Comparison of the target volume dose in cranial irradiation with different treatment planning techniques in children under 5 years of age with acute lymphoblastic leukemia

ALL is a malignant disease of lymphoid progenitor cells affecting both children and adults.ALL is the most common type of cancer in childhood and accounts for 30% of all childhood cancers.ALL treatment has four main phases: remission, reinforcement therapy, preventive and therapeutic central nervous system therapy, maintenance therapy. Cranial radiotherapy is an important treatment modality for the treatment and prophylaxis of CNS in the treatment of ALL.The goal of cranial radiotherapy is to give full treatment does to all meningeal structures and to protect the lenses.The target volume (brain tissue) for cranial irradiation includes the entire intracranial subarachnoid space and meningeal extension along the optic nerves and the upper cervical spinal cord.Adequate margins at the base of the skull, including the cribriform plate and temporal fossa, are critical for optimal treatment of the meninges in these areas and for the prevention of marginal recurrence. The 3DCRT technique is the standard treatment technique available for cranial irradiation for ALL patients.In clinical applications, two laterally opposed fields are generally used in all brain radiation treatments with conformal method.Skin Sparing Effect occurs at 1.5 cm in two parallel side irradiations with 6MV energy. Thickness of the head bone of children under 5 years is between 0.5-1 cm.This results in a low-dose area in the meningeal region in cranial irradiation in pediatric patients because the sides of the skull are thin. Furthermore, the dose received by the meningeal region directly affects the scalp dose. In this study, 10 pediatric patients with ALL diagnosed under the age of 5 years who had undergone treatment with 3DCRT plans were selected.Contouring was performed by the radiation oncologist using the available CT images of the patients. 3DCRT and VMAT treatment plans were done by transferring CT images and patient contours to treatment planning systems (Elekta Precise Plan 2.12 and Elekta CMS-Monaco v3.2).Using a full arc with the VMAT treatment technique, a plan similar to the 3DCRT plan was prepared and it was aimed to take the full dose of the low dose region without protecting this region.We tried to give the lowest dose possible to the critical organs while giving the treatment dose to the target volume.Both treatment plans were re-planned to give all patients a total dose of 12 Gy in 8 fractions. 3DCRT and VMAT treatment techniques were compared in terms of target volumes and doses taken by critical organs.3DCRT and VMAT treatment techniques were compared in terms of maximum (D_(%2)), minimum (D_(%98)), and mean doses (D_mean) received by PTV and brain .They were also compared in terms of percentage volume values that received 107% of the planned dose (V_(%107)). Homogeneity Index (HI) and Conformity Number (CN) values of PTV were compared for 3DCRT and VMAT treatment techniques using dose values that received 2% (D_(%2)), 98% (D_(%98)) and 50% (D_(%50)) of the treatment dose. DVH were used to compare the D_max, D_min, D_mean, D_(%2) and D_(%98) dose values of the critical organs for both treatment techniques. Target volumes, OARs, HI and CN values were compared terms of minimum, maximum and mean doses values between two treatment techniques.The advantages and disadvantages of the techniques were evaluated statistically. There was a significant difference between the 3DCRT and VMAT treatment techniques for the maximum dose (D_(%2 )) averages of PTV (p = 0,005), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique.There was a significant difference between the 3DCRT and VMAT treatment techniques for the minimum dose (D_(%98)) averages of PTV (p =0,007), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique.There was not significant difference between the 3DCRT and VMAT techniques in terms of the mean doses (D_mean) of PTV (p = 0.799). There was a significant difference between the 3DCRT and VMAT techniques in terms of percentage volume (V_(%107))averages that PTV received 107% of the treatment dose (p = 0.028), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique. There was a significant difference between 3DCRT and VMAT techniques in terms of HI values for PTV (p = 0.005), and since the HI values obtained by VMAT treatment technique were closer to 0, the VMAT technique was more advantageous compared to the 3DCRT treatment technique.Similarly, a significant difference was found between the 3DCRT and VMAT techniques in terms of CN values (p = 0.005) and the VMAT technique was more advantageous than the 3DCRT technique, since the CN value obtained by the VMAT treatment technique was closer to 1. There was a significant difference between the 3DCRT and VMAT treatment techniques in terms of the maximum dose (D_(%2 )) average for the brain (p = 0.028), and the results showed that the VMAT treatment technique was superior to the 3DCRT treatment technique.When the minimum dose (D_(%98 )) averages of the brain were evaluated, there was a significant difference between the 3DCRT and VMAT techniques (p = 0.005), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique.There was not significant difference between 3DCRT and VMAT techniques for the mean doses (D_(mean )) of brain (p = 0.646). There was a significant difference between the 3DCRT and VMAT techniques in terms of percentage volume (V_(%107)) averages that the brain received 107% of the treatment dose (p = 0.028), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique. There was a significant difference between the 3DCRT and VMAT techniques in terms of the maximum dose (D_(max )) average for the cribriform plate (p = 0.005), and the 3DCRT technique was found to be more advantageous than the VMAT technique.There was not significant difference between the 3DCRT and VMAT techniques in terms of mean doses (D_(mean )) of cribriform plate (p = 0.126).There was not significant difference between the 3DCRT and VMAT techniques in terms of percentage volume (V_(%95)) averages that the cribriform plate received 95% of the treatment dose (p = 1,000). There was a significant difference between the 3DCRT and VMAT techniques in terms of maximum dose (D_(%2 )) averages for scalp (p = 0.005), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique.There was not significant difference between the 3DCRT and VMAT techniques when the mean doses (D_(mean )) for scalp were evaluated (p = 0.415). There was not statistical significant difference was found between VMAT and 3DCRT treatment techniques in terms of low doses (D_(%98 )) of scalp (p = 0.508). There was a significant difference between 3CMRT and VMAT treatment techniques for maximum dose (Dmax) averages of chiasma (p = 0.007). In terms of maximum doses of chiasm, the 3DCRT treatment technique was found to be more advantageous than the VMAT treatment technique. There was a significant difference between the 3DCRT and VMAT techniques in terms of maximum dose (Dmax) means for the right eye (p = 0.005), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique. Similarly, there was a significant difference between the 3DCRT and VMAT techniques for maximum dose (Dmax) averages of the left eye (p = 0.005), and the VMAT treatment technique was found to be more advantageous than the 3DCRT treatment technique.There was a significant difference between the 3DCRT and VMAT techniques for the mean dose (D_(mean )) of the right eye (p = 0.037) and the 3DCRT treatment technique was found to be more advantageous than the VMAT treatment technique.Similarly, there was a significant difference between 3DCRT and VMAT techniques for the mean dose (D_(mean )) of the left eye (p = 0.005), and the 3DCRT treatment technique was found to be more advantageous than the VMAT treatment technique. There was not found significant difference between the 3DCRT and VMAT treatment techniques when the maximum dose (Dmax) averages were evaluated for the right and left lenses. There was not significant difference between the 3DCRT and VMAT treatment techniques in terms of maximum dose (Dmax) averages for right and left optic nerves. There was a significant difference in the maximum dose (Dmax) averages for the brainstem between the 3DCRT and VMAT techniques (p = 0.008), and the 3DCRT treatment technique was found to be more advantageous than the VMAT treatment technique in terms of the maximum doses received by the brainstem. As a result of this study, dose homogeneity and PTV coverage of target volumes were improved with VMAT treatment technique.However, it was observed that higher doses were obtained with VMAT technique compared to 3DCRT treatment technique in critical organs.The lens is very sensitive to radiation. For this reason, it should be protected with block or MLC during the treatment and even if possible by using both together. In treatment plans using protection blocks for the lens in the 3DCRT technique, the lenses received lower doses than the VMAT technique. Planning technique should be determined for cranial radiotherapy of ALL by considering target volume coverage, tolerance doses of critical organs, patient age and condition. According to the consensus of the radiation oncologist and medical physicist, VMAT treatment technique has been shown to be an alternative to the 3DCRT technique used as the standard treatment technique in cranial radiotherapy.