A Novel Technique to Validate Dosimetry for Single-Isocenter Multiple-Target VMAT Stereotactic Radiosurgery

Each year, 170,000 cancer patients in the United States develop brain metastases. Many of them present with multiple small lesions. Historically, Linac-based stereotactic radiosurgery (SRS) was used to treat single solitary brain metastasis with a diameter of less than 3.0 cm, while whole brain radiation therapy (WBRT) was used to treat multiple brain metastases mainly as palliative therapy. Evidence-based practices reveal that WBRT results in poor treatment outcomes, with high local recurrence rates, decreased cognitive function, and even the onset of dementia. Recently, volumetric modulated arc therapy (VMAT) SRS has been tested as an alternative treatment to WBRT. Owing to its inherent complexity and high risk, it is imperative to perform rigorous testing prior to its clinical implementation. In this paper, we present a novel technique for dosimetry validation of VMAT SRS.

Considerations and Experience in the Treatment of Lung Cancer with VMAT SBRT + DIBH in Arms-Down Position

The arms-up position is the most common treatment position adopted for lung cancer patients treated with radiation therapy. However, many elderly or frail patients have shoulder problems and cannot tolerate such an overstretched position for an extended period. Therefore, the arms-down position becomes the only alternative for this group of patients during radiation therapy. Even though the arms-down position is not ideal, it does provide a stable and comfortable patient immobilization position for radiation treatments that require a longer delivery time, such as stereotactic body radiation therapy (SBRT). In this study, we designed a protocol to treat lung cancer patients with VMAT stereotactic body radiation therapy (VMAT SBRT) and deep inspiration breath-hold (DIBH) in the arms-down position. Our initial clinical experience with this protocol indicates that it is reliable for patient immobilization and accurate in delivered dosimetry.

A Systematic Approach to Patient-Specific Quality Assurance for Volumetric Modulated Arc Therapy

We developed the first non-commercial treatment planning system for volumetric modulated arc therapy(VMAT) in the United States. Because VMAT involves multi-parameter modulations, it is imperative to develop a comprehensive, rigorous and yet, practical procedure for routine patient-specific quality assurance(QA). In this paper, we presented our own approach as being currently implemented in our institution.Our patient-specific QA procedure involves multi-levels: pre-treatment QA,on-treatment QA, and posttreatment QA. The pre-treatment QA focuses on dosimetry verification, which is done with the commercial Map CHECK in Map PHAN mounted on an isocentric mounting fixture(IMF). This method is also referred to the fixed-gantry technique,i.e., the beams always remain perpendicular to the detector plane. The on-treatment QA involves in vivo optically stimulated luminescent dosimetry(OSLD).Prior to the treatment, two nano Dot TM OSLD dosimeters are placed on the patient abdomen under 1 cm bolus at the isocenter location. The irradiated dosimeters are then read by a nano Dot TM reader and the average reading of the two is calculated. The post-treatment QA involves the analysis of the Dyna Log and DLog files. The Dyna Log is a treatment log file that contains the planned and actual leaf positions at a given gantry angle. The DLog is a treatment log file that contains the planned segmented treatment table(STT) and the corresponding segment boundary samples, i.e., the actual delivered MU and gantry angle increment at each control point.