Using max standardized uptake value from positron emission tomography to assess tumor responses after lung stereotactic body radiotherapy for different prescriptions.

PURPOSE: To retrospectively investigate tumor responses of lung SBRT patients for different prescriptions. To analyze the relation between optimal biologically equivalent dose (BED) and tumor responses. METHODS AND MATERIALS: Tumor responses after lung SBRT were compared by examining 48 treatments used four prescriptions. This study used simplified tumor response criteria: (a) Complete Response (CR) - post max SUV (SUVpost ) after SBRT in the treated tumor region was almost the same as the SUVs in the surrounding regions; (b) Partial Response (PR) - SUVpost was smaller than previous max SUV (SUVpre ), but was greater than the SUVs in the surrounding regions; (c) No Response (NR) - SUVpost was the same as or greater than SUVpre . Some SUVpost reported as mild or favorable responses were classified as CR/PR. BED calculated using α/ß of 10 Gy were analyzed with assessments of tumor responses for SBRT prescriptions. RESULTS: For the prescriptions (9 Gy × 5, 10 Gy × 5, 11 Gy × 5, and 12 Gy × 4) historically recommended by RTOG, we observed that higher BED10 and lower tumor volume would achieve a higher complete response rate. The highest complete response rate was observed for smallest tumor volume (PTVave  = 6.8 cc) with higher BED10 (105.6) of 12 Gy × 4 prescription. For 11 Gy × 5 prescription, the BED10 (115.5) was the highest, but its complete response rate (58%) was lower than 79% of 12 Gy × 4 prescription. We observed the PTVave of 11 Gy × 5 prescription was more than double of the PTVave of 12 Gy × 4 prescription. For the same lung SBRT prescription (BED10  > 100) earlier staging tumor had more favorable local control. CONCLUSION: We demonstrated post max SUV read from PET/CT could efficiently and accurately assess tumor response after lung SBRT. Although SBRT with prescriptions resulting in a BED10  > 100 experienced favorable tumor responses for early staging cancer, escalation of BED10 to higher levels would be beneficial for lung cancer patients with later staging and larger volume tumors.

Dosimetric comparison between 3DCRT and IMRT using different multileaf collimators in the treatment of brain tumors.

We investigated the differences between 3-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT), and the impact of collimator leaf-width on IMRT plans for the treatment of nonspherical brain tumors. Eight patients treated by 3DCRT with Novalis were selected. We developed 3 IMRT plans with different multileaf collimators (Novalis m3, Varian MLC-120, and Varian MLC-80) with the same treatment margins, number of beams, and gantry positions as in the 3DCRT treatment plans. Treatment planning utilized the BrainLAB treatment planning system. For each patient, the dose constraints and optimization parameters remained identical for all plans. The heterogeneity index, the percentage target coverage, critical structures, and normal tissue volumes receiving 50% of the prescription dose were calculated to compare the dosimetric difference. Equivalent uniform dose (EUD) and tumor control probability (TCP) were also introduced to evaluate the radiobiological effect for different plans. We found that IMRT significantly improved the target dose homogeneity compared to the 3DCRT. However, IMRT showed the same radiobiological effect as 3DCRT. For the brain tumors adjacent to (or partially overlapping with) critical structures, IMRT dramatically spared the volume of the critical structures to be irradiated. In IMRT plans, the smaller collimator leaf width could reduce the volume of critical structures irradiated to the 50% level for those partially overlapping with the brain tumors. For relatively large and spherical brain tumors, the smaller collimator leaf widths give no significant benefit.

A review of intensity-modulated radiation therapy.

Intensity-modulated radiation therapy (IMRT) is a sophisticated form of three-dimensional treatment planning and delivery. In some situations, IMRT allows more conformal radiation therapy to complex targets within the lung. As problems related to organ motion are increasingly addressed, the use of IMRT in the treatment of lung cancer, particularly in non-small cell lung cancer and mesothelioma, continues to rise.

Visual sensations during megavoltage radiotherapy to the orbit attributable to Cherenkov radiation.

During megavoltage photon and electron beam radiotherapy treatment involving the eye, patients commonly report visual sensations; "nerve stimulation" is the conventional explanation. We propose that the phenomenon can be attributed to Cherenkov radiation inside the eye. The threshold electron energy for Cherenkov radiation in water is 260 keV. The human retina is able to perceive approximately 5-14 visible photons in 0.001 s. A single 500 keV electron traversing 1 mm of water will induce nearly 15 Cherenkov visible range photons. We propose that a portal image involving the eye will produce sufficient Cherenkov radiation to be detected by the retina.

The dosimetric effect of inhomogeneity correction in dynamic conformal arc stereotactic body radiation therapy for lung tumors.

For patients treated with lung stereotactic body radiation therapy (SBRT) using dynamic conformal arcs, the influence of inhomogeneity correction (IC) on normal tissue and tumor dosimetry was studied. For the same numbers of monitor units, the planning target volume equivalent uniform doses calculated without path-length IC were lower than those calculated with IC (mean difference 18%, range 1-34%; p < 0.0001). Normal lung dose differences were of the same magnitude in opposite direction. In reports of SBRT, it will be helpful to maintain clear communication about the type of IC used to avoid future uncertainties about true normal tissue tolerance and tumor dose-response relationships.

New radiation therapy techniques for the treatment of head and neck cancer.

This article reviews the most recent technology used in the treatment of head and neck cancer. It discusses brachytherapy, new ways to mix radionuclides for enhanced radiobiologic effects, and different fractionation schemes that have grown in clinical importance. Intensity-modulated radiotherapy has become a mainstay in head and neck cancer treatment, and the authors discuss several popular and emerging approaches. Patient immobilization and imaging are also discussed.

Dose correlation for thoracic motion in radiation therapy of breast cancer.

This work investigates the dose correlation for deformed objects due to thoracic motion for radiotherapy treatment of breast cancer. An analytical model has been developed to reconstruct patient anatomy based on the assumption that the body will expand or compress proportionally during respiration. The patient geometry at any phase during a breathing pattern is reconstructed using the CT data taken at the inspiration and expiration phases and the breathing level which can be related to the measured chest wall motion. A correlation between the voxels in the inspiration (or expiration) geometry and the voxels in the reconstructed geometry at any phase of the breathing pattern is established so that the dose can be accumulated during a treatment. The method has been implemented for treatment planning dose calculation by interfacing with a Monte Carlo code. The patient geometry files for different phases of the breathing pattern are generated and the three-dimensional dose data are obtained from the Monte Carlo simulations. The final dose distribution is reconstructed from the dose data at different breathing phases based on patient's breathing pattern associated with chest wall movements.