Influence of the SURLAS applicator on radiation dose distributions during simultaneous thermoradiotherapy with helical tomotherapy

• Published in: Physics in medicine & biology Vol. 53; no. 10; pp. 2509 - 2522
• Main Authors: Novák, Petr, Peñagarícano, José A, Nahirnyak, Volodymyr, Corry, Peter, Moros, Eduardo G
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 21.05.2008
• Subjects: Humans; Hyperthermia, Induced - instrumentation; Hyperthermia, Induced - methods; Metals; Phantoms, Imaging; Radiation Dosage; Radiotherapy - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Reproducibility of Results; Sensitivity and Specificity; Time Factors; Tomography, X-Ray Computed; Ultrasonic Therapy - instrumentation; Ultrasonic Therapy - methods
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/53/10/004

Simultaneous thermoradiotherapy has been shown to maximize the effect of hyperthermia as a radiation sensitizer in cancer treatment. Here we follow our previous work on feasibility of thermoradiotherapy with the scanning ultrasound reflector linear array system (SURLAS) and TomoTherapy HiArt treatment system, and investigate the influence of the SURLAS hyperthermia applicator on delivered radiation dose with the TomoTherapy. A radiation treatment plan was calculated and the treatment was delivered to a phantom with SURLAS on top simulating the likely clinical setup. Proper positioning of the SURLAS was assisted with a magnetic position-and-orientation tracking device (POTD) and was verified with megavoltage-computed tomography. The delivered dose was measured with an ionization chamber (point measurement) and a radiographic film (2D dose distributions). The planned and delivered point dose data agreed within 0.61% +/- 0.63%. Planar dose data agreed within a dose difference of < or =3% of the maximum dose, and a distance-to-dose-agreement of < or =1 mm. The susceptibility of the delivered radiation dose on correct SURLAS positioning was studied as well. The largest dose discrepancy was measured for a position for which a maximum number of radiation beams intersected the incorrectly positioned SURLAS within one TomoTherapy gantry rotation. The point dose disagreed by 6.14% +/- 0.52%, and 2.25% of pixels of the 2D dose distribution did not pass the 3% dose difference/1 mm distance-to-dose-agreement criteria. Our study showed that correct positioning of the SURLAS applicator had an influence on the delivered radiation dose. Delivered and planned dose distributions were in an excellent agreement when SURLAS was positioned according to the treatment plan. Moving the applicator from its planned position was found to cause a modification of delivered dose distributions. A precise and reproducible positioning of the applicator was assured with a POTD.