Feasibility of Estimating Patient-Specific Dose Verification Results Directly from Linear Accelerator Log Files in Volumetric Modulated Arc Therapy

The feasibility of estimating patient-specific dose verification results directly from linear accelerator (linac) log files has been investigated for prostate cancer patients who undergo volumetric modulated arc therapy (VMAT). Twenty-six patients who underwent VMAT in our facility were consecutively selected. VMAT plans were created using Monaco treatment planning system and were transferred to an Elekta linac. During the beam delivery, dynamic machine parameters such as positions of the multi-leaf collimator and the gantry were recorded in the log files;subsequently, root mean square (rms) values of control errors, speeds and accelerations of the above machine parameters were calculated for each delivery. Dose verification was performed for all the plans using a cylindrical phantom with diodes placed in a spiral array. The gamma index pass rates were evaluated under 3%/3 mm and 2%/2 mm criteria with a dose threshold of 10%. Subsequently, the correlation coefficients between the gamma index pass rates and each of the above rms values were calculated. Under the 2%/2 mm criteria, significant negative correlations were found between the gamma index pass rates and the rms gantry angle errors (r = 0.64, p < 0.001) as well as the pass rates and the rms gantry accelerations (r = 0.68, p < 0.001). On the other hand, the rms values of the other dynamic machine parameters did not significantly correlate with the gamma index pass rates. We suggest that the VMAT quality assurance (QA) results can be directly estimated from the log file thereby providing potential to simplify patient-specific prostate VMAT QA procedure.

Usability of Deformable Image Registration for Adaptive Radiotherapy in Head and Neck Cancer and an Automatic Prediction of Replanning

Deformable image registration (DIR) has been an important component in adaptive radiotherapy (ART). Our goal was to examine the accuracy of ART using the dice similarity coefficient (DSC) and to determine the optimal timing of replanning. A total of 22 patients who underwent volume modulated arc therapy (VMAT) for head and neck (H&N) cancers were prospectively analyzed. The planning target volume (PTV) was to receive a total of 70 Gy in 33 fractions. A second planning CT scan (rescan) was performed at the 15th fraction. The DSC was calculated for each structure on both CT scans. The continuous variables to predict the need for replanning were assessed. The optimal cut-off value was determined using receiver operating characteristic (ROC) curve analysis. In the correlation between body weight loss and DSC of each structure, weight loss correlated negatively with DSC of the whole face (rs = -0.45) and the face surface (rs = -0.51). Patients who required replanning tended to have experienced rapid weight loss. The threshold DSC was 0.98 and 0.60 in the whole face and the face surface, respectively. Patients who showed low DSC in the whole face and the face surface required replanning at a significantly high rate (P < 0.05 and P < 0.01). Weight loss correlated with DSC in both the whole face and the face surface (P < 0.05 and P < 0.05). The DSC values in the face predicted the need for replanning. In addition, weight loss tended to correlate with DSC. DIR during ART was found to be a useful tool for replanning.

DICOM-RT Plan Complexity Verification for Volumetric Modulated Arc Therapy

The purpose of this study was to investigate the relationship between plan parameters verified with DICOM-RT and dosimetric results for volumetric modulated arc therapy (VMAT). We investigated three treatment locations: prostate cancer (ten cases), maxillary sinus cancer (four cases), and malignant pleura mesothelioma (four cases) with treatment plans generated by a MonacoTM treatment planning system (TPS), and delivered with an Elekta SynergyTM linear accelerator. We calculated plan parameters, including gantry and multileaf collimator (MLC) positions, Monitor Units (MU), and millimeters of MLC motion per degree of gantry rotation (mm/degree), and performed quality assurance (QA) with a DICOM-RT plan verification system. We measured the VMAT dose with a two-dimensional diode array detector. The average gamma passing rate with percent dose acceptance criteria and distance to agreement criteria of 2 mm and 2% (2 mm/2%) were 97.4%, 97.8% and 92.0% for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The mean 95th percentile value for DICOM-calculated mm/degree was 4.0, 5.2, and 11.1 for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The gamma passing rate showed a correlation with calculated mm/degree, with a coefficient of determination (R2) of 0.60. Higher calculated mm/degree values led to increased dosimetric errors. We conclude that dose distribution calculated by a TPS is more reliable at smaller mm/degree.

Predicting Delivery Error Using a DICOM-RT Plan for Volumetric Modulated Arc Therapy

The purpose of this study was to investigate the prediction of mechanical error using DICOM-RT plan parameters for volumetric modulated arc therapy (VMAT). We created plans for gantry rotation arcs of 360° and 180° (full-arc and half-arc VMAT) for six maxillary sinus cancer cases using a Monaco treatment planning system, and delivered the doses with a linear accelerator. We calculated DICOM-RT plan parameters, including gantry, multileaf collimator (MLC) positions and Monitor Units (MU). We compared plans with regard to gantry angle per MU (degrees/MU) and MLC travel per MU (mm/MU) for each segment. Calculated gantry angle/MLC position speeds and errors were evaluated by comparison with the log file. On average, the half-arc VMAT plan resulted in 47% and 35% fewer degrees/MU and mm/MU than the full-arc VMAT plan, respectively. The root mean square (r.m.s.) gantry and MLC speeds showed a linear relationship with calculated degrees/MU and mm/MU, with coefficients of determination (R2) of 0.86 and 0.72, respectively. The r.m.s. gantry angle and MLC position errors showed a linear relationship with calculated degrees/MU and mm/MU with R2 of 0.63 and 0.76, respectively. Deviations from plan parameters were related to mechanical error for VMAT, and provided quantitative information without the need for VMAT delivery. These parameters can be used in the selection of treatment planning.

Impact of preoperative chemoradiotherapy using concurrent S-1 and CPT-11 on long-term clinical outcomes in locally advanced rectal cancer

BACKGROUND Preoperative chemoradiotherapy regimens using a second drug for locally advanced rectal cancer are still under clinical investigation.AIM To investigate the clinical outcomes of patients with locally advanced rectal cancer treated with preoperative chemoradiotherapy using tegafur/gimeracil/oteracil(S-1)plus irinotecan(CPT-11).METHODS This was a single-center retrospective study of 82 patients who underwent radical surgery for rectal cancer after chemoradiotherapy with S-1(80 mg/m2/d),CPT-11(60 mg/m2/d),and radiation(total 45 Gy)between 2009 and 2016.The median follow-up was 51 mo(range:17–116 mo).RESULTS Twenty-nine patients(35.4%)had T3 or T4 rectal cancer with mesorectal fascia invasion,36(43.9%)had extramural vascular invasion,24(29.8%)had N2 rectal cancer and eight(9.8%)had lateral lymph node swelling.The relative dose intensity was 90.1%for S-1 and 92.9%for CPT-11.Seventy-nine patients(96.3%)underwent R0 resection.With regard to pathological response,13 patients(15.9%)had a pathological complete response and 52(63.4%)a good response(tumor regression grade 2/3).The 5-year local recurrence-free survival,relapsefree survival and overall survival rates were 90.1%,72.5%and 91.3%,respectively.We analyzed the risk factors for local recurrence-free survival by Cox regression analysis and none were detected.Previously described risk factors such as T4 stage,mesorectal fascia invasion or lateral lymph node swelling were not detected as negative factors for local recurrence-free survival.CONCLUSION We demonstrated good compliance and favorable tumor regression in patients with locally advanced rectal cancer treated with preoperative S-1 and CPT-11.

Histopathological Evidence for Irradiation Angiopathy in Head and Neck Cancer

Objective: To evaluate the incidence of cervical angiopathy caused by radiation therapy for head and neck cancer. Methods: Segments of 57 cervical arteries were obtained during surgery for head and neck malignant tumors and divided into two groups (irradiated group and non-irradiated group) based on the treatment prior to vascular resection. In order to evaluate vascular injury after radiation therapy, we examined the degree of medial atrophy, medial fibrosis, smooth muscle cell (SMC) differentiation in the media and intima, intimal hyperplasia and endothelial cell (EC) injury. Sections of arterial segments were stained with hematoxylin-eosin, Elastica van Gieson and Masson’s trichrome, and immunohistochemistry for α-smooth muscle actin (α-SMA), smoothelin, S100A4 and CD31 in the resected vessels was conducted. Results: The median interval between the completion of radiation therapy and vascular resection was nine months. No significant differences were observed between the two groups in terms of medial atrophy, medial fibrosis and intimal hyperplasia. The ratio of the smoothelin-positive area per α-SMA-positive area in the media and the S100A4-positive proportion in the intima, indicating the degree of differentiation of the medial SMC and dedifferentiation of the intimal SMC, respectively, showed no significant differences, despite the tendency toward a lower smoothelin-positive area per α-SMA-positive area in the media of the irradiated arteries. The EC coverage revealed on CD31 immunohistochemistry was significantly decreased, with mural thrombus adhesion, in the irradiated group. Conclusions: The ECs of small arteries are damaged by irradiation. Although we did not confirm the statistical significance of medial SMC dedifferentiation, a decreased expression of smoothelin tended to be observed in the media of the irradiated arteries. Our findings provide histopathological evidence of irradiation angiopathy in head and neck cancer and may help to improve the surgical safety of microvascular anastomosis and determine the treatment strategy for head and neck tumors.

PERCIST用于头颈部鳞状细胞癌患者放化疗疗效评价及预后预测

目的探讨PET实体瘤疗效评价标准(PERCIST)评价头颈部鳞状细胞癌(HNSCC)患者放化疗疗效及预测复发和死亡的价值。方法42例患者(平均年龄63岁,范围20~79岁)在放化疗前及放化疗后约3个月(平均95d,范围70~119d)行脱氧葡萄糖(FDG)-PET/CT显像,其中包括10例鼻咽癌、13例口咽癌、11例下咽癌及8例喉癌。与PERCIST相关的无进展生存时间(PFS)和总生存时间(OS)采用对数秩检验和Cox回归分析进行统计学处理。结果PERCIST确定的完全代谢反应(CMR,即病灶FDG摄取降低至肝脏的平均活度水平以下或病灶FDG摄取与周围组织无明显差别)、部分代谢反应[PMR,即经去脂体质量校正的高峰标准摄取值(SULpeak)下降30%及以上]、稳定代谢反应(SMD,即FDG摄取无明显变化)和病灶代谢增加(PMD,即SULpeak增加30%及以上)的患者数分别为30例(71.4%)、9例(21.4%)、3例(7.1%)和0例。