ESTRO 37 Abstract book

ESTRO 37

S439

PO-0841 Kidney-sparing whole abdominal irradiation in Wilms Tumor: potential advantages of VMAT technique M.J. Chen 1 , C.R. Leao 2 , A.L. Carioca 3 , R.C.P. Simoes 1 , F.S. Belletti 1 , M.L.S. Figueiredo 1 , M.S. Cypriano 1 1 Grupo de Apoio ao Adolescente e a Criança com Cancer, Radiation Oncology, Sao Paulo, Brazil 2 A.C.Camargo Cancer Center, Radiation Oncology, Sao Paulo, Brazil 3 Hospital das Clinicas da Faculdade de Medicina da Universidade de Sao Paulo, Radiation Oncology, Sao Purpose or Objective Adjuvant whole abdomen irradiation (WAI) is a key component of Wilms Tumor (WT) treatment and caution is necessary to spare the remaining kidney from radiation doses. This study aims to present a preliminary experience that demonstrates the dosimetric advantages of kidney-sparing Volumetric Modulated Arc Therapy (VMAT), compared to Three-Dimensional Conformal Radiotherapy (3D-CRT) for WAI. Material and Methods Seven cases of children with WT and submitted to WAI with VMAT were selected. Median WAI doses were 15 Gy (15 - 25,5) and median dose to the remaining kidney were 7,4 Gy (7 – 8,5). Two patients also received flank boost with 10,8 Gy and 1 patient received whole lung irradiation with 12 Gy, as per treatment protocol. For comparison purposes, similar VMAT and 3D-CRT treatment plans were performed, for each patient, all of them following the SIOP 2001 protocol radiotherapy guidelines regarding target (PTV) coverage and organ sparing. VMAT plans used multiple arcs and aimed to provide high and homogeneous PTV coverage while reducing maximum and median dose to remaining kidney. 3D-CRT plans used AP-PA fields and 'partial transmission” blocks to provide high PTV coverage while reducing maximum dose to remaining kidney. Differences were dosimetrically evaluated regarding maximum doses (Dmax) and median doses (Dmed) to the kidney and heart, Dmax, doses to 95 % and 2 % of the PTV (D95, D2), volume of the PTV receiving 100 %, 98 %, and 95 % of prescribed doses (V100%, V98%, V95%). Prescription doses, for comparison purposes were 10 x 1,5 Gy. Paulo, Brazil

30-36 Gy of RT, the pattern of relapse shifts to more out- of-field relapses. The present study investigates changes in dose to the organs at risk (OARs) if an additional 9-Gy boost is added to the standard 21 Gy in pHL. Material and Methods Ten pediatric patients with stage I-II mediastinal Hodgkin lymphoma received consolidative RT following 4-5 cycles of ABVE-PC chemotherapy and were enrolled on an IRB- approved outcomes tracking protocol. Involved-site RT (ISRT) treatment volumes were developed according to the ILROG guidelines. Additionally, a residual ISRT (rISRT) volume was developed based on all residual anatomic disease >1 cm, contoured as the post-chemotherapy GTV with an expansion to account for motion according to the 4D-CT simulation scan to make the iGTV and finally a 5- mm margin for the PTV rISRT. Four treatment plans were evaluated retrospectively to evaluate radiation dose to the OARs. These plans included an ISRT plan to 21 Gy, ISRT plan to 30 Gy, rISRT plan to 30 Gy, and a combo plan to 30 Gy (ISRT to 21Gy + rISRT to 9 Gy). Treatment plans were developed to ensure ITV V100%>99% and PTV D95>95%. Results Table 1 reports the median of the mean dose to the OARs and the range for the 4 treatment plants. Among the 4 plans, the 30 Gy rISRT plan consistently delivered the lowest mean heart dose, mean left anterior descending coronary artery dose, mean lung dose, mean breast dose, and integral body dose. When comparing the 21 Gy ISRT plan to the 30 Gy combo (ISRT+rISRT) plan, despite increasing the prescribed dose by 42%, the mean OAR dose increased by 17% (heart), 11% (LAD), and 22-26% (breast, lung, and body). In absolute terms, the mean heart dose only increased 1.4 Gy, LAD by 1 Gy, lungs by 1.7 Gy, breasts by 1 Gy, and body by 15 Joules.

Table 1. Mean dose to the OARs by plan ISRT 21 ISRT 30 ISRT

+

rISRT 30 median (range) 4.6 (0.4- 11.2) 3.15 (0- 28.9) 4.8 (2.5- 7.4)

rISRT median (range)

median (range)

median (range)

Heart, Gy

8.5 (4.4- 13.2)

12.1 (6.3- 18.9) 21.25 (0.4- 33) 9.65 (6.4- 11.8) 6.3 (1.9- 14.6) 78.7 (61.2- 139.7)

9.8 (4.9- 15.2) 16.9 (0.3- 30.9) 8.15 (5.4- 10.6) 5.5 (1.6- 13.4) 68.9 (51.7- 125.2)

LAD, Gy 14.9 (0.3- 23)

Lungs, Gy Breast, Gy

6.75 (4.5- 8.2) 4.4 (1.3- 10.2) 55.0 (43.5-98)

3 (0.9-9.1)

Body, Gy

40.4 (18.7- 95.2)

Conclusion Despite an increase in RT dose to the residual disease by 42% with a 9-Gy boost, the impact on dose to the OARs in the mediastinum was relatively small when added to the standard 21 Gy ISRT field. Among pHL requiring RT, a prospective trial evaluating a boost to 30 Gy is warranted. Figure 1. (left to right) Prechemotherapy PET, ISRT, and rISRT (anatomic disease after chemotherapy)

Results After median follow-up time of 16,2 months (11,7 – 29,5), no acute significant intestinal toxicity was observed and median creatinine clearance varied from 116,4 to 100 ml/min/1,73m² (within normal range, Schwartz formula), before WAI and at last follow-up. Two recurrences were observed, 1 pulmonary and 1 hepatic, none inside the peritoneal cavity. For comparative plans, Dmax and Dmed were lower for the remaining kidney with VMAT than with 3D-CRT. VMAT was associated with better PTV coverage as compared to 3D-CRT, with superior results for all of the evaluated parameters (D95, D2, V100%, V98%, V95%) ( p = 0.018).