Gamma Ray Spectroscopy for Dose Rate Constants

描述(申请人提供)：在前列腺内永久植入碘-125粒子或钯-103放射性粒子已成为精心挑选的前列腺癌患者的一种流行的放射治疗形式。该手术是微创的，通常在门诊一天的外科病房进行。与治疗相关的发病率，如尿失禁和性阳萎，粒子植入的发生率相当低，在选定的患者中，癌症的控制与手术等其他治疗方法一样好。由于这些原因，公众对种子植入的兴趣正在迅速增长。放射治疗的临床成功在很大程度上取决于能否提供所需的处方剂量。对于前列腺癌种子植入物，这样的能力既影响到将放射性种子放置在预先设计的空间图案中以获得足够的空间剂量覆盖的准确性，也影响到每个种子的基本剂量学性质的准确性。该项目的主要目标是开发一种新的方法来确定用于前列腺癌种子植入的间质内近距离放射治疗种子的剂量率常数，这是AAPM TG-43公式中唯一的绝对量。新方法利用高分辨率伽马射线能谱，在不需要知道空气比释动能强度的情况下，能够确定剂量率常数。我们的假设是，提出的基于伽马能谱的新方法优于目前公认的使用LiF热释光二极管的标准实验方法。它有可能提高前列腺癌种子植入剂量学的准确性和一致性。绝对剂量学的这种改进将影响所有近距离放射治疗患者的临床实践，因为与随机误差不同，不同型号的近距离治疗源的绝对剂量学参数的误差会以系统的方式和相同的方向影响所有患者。由于前列腺近距离放射治疗现在已经成为选定患者的首选治疗方法，并且这种受欢迎程度导致了许多用于临床实施的新的种子设计，我们假设伽玛射线能谱可以用来减少剂量率常数的不确定性，并改善大量前列腺癌患者的剂量学。

DESCRIPTION (provided by applicant): Permanent implantation of either iodine-125 seeds or palladium-103 radioactive seeds in the prostate has become a popular form of radiation therapy for carefully selected prostate cancer patients. The procedure is minimally invasive and is usually performed in a one-day surgery unit on an outpatient basis. The treatment related morbidity such as urinary incontinence and sexual impotence is fairly low for seed implantation, and control of the cancer in selected patients is as good as that with other treatment modalities such as surgery. For these reasons the public interest in seed implantation is growing rapidly. The clinical success of radiation therapy has been highly dependent on the capability of delivering a desired prescription dose. For prostate seed implant, such a capability is impinged on both the accuracy of placing the radioactive seeds in a predesigned spatial pattern for adequate spatial dose coverage and on the accuracy of the fundamental dosimetry properties of each individual seed. The primary objective of this project is to develop a new method for determination of dose rate constant, the only absolute quantity in the AAPM TG-43 formalism, for interstitial brachytherapy seeds that are used for prostate seed implants. The new method utilizes high-resolution gamma ray spectrometry and would be capable of determining the dose rate constant without the need of knowing the air kerma strength. Our hypothesis is that the proposed new method based on gamma ray spectrometry is superior to currently accepted standard experimental method using LiF TLDs. It has the potential of improving the accuracy and consistency of the dosimetry of prostate seed implants. This improvement in absolute dosimetry will impact the clinical practice of all brachytherapy patients because unlike random errors, errors in absolute dosimetry parameters for different models of brachytherapy sources affect all patients in a systematic fashion and in the same direction. Since prostate brachytherapy has now become a treatment method of choice for selected patients and this popularity has led to the introduction of many new designs of seeds for clinical implementation, we hypothesize that gamma ray spectroscopy can be used to reduce the uncertainty in dose rate constants and improve the dosimetry in a large number of prostate cancer patients.