Radiobiological Modeling in Radiotherapy Treatment Planning

At this stage the patient first meet their radiation technologists, too (called " Therapists Radiation or Radiotherapy and radiology technicians "). The technician is trained to administer radiation dose prescribed by the doctor. It is also responsible for helping you achieve a comfortable position that will be the best to allow photons or electrons X-rays pass through the body part being treated. He or she will provide special accessories or foam supports for the patient to stay in the same position for each treatment. The patients also know his medical physicist. A medical physicist made the remarks on the physical aspects of the treatment plan.

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ntroduction: The three major components of the dose under a shielding block namely:-Iran Research Centre For Science & Technology In Medicine (1) the transmitted primary dose, which depends on the energy of the primary radiation and the thickness of the block;(2) the external scatter component which depends on the head geometry, field size and proximity of the patient to the blocking tray; and (3) the phantom scatter which depends on the energy of the primary beam, the shape and size of the unshielded area, the depth of point of interest and its proximity to the edge of the unshielded area.

The purpose of the study was to determine the effect of out-of-field photon beam radiotherapy to the cell survival. In studying the effects, three parameters have been investigated which are the intercellular communications, photon beam energies and different type of cells. In this study, two different types of cells were prepared which are HeLa and T24 cancer cells. Cells were irradiated in two different conditions, one with intercellular communication with the infield cell and one without the communication. Irradiations were done using 6 MV and 10 MV of photon beam energies. Cells survival was determined by clonogenic assay. The data showed that when intercellular communication was present, the cell death was increased thus decrease in survival fraction. However, this effect only demonstrated at 10 MV rather than 6 MV. 6 MV of energy was insufficient to produce the effect of intercellular communication towards the cell survival with 300 cGy dose delivered to the cell. In a comparison of cell type, higher cell death was exhibited by HeLa as compared to T24 cells. In a nutshell, it appeared that the communication status and photon energy level was the determinant of survival difference. Since the effect is not solely based on scattered radiation, thus, the intercellular communications become a significant issue. Inhibition of intercellular communication will increase the cell survival. Although the cell survival was reduced when using 6 MV compared to 10 MV of photon energy but it was insufficient to prove the effect of intercellular communication. For the cell comparison, T24 was said to be more radioresistant since higher survival fraction from HeLa cells.

Purpose: To present a comparison of the accuracy of two commercial electron beam treatment planning systems: one uses a Monte Carlo algorithm and the other uses a pencil beam model for dose calculations. Methods and Materials: For the same inhomogeneous phantoms and incident beams, measured dose distributions are compared with those predicted by the commercial treatment planning systems at different source-to-surface distances (SSDs). The accuracy of the pencil beam system for monitor unit calculations is also tested at various SSDs. Beam energies of 6 –20 MeV are used. Results: The pencil beam model shows some serious limitations in predicting hot and cold spots in inhomogeneous phantoms for small low-or high-density inhomogeneities, especially for low-energy electron beams, such as 9 MeV. Errors (>10%) are seen in predicting high-and low-dose variations for three-dimensional inhomogeneous phantoms. The Monte Carlo calculated results generally agree much better with measurements. Conclusions: The accuracy of the pencil beam calculations is difficult to predict because it depends on both the inhomogeneity geometry and location. The pencil beam calculations using CADPLAN result in large errors in phantoms containing three-dimensional type inhomogeneities. The Monte Carlo method in Theraplan Plus dose calculation module is shown to be more robust in accurately predicting dose distributions and monitor units under the tested conditions.

Accurate, robust and reproducible segmentation of positron emission tomography (PET) images is very important both in terms of radiotherapy planning as well as treatment assessment. However, due to high noise and poor resolution of PET scanner, it still remains a daunting task. Threshold based segmentation methods are proved to be robust to noise and resolution compared to other segmentation methods (e.g. clustering, gradient based etc.). Numerous publications deal with the topic. This paper reviews different fixed and adaptive threshold methods proposed in literature in a common mathematical framework. The paper also highlights the purpose of segmentation of PET images from two perspectives – radiotherapy planning and treatment response. A few recommendations are suggested at the end.

PURPOSE Traditionally, unidirectional leaf-sweeping schemes have been employed to deliver IMRT plans using the dynamic multileaf collimator (DMLC) technique. The goal of this research is to investigate the potential impact of relaxing the leaf-motion restrictions in DMLC IMRT on the beam-modulation quality and the delivery efficiency. METHODS This research relaxes the initial and final leaf-position constraints as well as the unidirectional leaf-motion restriction that have been traditionally imposed on DMLC leaf sequencing and develops exact and heuristic solution approaches to allow for an unconstrained and bidirectional leaf motion. The exact approach employs mixed-integer programming (MIP) techniques and the proposed heuristic method uses stochastic search algorithms while utilizing the special structure of the problem. The trade-off between beam-modulation quality and delivery efficiency is quantified and compared to that of unidirectional leaf-sweeping schemes. RESULTS The per...

Purpose: Tomotherapy consists of helical radiotherapy using a computed tomography (CT)-like gantry and a rotating radiation beam that passes through the target area of interest; this modality has been used in the management of primary central nervous system tumors and viscera-based malignancies. It provides unprecedented accuracy in beam delivery allowing for an increase in tumour dose, thereby increasing the likelihood of cancer cure while at the same time reducing treatment complications in healthy tissues. The main purpose of Study is to Investigate Tumor motion limitation for effective radiotherapy of Lung Cancer specifically for Helical Tomotherapy in Harbin Medical University Affiliated Cancer Hospital. Simultaneous and continuous movements of tomotherapy subsystems (gantry, couch, and binary multi-leaf collimator) can lead to inaccurate dose delivery, when combined with tumor motion.

Methods: In this present study, we have investigated the influence of tumour motion and strategies to reduce the resulting dose differences for helical tomotherapy, through computer simulations and film measurements performed in a dynamic body phantom. Three distinctively different types of dose discrepancies have been isolated: dose rounding, dose rippling, and the intensity-modulated radiation therapy (IMRT) asynchronization effect. Each effect was shown to be affected by different combinations of tumour motion and treatment parameters. In clinical practice using a conventional fractionation scheme, the dose rounding effect remains the major concern, which can be compensated by assigning a larger treatment margin around the tumour volume. For hypofractionation schemes, the IMRT asynchronization effect can become an additional concern by introducing dose discrepancies inside the target volume, necessitating the use of a motion management technique.

Results: Three different types of dissimilarities arising from the presence longitudinal tumour motion during helical tomotherapy were identified. Their characteristics were investigated through both computer simulation modeling and experimental verification using a motion phantom with film. The characteristics of the three different motion-induced dose discrepancies were illustrated, and the dosimetric significance of each effect was described.
Conclusion: Investigated measured data within +0.5 % and +1.5 % inside the PTV region for the non-IMRT and IMRT tomotherapy deliveries, respectively. Various potential solutions to minimize the effect of target motion were also discussed, and each proposed method needs to be investigated for its effectiveness in suppressing the three dose discrepancies described here. The computer simulation model could also prove useful during the patient selection process for the different approaches of minimizing dose artifacts

Keywords: Motion Management; Helical Tomotherapy; Lung Cancer; Respiratory Gating

Purpose: Traditionally, unidirectional leaf-sweeping schemes have been employed to deliver IMRT plans using the dynamic multileaf collimator (DMLC) technique. The goal of this research is to investigate the potential impact of relaxing the leaf-motion restrictions in DMLC IMRT on the beam modulation quality and the delivery efficiency.

Methods: This research relaxes the initial and final leaf-position constraints as well as the unidirectional leaf-motion restriction that have been traditionally imposed on DMLC leaf sequencing and develops exact and heuristic solution approaches to allow for an unconstrained and bidirectional leaf motion. The exact approach employs mixed-integer programming (MIP) techniques and the proposed heuristic method uses stochastic search algorithms while utilizing the special structure of the problem. The trade-off between beam-modulation quality and delivery efficiency is quantified and compared to that of unidirectional leaf-sweeping schemes.

Results: The performance of the developed approaches is tested on liver and head-and-neck cancer cases. Results validate that unconstrained leaf trajectories can significantly improve the beam-modulation quality at small beam-on time values. However, this gain reduces as the available beam-on time increases. Additionally, the proposed heuristic approach can achieve near-optimal solutions with significantly smaller computational effort compared to the MIP solution approach.

Conclusions: Unconstrained leaf trajectories have the potential to enhance the fluence-modulation quality for cases in which the available beam-on time is limited. This gain is primarily attributed to the relaxation of the initial and final leaf positions. The unidirectionality restriction alone does not appear to be a limiting factor.

Cervical cancer happens due to cell changes in women's cervix connecting with the uterus and vagina which can also affect the deeper tissues of the cervix and may spread to other parts of the body. In most cases, cervical cancer is caused by a sexually transmitted infection hosted by human papillomavirus (HPV). In this article, we stated about one of our prospective studies on the treatment of cervical carcinoma by radiotherapy and chemotherapy. The study consists of 60 patients of carcinoma cervix in stages II A to III B. Cases were divided into two groups and each group consists of 30 patients. One group was treated with concurrent Radiotherapy and Chemotherapy as radiotherapy-6000 cGy for 6 weeks, 5 days in a week, and chemotherapy-Inj. Cisplatin 30 mg/m2 on day 1, repeated every week for 6 weeks. Another group was treated with radiotherapy as 6000 cGy in 30 fractions for 6 weeks, 5 days in a week for 6 weeks. A comparison between concurrent chemo-radiotherapy and radiotherapy alone was studied. The mean age of the studied sample taken was 45.50 years. The objectives of the study are to compare the effect of treatment between the aforesaid two groups and observe the side effects on both arms during treatment.