A Comparative Study of Dosimetric Analysis of Three Different Sets of Five Fields and Seven Fields IMRT Plans for Prostate Cancer

The advent of Intensity Modulated Radiation Therapy (IMRT) is rapidly changing the field of Radiation Oncology. IMRT has the potential to improve clinical implementation of highly conformal non-convex dose distributions. Nonetheless, a number of IMRT approaches including coplanar and noncop-lanar beam techniques with 5 to 9 beams at different angles have been used in an effort to get the best dose distribution. The purpose of this study is to compare the dose to normal tissue and dose-limiting structures, conformity index, homogeneity index, number of monitor units required for the treatment of prostate cancer in 3 sets of five and seven beam IMRT plans and thus to select the best IMRT approach for patients with prostate cancer.

surrounding critical normal structures. Multiple studies have shown an improved tumor control rate with dose-escalated radiation therapy to prostate [1] [2] [3] [4] several single institution series has reported a reduction in late toxicity with the introduction of IMRT compared to 3DCRT, even with dose escalation [4] [5].
The use of IMRT in the treatment of localized prostate cancer is associated with significantly lower doses of radiation delivered to the rectum and bladder.
The ability of IMRT to reduce dose to nearby normal structures without sacrificing dose coverage of the target makes it an ideal treatment modality for prostate cancer.
The beam orientations used for the IMRT treatment of prostate cancer are still selected empirically, without any guideline. In the past several groups have investigated the number and orientations of beams in IMRT of prostate cancer [6] [7]. Practically in the treatment of prostate cancer by IMRT technique five to seven beams of different gantry angle are used.
The aim of this study is to compare the dose to normal tissues and dose-limiting structures such as rectum and urinary bladder, conformity index, homogeneity index, number of monitor units required for the treatment of prostate cancer when using the same prescription doses, same planning system and PTV margins with 3 sets of five and seven beam IMRT plans.

Methods & Material
A thermoplastic pelvic mask was used to immobilize the patients and CT reference isocenter were marked on the mask with the help of fidiucial lead balls.
Planning CT scan with 3 mm thickness was acquired in the treatment position from level L2-3 to the ischial tuberosity. They were placed in supine position with special instruction to keep their rectum empty and bladder comfortably full at the time of simulation and during each treatment fraction. CT slices of patient were transferred to Elekta focal-SIM contouring workstation via DICOM for contouring.

Statistical Analysis
Data was entered on excel sheet and ANOVA with turkey multiple comparison test and Kruskal-Wallis test with Dunn's Multiple Comparison Test was applied for parametric and non-parametric data respectively using Graph pad (version 5) software. A P-value ≤ 0.05 was considered statistically significant.        multiple comparison test as shown in Figure 11 and Table 9 and Table 10.

Result
For Homogeneity index of various IMRT plans there are non-significant (P > 0.05) difference between the various groups using ANOVA test with turkey multiple comparison test as shown in Figure 12 and as shown in Table 11 and Ta Figure 13 and Table 15.

Discussion
Prostate cancer is the most frequently diagnosed cancer among men in over M. K. Zope et al.  one-half of the countries of the world [10]. Several treatment alternatives exist for localized prostate cancer, including observation, prostatectomy, brachytherapy and external beam radiation therapy (EBRT). The outcome of the treatment of early prostate cancer has improved in recent years mainly due to the radiation dose escalation [11].
The major advantage of IMRT is the ability to decrease the dose to critical structures, which in turn lowers the radiation toxicity effects [12]. In recent years, dose escalation has been shown to improve the probability of local tumour   [13]. The increase of normal tissue integral dose with multiple beam radiation therapy during IMRT is also a major concern due to the potential risk of the secondary malignancies especially in younger patients [14].

Conclusion
Radiation therapy for prostate cancer has evolved drastically over the past few

Limitation of This Study
1) Small sample size.
2) The clinical correlation of doses received by OARs in this of acute & late toxicities was not done.
3) Require prospective, randomized study with large sample size and long term follow up for assessing significant clinical outcome.

Ethical Clearance
The study is a comparison of different treatment plans in the same data set.
However, there was no change in the patient's treatment plan for the proposed study. So ethical committee clearance was not required.
The study has been approved and allowed by the Head of the Institute.