Mohamed A. Majeed*; Maha H. Mokhtar
Association of Egyptian-American Scholars
Background:
Inverse planning is more dependent on specification of tumor volumes & sensitive structures, and their constraints. IMRT is advised as appropriate technique to protect OAR, while maintaining target conformity irradiation in the case of higher cancer dose radiotherapy. Few investigations tried to estimate the expected advantage with respect of 3DCRT.
Purpose:
Evaluate and analysis IMRT plans of patients group with prostate and head-neck cancer generated by forward and inverse planning.
Result:
Mean dose to prostate was 68.6 ± 0.8, 68.5 ± 0.6 Gy for inverse and forward IMRT respectively and V95% for both forward and inverse planning was 164.322 ±25.97 Gy and 164.468 ± 25.85 Gy respectively which were mainly the same coverage of target. Rectum-V50 equal 37.6 and 29.7 corresponding to forward and inverse planning, Bladder-V60 F= 19.9 versus I= 18.5 while D30% of rectum; F= 56.6 and I= 49, Bladder-D30%; F= 43.8and I= 49.1 Gy. A reduction of the inverse dose by 6-8 Gy for rectum was achieved but the dose for bladder has higher dose (5Gy) and could be achieved for most of the patents. Mean V95 for head & neck was Target70 = (59.05 and 68.5), Target60 = (56.9 and 57.4), Target54 = (52.6 and 54.6) for forward and inverse planning respectively. Obviously that conformity quality for inverse planning 0.83 superior about forward planning 0.73, it’s known conformity index equal 1, indicate that the total of the prescription dose is delivered to the PTV with no dose of this level to any adjacent tissue. For adjacent OAR in HN cases; Brain Stem dose was F-IMRT=44.9, I- IMRT =16.4, Spinal cord dose reduce from 49.7 in F-IMRT to 39.7 I-IMRT, right parotid dose was F-IMRT= 38.1, I-IMRT = 27.1, Left parotid dose was F-IMRT= 39.1, I-IMRT=24.7 Consecutively. Inverse planning gives better sparing for HN structure where reduction in above 10 Gy in both parotid, inverse planning can save cord more (reduction 20%) except brain stem slightly lower dose in forward IMRT.
Conclusion:
No significant difference was observed in prostate tumor between forward and inverse IMRT techniques while HN cases was marked relatively better organ at risk sparing with inverse compared to forward IMRT techniques with higher dose to tumor at the same time. So, it is necessary to take decision in which patients to do one or other technique depending on high priority/sensitive degree, plan complexity and tumor sites.
This article was published in 3alamaltanmya
sponsored by Future Builders International Academy
Led by Dr.Maha Fouad
