Saad El Din I, M.D *, Abd El AAl H, M.D *, Makaar W, M.D *, El Beih D, M.Sc †, Hashem W, M.Sc * *Department of Clinical Oncology and Radiotherapy, Kasr Al-Ainy Hospital, Cairo University, Egypt †Physics section in Department of Clinical Oncology and Radiotherapy, Kasr Al-Ainy Hospital, Cairo University, Egypt OBJECTIVES METHODS The work is a comparative study between two modalities of radiation therapy, the aim of which is to compare 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) in treating posterior fossa boost in children with high risk medulloblastoma; dosimetrically evaluating and comparing both techniques as regard target coverage and doses to organs at risk (OAR). 1. Huchet A, Caudry M, Belkacemi Y, et al. [Volume- effect and radiotherapy part two: Volume-effect and normal tissue]. Cancer Radiother 2003; 7:353–362. IMRT technique was clearly able to improve conformity index and homogeneity index. Also, it was able to significantly decrease the dose to most of the risk structures. Yet the cochlear doses did not differ significantly, and it was within the organ's tolerance in all plans. References Dosimetric comparison between conformal and IMRT planning PTV coverage at the (V95%) was significantly better in the 3D- CRT (97.35%) compared to the IMRT (95.94%) plans (p-value 0.000). Maximum dose in the target (V107%) was less in the 3D- CRT compared to the IMRT plans, with p-value Conformity index was significantly superior with IMRT plans compared to the 3D-CRT plans; and respectively. As for the dose homogeneity, it was also better in the IMRT plans but it did not reach the statistically significant value. IMRT plans delivered less doses to cochleae (Rt: 5.77 Gy & Lt: 5.93 Gy), these values were not significantly less than those of the 3D-CRT plans (Rt: 6.65 & Lt: 6.85) with p-value of and to the right and left cochleae respectively. The cochleae received 37.5% of the dose, with a total dose within the tolerance of the cochleae, after the two phases of treatment (42.75Gy). In the IMRT plans the cochleae received only 32.5% of the dose, with a total dose of 41.8 Gy. Of clinical importance was the significantly higher dose reaching the chiasma, chiasma PRV, optic nerves and eyes in the IMRT plans compared to the 3D-CRT plans. The doses to the brainstem, brainstem PRV, spinal cord and spinal cord PRV were significantly less in the IMRT plans (p-value 0.000) than those with the 3D-CRT plans. Doses to the right temporal lobes were higher in the IMRT plans, but those of the left temporal lobes were higher in the 3D-CRT plans, yet the differences didn't reach the significant level in both cases. RESULTS CONCLUSIONS The conformal 3D radiation therapy plan is not far beyond the intensity modulated radiation therapy concerning cochlear sparing in the treatment of posterior fossa boost in children with high risk medulloblastoma Beam's eye view for the beam orientation of the 3D-CRT. Color wash of the two plans at the cochlear level. DVH for the Rt cochlea.Dose-Volume statistics for normal tissues. 20 patients with high risk medulloblastoma were treated by 3D-CRT (Field-in-Field) technique. A dosimetric comparison was done by performing two plans for the posterior fossa boost, 3D-CRT and IMRT plans, for the same patient. Target volume delineation: The CTV posterior fossa (CTV pf ) boost volume encompassed the entire posterior fossa. The posterior fossa was defined on a planning CT scan, and MRI should be used to assist in the identification of the tentorium cerebelli. The CTV pf extended from the foramen magnum inferiorly, to the bony walls of the occiput and temporal fossae posteriorly and laterally, and superiorly to the tentorium cerebelli. The anterior borders of the brainstem and midbrain bind the posterior fossa contents anteriorly. The PTV posterior fossa (PTV pf ) consisted of a 0.5-cm geometric margin around the CTV pf. PTV pf was limited to the bony confines of the skull, except at the foramen magnum where it extended to the level of C1. The PTV pf extended anteriorly to the posterior clinoids, excluding the pituitary gland, and inferiorly to the C1-C2 junction. For the 3D planning: The posterior fossa boost was given using 2 lateral wide opposing fields; each field contained another smaller field given from the same angle i.e field-in-field technique (total of 4 fields). Shaping was done using the multileaf collimators (MLC); For the IMRT planning: Five fields isocentric technique using non-coplanar gantry angles. Dose limitation to risk organs in the IMRT plan: Optic chiasm 9 Gy, optic nerves 9 Gy, brainstem 18 Gy, and lenses 0 Gy. For the temporal lobes, the dose constraint was 10 Gy. For the cochlea, the dose constraint was 7 Gy. Dosimetric comparison between conformal and IMRT planning: A) Dose homogeneity within the target volume: comparison between V95 % and V107 % for each technique. Homogeneity index (HI) and conformity index (CI) were calculated for each case using the RTOG equations; 1 HI = Maximum isodose in the target CI= Volume of the reference isodose (95%) Reference isodose Target Volume B) Dose received by OAR will be compared for each contoured structure in terms of mean dose and maximum point dose.

Saad El Din I, M.D *, Abd El AAl H, M.D *, Makaar W, M.D *, Mashhour K, M.D *, El Beih D, M.Sc †, Hashem W, M.Sc * *Department of Clinical Oncology and Radiotherapy, Kasr Al-Ainy Hospital, Cairo University, Egypt †Physics section in Department of Clinical Oncology and Radiotherapy, Kasr Al-Ainy Hospital, Cairo University, Egypt OBJECTIVES METHODS The work is a comparative study between two modalities of radiation therapy, the aim of which is to compare 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) in treating posterior fossa boost in children with high risk medulloblastoma; dosimetrically evaluating and comparing both techniques as regard target coverage and doses to organs at risk (OAR). 20 patients with high risk medulloblastoma were treated by 3D-CRT (Field-in-Field) technique. A dosimetric comparison was done by performing two plans for the posterior fossa boost, 3D-CRT and IMRT plans, for the same patient. Target volume delineation: The CTV posterior fossa (CTV pf ) boost volume encompassed the entire posterior fossa. The posterior fossa was defined on a planning CT scan, and MRI should be used to assist in the identification of the tentorium cerebelli. The CTV pf extended from the foramen magnum inferiorly, to the bony walls of the occiput and temporal fossae posteriorly and laterally, and superiorly to the tentorium cerebelli. The anterior borders of the brainstem and midbrain bind the posterior fossa contents anteriorly. The PTV posterior fossa (PTV pf ) consisted of a 0.5-cm geometric margin around the CTV pf. PTV pf was limited to the bony confines of the skull, except at the foramen magnum where it extended to the level of C1. The PTV pf extended anteriorly to the posterior clinoids, excluding the pituitary gland, and inferiorly to the C1-C2 junction. For the 3D planning: The posterior fossa boost was given using 2 lateral wide opposing fields; each field contained another smaller field given from the same angle i.e field-in-field technique (total of 4 fields). Shaping was done using the MLC. For the IMRT planning: Five fields isocentric technique using non-coplanar gantry angles. Dose limitation to risk organs in the IMRT plan: Optic chiasm 9 Gy, optic nerves 9 Gy, brainstem 18 Gy, and lenses 0 Gy. For the temporal lobes, the dose constraint was 10 Gy. For the cochlea, the dose constraint was 7 Gy. Dosimetric comparison between conformal and IMRT planning: A) Dose homogeneity within the target volume: comparison between V95 % and V107 % for each technique. Homogeneity index (HI) and conformity index (CI) were calculated for each case using the RTOG equations; 1 HI = Maximum isodose in the target CI= Volume of the reference isodose (95%) Reference isodose Target Volume B) Dose received by OAR will be compared for each contoured structure in terms of mean dose and maximum point dose. 1. Huchet A, Caudry M, Belkacemi Y, et al. [Volume-effect and radiotherapy part two: Volume-effect and normal tissue]. Cancer Radiother 2003; 7:353–362. IMRT technique was clearly able to improve conformity index and homogeneity index. Also, it was able to significantly decrease the dose to most of the risk structures. Yet the cochlear doses did not differ significantly, and it was within the organ's tolerance in all plans. References PTV coverage at the (V95%) was significantly better in the 3D- CRT (97.35%) compared to the IMRT (95.94%) plans (p-value 0.000). Maximum dose in the target (V107%) was less in the 3D- CRT compared to the IMRT plans, with p-value Conformity index was significantly superior with IMRT plans compared to the 3D-CRT plans; and respectively. As for the dose homogeneity, it was also better in the IMRT plans but it did not reach the statistically significant value. IMRT plans delivered less doses to cochleae (Rt: 5.77 Gy & Lt: 5.93 Gy), these values were not significantly less than those of the 3D-CRT plans (Rt: 6.65 & Lt: 6.85) with p-value of and to the right and left cochleae respectively. The cochleae received 37.5% of the dose, with a total dose within the tolerance of the cochleae, after the two phases of treatment (42.75Gy). In the IMRT plans the cochleae received only 32.5% of the dose, with a total dose of 41.8 Gy. Of clinical importance was the significantly higher dose reaching the chiasma, chiasma PRV, optic nerves and eyes in the IMRT plans compared to the 3D-CRT plans. The doses to the brainstem, brainstem PRV, spinal cord and spinal cord PRV were significantly less in the IMRT plans (p-value 0.000) than those with the 3D-CRT plans. Doses to the right temporal lobes were higher in the IMRT plans, but those of the left temporal lobes were higher in the 3D-CRT plans, yet the differences didn't reach the significant level in both cases. RESULTS CONCLUSIONS The conformal 3D radiation therapy plan is not far beyond the intensity modulated radiation therapy concerning cochlear sparing in the treatment of posterior fossa boost in children with high risk medulloblastoma Beam's eye view for the beam orientation of the 3D-CRT. Color wash of the two plans at the cochlear level. DVH for the Rt cochlea. Dose-Volume statistics for normal tissues.