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

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.

A new metallic oxide semiconductor field effect transistor detector for use of in vivo dosimetry / 中华放射肿瘤学杂志

To investigate the application of a recently developed metallic oxide semiconductor field effect transistor(MOSFET)detector for use in vivo desimetry.Methods The MOSFET detector was calibrated for X-ray beams of 8 MV and 15 MV,as well as electron beams with energy of 6,8,12 and 18 MeV.The dose linearity of the MOSFET detector was investigated for the doses ranging from 0 up to 50 Gy using 8 MV X-ray beams.Angular effect was evaluated as well in a cylindrical PMMA phantom by changing the beam entrance angle every 15?clockwise.The MOSFET detector was then used for a breast cancer patient in vivo dose measurement, after the treatment plan was verified in a water phantom using a NE-2571 ion chamber,in vivo measurements were performed in the first and last treatment,and once per week during the whole treatment.The measured doses were then compared with planning dose to evaluate the accuracy of each treatment.Results The MOSFET detector represented a good energy response for X-ray beams of 8 MV and 15 MV,and for electron beams with energy of 6 MeV up to 18 MeV.With the 6 V bias,Dose linearity error of the MOSFET detector was within 3.0% up to approximately 50 Gy,which can be significantly reduced to 1% when the detector was calibrated before and after each measdurement.The MOSFET response varied within 1.5% for angles firm 270?to 90?.However,maximum error of 10.0% was recorded comparing MOSFET response between forward and backward direction.In vivo mea surement for a breast cancer patient using 3DCRT showed that,the average dose.deviation between measurement and calculation was 2.8%,and the maximum error was less then 5.0%.Conclusions The new MOSFET detector,with its advantages of being in size,easy use,good energy response and dose linearity,can be used for in vivo dose measurement.