Feasibility of optimizing the dose distribution in lung tumors using fluorine-18-fluorodeoxyglucose positron emission tomography and single photon emission computed tomography guided dose prescriptions.

The information provided by functional images may be used to guide radiotherapy planning by identifying regions that require higher radiation dose. In this work we investigate the dosimetric feasibility of delivering dose to lung tumors in proportion to the fluorine-18-fluorodeoxyglucose activity distribution from positron emission tomography (FDG-PET). The rationale for delivering dose in proportion to the tumor FDG-PET activity distribution is based on studies showing that FDG uptake is correlated to tumor cell proliferation rate, which is shown to imply that this dose delivery strategy is theoretically capable of providing the same duration of local control at all voxels in tumor. Target dose delivery was constrained by single photon emission computed tomography (SPECT) maps of normal lung perfusion, which restricted irradiation of highly perfused lung and imposed dose-function constraints. Dose-volume constraints were imposed on all other critical structures. All dose-volume/function constraints were considered to be soft, i.e., critical structure doses corresponding to volume/function constraint levels were minimized while satisfying the target prescription, thus permitting critical structure doses to minimally exceed dose constraint levels. An intensity modulation optimization methodology was developed to deliver this radiation, and applied to two lung cancer patients. Dosimetric feasibility was assessed by comparing spatially normalized dose-volume histograms from the nonuniform dose prescription (FDG-PET proportional) to those from a uniform dose prescription with equivalent tumor integral dose. In both patients, the optimization was capable of delivering the nonuniform target prescription with the same ease as the uniform target prescription, despite SPECT restrictions that effectively diverted dose from high to low perfused normal lung. In one patient, both prescriptions incurred similar critical structure dosages, below dose-volume/function limits. However, in the other patient, critical structure dosage from the nonuniform dose prescription exceeded dose-volume/function limits, and greatly exceeded that from the uniform dose prescription. Strict compliance to dose-volume/ function limits would entail reducing dose proportionality to the FDG-PET activity distribution, thereby theoretically reducing the duration of local control. Thus, even though it appears feasible to tailor lung tumor dose to the FDG-PET activity distribution, despite SPECT restrictions, strict adherence to dose-volume/function limits could compromise the effectiveness of functional image guided radiotherapy.

Acute and late morbidity of using a breast positioning ring in women with large/pendulous breasts.

PURPOSE: To assess acute and late effects of radiation therapy in women with breast cancer treated with a breast positioning ring. MATERIALS AND METHODS: Fifty-six patients with large and/or pendulous breasts were irradiated using a breast positioning ring. The incidence of acute morbidity was correlated with patient weight and breast 'size'. Cosmesis was scored at > or = 1 year following radiation therapy by the patients. Dose changes in the buildup region under the ring were measured using a computer-controlled scanning system. RESULTS: Moist desquamation (MD) occurred in 60.7% (34/56) of patients treated with the breast ring. The incidence of MD was more common in patients with larger breasts (P = 0.08), the severity necessitating a treatment interruption in 5 out of 56 (9%) patients. Cosmesis at > or = 1 year following radiation therapy was scored as > or = good by all patients. The surface dose under the ring was approximately 85% of the Dmax dose. CONCLUSIONS: The incidence or severity of acute MD in patients treated with a breast positioning ring appears high in patients with large pendulous breasts, and might be related in part, to the increased skin dose due to the positioning ring. To date, there appears to be no significant late normal tissue effects in patients treated with the positioning ring. Additional follow up is needed to assess the long-term consequences of the ring on cosmesis.

Advances in prevention of radiation damage to visceral and solid organs in patients requiring radiation therapy of the trunk.

BACKGROUND: As a part of multimodality therapy, many patients with tumors of the trunk receive radiation therapy. The major morbidity of this therapy is often secondary to incidental radiation damage to tissues adjacent to treatment areas. METHODS: We detail our use of saline breast implants placed in polyglycolic acid mesh sheets to displace visceral and solid organs away from the radiation field. RESULTS: Analysis of CT scans and dose volume histograms reveal that this technique successfully displaces uninvolved organs away from the radiation fields, thereby minimizing the radiation dose to such organs and tissues. CONCLUSION: We believe this is a safe and efficacious method to prevent radiation damage to visceral and solid organs adjacent to trunk tumor sites.