Interplay between organ (breathing) motion and leaf motion has been shown in the literature to have a small dosimetric impact for clinical conditions (over a 30 fraction treatment). However, previous studies did not consider the case of treatment beams made up of many few-monitor-unit (MU) segments, where the segment delivery time (1-2 s) is of the order of the breathing period (3-5 s). In this study we assess if breathing compromises the radiotherapy treatment with IMRT segments of low number of MUs. We assess (i) how delivered dose varies, from patient to patient, with the number of MU per segment, (ii) if this delivered dose is identical to the average dose calculated without motion over the path of the motion, and (iii) the impact of the daily variation of the delivered dose as a function of MU per segment. The organ motion was studied along two orthogonal directions, representing the left-right and cranial-caudal directions of organ movement for a patient setup in the supine position. Breathing motion was modeled as sin(x), sin 4 (x), and sin 6 (x), based on functions used in the literature to represent organ motion. Measurements were performed with an ionization chamber and films. For a systematic study of motion effects, a MATLAB simulation was written to model organ movement and dose delivery. In the case of a single beam made up of one single segment, the dose delivered to point in a moving target over 30 fractions can vary up to 20% and 10% for segments of 10 MU and 20 MU, respectively. This dose error occurs because the tumor spends most of the time near the edges of the radiation beam. In the case of a single beam made of multiple segments with low MU, we observed 2.4%, 3.3%, and 4.3% differences, respectively, for sin(x), sin 4 (x), and sin 6 (x) motion, between delivered dose and motion-averaged dose for points in the penumbra region of the beam and over 30 fractions. In approximately 5-10% of the cases, differences between the motion-averaged dose and the delivered 30-fraction dose could reach 6%, 8% and 10-12%, respectively for sin(x), sin 4 (x), and sin 6 (x) motion. To analyze a clinical IMRT beam, two patient plans were randomly selected. For one of the patients, the beams showed a likelihood of up to 25.6% that the delivered dose would deviate from the motion-averaged dose by more than 1%. For the second patient, there was a likelihood of up to 62.8% of delivering a dose that differs by more than 1% from the motion-averaged dose and a likelihood of up to ~30% for a 2% dose error. For the entire five-beam IMRT plan, statistical averaging over the beams reduces the overall dose error between the delivered dose and the motion-averaged dose. For both patients there was a likelihood of up to 7.0% and 33.9% that the dose error was greater than 1%, respectively. For one of the patients, there was a 12.6% likelihood of a 2% dose error. Daily intrafraction variation of the delivered dose of more than 10% is non-negligible and can potentially lead to biological effects. We observed [for sin(x),...

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Boron neutron capture therapy (BNCT) is based on the preferential targeting of tumor cells with 10 B and subsequent activation with thermal neutrons to produce a highly localized radiation. In theory, it is possible to selectively irradiate a tumor and the associated infiltrating IntroductionIn all conventional radiation therapy modalities, the sensitivity of the normal tissues is the limiting factor that determines the dose that can be delivered to tumor. A particular problem facing the radiation oncologist is the treatment of micrometastatic disease: tumor sites too small to be detected by current imaging or nuclear medicine techniques, or disease too widespread and diffuse to be treated without unacceptable damage to normal tissues. Boron neutron capture therapy (BNCT) is a binary therapy that has the potential to address these issues: selective targeting of high linear energy transfer (LET) radiation to tumor with sparing of the normal tissue; and the potential to deliver high-LET radiation to individual cells or micrometastatic sites. BNCT requires the selective delivery of a boron-labeled compound to tumor. The tumor region, invariably including some of the surrounding normal tissues, is then irradiated with low-energy neutrons. The nucleus of the minor stable isotope of boron, 10 B, absorbs (captures) a low energy (thermal) neutron, and immediately undergoes a fission reaction The short combined track lengths of the alpha (9 µm) and lithium (5 µm) particles produced by the boron neutron capture reaction essentially limits the radiation damage to cells containing 10 B. In practice, there is also a non-specific background dose to both tumor and the normal tissues from the neutron beam, and with currently available boron compounds there is a low level of boron in the normal tissues. However, the therapeutic ratio in BNCT is primarily governed by the tumor-targeting capacity of the boron delivery agent. A number of Phase I and Phase I/II safety and dose escalation BNCT clinical studies have been carried on patients with glioblastoma or melanoma. Historically, glioblastoma has been the target for BNCT clinical applications, due in large part to the poor prognosis for these patients with the best conventional treatments. This situation is as true today as it was at the time of the first clinical trial of BNCT in 1951. This article will review: i) BNCT dosimetry; ii) boron delivery agents; iii) macroscopic and microscopic boron detection methods; iv) neutron beams; v) the radiobiology of BNCT; vi) current BNCT clinical studies; and vii) future developments. Boron Delivery AgentsA boron compound with a high degree of tumor specificity, long retention in the tumor, and complete clearance from blood and normal tissues would be optimal for BNCT, producing very substantial therapeutic ratios. The short-range of the alpha particles and lithium ions released from the boron neutron capture reaction make BNCT critically dependent on the boron delivery agent in two ways: i) there is a minimum requirement for accumulation...

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