Estimated clinical benefit of combining highly conformal target volumes with Volumetric-Modulated Arc Therapy (VMAT) versus conventional flank irradiation in pediatric renal tumors

Joeri Mul; Enrica Seravalli; Mirjam E Bosman; Cornelis P van de Ven; Annemieke S Littooij; Martine van Grotel; Marry M van den Heuvel-Eibrink; Geert O Janssens

doi:10.1016/j.ctro.2021.04.007

Estimated clinical benefit of combining highly conformal target volumes with Volumetric-Modulated Arc Therapy (VMAT) versus conventional flank irradiation in pediatric renal tumors

Clin Transl Radiat Oncol. 2021 May 3:29:20-26. doi: 10.1016/j.ctro.2021.04.007. eCollection 2021 Jul.

Authors

Joeri Mul^{1

2}, Enrica Seravalli², Mirjam E Bosman², Cornelis P van de Ven¹, Annemieke S Littooij³, Martine van Grotel¹, Marry M van den Heuvel-Eibrink¹, Geert O Janssens^{1

2}

Affiliations

¹ Princess Máxima Center for Pediatric Oncology, Heidelberglaan 25, 3584 CS, Utrecht, the Netherlands.
² Department of Radiation Oncology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands.
³ Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands.

Abstract

Background: For decades, Anterior-Posterior/Posterior-Anterior (AP/PA) photon beams were standard-of-care for flank irradiation in children with renal cancer. Recently, highly conformal flank target volumes were defined correcting for postoperative organ shift and intra-fraction motion.By radiotherapy treatment plan comparison, this study aims to estimate the clinical benefits and potential risks of combining highly conformal target volumes with Volumetric-Modulated Arc Therapy (VMAT) versus conventional target volumes with AP/PA beams for flank irradiation.

Materials and methods: Twenty consecutive renal tumor cases (left/right-sided:10/10; median age:3.2 years) were selected. Highly conformal flank target volumes were generated for VMAT, while conventional target volumes were used for AP/PA. For each case, the dose to the organs at risk (OARs) and Total Body Volume (TBV) was calculated to compare VMAT with AP/PA treatment plans for a prescribed dose (PD) of 14.4/1.8 Gy. Dose constraint violation of the tail of the pancreas and spleen (D_mean < 10 Gy), heart (D₅₀ < 5 Gy) or mammary buds (D_mean < 10 Gy) were prioritized as potentially beneficial for clinics.

Results: Highly conformal Planning Target Volumes (PTV) were smaller than conventional volumes (mean ΔPTV_AP/PA-PTV_VMAT: 555 mL, Δ60%, p=<0.01). A mean dose reduction favoring VMAT was observed for almost all OARs. Dose constraints to the tail of the pancreas, spleen, heart and mammary buds were fulfilled in 8/20, 12/20, 16/20 and 19/20 cases with AP/PA, versus 14/20, 17/20, 20/20 and 20/20 cases with VMAT, respectively. In 12/20 cases, VMAT prevented the dose constraint violation of one or more OARs otherwise exceeded by AP/PA. VMAT increased the TBV receiving 10% of the PD, but reduced the amount of irradiated TBV for all higher doses.

Conclusion: Compared to 14.4 Gy flank irradiation using conventional AP/PA photon beams, an estimated clinical benefit by dose reduction to the OARs can be expected in 60% of the pediatric renal tumor cases using highly conformal flank target volumes combined with VMAT.

Keywords: 95% CI, 95% Confidence Interval; AP/PA, Anterior-Posterior/Posterior-Anterior; CT, Computed Tomography; CTV, Clinical Target Volume; Conformal radiotherapy; GTV, Gross Tumor Volume; ID, integral dose; IMRT, Intensity-Modulated Radiotherapy; ITV, Internal Target Volume; MRI, Magnetic Resonance Imaging; OARs, organs at risk; Organs at risk; PD, Prescribed Dose; PTV, Planning Target Volume; Pediatric renal tumors; RT, radiotherapy; SIOP-RTSG, International Society of Pediatric Oncology – Renal Tumor Study Group; Side-effects; TBV, Total Body Volume; VMAT; VMAT, Volumetric-Modulated Arc Therapy; Wilms tumor; vs, versus.