inoperable T4 breast cancer

A 48-year-old woman presented with a 15-cm diameter tumor in her left breast with fixation to the chest wall and palpable axillary lymph nodes. Pathology study showed pure-type mucinous carcinoma. Pretreatment staging investigations showed multiple lung metastases, which resulted in the diagnosis of T4N2M1 breast cancer. Four cycles of cyclophosphamide 700 mg/m2/epirubicin 70 mg/m2 (CE) were performed initially, but the tumors decreased only within the treatment response criteria of stable disease (SD). The second regimen of docetaxel could not continue due to drug allergy. Two more cycles of CE did not improve the situation. Then, treatment was continued with full-dose capecitabine with local radiotherapy. She received radiotherapy to the left breast and axillary region with 60 Gy/30 fractions/6 weeks and concomitant capecitabine 2400 mg/body twice daily for 21 days; the cycles were repeated every 28 days. After radiotherapy, tumors decreased in size, and the skin ulceration disappeared. She continued to receive capecitabine on the same schedule. She now has no palpable tumor in her left breast and no tumor in the axilla or lung on CT. She is alive and well 6 years after radiotherapy.

Stereotactic Body Radiotherapy for Spinal Metastases: Clinical Experience in 134 Cases From a Single Japanese Institution

Object: This study aimed to clarify the outcomes of stereotactic body radiotherapy for spinal metastases with a uniform dose fractionation schedule in our institution. Materials and Methods: Patients treated with spine stereotactic body radiotherapy were retrospectively reviewed. The prescribed dose was 24 Gy in 2 fractions. End points were local control, pain control, and adverse events. Local control was defined as elimination, shrinkage, or stable disease in the tumor on imaging evaluations. Pain status was measured on a scale of 0 to 10 by patients’ self-reports, and pain response was defined as the time at which pain scale score decreased by 2 or more from the baseline score without increase in analgesics. In addition, various treatment- and tumor-specific factors were evaluated to determine predictive values for local and pain control. Results: This study included 134 lesions in 131 patients, with: lesion histopathology, lung/colorectal/thyroid/renal/breast/prostate/sarcoma/other cancer, 24/22/18/14/12/10/6/25; reirradiation stereotactic body radiotherapy, 82 (61.2%) cases; and postoperative stereotactic body radiotherapy for epidural spinal cord compression, 45 (33.6%) cases. Median follow-up after stereotactic body radiotherapy was 9 months. The 1-year local control rate was 72.3%. Seventy (79.5%) of the 88 cases with pain from spinal metastases achieved pain response. The 1-year pain progression-free rate was 61.7%. Regarding metastases from colorectal cancer, local and pain control rates at 1 year were significantly lower compared with other cancer types (local control rate, 34.1% vs 81.8%; P < .01; pain progression-free rate, 36.9% vs 69.9%; P = .02). On multivariate analysis, colorectal cancer metastases and radiation history were identified as independent predictors of lower local and pain control rates. Radiation-induced myelopathy, radiculopathy, and vertebral compression fractures were observed in 0, 2 (1.5%), and 16 (11.9%) cases, respectively. Conclusions: This study showed that spine stereotactic body radiotherapy achieved good local and pain control, with a clinically acceptable safety profile. However, stereotactic body radiotherapy may be less effective against spinal metastases from colorectal cancer.

SU‐E‐T‐465: Assessment of the Effect of Respiration Motion and Setup Error during Whole Breast Irradiation : Comparison of Standard Physical Wedges, Electric Compensation, and Field in Field Technique

Purpose: We studied the dosimetric impact of respiration motion and setup error on tangential whole breast irradiation for the Japanese patient. We compared between three different techniques; standard physical wedges (SW), electric compensator (EC), and field in field technique (FF). Methods: We performed treatment planning for sixteen patients using each technique. To take the respiration motion and setup error into account, we made plans with the isocenters shifted by ±5mm vertically, longitudinally, and laterally. For the vertical direction, we added ±10mm isocenter displacement plan, because respiration movement in the anterior — posterior (AP) direction is the largest. Mean dose, D95, V95, homogeneity index for CTV, V20 for lung, and V105 for body were evaluated for these plans. For AP respiratory motion, we assumed that the isocenter moves as sine function and DVH parameters were averaged over one period. For the daily setup error, we assumed the distribution of isocenter shifts have the Gaussian form, and calculated setup frequency weighted DVH parameters. Results: In all irradiation techniques, AP movement has a significant impact on the dose distribution. The effect of respiration motion and setup error on dose distribution is the largest for EC. Especially CTV V95 decrease by 4.5 % from original plan. But even if these movement effects are considered, target dose coverage using EC (CTV V95:94.8%), or FF (95.3%) is enough in clinically. For lung dose, the moving effect is almost same between these techniques. Conclusions: In this study, EC and FF irradiation techniques is more sensitive for respiration and setup movement than SW. But these deviations from original plan are clinically negligible. Furthermore, EC or FF decreased hotspots dramatically. As a result, we conclude that EC or FF technique is more meaningful than SW in terms of dosimetric impact.

SU-E-T-575: Comparison of Total Scatter Factor for SRS Measured by Various Detectors

Purpose: Total scatter factor is one of the most important parameters in commissioning for stereotactic radiosurgery. We compared total scatter factors which were measured by various detectors. Methods: We attached circular collimators (7.5mm, 10.0mm, 12.5mm, 15.0mm, 17.5mm, 20.0mm, 25.0mm and 30mm diameters at isocenter) for stereotactic radiosurgery (BrainLAB) to Varian Clinac 21EX and irradiated 400MU of 10MV (600MU/min) to the detectors at 3cm depth in the water or water equivalent phantom. Total scatter factor was measured by PinPoint 3D chamber (PTW31016), diode detectors (Edge detector (Sun Nuclear), SFD (iba)) and GAFCHROMIC Film EBT2 (ISP). Data were analyzed using MATLAB (MathWorks). Results: We obtained total scatter factors of 0.74 (Edge detector), 0.71 (SFD), 0.67(EBT2), 0.62 (PinPoint 3D Chamber) in 7.5mm diameter collimator. These scatter factors were normalized by largest collimator (30mm) reading of each detector. For the decision of total scatter factors, we normalized these values by 15mm diameter collimator, and averaged diode detectors and EBT2 less than 15mm. We adopted PinPoint 3D chambers data for 15mm and over. Conclusions: To obtain total scatter factor precisely, we need to take a measurement with various detectors and evaluate the results carefully. As the next step, we are preparing for Monte Carlo simulation to compare with measured data.

SU-E-T-328: Evaluation of Radiation Dosimetry of Bolus Electron Conformal Therapy (ECT)

Purpose: To evaluate the radiationdosimetry of bolus electron conformal therapy (ECT) using new commercially available bolus fabrication software.Methods: A customized electron bolus was designed using 3D planning system (TPS) Eclipse Ver.8.6.15 (Varian) and p.d ECT (.decimal) software.Computed tomography(CT)images of tough water was obtained and the planning target volume (PTV) was assumed. The proximal surface of the bolus was designed to conform to the 90% isodose line to the distal surface of the PTV using p.d ECT. Dose was calculated with a pencil beam algorithm for review with TPS. Based on structure set from TPS, bolus was fabricated using a computer‐controlled milling machine. To evaluate the dose distribution, CTimages with the bolus on the tough water were acquired and final dose distribution was computed. Gafchromic EBT 2 film (Lot A09171002, ISP) were sandwiched between tough water at 1, 2 and 3 cm depth from the bottom of bolus and irradiated at same geometry with planning. Film was scanned by EPSON GTX970 scanner and that 2D dose distribution is compared with calculation. Results: 2D dose distribution showed qualitative agreement between calculation and measurement, absolute dose value is corresponded within 3% in the region of PTV. The pass rates of the gamma test were greater than 90% at 3 cm depth Conclusions: In this study the dose distribution for bolus ECT was measured by EBT 2 film. The 3D electron bolus which is fabricated by p.d ECT software reproduce the accurate dose distribution that is calculated with TPS.

SU‐GG‐T‐228: A New Technique to Measure Orthogonal Dose Distribution in Phantom for IMRT QA with Gafchromic EBT2 Film

Purpose: To demonstrate the feasibility of a new technique for patient specific IMRT QA. Method and Materials: Two prostate plans with the prescription of 76 Gy (23 initial and 15 boost fractions) were used for this study. The dynamic MLC fields planned by Eclipse 6.5 were delivered to QA phantom by Varian Clinac 21EX. To measure the dose distribution on the coronal plane, a film (Gafchromic EBT2, ISP) placed on coronal plane of isocenter in the phantom was exposed by all fields with the planned gantry angles. For sagittal plane measurement, film was still placed on the coronal plane in the phantom and irradiated by all fields with adding 90 degrees to planned gantry angle. It is because the phantom has a 90 degree rotational symmetry shape. The coronal and sagittal dose distributions in the phantom were calculated by Eclipse (AAA 7.5.18) without any modification. The exposed films were scanned by an EPSON V700 scanner. The films were analyzed using the MapCHECK software (Sun Nuclear Corporation), which uses the red channel for film analysis. Dose distributions were analyzed using 3%/3 mm criteria and 10% threshold. The planar dose distributions obtained with the film was normalized to the center of axis which is Farmer chamber dosimetry measurement was made. MapCHECK were used for each filed QA as a reference. Results: The average pass rate of initial and boost plan of case #1 were 98.1 % and 99.7 % by film, 94.2 % and 94.0 % by MapCHECK (MU weighted), for case #2, 95.8 % and 98.7 % by film, 92.0 % and 96.1 % by MapCHECK. Conclusion: These results attest to the usefulness of the new technique for patient specific IMRT QA. We are applying this QA technique to VMAT QA.

SU‐FF‐T‐464: Field in Filed Technique for Total Body Irradiation

Purpose: To evaluate a technique for total body irradiation (TBI) developed and adopted in our institution. Method and Materials: This technique has left and right lateral opposing field. The patient lies on the couch made by Stylofoam with legs semi‐collapsed. The arms are folded and positioned on the chest. Three types of fields are used for this technique, one whole body open field and 2 subfields. One subfield covers from chest to pelvis, and another subfield covers pelvis part. MLCs are only used for the former subfield to cover lung. The source to axis distance (SAD) is set to be 470 cm. The dose rate at the 470 cm SAD of three locations (head, abdomen, and pelvis) had measured directly by Farmer chamber with varying the thickness of solid water in advance. These measurements were performed for the following three reference points in the body, head, abdomen, and pelvis. This procedure enables us to calculate the value of cGy/MU at 470 cm SAD with any depth beforehand. We have implemented this technique to two patients. Both are prescribed 3Gy × 4 fx (BID) = 12 Gy. To evaluate the dose uniformity and to crosscheck the MU number calculated by the above method, Eclipse Ver. 6.5 with AAA 7.5.18 was used to calculate the dose distribution in the patient body. Results: Average dose at the midline was 11.99 ± 0.84 Gy, error shows 1 standard deviation. The MU difference between MU calculation and Eclipse was less than 4 %. Both cases has mean lung dose of 20% less than the prescription. Conclusion: It was found that reliable MU and acceptable dose distribution is able to be achieved without any special TBI devices or techniques, such as compensators on the gantry head or couch movement.