الفهرس 
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Abstract
Abstract:
Background: Radiotherapy is the most treatment modality used for treating the head and cancer patients concurrent with chemotherapy, and intensity-modulated radiotherapy is the latest radiotherapy treatment technique for such cancers.
The use of IMRT in the head and neck cancers is due to the complex target shape of the target and the large number of healthy organs located very near the target, where the IMRT treatment technique has the ability to paint the dose around the target and better sparing of healthy organs, this is done as a result of steep radiation dose gradient accomplished by IMRT.
With the long course of radiotherapy of the head and neck, which lasts one month and a half, and with the effect of chemotherapy, the patients may face anatomical changes during the course, which could lead to changes in the dosimetric outcomes of the IMRT plan.
Purpose: investigate the effect of the anatomical changes for patients during the IMRT course, first, by projecting the IMRT plan on newly acquired CT images every specific time interval to evaluate the dose delivery to the target and organs at risk.
Second, to make new plans (adaptive plans) every certain number of treatment sessions to take into account the anatomical changes, so maintain or improve the dosimetric outcomes of the IMRT plan through the entire treatment course.
Also, monitoring the conformity, homogeneity, and gradient indices during the IMRT course and improving those indices during the IMRT course with adaptive planning.
Besides, reducing the late normal tissue complications due to radiation toxicity to healthy organs resulted from using the same IMRT plan during the entire radiotherapy course by using an adaptive IMRT plan strategy.
Materials and methods: Fifty-five patients diagnosed with head and neck cancers were treated with IMRT concurrent with chemotherapy.
Patients were undergoing CT simulation before the beginning of IMRT treatment, with MRI and PET to get a clear vision of the gross tumor, and the contouring of the target and organs at risk was done by a radiation oncologist.
SIB-IMRT plan was achieved for all patients with nine equally spaced beams of 6 MV energy and dose prescription of 70 Gy/33 fractions for PTVP, 60 Gy/33 fractions for PTV60 and 54/33 fractions to PTV54.
After 10 and 20 treatment sessions, the patients underwent new CT simulations and were mentioned as CT2 and CT3, respectively. And first, a fusion between initial CT and CT2 was done to determine the PTVs and organs at risk, where the radiation oncologist re-contoured the target and organs at risk.
The second image fusion process between CT2 and CT3 was done, and the above procedures were repeated.
An anatomic comparison between CT1, CT2, and CT3, including the patient’s weight loss, GTV volume changes, patient’s separation changes at the center of different organs at the x and y-axis of axial CT images, and patient’s separation changes at plan isocenter was made.
Also, a positional comparison was done between the three acquired CTs to measure the distance changes between the target and organs at risk at each CT.
The initial plan is reconstructed on CT2 with the same IMRT constraints and parameters and called hybrid plan 1 (Hplan1), where the location of the isocenter at Hplan1 is determined using radio-opaque markers at the initial plan isocenter at the time of CT2 acquirement, and also using the bony anatomy for double-checking of isocenter location.
The above procedures were repeated at CT2, where the initial plan was reconstructed at CT3, and a plan called hybrid plan 2 (Hplan2) was generated.
A new plan with new IMRT constraints was generated on CT2 and CT3, taking into account the anatomic and positional changes, and called adaptive plan1 and adaptive plan2 (Aplan1 and Aplan2), where the adaptive plans were approved by the radiation oncologist.
Dosimetric changes, including dose changes for target and organs at iplan, Hplan1, and Hplan2 were evaluated, then a new dosimetric evaluation between iplan, Aplan1, and Aplan2 was done.
The conformity, homogeneity, and gradient indices were calculated and compared between iplan, Hplan1, Hplan2, Aplan1, and Aplan2.
The late normal tissue toxicity for organs due to radiation was compared for the iplan, Hplans, and Aplans to find the percent of patients that will develop a certain radiation effect resulted from using the same plan during all treatment sessions.
Finally, a PTVP margin correction as a result of GTV volume reduction was obtained, so the correction can be used to relatively maintain the initial plan quality throughout the treatment course.
Results: Anatomically, all patients showed a significant decrease in weight at CT2 and CT3 compared to CT1, with more weight loss at CT3 than CT2.Also, the GTV volume showed significant regression in its volume at CT2 and CT3 compared to CT1. Besides, the parotid glands showed a significant volume reduction at CT2 and CT3 compared to CT1.
Moreover, all patients showed significant regression in separation at the center of all organs at the x and y-axis for CT2 and CT3 compared to CT1.
Positionally, the distance between GTV (and PTVP) was significantly increased for all organs except for parotid glands (insignificantly decreased) at CT2 and CT3 compared to CT1.
On the dosimetric side, at a low radiation dose gradient, approximately half of the organs showed a significant increase in dose delivery at Hplan1 and Hplan2 compared to iplan, and for the other half, the increment in dose was insignificant.
At high radiation dose gradient, all organs showed a significant increase in dose delivery at Hplan1 and Hplan2 compared to iplan.
At low radiation dose gradient, approximately 80% of organs showed significant decrease in dose delivery at Aplan1 and Aplan2 compared to iplan.
Furthermore, all organs (except parotid glands) at high radiation dose gradient showed a significant decrease in dose delivery at Aplan1 and Aplan2 compared to iplan.
The conformity index showed significant regression in its value at Hplan1 and Hplan2 compared to iplan; then its value showed a non-significant regression at Aplan1 and Aplan2 compared to iplan.
The homogeneity index showed significant regression of its value at Hplan1 and Hplan2 compared to iplan, and a significant regression at Aplan1 compared to iplan (but improved compared to Hplan1) and a non-significant regression at Aplan2 compared to Aplan1.
The radiation dose gradient index was significantly increased at Hplans compared to iplan, while its value was significantly improved at Aplan1 compared to iplan and then significantly decreased at Aplan2 compared to Aplan1.
Using Hplans (using the same plan without taking into account the anatomical changes) will increase the late toxicity complications, where 63% of patients will face permanent neurological effects, 9% of patients will have a 2% risk of myelopathy due to dose excess to the spinal cord, and 35% of patients will have the development of osteoradionecrosis.
While with the Adaptive strategy, we could lower or maintain the dose to approximately all organs (except for parotid glands). This led us to prevent the development of late toxicity complications.