IMRT planning of localized prostate cancer versus 3DCRT versus conventional RT: dosimetric study

ABSTRACT

Many trials emphasized positive local control rate and biochemical free survival with escalation of dose to the prostate in early stages of prostate cancer but the problem was the high toxicity rate of the nearby critical organs. This study was designed to compare conventional radiotherapy [RT], three-dimensional conformal radiotherapy [3DCRT] and intensity modulated radiotherapy [IMRT] for localized prostate cancer irradiation and the ability of 3DCTR and IMRT to escalate the prostate dose and at the same time reduce the dose to the rectum, bladder and small bowel in order to improve the local control rate and the tolerance of pelvic irradiation. Ten patients with stages T1c-T2b were referred for definitive radiotherapy in the Radiation Oncology Department of the University of Alabama at Birmingham, AL; USA. For each patient three treatment planning were done; the conventional plan [C-RT] was applied by initial 3-field technique then a boost by 4-field technique. The 3DCRT was applied by 6-field technique and the IMRT plan was given by 5 equally spaced fields .The total prescribed dose for the three plans was 75.60 Gy;1.8 Gy / fraction; 5fractions weekly. Three plans were compared as regard the coverage of the target volumes [GTV and PTV] and the radiation doses to the organs at risk [OARs] by means of the dose volume histogram [DVH]. The treatment planning of all plans were achieved by the use of the Eclapse machine [Varian Medical Systems, Palo Alto; CA]. The cumulative DVH of the three plans showed that both the GTV and PTV were uniformly covered by the prescribed dose and there was no significant difference between the three plans in spite that the IMRT plan was slightly better than the other two plans. As regard the nearby critical organs [OARs], the IMRT plan had the best sparing distribution and both the rectum and bladder received the lowest doses [rectum V70 and V50 were 13% and 26% respectively and for the bladder V70 and V50 were 12% and 26% respectively] versus 25% and 60% for the rectum and 18% and 28% for the bladder in the 3DCRT versus 91% and 100% for the rectum and 47% and 63% for the bladder in the C-RT plan. Moreover the IMRT plan reduced significantly the dose to the femoral heads followed by the conventional plan while the dose to the bowel in the three plans was very low and there was no difference between them. The dose escalation could be performed with IMRT to achieve increased Tumor Control Probability [TCP] while maintaining the Normal Tissue Complication Probability [NTCP] less than those from conventional and 3D conformal irradiation of the early prostate carcinoma