Small radiation fields are abundantly used in modern radiotherapy techniques like in IMRT and SRS. In order to commission these techniques, dosimetric data for small fields is required. The purpose of this study is to compare dosimetric measurements with two different ion chambers cc13, and cc01 for smaller fields. Dosimetric measurements are beam profile, output factor, pdds, and collimator factor. Dosimetric data is acquired in water phantom for two different photon beam energies 6 MV and 15 MV with zero gantry angle. In beam profiles cc13 chamber, measure wider penumbra as compare to cc01. And this wider measurement of penumbra occurs for smaller as well as for larger field sizes. Accumulated relative error in the measurement of penumbra for number of field sizes and 6 MV at dmax, and at 10 cm depth are 34.32% and 27.72% respectively. Accumulated relative error in the mea-surement of penumbra for number of field sizes and 15 MV at dmax, and at 10 cm depth are 28.49% and 23.92%. In case of output factor for smaller fields cc13 underestimates the output factor relative to cc01, with non-linear increase for smaller fields. But for larger fields, this increase in output factor is almost linear difference of two chambers is decreased. For very smaller fields <2 cm × 2 cm, relative error in output factor of cc13 and cc01 is greater than 5% and rapidly increases with decreasing field size. But for lager fields, this relative error is negligible. In measurement of pdds after the buildup region difference occurs in the response of two chambers cc13 and cc01 for smaller fields. For field sizes ≤2 cm × 2 cm average cc13-cc01 at various depths 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, and 80 cm is almost greater than 0.5 cm. And similarly as output factor, this difference (cc13-cc01) increases with field size decreasing.

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Background: The treatment of medulloblastoma involves surgery, radiotherapy, and adjuvant chemotherapy. In radiotherapy, craniospinal irradiation (CSI) is prescribed, where two lateral cranial fields and one or two spinal beams are applied in CSI. Different multi-field techniques (coplanar and/or noncoplanar) are used to register the prescribed dose. The purpose of this study was to assess plan quality in terms of dose coverage of the spine with both photon and electron beam therapy and the sparing of organs at risks (OARs).Methods: Ten pediatric patients (ages 6 to 10 years) were immobilized in the prone position for simulation. The Clinical Target Volume (CTV) of the organ under treatment, Planning Target volume (PTV) of the organ under treatment, and OARs were contoured. Prowess Panther (v4.71) was used for dose computations. Two lateral parallel-opposed 6 MV photon cranial fields with the spinal beam(s) (either 6 Photons or 21 MeV electrons) were used in planning. Electron beams were added posteriorly on the spine with parallel-opposed cranial fields. The treatment plans were computed for 3600 c Gy in 21 fractions.Results: For comparable conformity number of electron versus photons beam plans (0.68 ± 0.41 versus 0.66 ± 0.47, is not significantly different at p < 0.05) and homogeneity index (1.22 ± 0.03 versus 1.25 ± 0.04, is significantly different at p < 0.05), the photon doses were higher for underlying OARs (heart, liver, and thyroid) and were lower for partially in-field organs (lungs and kidneys) compared to electrons.Conclusions: The underlying organs i.e., thyroid, heart, and liver receive a lesser dose in case of electrons, while partially in-field organs are exposed more compared to photons mainly due to the ballooning effect in electrons. The study shows that both electrons and photons can be used for CSI. However, the electron may be preferred due to its better sparing of underlying structures.

Cancer, which is the uncontrolled division of cells, is a leading fatal disease in the world with high mortality rates. It can be treated using several methods, including radiotherapy, which involves ionizing radiation. Radiotherapy on the basis of source placement has two types, i.e. brachytherapy and external beam radiotherapy. External beam radiotherapy has evolved from 2-D conventional therapy to 3-D Conformal radiotherapy (3D-CRT) and then intensity-modulated radiotherapy (IMRT). Modern radiation therapy techniques such as IMRT improve dose conformity and sparing of organs at risk. Volumetric modulated arc therapy (VMAT) is a newly developed technique that uses treatment in arcs. In this report, a dosimetry comparison was performed between IMRT and VMAT. This study was conducted in the Radiotherapy Department of the Institute of Nuclear Medicine and Oncology Lahore (INMOL). Two types of cancer patients were selected for this comparison, i.e., five patients with Nasopharyngeal Carcinoma and ten patients with Prostate Carcinoma. Simulation of these patients was done with the help of a CT Simulator. The oncologists delineated all target volumes and organs. Then suitable fields/arcs were applied, which cover volumes effectively. This was followed by the optimization of plans for both techniques for every patient. Finally, evaluating parameters were compared, including volume coverage, conformity index, homogeneity index, organ doses, and monitor units. We obtained better results of target conformity indices from VMAT (1.16 and 1.25) than IMRT (1.24 and 1.30). VMAT was better in organ sparing too. Also, VMAT shows very few monitor units (468 and 733) as compared to IMRT (2325 and 2149). On the basis of the results obtained, it was concluded that VMAT is better than IMRT. This technique will enhance treatment efficiency as it takes less time to obtain the required results. Also, a very less scatter dose will be delivered to the patient.