الفهرس 
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Abstract
Breast cancer is a group of diseases that affects breast tissue. Both women and men can get breast cancer, though it is much more common in women. Other than skin cancer, breast cancer is the most common cancer among women worldwide. Some women are at higher risk for breast cancer than others because of their personal or family medical history or because of certain changes in their genes.
Breast cancer survival depends on a person‟s diagnosis and treatment. A main factor in survival is breast cancer stage. People with non-invasive (stage 0) and early stage invasive (stages I and II) breast cancers have a better chance of survival than those with later stage cancers (stages III and IV).
Most women with early stage breast cancer will have some type of surgery, which is often combined with other treatments to reduce the risk of recurrence, such as radiation therapy, chemotherapy, hormonal (endocrine) therapy, and/or targeted therapy. Radiation therapy is considered an important tool for treating cancer and is often used in conjunction with other therapies, such as chemotherapy or tumor removal surgery. Radiotherapy has an important role in the treatment of breast cancer at every stage. After surgery, radiation is often used to destroy cancer cells remaining in the breast, chest wall, or underarm area. Breast cancer surgery is almost always followed by radiation therapy to reduce the risk of breast cancer recurrence by about 50% and the relative risk of breast cancer death by about 20% in most patients. Some mastectomy-treated patients also benefit from radiation if their tumor is larger than 5 cm or if their cancer is found in the lymph nodes.
Radiotherapy (RT) of the breast requires whole breast irradiation followed by a small boost area of treatment to the original tumor bed. An additional boost dose of 10 Gy delivered to the tumor bed has shown an additional gain in decreasing local recurrence in patients.
The delivery of the boost dose to tumor bed has been performed sequentially following to the whole breast radiation therapy (RT). Accurate localization of the tumor bed is essential. Cavity is delineated by the Radiation Oncologist (RO) at the time of the initial planning CT.
It was usual to deliver the boost dose to the tumor bed by using the electron beam. But today there are other boost techniques using the photon beam. Up till now, it is unclear which technique is recommended. So investigations are needed to describe the differences between them and to modify a new technique to irradiate breast with minimal side effects on lungs, heart, LAD and normal breast tissues.
Accordingly, this work was conducted aiming to compare between delivering the boost dose for left breast cancer once by using electrons and once by using photons, taking into consideration that the left breast is nearer to the heart than the right breast. So, the doses received by the organs at risk, in this case, also, considered, as a mean of comparing.
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For this purpose, twenty five female patients confirmed with histological breast tumors from a hospital in Alexandria city, with age range (30 - 60) were recruited in this study from 1st January 2015 to 30th March 2017.
The patients were divided into two groups, according to the size of the breast, namely; small breast group (10 patients), and large breast group (15 patient). For each patient, a CT scan was obtained. The slices were taken from the mid- neck to the upper abdomen.
The CT data was imported to the contouring workstation via local area network system. The images from the CT scanner were transferred to the planning system.
Acquisitioning the contour of the planning target volume (PTV) and the critical volumes of organs at risk (OARs) according to the Radiation Therapy Oncology group (RTOG). The organs at risk considered in this work were heart, LAD, and left lung.
The prescribed dose of PTV was 10 Gy in 5 fractions and the dose rate of the irradiation field was 300 MU/min. The treatment plans, created by the medical physicist, were as follows:
1- Beams placing using 6 MV photons: The gantry angles were designed as ≤ 305° and ≥ 125 ° , the collimator angles were designed as ≤ 0° and ≥ 5°as given by Digital reconstructed radiograph, and Room Eye View( REV).
2- Choosing 18 ,21 MeV electron beams: The gantry angles designed as ≤ 395° and ≥ 0 ° , the collimator angles designed as ≤ 20° and ≥ 0° that shown in Digital reconstructed radiograph, and Room Eye View (REV).
On using electron beam from a linac, the photon collimator must be opened to the appropriate setting for a given electron applicator.
Typical electron applicator sizes at normal source surface distance were: Circular with diameter: 5 cm, Square: 10×10 cm2. 6 MV Photon, 18 Mev in small breast and 6 MV Photon, 21 Mev in large breast were used.
3- Evaluating the resulting calculations of the dose distribution of the photon and electron plans based on the following criteria were compared: (For the planning target volume)
a- The homogeneity index (HI), b-The uniformity index (UI), c- The Dose Volume Histogram (DVH) data were used to obtain the following:
The doses ( D2%, D5%, D95% and D98% covered by 2%,5%,95%,98% of the planning target volume), the volumes (V95%, V100% andV105%) received by (95%, 100%, and105 %) of the the planning target volume, and the minimum, maximum and mean doses received by the planning target volume.
4- For the organs at risk, i.e. Lt Lung, Heart, LAD and Lt Breast - PTV, the minimum, maximum and mean doses were estimated while for Lt Lung and Heart the V2%, V5 % and V7% were also estimated.
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Results:
A- Planning Target Volume (PTV)
1- Doses received by the Planning Target Volume (PTV)
The results revealed that, in case of the doses D2%,D5%,D95%, and D98%, received by the corresponding volumes of the PTV, highly significant difference occurred between the electrons and photons received by the small and large breasts, at the level of significance (p<0.001), except in case of D50%.
However, in case of the doses Dmax, Dmin, highly significant difference occurred between the electrons and photons received by the small and large breasts, at the level of significance (p<0.001), except in case of Dmean, where, no significant difference occurred at the level (p<0.05) in case of the large breast , but at this level of significance, occurred in case of small breast (p < 0.019).
2- Volumes coverage of the Planning Target Volume (PTV),by the prescribed dose:
In case of V95 and V107 (volumes of the PTV covered by 95% and 107% of the prescribed dose), highly significant difference occurred between the electrons and photons received by the small and large breasts, at the level of significance (p<0.001), except in case of V100, where, nosignificant difference occurred at the level (p<0.05) in case of the large breast , but at this level of significance, occurred in case of small breast (p < 0.026).
3- Homogeneity index (HI), Uniformity Index (UI), Conformity Index (CI), and Global Max:
In case of HI, UI, and global max, highly significant difference occurred between the electrons and photons received by the small and large breasts, at the level of significance (p<0.001), except in case of CI, where, no significant difference occurred at the level (p<0.05) in case of either the large or the small breast (p = 0.147, p = 0.545, respectively ).
B- Organs at risk (OARs):
1-The Left Lung:
Doses received by Left Lung
In case of Dmax, no significant difference occurred, while the significance occurred in case of Dmin at the level (p< 0.001), between electrons and photons received by the large and small breast, also with the Dmean in case
- Volume % of the Left Lung covered by the prescribed dose
In case of V2, V5, and V7 significant difference occurred at the level (P<0.001), in case of the large breast, but at the level of (P<0.05) , in case of the small breast.
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b-The Heart
Doses received by The Heart
The highly significant difference at the level (P<0.001) occurred in case of Dmin, and in the while in case of Dmean in case of large breast only. However, significant difference at the level (P<0.05) occurred in case of Dmean in small breast, with no significant difference at this level in case of Dmax in small breast.
-Volume % of the Heart covered by the prescribed dose
The results revealed that, in case of the volumes V2,V5, and V7 received by the heart with 2%, 5%, and 7% of the prescribed dose , highly significant difference occurred between the electrons and photons received by the small and large breasts, at the level of significance (p<0.001), in case of V2, with significant difference at level (p<0.003), in case of V5 and V7 in case of large breast with no significant difference at the level (p<0.05) in V2 and V5 in case of small breast except in case of V7 in case of small breast where significant difference occurred at the level ( P = 0.24).
c- The Left Anterior Descending (LAD) and Left Breast - PTV
Doses received by Left Anterior Descending and Left Breast - PTV
The highly significant difference at the level (P<0.001) occurred in case of Dmin with LAD and Left Breast - PTV in case of large and small breast and with small breast in case of Left Breast – PTV with relatively less significant level in Dmin and Dmean in LAD (P = 0.002) in case of large breast, and with no difference in case of large breast in LAD and in both breasts in Left Breast – PTV with the Dmean.