Dosimetric comparison of three different treatment techniques in extensive scalp lesion irradiation.

BACKGROUND AND PURPOSE: This study compared lateral photon/electron plan (3DCRT), intensity modulated radiation therapy (IMRT) plan, and high dose rate (HDR) brachytherapy plan for total scalp irradiation. MATERIALS AND METHODS: The techniques were planned on a patient with squamous cell carcinoma of the scalp for a prescribed dose of 60 Gy. Conformity indexes and dose volume histograms were used for the comparison. RESULTS: Clinical target volume coverage factors for 3DCRT, IMRT, and HDR were 0.976, 0.998, and 0.967, and Conformation Numbers were 0.532, 0.713, and 0.761, respectively. The dose gradient across the target was 59-136%, 91-129%, and 58-242% for 3DCRT, IMRT, and HDR techniques, respectively. The 3DCRT and IMRT techniques produced low optical structure doses. 3DCRT produced hotspots in the brain, while IMRT produced brain sparing. HDR produced the highest integral doses to the brain and optical structures. CONCLUSIONS: IMRT provided the best target dose homogeneity and coverage, and delivered clinically acceptable doses to normal structures. HDR produced the most conformal plan, but the total dose delivered is limited by doses to the brain and eyes. HDR is a clinically feasible alternative for less extensive lesions, lower prescription doses, and for patients who cannot lie on the treatment table.

Case study of radiation therapy treatment of a patient with a cardiac ventricular assist device.

A patient with a cardiac ventricular assist device (VAD) with computer-controlled driver presented to our department for radiation therapy. The treatment plan was 4500 cGy to the rectum over 25 fractions with 15MV photon beams. All beams avoided the pump and leads. The response to electromagnetic interference (EMI) was evaluated by observing a duplicate driver in the treatment configuration as the patient's fields were delivered to a solid water equivalent phantom. Pretreatment dose assessment included calculations with Pinnacle treatment planning system, AAPM TG36 data analysis, and MOSFET measurements on the surface of the driver during the phantom irradiation. During the first patient treatment, MOSFETs were placed on the pump and leads, approximately 1cm from the left lateral treatment portal. No additional shielding was applied to the VAD. EMI was absent and the VAD operated normally during the pretreatment test and throughout the treatment course. Radiation to the driver was too low to be detected by the MOSFETS. Cumulative dose estimates to the pump were 425 cGy to 0.1cc (DVH), 368 cGy (TG36), and 158.5 cGy (MOSFET). MOSFET readings to the leads were 70.5 cGy. External beam radiation treatment was safely delivered to a VAD dependent patient. The VAD exhibited no adverse response to EMI and doses up to 425 cGy. Our results are based on one case and further study is encouraged.

Technical note: on cerrobend shielding for 18-22 MeV electron beams.

The purpose of this study is to investigate (1) the depth at which the measurement of the block transmission factor should be made, and (2) the level of the transmission of 18 and 22 MeV electron beams through conventional Cerrobend. We measured the block transmission in water phantom as ionization profiles across the beam and as ionization distributions along the central axis of the beam for 18 and 22 MeV electron beams, for cone sizes ranging from 6 x 10 cm2 to 25 x 25 cm2. In our analysis, we separated the bremsstrahlung component produced in the Cerrobend block from the component originating in the head in the transmitted dose under the standard Cerrobend block. The block transmission for both beam energies and cone sizes was maximum on the central axis of the beam at depths between 0.4 and 0.7 cm. For the 18 MeV beam, the maximum transmission was 6.2% for the 6 x 10 cm2 cone, and 7.4% for the 25 x 25 cm2 cone. For the 22 MeV beam, it was 9.5% for the 6 x 10 cm2 cone, and 11.3% for the 25 x 25 cm2 cone. For the 22 MeV beam and 15 x 15 cm2 cone, it takes 2.95 and 1.4 cm of Cerrobend to reduce the maximum block transmission to 5% and 10%, respectively. The maximum dose under a blocked electron beam occurs on the central axis closer to the surface than it does for the open beam, and the block transmission factor should be defined at this shallower depth. To decrease the block transmission factor to the level of 5% on the central axis, electron beams with energy 18 MeV and greater require additional shielding.

Clinical and dosimetric experience with MammoSite-based brachytherapy under the RTOG 0413 protocol.

MammoSite balloon brachytherapy is a relatively new technique for partial breast irradiation. The present paper focuses on the treatment planning, dosimetry, and quality assurance aspects of that treatment, based on the Radiation Therapy Oncology Group 0413 randomized prospective trial (RTOG 0413) protocol. We investigate the usefulness of evaluating implants for treatment appropriateness according to the full set of RTOG criteria as compared with the manufacturer's guidelines. We describe our methods to improve MammoSite balloon implants that would otherwise not comply with the protocol. The initially acquired computed tomography (CT) images are evaluated for tissue conformance, balloon surface-to-skin distance, and balloon symmetry. If the implant fails to meet the foregoing criteria, corrective action such as delay in the CT scan, balloon manipulation, or fluid volume adjustment is taken, and the patient is re-scanned. If the corrective action appears to be successful, three dimensional treatment planning and dose-volume histogram analysis is performed to evaluate the geometric and dosimetric parameters with regard to the RTOG 0413 protocol. The evaluated parameters include, volume ratio of the lumpectomy cavity to the ipsilateral breast, target volume coverage, tissue-balloon conformance, balloon symmetry, minimal balloon surface-to-skin distance, maximum skin dose, and normal breast tissue dose-volume parameters V150 and V200. Among our implants, 21.7% did not initially meet the RTOG 0413 acceptance criteria. Asymmetry and poor conformance values reduce the target volume coverage, and so an implant with moderate conformance and asymmetry can be within the manufacturer's guidelines, but still not meet the RTOG criteria. Our intervention corrected all but one of the implants that failed to meet the criteria. Manipulating the cavity and adjusting the balloon volume may salvage an implant and meet the strict geometric and dosimetric criteria imposed by the RTOG 0413 protocol.