[en] Intensity-modulated radiation therapy (IMRT) is commonly delivered using the dynamic or segmental mode of multileaf collimators (DMLC or SMLC). Both methods are designed to deliver intensity-modulated beams as determined by inverse planning software. In this study, we have used the Helios IMRT planning system to generate ideal treatment plans for 10 cases of 2 common treatment sites (prostate and head and neck) and have investigated the actual treatment fluence distributions generated for each of the MLC leaf motion choices. The 2 dose delivery techniques were dosimetrically compared to each other and to the treatment plans. For each technique, point doses were measured in a water phantom using ionization chambers. Also for each technique, 2-dimensional dose distributions at a selected depth in a plastic phantom were obtained, using extended range film. The total delivery time and the number of monitor units (MU) delivered by each method were also compared. Our results indicate that the 2 delivery methods produce comparable results dosimetrically. For the cases reviewed, the delivery time was an average of 15% longer for SMLC deliveries, while the number of MUs (beam-on time) required by SMLC was an average of 15% fewer, than that for the DMLC. In the interest of simplicity, lower beam-on time, and potentially fewer mechanically-related problems, we think that the SMLC delivery technique may be the better choice when Helios is used for planning and Varian linear accelerators are used for delivery

[en] 

Objective

To investigate whether a 18F-FDG PET/CT (PET/CT)-based diagnostic strategy adds decisive new information compared to conventional imaging in the evaluation of salivary gland tumours and the detection of cervical lymph node metastases, distant metastases, and synchronous cancer in patients with salivary gland carcinoma.

Methods

The study was a blinded prospective cohort study. Data were collected consecutively through almost 3 years. All patients underwent conventional imaging—magnetic resonance imaging (MRI) and chest X-ray (CXR)—in addition to PET/CT prior to surgery. Final diagnosis was obtained by histopathology. MRI/CXR and PET/CT were interpreted separately by experienced radiologists and nuclear medicine physicians. Interpretation included evaluation of tumour site, cervical lymph node metastases, distant metastases, and synchronous cancer.

Results

Ninety-one patients were included in the study. Thirty-three patients had primary salivary gland carcinoma and eight had cervical lymph node metastases. With PET/CT, the sensitivity was 92% and specificity 29% regarding tumour site. With MRI/CXR, the sensitivity and specificity were 90% and 26%, respectively. Regarding cervical lymph node metastases in patients with salivary gland carcinoma, the sensitivity with PET/CT was 100% and with MRI/CXR 50%. PET/CT diagnosed distant metastases in five patients, while MRI/CXR detected these in two patients. Finally, PET/CT diagnosed two synchronous cancers, whereas MRI/CXR did not detect any synchronous cancers.

Conclusions

Compared with MRI/CXR PET/CT did not improve discrimination of benign from malignant salivary gland lesions. However, PET/CT may be advantageous in primary staging and in the detection of distant metastases and synchronous cancers.