Water-filled balloon in the postoperative resection cavity improves dose distribution to target volumes in radiotherapy of maxillary sinus carcinoma.

Postoperative radiotherapy is a major treatment for patients with maxillary sinus carcinoma. However, the irregular resection cavity poses a technical difficulty for this treatment, causing uneven dose distribution to target volumes. In this study, we evaluated the dose distribution to target volumes and normal tissues in postoperative intensity-modulated radiotherapy (IMRT) after placing a water-filled balloon into the resection cavity. Three postoperative patients with advanced maxillary sinus carcinoma were selected in this trial. Water-filled balloons and supporting dental stents were fabricated according to the size of the maxillary resection cavity. Simulation CT scans were performed with or without water-filled balloons, IMRT treatment plans were established, and dose distribution to target volumes and organs at risk were evaluated. Compared to those in the treatment plan without balloons, the dose (D98) delivered to 98% of the gross tumor volume (GTV) increased by 2.1 Gy (P = 0.009), homogeneity index (HI) improved by 2.3% (P = 0.001), and target volume conformity index (TCI) of 68 Gy increased by 18.5% (P = 0.011) in the plan with balloons. Dosimetry endpoints of normal tissues around target regions in both plans were not significantly different (P > 0.05) except for the optic chiasm. In the plan without balloons, 68 Gy high-dose regions did not entirely cover target volumes in the ethmoid sinus, posteromedial wall of the maxillary sinus, or surgical margin of the hard palate. In contrast, 68 Gy high-dose regions entirely covered the GTV in the plan with balloons. These results suggest that placing a water-filled balloon in the resection cavity for postoperative IMRT of maxillary sinus carcinoma can reduce low-dose regions and markedly and simultaneously increase dose homogeneity and conformity of target volumes.

Retrospective dosimetry study of intensity-modulated radiation therapy for nasopharyngeal carcinoma: measurement-guided dose reconstruction and analysis.

BACKGROUND: Conventional phantom-based planar dosimetry (2D-PBD) quality assurance (QA) using gamma pass rate (GP (%)) is inadequate to reflect clinically relevant dose error in intensity-modulated radiation therapy (IMRT), owing to a lack of information regarding patient anatomy and volumetric dose distribution. This study aimed to evaluate the dose distribution accuracy of IMRT delivery for nasopharyngeal carcinoma (NPC), which passed the 2D-PBD verification, using a measurement-guided 3D dose reconstruction (3D-MGR) method. METHODS: Radiation treatment plans of 30 NPC cases and their pre-treatment 2D-PBD data were analyzed. 3D dose distribution was reconstructed on patient computed tomography (CT) images using the 3DVH software and compared to the treatment plans. Global and organ-specific dose GP (%), and dose-volume histogram (DVH) deviation of each structure was evaluated. Interdependency between GP (%) and the deviation of the volumetric dose was studied through correlation analysis. RESULTS: The 3D-MGR achieved global GP (%) similar to conventional 2D-PBD in the same criteria. However, structure-specific GP (%) significantly decreased under stricter criteria, including the planning target volume (PTV). The average deviation of all inspected dose volumes (DV) and volumetric dose (VD) parameters ranged from - 2.93% to 1.17%, with the largest negative deviation in V100% of the PTVnx of - 15.66% and positive deviation in D1cc of the spinal cord of 6.66%. There was no significant correlation between global GP (%) of 2D-PBD or 3D-MGR and the deviation of the most volumetric dosimetry parameters (DV or VD), when the Pearson's coefficient value of 0.8 was used for correlation evaluation. CONCLUSION: Even upon passing the pre-treatment phantom based dosimetric QA, there could still be risk of dose error like under-dose in PTVnx and overdose in critical structures. Measurement-guided 3D volumetric dosimetry QA is recommended as the more clinically efficient verification for the complicated NPC IMRT.

Correction to: Retrospective dosimetry study of intensity-modulated radiation therapy for nasopharyngeal carcinoma: measurement-guided dose reconstruction and analysis.

The original version of this article [1] unfortunately contained a mistake.

Incidence and dosimetric parameters for brainstem necrosis following intensity modulated radiation therapy in nasopharyngeal carcinoma.

OBJECTIVES: To clarify the incidence of brainstem toxicity and perform a dose-volume analysis for the brainstem after long-term follow-up of a large cohort of nasopharyngeal carcinoma (NPC) patients who underwent intensity-modulated radiation therapy (IMRT). MATERIALS AND METHODS: All patients with NPC treated with IMRT at Sun Yat-sen University Cancer Center between April 2009 and March 2012 were retrospectively reviewed. A total of 1544 patients with follow-up >12months and detailed treatment plan data were included. Radiotherapy was administered using the simultaneous integrated boost technique in 2.0-2.48Gy per fractions/28-33 fractions. Brainstem necrosis was defined as lesions with high signal intensity on T2-weighted images and low signal intensity on T1-weighted images, with or without enhancement after administration of contrast in follow-up MRI. RESULTS: After median follow-up of 79.7months (range, 12.2-85.6months), 2/1544 (0.13%) patients developed brainstem necrosis after intervals of 12.3 and 18.5months. Actuarial incidence of brainstem necrosis was 0.07%, 0.13%, 0.13% and 0.13% after 1, 2, 3 and 5years, respectively. Overall, 384 (24.9%), 153 (9.9%), 67 (4.3%), 39 (2.5%), 78 (5.1%), and 114 (7.4%) patients had excessive doses of Dmax≥64Gy, D1cc>59Gy, D2cc>59Gy, aV50>5.9cc, aV55>2.7cc and aV60>0.9cc respectively, of whom only two developed brainstem necrosis. CONCLUSIONS: Brainstem necrosis is rare in NPC. The definitive criteria based on conventional radiotherapy cannot accurately predict the occurrence of brainstem necrosis after IMRT, thus more flexible definitive criteria with strict restrictions need to be defined.

[Quality control for multileaf collimator leaf position accuracy using amorphous silicon electronic portal imaging devices].

BACKGROUND AND OBJECTIVE: The multi-leaf collimator (MLC) leaf position deviation of the linear accelerator (LINAC) can result in dose distribution errors during intensity modulated radiotherapy (IMRT), which would cause treatment failure and serious injury to the patients. This study was to develop a simple method to control the MLC leaf position accuracy. METHODS: Elekta LINAC, Elekta iView aSi electronic portal imaging devices (EPIDs) and an 8MV photon beam were used. A digital image designed by a treatment planning system (TPS) was acquired using the EPIDs and was analyzed to compute the MLC leaf position coordinates. The position error was thus obtained by comparing the coordinates in the image with those in the TPS DicomRT file, which was used to quickly adjust the MLC leaf position. RESULT: The leaf deviation of leaf position accuracy was kept less than 1 mm. CONCLUSION: Quality control for MLC leaf position accuracy using EPIDs is simple and adequate.

[Impact of changing gross tumor volume delineation of intensity-modulated radiotherapy on the dose distribution and clinical treatment outcome after induction chemotherapy for the primary locoregionally advanced nasopharyngeal carcinoma].

BACKGROUND AND OBJECTIVE: The gross tumor volume (GTV) obviously reduces after induction chemotherapy (IC) for primary locoregionally advanced nasopharyngeal carcinoma (NPC). This study was to investigate the impact of changing gross tumor volume delineation on the dose distribution and clinical treatment outcome after IC. METHODS: From January 2008 to April 2009, 24 patients with Stage III-IVb primary locoregionally advanced NPC were treated with TPF regimen IC followed by intensity-modulated radiotherapy (IMRT) with concurrent chemotherapy . The primary GTVs were delineated into two parts: the post-IC primary GTV (GTVpost-IC-NP), and the region of pre-IC primary GTV minus GTVpost-IC-NP (GTVpre-post-IC-NP). The dose distributions of two plans with GTVpost-IC-NP or pre-IC primary GTV were assessed by analyzing ten cases. The clinical treatment outcome and toxicity of all patients were observed. RESULTS: The post-IC GTV was significantly smaller than the pre-IC GTV (primary GTV 25.5 cm3 vs. 51.1 cm(3),P=0.001; lymph nodes GTV 9.1 cm(3) vs. 31.4 cm(3), P=0.035; primary + lymph nodes GTV 33.2 cm(3) vs. 82.6 cm(3),P=0.004), the overall GTV with an average shrinkage of 61%. The high dose region was also smaller after IC (volumes covered by 64.4 Gy were 422.9 cm3 vs. 457.9 cm3, P=0.003; 274.2 cm(3) vs.334.5 cm(3) by 68 Gy, P=0.041). The complete response rate was 38% after IC, and 100% three month after radiotherapy. The toxicity of following IMRT with concurrent chemotherapy was similar to that of IMRT with concurrent chemotherapy alone. With median follow-up of 9 months, the locoregionally control rate was 100% and only one patient presented metastasis 15 months after treatment. CONCLUSIONS: TPF regimen IC could significantly reduce tumor volume. The following IMRT with GTVpost-IC-NP plan reduced the high dose region, which didn't add toxicity while had excellent short-term treatment outcome.

[Application of amorphous silicon electronic portal imaging device (a-Si EPID) to dosimetry quality assurance of radiation therapy].

BACKGROUND & OBJECTIVE: Due to its good dosimetric properties, amorphous silicon electronic portal imaging device (a-Si EPID), as a rapid two-dimensional dosimetric measurement device, presents an attractive prospect in routine quality assurance (QA) test, dosimetric verification of intensity-modulated radiotherapy treatment (IMRT) and in vivo dose monitoring. This study was to explore the application of a-Si EPID as a detector for dosimetric QA of linear accelerator radiotherapy, and setup the calibration module. METHODS: The imaging calibration procedure of conventional a-Si EPID was modified for dosimetric measurement by acquiring the traditional "flush field" from integrated subfields to correct the dosimetric responding difference in pixel sensitivity. The energy dependence of the a-Si EPID detectors was analyzed through off-axis dose response curves. Calibrated dose profile obtained with a-Si EPID was compared with the measuring results of ion chamber in a 3-D water phantom. RESULTS: The calibrated dose profiles measured with a-Si EPID showed a deviation within 2% in high dose regions, but dropped much steeply in the penumbra region, as compared with that scanned using ion chamber in water. CONCLUSION: With the modeling management set up in this research, a-Si EPID can be applied for dosimetric QA of linear accelerator in radiotherapy.